JP6230358B2 - Optical distance measuring device - Google Patents

Description

  The present invention relates to an optical distance measuring device that realizes measurement and observation of a surface state profile or a surface state of a cell or the like with irradiation of laser light with extremely high resolution, and improves the resolution of an optical instrument such as a microscope, and The present invention is suitable for an apparatus that accurately and accurately observes and measures path difference information and the like by accurately reproducing missing spatial frequency information acquired by a lens.

  With a conventional optical microscope, it was impossible to observe or measure a measurement object below the diffraction limit. As an alternative, probe microscopes (STM, AFM, NFOS, etc.) and scanning electron microscopes have been developed and used in many fields. Since this scanning electron microscope uses a very thin beam as a scanning electron probe, the resolution is high and the depth of focus is significantly larger than that of an optical microscope. However, in order to observe a measurement object with low conductivity such as a cell, it is necessary to coat a sample that is the measurement object with platinum palladium or gold having good conductivity. For this reason, the cells themselves are often damaged, and as a matter of course, it is impossible to observe and measure living cells.

  A probe microscope measures the distance from the measurement object by using an atomic force, tunnel current, optical near field, etc. It is. However, it is difficult to move the probe at high speed, and it is difficult to handle because the distance to the object to be measured is very close, and it takes a lot of time to acquire two-dimensional information. .

On the other hand, confocal microscopes, digital hologram microscopes, and the like are known as conventional means for detecting optical path differences.
The former confocal microscope irradiates a measurement object with a spot, and the objective lens or measurement object is set so that the amount of light received by the light receiving element disposed at the confocal position via the pinhole is maximized. By moving the object, the height information and the path difference information of the measurement object are acquired.
Further, the latter digital hologram microscope irradiates a measurement object with a substantially parallel laser beam, collects the light diffracted by the measurement object with an objective lens, and provides a reference plane wave and an area such as a CCD. A hologram is created by causing interference on the sensor, and the wavefront from the original measurement object is restored by analyzing the interference fringes by calculation to obtain path difference information.

  However, in the former confocal microscope, basically, if there is a phase distribution in the spot, the beam is deformed and becomes erroneous information. In particular, if the object to be measured has a wavefront that changes in phase, such as a change in refractive index of a cell or the like, the reliability of the value must be poor. In addition, since it is necessary to move the objective lens and the measurement object so that the received light quantity becomes maximum, the real-time property is lacking.

In the latter digital hologram microscope, the light diffracted by the objective lens is collected and the wavefront is reproduced to obtain information, but the spatial frequency that can be collected by the objective lens is limited by the cutoff frequency of the objective lens due to the NA. At the same time, the frequency that can be acquired almost linearly from the DC to the cut-off frequency decreases. This is the so-called MTF curve.
Therefore, the acquired wavefront information does not accurately reflect the spatial frequency information that the measurement object actually has, and gives incorrect path difference information.

  On the other hand, a method is also known in which a Fourier transform surface is prepared in a part of the imaging optical system, a phase type spatial modulator is disposed on the Fourier transform surface, and phase modulation is applied to the 0th-order diffracted light. As shown in Patent Document 2 and Non-Patent Documents 1 and 2 below, this method has a phase difference of 90 degrees, 180 degrees, and 270 degrees that is different by 90 degrees between the 0th order diffracted light and the 1st order diffracted light. A total of four types of generated images are picked up by a CCD camera arranged on the imaging plane of the lens, and the optical distance is measured from the mutual calculation of these four types of images.

However, since any method based on this method forms an image using a lens, it has the characteristics of the MTF of the lens as described above, so that the loss of information amount increases as the spatial frequency increases. Arise. For this reason, it must be said that the reliability of the quantified information is poor in these methods.
In addition, it is impossible to produce a phase difference only in the 0th-order diffracted light. This is because the 0th-order diffracted light is transmitted without being modulated from the sample to be measured, but the 0th-order diffracted light includes low-order 1st-order diffracted light that overlaps the 0th-order diffracted light region. This is because the 0th order diffracted light and the 1st diffracted light cannot be substantially distinguished.
Furthermore, when acquiring an image with four different phases, it is necessary to switch the modulation of the spatial light modulator, and the image acquired by the CCD camera is information shifted in time. Therefore, it was difficult to say that it correctly reflected changes in the process that change relatively quickly.

  On the other hand, in order to minimize the influence that this image becomes information shifted in time, it is conceivable to apply this method in a very narrow region near the periphery of the spread of the 0th-order diffracted light. In this way, there is a possibility that the frequency dependence of the spatial frequency and the influence of the first order diffracted light included in the zeroth order diffracted light can be reduced. However, in this case, since only a very narrow range of light can be acquired effectively, the amount of light is extremely reduced, making it difficult to obtain information with a good SN ratio.

There is also a known demand for analyzing a chemical change of a cell or the like by causing the cell or the like to perform fluorescent color development at a specific wavelength. However, the imaging optical system inherently has an aperture limitation by the objective lens, so that the spatial frequency that can be taken in is limited, and at the same time, the contrast of the spatial frequency gradually decreases linearly as the frequency increases.
For this reason, when the fluorescent color is developed in the structure portion having a high frequency, the contrast is lowered, and it is difficult to perform accurate density measurement or the like.

  On the other hand, heterodyne interferometry is well known for measuring distances with high accuracy and measuring and observing minute objects with high accuracy. Here, the optical heterodyne method using light is described, but the same concept is applied to other electromagnetic waves. In this optical heterodyne method, two laser beams having different frequencies are caused to interfere with each other, a beat signal having a frequency difference between the two is generated, and a phase change of the beat signal is detected with a resolution of about 1/500 of a wavelength. . That is, according to this optical heterodyne method, the distance to the measurement object can be measured while measuring the change in the height direction of the surface, or the measurement object itself can be measured and observed.

  In Japanese Patent Application Laid-Open No. 59-214706 of Patent Document 1 below, two beams having different wavelengths are generated adjacent to each other using an acousto-optic device, and a phase change between these two beams is detected. A method for accumulating phase changes to obtain a surface profile is disclosed. However, in this patent document 1, unevenness information is obtained by making two beams close to each other slightly larger than the beam profile, detecting an average phase difference in the two beam profiles by heterodyne detection, and integrating sequentially. It was what you get.

  Therefore, according to this Patent Document 1, the unevenness information can be measured for the measurement object that is assumed to be flat such as a semiconductor wafer, but the information in the beam profile is I couldn't pull it out. For this reason, the resolution in the beam profile that is in-plane cannot be increased.

  On the other hand, a technique called a DPC (Differential Phase Contrast) method is conventionally known. This is a technique that was first applied to an electron microscope by Dekkers and de Lang, and was later extended to an optical microscope by Sheppard and Wilson et al. This DPC method is a far field with respect to the electromagnetic wave irradiated to the sample, and is a result of interference between the zeroth-order diffracted light and the first-order diffracted light detected by detectors arranged symmetrically with respect to the irradiation axis of the electromagnetic wave. By obtaining the differential signal, the profile information of the sample is obtained. However, in this DPC method, if the spatial frequency becomes high, the 0th-order diffracted light and the 1st-order diffracted light cannot interfere with each other, and as a result, the spatial frequency is not reproduced, and measurement may not be possible.

In other words, in conventional imaging microscopes using electromagnetic waves, including general devices using electromagnetic waves, the resolution that is the limit of Abbe's theory could not be exceeded. This limit was a result of the diffraction phenomenon of waves, and was regarded as a theoretical limit that could not be exceeded. Therefore, it has been difficult to overcome the limitations due to the substantial wavelength used not only in the optical microscope but also in the electron microscope.
Further, in various conventional microscopes based on the imaging optical system, the spatial frequency that can be obtained is limited by the lens aperture limitation, and at the same time, the contrast of the sample gradually decreases as the spatial frequency increases. For this reason, it has been difficult to accurately acquire density information by using path difference information such as phase information and fluorescent color development.

JP 59-214706 A Special table 2007-524075 gazette

Opt. Lett. 29 (21), 2503-2505 (2004) Opt. Exp. 19 (2), 1016-1026 (2011)

  As described above, in the distance measuring device using the conventional heterodyne detection, the distance cannot be measured with a resolution equal to or lower than the wavelength of the applied electromagnetic wave. Therefore, even if the electromagnetic wave irradiation region is made smaller than the wavelength, it was only possible to calculate the average distance of the region that is equal to or greater than the wavelength.

Similarly, in a conventional optical measuring device using heterodyne detection, a main object to be measured is a flat surface such as a semiconductor wafer. For this reason, in order to increase the in-plane resolution, a near field such as an electron microscope or an AFM (atomic force microscope) must be used.
However, with respect to the electron microscope, it is necessary to process living organisms, cells, and the like in particular, so it has been impossible to observe living and measure the refractive index distribution. On the other hand, AFM is not suitable for observation of living organisms and cells because the processing speed is not sufficient, so it is not possible to see changes in state in real time. It was not easy to use.

Here, the OTF characteristic of the objective lens in the conventional microscope using the imaging optical system will be described below.
In a conventional microscope using an imaging optical system, the first-order diffracted light component and the zero-order diffracted light component of the symmetrical object captured by the objective lens interfere to form an image. For this reason, unless the first-order diffracted light is incident on the lens opening, the spatial frequency is not reproduced. On the other hand, since the diffraction angle of the first-order diffracted light gradually increases from a low frequency to a high frequency, the amount of the first-order diffracted light input to the lens decreases. As a result, the frequency at which the first-order diffracted light is not input is cut off, and the degree of modulation gradually decreases in the middle from the low frequency to the high frequency.

The above is the OTF characteristic of the objective lens. Therefore, since the first-order diffracted light input to the objective lens is naturally limited in the imaging system, the resolution is naturally limited in relation to the spatial frequency of the measurement object to be reproduced.
On the other hand, in an optical system that forms an image using an objective lens, such as the digital hologram microscope described above, the laser light diffracted by the object to be measured is incident on an objective lens having a limited aperture size. At the time, the information is a part of the spatial frequency of the laser beam missing. That is, as the spatial frequency increases, the spatial frequency input to the objective lens gradually decreases. For this reason, the hologram produced by interfering with the reference wavefront does not reflect the original information of the measurement object. As a result, the path difference information reproduced by calculation is completely erroneous information.

The above qualitative explanation is quantified and explained in detail below.
As shown in FIG. 17, it is assumed that a parallel light beam is incident on an objective lens 31 having an aperture radius a and a focal length f. In FIG. 17, the irradiation optical axis is represented by the optical axis L0, and the inclined optical axis inclined by the angle Θ with respect to the optical axis L0 is represented by the optical axis L1. A microscope using normal imaging is a transmission type in which the light beam passes through the sample S as shown in FIG. 17, but may be considered as a reflection type in which the light beam is folded back on the sample S. In order to simplify the formula, it is treated as a one-dimensional opening.

For simplicity, it is assumed that the sample S has a sine wave shape having a height h and a pitch d. That is, the optical phase θ is expressed by the following formula.
θ = 2π (h / λ) sin (2πx / d) (1) Equation The amplitude E of the light diffracted from the sample S is the Fourier of the equation (1) on the plane separated by the focal length f. Since it is given as a convolution of the transformation and the aperture of the lens, it is expressed as follows. However, the Bessel function that is the Fourier transform of the phase of equation (1) is assumed to be ± 1st order.

Here, the Fourier transform of equation (2) contributes to imaging.
Accordingly, the intensity I is expressed by the following equation (3).

  The meaning of this equation is that information with a pitch smaller than d = λf / 2a = 0.5λ / NA is lost. This coincides with the beam diameter of the rectangular aperture (since the first dark ring radius w of sinc (ka) = 0 satisfies ka = π, w = 0.5λ / NA). Further, even when d> 0.5λ / NA, the smaller the d is, the lower the modulation degree is. If the relationship between the spatial frequency of 1 / d and the modulation factor is shown, this is MTF. However, simply forming the phase information does not form an image with contrast, and the contrast is generated using an optical element or the like that causes phase delay in the 0th-order diffracted light as in a phase contrast microscope. Such means are necessary.

  As described above, in a normal imaging optical system, the limit of the spatial frequency reproduced by the NA of the objective lens 31 is necessarily d = λf / 2a = 0.5λ / NA, which is smaller than this value. Things will not be reproduced in any way. Accordingly, conventional optical microscopes including digital hologram microscopes that acquire information using an objective lens cannot acquire accurate intensity information and path difference information.

  The present invention has been made in view of the above background, and has a high in-plane resolution and a high resolution with respect to height and refractive index distribution outside the surface, and a spatial frequency that cannot be obtained by a normal imaging optical system. It is an object of the present invention to provide an optical distance measuring device that has high spatial resolution and no spatial frequency loss by accurately acquiring and reproducing spatial frequency information possessed by a measurement object.

An optical distance measuring device according to claim 1 is a light source that irradiates a measurement object with a light beam;
A separation element that converts a light beam including the 0th-order diffracted light and the 1st-order diffracted light generated by being diffracted by the measurement object as the light beam is incident into two light beams;
A first delay element that delays the travel of a part of the diffracted light beams constituting each of the light beams divided by the separation element;
A first light-receiving element comprising a pair of divided light-receiving elements that are detected in two parts in a state where the zero-order diffracted light and the first-order diffracted light partially delayed by the first delay element are caused to interfere with each other;
A second delay element for delaying the progress of a part of the diffracted light beams constituting each of the other light beams divided by the separation element with a phase different from that of the first delay element;
A second light-receiving element comprising a pair of divided light-receiving elements that are detected in two parts in a state in which the zero-order diffracted light and the first-order diffracted light partially delayed by the second delay element are caused to interfere with each other;
The phase of the pair of divided light receiving elements of the second light receiving element is different from each other between the electric signals of the two kinds of light receiving outputs detected while the phases of the pair of divided light receiving elements of the first light receiving element are different from each other. An output sum / difference detection unit for detecting an output value of a sum or a difference between electrical signals of two types of detected light reception outputs;
including.

The operation of the optical distance measuring device according to claim 1 will be described below.
In the present invention, the light beam irradiated from the light source to the measurement object is diffracted as it enters the measurement object, and the light beam including the 0th-order diffracted light and the first-order diffracted light is emitted. The separation element divides this light beam into two light beams, and the first delay element delays the progress of a part of the diffracted light beams that constitute one of the divided light beams. Then, assuming that the 0th-order diffracted light and the 1st-order diffracted light are caused to interfere with each other, the pair of split light-receiving elements of the first light-receiving element detects the light in this state separately.

On the other hand, the second delay element delays the progress of a part of the diffracted light beams constituting the other split light beam with a phase different from that of the first delay element. In the same manner as described above, the pair of divided light receiving elements of the second light receiving element separately detect the light in this state, with the 0th order diffracted light and the 1st order diffracted light being caused to interfere with each other.
Further, the output sum and difference detection unit, between the first of the two light-receiving output of the electric signals each phase a pair of light receiving elements is detected while being the difference in the light receiving element and the pair of division of the second light-receiving element The output value of the sum or difference between the electrical signals of the two types of light receiving outputs detected while the phases of the light receiving elements are different from each other is detected.

Therefore, according to this claim, the optical distance is quantified by detecting the light in each state with different phases by each pair of divided light receiving elements of the two types of light receiving elements, and further, the information Can be appropriately amplified electrically. For this reason, the reliability of the quantified information is increased by performing frequency filtering electrically appropriately in consideration of the characteristics of the MTF of the lens so as not to cause a loss of information amount.
Also, since spatial frequency information can be converted into electrical frequency by heterodyne detection or analysis of the modulation frequency itself, low-order first-order diffracted light that overlaps the zero-order diffracted light region from a total of four different phase information. Can be distinguished from zero-order diffracted light.
Further, since images having different phases can be simultaneously captured by the total of four divided light receiving elements, the information does not become time-shifted information. For this reason, it is possible to obtain information that correctly reflects changes in the process that change relatively quickly. Along with this, a decrease in the amount of light is suppressed, and information with a good SN ratio is obtained.

In summary, the microscope to which the present invention is applied has a very high in-plane resolution and can measure the height and refractive index distribution by performing two-dimensional scanning once, so that it remains alive. 3D measurement such as state changes of cells and micromachines can be performed in real time. For this reason, it has the big characteristic which cannot be compared with the laser scanning confocal microscope etc. which acquire the conventional 2-dimensional information and integrate | accumulate in a 3-dimensional direction.
Furthermore, when the present invention is applied to a transmission microscope, living organisms and cells can be observed and measured with high resolution without being fluorescently colored. For this reason, it has the big characteristic which the electron microscope which inactivates a cell etc. and measures does not have.

  As described above, according to the present invention, the in-plane resolution is high, and the resolution for the height and refractive index distribution is high in the out-of-plane, and the spatial frequency that cannot be obtained by a normal imaging optical system is obtained and measured. By accurately reproducing the spatial frequency information possessed by the object, an optical distance measuring device having high resolution and no spatial frequency loss can be provided.

The operation of the optical distance measuring device according to claims 2 to 6 will be described below.
The separation element according to claim 1 is disposed on an inclined optical axis having an inclination, and includes a lens that converts a light beam including 0th-order diffracted light and 1st-order diffracted light into a parallel light beam, and a beam splitter that divides the light beam into these two light beams. By being configured, it is possible to reliably split a light beam including 0th-order diffracted light and 1st-order diffracted light.

  The first delay element and the second delay element according to claim 1 are a quarter-wave plate, a half-wave plate, or a diffraction grating, and delay the phase of the light beam by 90 degrees or 180 degrees. Thus, a total of four pieces of information with different phases can be reliably generated. Furthermore, a prism such as a rhomboid prism is disposed between the first delay element and the first light receiving element and between the second delay element and the second light receiving element, respectively. Thus, before detecting the 0th-order diffracted light and the 1st-order diffracted light, these diffracted lights can be reliably interfered.

  As described above, the optical distance measuring device of the present invention has high in-plane resolution and high resolution with respect to height and refractive index distribution outside the surface, and cannot be obtained by a normal imaging optical system. By acquiring a precise spatial frequency and accurately reproducing the spatial frequency information of the measurement object, it is possible to obtain an excellent effect that the optical distance can be quantitatively calculated with high resolution and no spatial frequency loss.

  In addition, since the frequency of the signal detected by each light receiving element corresponds to the spatial frequency, the path that correctly reflects the spatial frequency of the sample is changed by changing the frequency amplification corresponding to the MTF curve of the lens. Difference information can be acquired. Furthermore, when it is desired to observe the path difference information and the intensity information of the fine portion of the sample, the high frequency region of the spatial frequency can be emphasized by performing the electrical high frequency enhancement.

  Furthermore, the fusion with the heterodyne method enables phase changes and intensity changes to be detected with extremely high accuracy, and increases the gain of the detection circuit system even if the light received by the light receiving element is very weak. Since it can be detected with high accuracy and the signal to be detected is only a modulated signal, it is not affected by ambient light, so that it can be detected with higher accuracy. This makes it possible to observe and measure with very high resolution even for very weak and low-contrast phase information and slight refractive index changes.

It is a block diagram of the optical system applied to the Example which concerns on the optical distance measuring device of this invention. It is a figure which expands and shows the objective lens of FIG. 1, and a measurement object peripheral part. It is explanatory drawing showing the light irradiation area | region on the measuring object in the optical system of FIG. It is a block diagram of the other optical system applied to the Example which concerns on the optical distance measuring device of this invention. It is a block diagram of the optical system which shows Example 1 which concerns on the optical distance measuring device of this invention. It is a figure which shows the relationship between the light beam of the one optical path branched in Example 1, and the delay element 43A, Comprising: It is the figure which displayed the semicircle beams BA and BB which comprise a light beam mutually separated. It is a figure which shows the relationship between the light beam of the other optical path branched in Example 1, and the delay elements 43B and 43C, Comprising: It is the figure which separated and displayed the semicircle beams BC and BD which comprise a light beam. FIG. 7 is a diagram showing a state where the semicircular beam BA and the semicircular beam BB shown in FIG. FIG. 4 is a schematic diagram showing a 0th-order diffracted light area and a ± 1st-order diffracted light area when the phase pitch d in Example 1 is 0 <λf / d <a / 2, where (A) shows the 0th-order diffracted light J0; B) shows the first-order diffracted light J1, and (C) shows -1st-order diffracted light -J1. It is a figure which shows how to overlap each diffracted light in Example 1, Comprising: (A) shows the state which shifted 0th-order diffracted light J0, (B) shows the state which shifted a part of 1st-order diffracted light J1, (C) shows a state where the other part of the first-order diffracted light J1 is not shifted, and (D) shows a state where the -1st-order diffracted light -J1 is shifted. It is a figure which shows the graph showing the characteristic curve of a present Example. It is a block diagram of the optical system which shows the modification of Example 1 which concerns on the optical distance measuring device of this invention. It is a block diagram of the optical system which shows Example 2 which concerns on the optical distance measuring device of this invention. It is a block diagram of the optical system which shows Example 3 which concerns on the optical distance measuring device of this invention. It is a block diagram of the optical system which shows Example 4 which concerns on the optical distance measuring device of this invention. It is a block diagram of the optical system which shows Example 5 which concerns on the optical distance measuring device of this invention. It is a principle figure explaining the principle of a normal image formation optical system.

  Embodiments 1 to 5 of the optical distance measuring device according to the present invention will be described below in detail with reference to the drawings.

The concept of the optical system applied to the embodiment of the optical distance measuring device according to the present invention will be described below.
Coherent light such as a laser emitted from a light source is modulated into light of substantially two different frequencies by an acousto-optic device or a spatial modulator as the first means. At this time, for example, when an acoustooptic element is used, the diffraction fringes are modulated by the interaction between the surface acoustic wave of the acoustooptic element and light. The light that has undergone Doppler shift undergoes frequency modulation and is emitted as first-order diffracted light. On the other hand, when a spatial light modulator is used, the same effect can be obtained by modulating the diffraction fringes written in the spatial light modulator.

  In this way, the light subjected to frequency modulation is emitted from the first means while being separated into two lights close to each other. The two light beams are scanned two-dimensionally by a pupil transmission optical system, a two-dimensional scanning device, or the like, which is a second means, and the sample is irradiated by an objective lens, etc., which is a third means. A light receiving element that is located away from the sample and is divided into two or more along the separation direction of the two lights is referred to as a fourth means. This light receiving element receives light reflected from the sample or passed through the sample G1 as light across a boundary extending in a direction substantially perpendicular to the separation direction of the two lights.

In this way, the light received by the light receiving element is photoelectrically converted. The fifth means amplifies while changing the amplification degree in accordance with the frequency of each electric signal photoelectrically converted by the light receiving element of the fourth means for each region sandwiching the boundary line.
Then, in the signal comparator as the fifth means, the direction substantially perpendicular to the separation direction of the two lights is defined as a boundary line, and the difference signal or sum of the outputs at the symmetrical positions across the boundary line. Create a signal. The difference signal or the sum signal is subjected to heterodyne detection in a data processing unit which is a sixth means, thereby detecting a phase difference or detecting an intensity difference.

  The detected phase difference and intensity difference indicate the height information of the profile of the sample surface in the case of reflection, and indicate information such as thickness and refractive index distribution, that is, path difference information in the case of transmission. At this time, the light irradiation areas A and B shown in FIG. 3 may be considered as diffraction limited spot diameters narrowed by the objective lens.

Hereinafter, the operating principle of the present optical system will be described in detail.
Assume that the center distance Δx between the two light irradiation areas A and B shown in FIG. 3 is set to be equal to or less than the diffraction limit of these lights. In this case, the irradiation areas A and B of each light are not lower than the diffraction limit of Abbe's theory, but are light with different frequencies slightly shifted, so that these lights are subjected to heterodyne detection. , Differential information can be obtained. At this time, if the sum signal of each light receiving element arranged in two or more is used, it is substantially equivalent to a kind of differential interference microscope of an optical microscope. If these difference signals are used, A much higher lateral resolution is obtained.

Think in one dimension for simplicity. First, the phase distribution of the profile d (x) of the measurement object G1, which is a sample such as a microorganism, is set as Ae ^{jθ (x)} . Here, θ (x) = 2πd (x) / λ. In the case of reflection as in the present optical system, the path difference is doubled, so half of the observed θ (x) may be used as height information.
As described above, the center distance between the two light irradiation areas A and B on the measurement object G1 is Δx, and the complex amplitude distribution of light is u (x). In this case, in a place sufficiently away from the measurement object G1, the Fourier transform of the product of the profile of the measurement object G1 and the beam profile is performed.

In this optical distance measuring device, the light received by one light receiving element is modulated by ej ^{(ωc-ωm) t} , and the other light received by the center distance Δx is separated. The light received by the element is modulated by ej ^{(ωc + ωm) t} .
Accordingly, the complex amplitude distribution E on each light receiving element is as follows.
E = ∫ (Ae ^{jθ (x)} u (x) e ^jkx dx · e ^{j (ωc-ωm) t} + Ae ^{jθ (x + Δx)} u (x) e ^jkx dx · e ^{j (ωc + ωm) t} )

When the intensity I is detected by each of the light receiving elements, I = EE ^* and further heterodyne detection of 2ωm is performed, so that the following equation (4) is obtained.
I (k) = A ² ∫e ^{j (θ (x) −θ (x ′ + Δx ′)} u (x) u (x ′) e ^{jk (x−x ′)} dxdx′e ^−j2ωmt
+ A ² ∫e ^{−j (θ (x) −θ (x ′ + Δx ′)} u (x) u (x ′) e ^{jk (x−x ′)} dxdx′e ^j2ωmt (4)

Then, the approximate center of the two irradiation areas A and B where the two lights overlap is the boundary line C in FIGS. 2 and 3, and is a position between which the boundary line C is sandwiched, and the irradiation areas A and B are separated. Two light receiving elements are arranged apart from the measurement object G1 corresponding to the positions along the direction. First, consider what the sum signal of the signals received by the two light receiving elements will be. Since it is considered to be a Fourier transform plane at a position away from the measurement object G1, if the maximum spatial frequency that can be received by the light receiving element is Kmax, the intensity I of the sum signal can be obtained from the following equation.
I = ∫I (k) dk (integration range is -Kmax to Kmax)
= A ² ∫cos (θ (x) −θ (x ′ + Δx ′) − 2ωmt) u (x) u (x ′) sin (Kmax (x−x ′)) / (x−x ′) dxdx ′

If the light receiving element is enlarged and arranged to receive a wide spatial frequency,
Since sin (Kmax (x−x ′)) / (x−x ′) = Kδ (x−x ′), the following equation (5) is obtained.
I = A ² ∫cos (θ (x) −θ (x + Δx) −2ωmt) u (x) ² dx (5)

That is, the phase difference between the separation positions of the two lights is integrated by the weight of the light profile.
When the equation (5) is modified, the following equation is obtained.
Iq = A ² ∫cos (θ (x) −θ (x + Δx) u (x) ² dx · cos (2ωmt)
Ii = A ² ∫sin (θ (x) −θ (x + Δx) u (x) ² dx · sin (2ωmt)

Therefore, the observed phase difference Θ is represented by the following equation (6) by orthogonal transformation.
Θ = tan ⁻¹ (∫sin (θ (x) −θ (x + Δx)) u (x) ² dx / ∫cos (θ (x) −θ (x + Δx)) u (x) ² dx)・ ・ ・ ・ ・ (6)

On the other hand, considering the difference signal between the two light receiving elements, the following equation is obtained in the same manner as in the case of the sum signal.
I = ∫I (k) dk (integration range is 0 to Kmax) −∫I (k) dk (integration range is −Kmax to 0)
= A ² ∫sin (θ (x) −θ (x ′ + Δx ′) − 2ωmt) u (x) u (x ′) (cos (Kmax (x−x ′) − 1) / (x−x ′ dxdx '

If the light receiving element is enlarged and arranged to receive a wide spatial frequency,
Since (cos (Kmax (x−x ′) − 1) / (x−x ′) = δ ′ (x−x ′) + 1 / x (δ (x) −1), the following equation (7) become that way.
I = A ² ∫d / dx (sin (θ (x) −θ (x + Δx) −2ωmt)) u (x) ² dx (7) Equation (7) Then, it becomes as follows.
Iq = A ² d / dx (sin (θ (x) −θ (x + Δx)) u (x) ² dx · cos (2ωmt)
Ii = −A ² ∫d / dx (cos (θ (x) −θ (x + Δx)) u (x) ² dx · sin (2ωmt)

Therefore, the phase difference Θ observed by the orthogonal transformation is expressed by the following equation (8).
Θ = tan ⁻¹ (−∫d / dx (cos (θ (x) −θ (x + Δx)) u (x) ² dx / ∫d / dx (sin (θ (x) −θ (x + Δx )) u (x) ² dx) (8)

Here, the expression (6) is compared with the expression (8). The following points are qualitatively understood.
First, the equation (6) shows the phase difference obtained as a result of smoothing the phase difference between two points separated by the center distance Δx between the irradiation areas A and B with the weight function of u (x). The average phase difference in the irradiation areas A and B is shown. This is a process equivalent to a differential interference microscope.
On the other hand, in the equation (8), the differential of the phase difference between the two points separated by the center distance Δx between the irradiation areas A and B is smoothed by the weight function u (x). It will be restored.
Therefore, it is possible to acquire phase difference information and position information with a lateral resolution corresponding to the degree of separation between the irradiation areas A and B.

Although the case where two light receiving elements are arranged is described here, a plurality of light receiving elements are separated from the measurement object G1 along the separation direction of the two lights in the vicinity of the center of the overlapping area of the irradiation areas A and B. The same applies to the case where they are arranged. In particular, when a difference output is obtained, a difference calculation is performed between a plurality of corresponding light receiving elements among the plurality of light receiving elements arranged corresponding to the vicinity of the center of the overlapping portions of the irradiation areas A and B. You can do it.
If only the sum output of a plurality of light receiving elements is used, the same can be realized by using one light receiving element.

  In order to simplify the explanation, the formula is simplified assuming that the spatial frequency to be acquired is wide. However, when the spatial frequency that can be acquired is not large, the δ function portion in the formula becomes a convolution. However, the resolution is essentially improved. In this case, some blurring occurs in the profile of the measurement object G1.

In the above description, the phase has been described in detail, but the same can be said for the intensity. In particular, for a profile change smaller than that of the irradiation regions A and B, a pattern in the far field of interference fringes formed by interference between the zeroth-order diffracted wave and the first-order diffracted wave of the Fourier transform of the irradiated region. Is different between the two light receiving elements. For this reason, the difference signal of the light receiving element appears as an intensity difference reflected in the inclination of the profile.
As described above, by using heterodyne detection and processing spatial frequency information on the Fourier transform plane, it is possible to bring about a very high improvement in lateral resolution, particularly in the difference calculation.

  That is, in heterodyne detection based on the sum signal of each photoelectrically converted signal, the phase difference between two points that are separated by the center distance of the two light beams is smoothed by the weight function of u (x), and this result Represents the phase difference obtained. For this reason, the heterodyne detection based on this sum signal indicates an average phase difference in the beam, which is a process equivalent to a differential interference microscope.

On the other hand, in heterodyne detection based on the difference signal between the photoelectrically converted signals, the differential of the phase difference between two points separated by the center distance of the beam is smoothed with a weight function of u (x). So, it is roughly restoring the original function.
As described above, when the beam is scanned by the pupil transmission optical system, the phase difference and the position information can be acquired with the lateral resolution corresponding to the beam separation degree.

  In the above description, the case where the light receiving element divided into two with the optical axis as a boundary line is applied is described, but the same applies to the case where a plurality of light receiving elements are arranged away from the sample along the beam separation direction. In particular, when a difference output is obtained, it may be performed between adjacent light receiving elements across a boundary line. If only the sum output of a plurality of light receiving elements is used, the same can be realized by using one light receiving element. In particular, the sum output is effective when the sample has an intensity pattern with different absorptance and reflectance. For example, this is the case when the object is stained with cells.

If there is an inclination of the profile in the beam with respect to the sample, the direction in which light is reflected or transmitted is qualitatively different, so that a difference output as intensity is given to the two light receiving elements. More specifically, if there is a profile change smaller than the beam diameter, the far field of interference fringes formed by the interference between the zeroth-order diffracted wave and the first-order diffracted wave of the Fourier transform in the region irradiated with light. The pattern in is different between the two light receiving elements. For this reason, the difference signal between these two light receiving elements appears as an intensity difference reflecting the inclination of the profile.
Although the details will be described later, since the spatial frequency by the objective lens is converted into an electrical frequency signal by scanning the beam and the light receiving element, the gradual decrease of the spatial frequency inherent in the objective lens is expressed by the electrical amplification degree. By correcting, it is possible to completely restore the spatial frequency that can be obtained by the objective lens.

Hereinafter, an optical system applied to an embodiment of an optical distance measuring device according to the present invention will be specifically described with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of an optical system apparatus applied to the embodiment. As shown in FIG. 1, between a laser light source 21 that is a light source from which laser light is emitted and an acousto-optic device (AOD) 23 that is a first means to which the operation is controlled by connecting an AOD driver 24. In addition, a collimator lens 22 is arranged.
Further, the acousto-optic element 23 includes a pupil transmission magnifying lens system 25 comprising two groups of lenses, a two-dimensional scanning device 26 for two-dimensionally scanning the input laser light, and separating and emitting the input laser light. The polarizing beam splitters 27 are arranged in order. However, the pupil transmission magnifying lens system 25, the beam splitter 27, and the two-dimensional scanning device 26 may be arranged in this order with respect to the acoustooptic device 23.

Further, a pupil transmission lens system 30 comprising two groups of lenses is located adjacent to the polarization beam splitter 27, and an objective lens 31 is arranged next to the object G1 for measurement. That is, these members are arranged along the optical axis L. On the other hand, a light receiving element 28 and a light receiving element 29, which are optical sensors, are disposed at positions adjacent to the polarization beam splitter 27 in a direction orthogonal to the direction in which the optical axis L passes.
The light receiving elements 28 and 29 are connected to a signal comparator 33 that compares signals from the light receiving elements 28 and 29, respectively. The signal comparator 33 finally processes the data and the profile of the measurement object G1. Etc. are connected to a data processing unit 34 for obtaining the above.

  The laser light source 21 is a gas laser such as He—Ne, a semiconductor laser, or a solid laser, and generates coherent laser light. The laser light is converted into a parallel light beam by the collimator lens 22 and is incident on the acoustooptic device 23. At this time, the incident beam diameter of the laser light is optimized using a diaphragm mechanism (not shown) or the like in consideration of the pupil transmission magnifying lens system 25 in the subsequent stage. Further, a DSB modulation signal such as sin (2πfct) sin (2πfmt) is applied as a modulation signal to the acoustooptic device 23 from the AOD driver 24.

When such modulation is performed, the acoustooptic device 23 to which two frequency modulations of fc + fm and fc-fm have been applied generates an acoustic dense wave corresponding to the pitch d of the Bragg diffraction grating. That is, if the velocity of the ultrasonic wave is Va and the applied frequency is f, d = Va / f. Specifically, the beam, which is laser light incident on the acoustooptic device 23, is separated into ± first-order diffracted light by the dense waves, and each diffracted light is modulated at a frequency of frequency fc ± fm. For example, TeO ₂ is used as the material of the acoustooptic device 23, and the sound velocity of this material is 660 m / s.

  When 40 MHz is selected as the frequency fc of the carrier frequency, d = 16.5 μm, and when the He—Ne laser is used for the laser light source 21, the diffraction angle θ is about 2.19791 degrees. In FIG. 1, the optical axis L is illustrated as not changing. However, in practice, the optical system after the acoustooptic element 23 is tilted by the diffraction angle θ or a bias is applied to the two-dimensional scanning device 26. In this case, the inclination of the diffraction angle θ is effectively given.

  When a frequency fm of about 10 kHz is added to this carrier frequency, the ± first-order diffracted light becomes θ = 2.19847 degrees and θ = 2.19737 degrees, and is modulated at 40.01 MHz and 39.99 MHz, respectively. When laser light is incident on the objective lens 31 while maintaining this angle, if the focal length of the objective lens 31 is 2 mm and NA 0.9, the center distance of the beam is about 0.6 μm, and the diffraction at this time The limit is w = 0.857 μm. That is, the beam separation degree is made smaller than that of the diffraction limited system.

  If the beam separation, which is the center distance of the beam, is further reduced, the resolution can be improved. However, if the frequency of the heterodyne detection is lowered, the processing speed becomes slow. In this case, if an acoustooptic device having a higher sound speed is used, the Bragg diffraction grating pitch d can be increased, and the processing speed can be improved. In fact, a sound velocity Va of about 4.2E + 3 m / s is also known and is commercially available.

  Here, the pupil transmission magnifying lens system 25 disposed between the acoustooptic element 23 and the polarization beam splitter 27 transmits the position of the exit surface of the acoustooptic element 23 to the next two-dimensional scanning device 26 in a conjugate manner. This is an optical system. The light that has passed through the pupil transmission magnifying lens system 25 is sent to the two-dimensional scanning device 26. By the pupil transmission lens system 30 that is conjugated to the pupil position of the objective lens 31, the light from the two-dimensional scanning device 26 is The light enters the objective lens 31 as ± first-order diffracted light having an angular difference.

That is, by inputting two DSB-modulated signals having a carrier frequency fc and a modulation frequency fm from the outside to the acoustooptic device 23 via the AOD driver 24, these two light beams that are very close to each other can be created.
As described above, the pupil transfer lens system 25 that transmits the substantial pupil position of the acoustooptic device 23 to the pupil position of the two-dimensional scanning device 26, the two-dimensional scanning device 26 that scans light on the surface, and the two-dimensional Through the pupil transmission lens system 30 for transmitting the pupil position of the scanning device 26 to the pupil of the objective lens 31, light beams emitted in two directions that are very close to each other are incident on the objective lens 31.
In this way, two beams that are very close to each other and have the same diameter can be obtained, such as a beam LA indicated by a solid line and a beam LB indicated by a dotted line in FIG.

  As a result, the beams LA and LB which are light beams converged by the objective lens 31 scan the measurement object G1 on the surface as two very close spots. Since these two spots become two signals of frequency fc + fm and frequency fc-fm, a signal reflecting unevenness information and refractive index distribution of the measurement object G1 can be obtained by performing heterodyne detection on these signals.

  The frequency of the two beams LA and LB is “light frequency + carrier frequency fc ± modulation frequency fm”. When the center distance between two close beams is set below the diffraction limit as described above, each beam does not fall below the diffraction limit of Abbe's theory, but with slightly shifted light at different frequencies. Therefore, differential information can be acquired by performing heterodyne detection. Further, the light receiving element 29 shown in FIG. Then, with the optical axis L as a boundary line, these light receiving elements are arranged so as to have a dark line in a direction perpendicular to the beam separation direction across the boundary line, and a beat signal is obtained from the sum signal or difference signal. To get. At this time, if a sum signal is used, it is substantially equivalent to a differential interference microscope, and if a difference signal is used, a much higher lateral resolution can be obtained.

Here, the property of the light transmitted to the measuring object G1 will be specifically described. The light narrowed down by the objective lens 31 becomes two adjacent beams LA and LB as shown in FIG. 2, and is sent to the measurement object G1. Note that the complex amplitude Ea of the beam LA and the complex amplitude Eb of the beam LB are expressed by the following equations.
Ea = Aexpj (2π (fo + fc + fm) t)
Eb = Bexpj (2π (fo + fc-fm) t + δ)
Δ in the expression of the complex amplitude Eb represents the phase difference in the height direction of the beam LB with respect to the beam LA, and fo represents the frequency of light. Note that, as described above, the interval between the two beams is determined by the modulation frequency fm applied to the acoustooptic device 23, and is thus independent of the scanning speed.

  The two beams LA and LB reflected by the measurement object G1 shown in FIGS. 1 and 2 are guided to the light receiving element 29 via the objective lens 31, the pupil transfer lens system 30, and the polarization beam splitter 27. If the light receiving element 29 is arranged at a position conjugate with the position of the two-dimensional scanning device 26, the two beams LA and LB return to the same position, so that the phase difference δ between the two beams LA and LB becomes a beat signal. Detected.

That is, since the light receiving element 29 has a structure having a photoelectric conversion unit (not shown), the intensity I of the two beams LA and LB on the light receiving element 29 is a value based on the following formula and the photoelectric conversion of the light receiving element 29 is performed. Is sent to the signal comparator 33.
I = (Ea + Eb) (Ea + Eb) ^* = A ² + B ² + 2ABcos (2π * 2fmt + δ)
Accordingly, the phase difference δ can be measured by performing phase comparison of heterodyne detection at a frequency of 2 fm using the signal comparator 33 shown in FIG. In this way, phase information is acquired.

  By the way, the light receiving element 28 disposed opposite to the light receiving element 29 with the polarization beam splitter 27 in between also has a structure having a photoelectric conversion unit (not shown). A beat signal of an incident beam of diffracted light generated by the acoustooptic device 23 is incident on the light receiving device 28 and detected by the photoelectric conversion unit of the light receiving device 28. That is, since the phase difference generated in the optical system or the like up to the acoustooptic device 23 is detected by the photoelectric conversion unit of the light receiving device 28, the light receiving device 28 serves to provide a phase reference.

  On the other hand, as described above, in the light receiving element 29, a beat signal obtained by adding phase difference information between the two beams of the beam LA and the beam LB is detected by the photoelectric conversion unit in the light receiving element 29 and is sent to the signal comparator 33. Sent. Therefore, the true phase difference δ is detected by performing the two phase comparisons in the signal comparator 33. The true phase difference δ is δh = λδ / 4π, which is the average phase difference between the beam LA and the beam LB, that is, difference information of the average height h. Here, λ represents the wavelength of the laser light emitted from the laser light source 21.

  If these pieces of information are sent to a data processing unit 34 composed of a CPU, a memory, etc. connected to the signal comparator 33, the data processing unit 34 records this information together with the plane scanning information, and the measurement object G1 is recorded. Surface profile information can be easily derived. Further, acquiring higher-speed data can be realized by using the acoustooptic device 23 having the highest sound speed Va as much as possible.

On the other hand, in the present optical system, in order to perform heterodyne detection, a part of the irradiated modulation signal is extracted by the beam splitter 27 and a reference signal is obtained by the light receiving element 28. Then, a differential output is obtained from the reference signal and the signal detected by the light-receiving element 29 divided into two, the phase difference information and the intensity information are obtained by the signal comparator 33, and sent to the data processing unit 34.
The data processing unit 34 displays the information acquired together with the scanning information as an image or data form on a display or stores it as data in a memory.

  However, the light receiving element 28 is not necessarily required, and may be compared with a signal output to the acoustooptic element 23, that is, a signal itself applied to the acoustooptic element 23. In this case, a delay occurs due to a circuit system, an acoustooptic device, or the like. However, if it is corrected in advance, it does not have a great influence on phase difference detection or the like.

  Further, two very close spot lights that scan the surface of the measuring object G1 on the surface are lights having different frequencies. However, the use of a magnifying optical system such as the pupil transfer lens systems 25 and 30 can substantially make the spot very close even at a high frequency. Thus, high-speed information acquisition can be performed by high-speed scanning.

  As described above, using such an optical system makes it possible to acquire three-dimensional measurement data every time two-dimensional scanning is performed. For this reason, according to the present optical system, it is possible to observe and measure the state change of cells and microorganisms, the transient change of the surface state, and the like at high speed.

  On the other hand, the two lights obtained in this way can have a very low degree of separation by the above-described method, and are substantially the same as the information scanned with one beam. On the other hand, the DPC method described above is a method of scanning with one beam and obtaining a differential output of at least two divided light receiving elements arranged in the far field.

  In other words, compared to the DPC method, in the method further using the present heterodyne method, the phase change and the intensity change can be detected with high accuracy by performing the heterodyne detection, and the light received by the light receiving element 29 is reduced. Even if it is very weak, it can be detected with high accuracy by increasing the gain of the detection circuit system, and since the detected signal is only the modulation signal, it is not affected by disturbance light. High-precision detection can be performed.

  In addition, since a 3D stereoscopic image can be displayed by using a commercially available autostereoscopic display or a 3D display using polarized glasses, the apparatus should be useful in education, research, and medicine. Can do. At this time, since the degree of overlap of the two beams is made smaller than the beam diameter, the path difference between the two beams hardly occurs. For this reason, the influences of disturbances and vibrations are generated simultaneously by the two beams, and these influences are offset.

  On the other hand, in this optical system, an example in which the degree of beam separation is much smaller than the individual beam diameters is shown. However, by increasing the modulation frequency, the optical system of the present invention is useful even when the beam separation degree is increased and the degree of separation of the beam diameter is required.

  In this optical system, an example using a two-dimensional scanning device has been described. However, if the application requires simple data in only one direction, the two-dimensional scanning device is replaced with a one-dimensional scanning device. The same effect can be obtained. As these one-dimensional scanning devices, galvanometer mirrors, resonant mirrors, rotating polygon mirrors, and the like can be employed. In addition, the two-dimensional scanning device can be realized by preparing two one-dimensional scanning devices for the X direction and the Y direction and passing through the pupil transfer lens system. Further, a micromirror device using a micromachine technique may be used. As this micromirror device, both one-dimensional and two-dimensional devices are known and commercialized.

  As described above, by processing the spatial frequency information on the Fourier transform plane, it is possible to bring about a very high lateral resolution improvement, particularly in the difference calculation. Similarly, as described above, the intensity difference signal is data that reflects the height of the profile data.

This optical system is a case where the reflection optical system described in the above description is replaced with a transmission optical system.
FIG. 4 is a block diagram showing an apparatus using a transmission type optical system according to the present optical system. Since the main optical system is the same as the above optical system, the description thereof will be omitted. However, in this optical system, as shown in FIG. 4, the light collected by the objective lens 31 is transmitted through the measurement object G2. For this reason, the light receiving element 49 is characterized in that it is disposed on the opposite side of the objective lens 31 with the measurement object G2 interposed therebetween. In other words, in the case of this optical system, the light receiving element 49 divided in such a manner that a dark line extends in a direction perpendicular to the separation direction of the two beams is arranged on an extension line of the optical axis L of the objective lens 31.

  As described above, according to the present optical system, the light receiving element 49 can be arranged close to the measurement target G2 as compared with the reflection type optical system, so that the spatial frequency that can be acquired can be set very high. . Therefore, by converting the signal gain of the electrical high frequency signal obtained by the adjacent light receiving element by the frequency in the same manner as this optical system, the MTF curve is flattened and used for measurement, or the high frequency enhancement is performed. It is possible to emphasize the refractive index change and shape change of cells and the like.

  In particular, permeation can play a major role in testing whether IPS and ES cells are normal and checking for the presence or absence of cancer cells because it allows real-time observation of the state of living cells without staining and non-invasiveness. Can do. This is a feature that is greatly different from a measuring instrument such as an electron microscope that cannot be observed unless the living body is killed even at a high magnification. As described above, particularly in transmission, the light receiving element can be arranged close to each other. This means that, as described above, since the light receiving element is equivalent to a kind of lens, it is possible to acquire even spatial frequency information impossible with an optical lens.

A first embodiment of the optical distance measuring device according to the present invention will be described below with reference to FIG. FIG. 5 is a schematic diagram showing the configuration of the optical distance measuring device of this embodiment.
In the following, for the sake of simplicity, a phase acquisition method using a single beam using a non-modulated DPC-like method will be described. However, through an acousto-optic element that creates a heterodyne signal and a one-dimensional or two-dimensional scanning system. The same can be said for the heterodyne method in which two beams that are very adjacent to each other are created.

  As shown in FIG. 5, a laser light source 21 that is a light source that emits light and is a semiconductor laser is disposed to face the objective lens 31 via an optical device (not shown). The light emitted from the laser light source 21 becomes parallel light by a collimator lens (not shown) and is incident on the objective lens 31. And the light which permeate | transmitted the objective lens 31 is converged and irradiated to the sample S which is a measurement object of a permeate | transmittance.

  In this embodiment, as shown in FIG. 5, a condenser lens 36 for condensing a light beam transmitted through the sample S and diffracted into a parallel light beam is inclined with respect to the optical axis L0 of the 0th-order diffracted light. It is installed. Thus, not only a part of the 0th-order diffracted light but also a part of the 1st-order diffracted light having a higher spatial frequency compared to the case where the same lens is used can be incorporated. In other words, in this embodiment, the light irradiated to the sample S is diffracted as it passes through the sample S to become 0th order diffracted light and 1st order diffracted light. Further, the condensing lens 36 in a state in which a part of the 0th-order diffracted light and a part of the 1st-order diffracted light are inclined by the optical axis L3 having an intermediate inclination angle between the 0th-order diffracted light and the 1st-order diffracted light. Is incident on. The condensing lens 36 is substantially a Fourier transform lens, and the Fourier transform pattern of the sample S is transmitted by the condensing lens 36.

  On the optical axis L3 below the condenser lens 36, a beam splitter 38, which is a separation element for splitting the parallel light beam emitted from the condenser lens 36 in the right direction, is disposed. The beam splitter 38 splits the beam, which is the light beam, into two optical paths, the optical path B1 where the light beam travels straight and the optical path B2 where the beam is bent at a right angle.

  A rhomboid prism 39 is disposed on the optical path B1 along the optical axis L3. One surface of the rhomboid prism 39 is a semi-transparent mirror 39A, and the surface opposite to the semi-transparent mirror 39A is a semi-transparent mirror 39B. A light receiving element is provided at a position where light passes through or reflects each surface to receive light. 40 and 41 are arranged. On the other hand, a rhomboid prism 49 similar to the rhomboid prism 39 is disposed on the optical path B2 orthogonal to the optical axis L3. One surface of the rhomboid prism 49 is a semi-transparent mirror 49A, and the surface opposite to the semi-transparent mirror 49A is a semi-transparent mirror 49B. A light receiving element is provided at a position where light passes through or reflects each surface. 50 and 51 are similarly arranged.

  The cross sections of the light beams in the optical paths B1 and B2 are each circular, but the light beams in the optical path B1 are divided into semicircular semicircular beams BA and BB obtained by dividing the light beam in the direction perpendicular to the paper surface of FIG. . Similarly, the beam of the optical path B2 is divided into semicircular semicircular beams BC and BD, which are divided in half in a direction perpendicular to the paper surface of FIG.

  Here, the semicircular beams BA and BC are areas on the right half of the traveling direction in FIG. 5 of the zero-order diffracted light, but include the low-frequency first-order diffracted light. This area is hereinafter referred to as a 0th-order diffracted light area. Semicircular beams BB and BD are areas including first-order diffracted light. This area is hereinafter referred to as a first-order diffracted light area. FIGS. 6 and 7 are diagrams showing the relationship between the respective light fluxes of the optical paths B1 and B2 branched into two and the delay elements. FIG. 6 shows the semicircular beams BA and BB separated from each other, and FIG. 7 shows the semicircular beams BC and BD separated from each other.

  The upper half of FIG. 6 (may be the lower half of FIG. 6) of the semicircular beam BA in the optical path B1 is a quarter wavelength plate and has a phase of π / 2 by the delay element 43A which is also the first delay element. Produces delayed light. Then, the semicircular beam BA and the semicircular beam BB are parallel-shifted by the semi-transparent mirror 39A and the semi-transparent mirror 39B of the rhomboid prism 39 and synthesized as shown in FIG. On the other hand, the upper half in FIG. 7 of the semicircular beam BD in the optical path B2 is a quarter-wave plate and generates light whose phase is delayed by π / 2 by the delay element 43B which is also the second delay element. Further, the lower half of FIG. 7 of the semicircular beam BD is a half-wave plate and generates light whose phase is delayed by π by the delay element 43C which is also the second delay element. Then, the semicircular beam BC and the semicircular beam BD are shifted in parallel by the semitransparent mirror 49A and the semitransparent mirror 49B of the same rhomboid prism 49, and are similarly synthesized.

  As described above, the semicircular beam BA where the delay element 43A is located is the 0th-order diffracted light area, and the semicircular beam BD where the delay element 43B is located is the 1st-order diffracted light area, but causes a phase difference of π / 2. The positional relationship between the delay elements 43A and 43B may be arranged in any way as long as they are different from each other. The delay element 43C may be positioned in the lower half of the semicircular beam BC.

  Here, the semicircular beams BA and BB of the optical path B1 synthesized by the rhomboid prism 39 are sent to the light receiving element 40 which is the first light receiving element. The semicircular beams BC and BD synthesized by the rhomboid prism 49 are sent to the light receiving element 50 which is the second light receiving element. The light receiving element 50 is a light receiving element corresponding to the light receiving element 40 in another optical path B2 branched by the beam splitter 38. On the other hand, the light receiving element 40 is formed by divided light receiving elements 40A and 40B which are divided into two in the direction perpendicular to the paper surface with the paper surface as a boundary. That is, the upper part of the light receiving element 40 is a divided light receiving element 40A, and the lower part is a divided light receiving element 40B. Similarly, the upper part of the light receiving element 50 is a divided light receiving element 50A, and the lower part is a divided light receiving element 50B.

  As described above, the light beam received by the light receiving element 40 is a combination of the semicircular beam BA in the 0th-order diffracted light area and the semicircular beam BB in the 1st-order diffracted light area. Accordingly, the upper half of the light beam obtained by causing the light of 1 / 2π phase delay in the 0th-order diffracted light area to interfere with the light in the 1st-order diffracted light area is received by the divided light receiving element 40 </ b> A in the upper part of the light receiving element 40. On the other hand, the lower half of the light beam in which the light in the 0th-order diffracted light area and the light in the 1st-order diffracted light area interfere with each other without phase delay is received by the divided light receiving element 40B in the lower part of the light receiving element 40.

  Similarly, the light beam received by the light receiving element 50 is a combination of the semicircular beam BC in the 0th-order diffracted light area and the semicircular beam BD in the 1st-order diffracted light area. Accordingly, the upper half of the light beam obtained by causing the light of 1 / 2π phase delay in the first-order diffracted light area and the light in the 0th-order diffracted light area to interfere with each other is received by the divided light-receiving element 50A in the upper part of the light-receiving element 50. On the other hand, the lower half of the light beam obtained by causing the light of the π phase delay in the first-order diffracted light area and the light in the 0th-order diffracted light area to interfere with each other is received by the divided light receiving element 50B in the lower part of the light receiving element 50.

  As described above, when the light in the 0th-order diffracted light area is used as a reference, the divided light-receiving element 40A receives the light in the 1st-order diffracted light area by 1 / 2π, and the divided light-receiving element 40B receives the light in the first-order diffracted light area in the same phase. The divided light receiving element 50A receives the light in the first-order diffracted light area with a delay of 1 / 2π, and the divided light-receiving element 50B receives the light in the first-order diffracted light area with a delay of π.

  Further, the divided light receiving elements 40A and 40B and the divided light receiving elements 50A and 50B are connected to the comparator 7 for comparing signals from the divided light receiving elements 40A and 40B and the divided light receiving elements 50A and 50B, respectively. . The comparator 7 is connected to a data processing unit 8 that finally processes data and obtains a profile of the sample S and the like. For this reason, the comparator 7 and the data processing unit 8 calculate the output sum and output difference between the divided light receiving elements 40A and 40B of the light receiving element 40 and the output sum and output difference between the divided light receiving elements 50A and 50B of the light receiving element 50. The output sum / difference detection unit is detected.

Next, what kind of information the interference light brings will be described.
In order to simplify the explanation, if the sample S has a sine wave shape with a height d and a pitch d, the optical phase θ is expressed by the following equation.
θ = 2π (h / λ) sin (2πx / d−θ0) (9) Equation (9) The amplitude E of the light diffracted from the sample S is (9) on the surface separated by the focal length f. Since it is given as a convolution of the Fourier transform of the equation and the aperture of the objective lens 31, it is expressed as follows. However, the Bessel function that is the Fourier transform of the phase in equation (9) is assumed to be ± 1st order.

The light having the amplitude E of the expression (10) is collected by the condenser lens 36. At this time, the light beam is tilted and condensed so that the optical axis L3 of the condensing lens 36 shown in FIG. 5 is at the position of the emission angle ξ that is an angle within the emission range of the 0th-order diffracted light corresponding to the opening of the objective lens 31. A lens 36 is disposed.
In order to simplify the following description, the inclination angle of the optical axis L3 is made to coincide with the emission angle ξ. However, if the 0th-order diffracted light J0 is incident, it may be larger or smaller than this angle. good. When the tilt angle of the optical axis L3 changes in this way, the 0th-order diffracted light area changes as described below, so that the interference region between the 0th-order diffracted light J0 and the first-order diffracted light J1 changes. Does not affect the quantification discussion.

  Hereinafter, in order to simplify the explanation, the condenser lens 36 is made to coincide with the NA of the objective lens 31. Here, the radius of the objective lens is a and the focal length is f. FIG. 9 is a schematic diagram showing the 0th-order diffracted light area and the ± 1st-order diffracted light area when the phase pitch d is 0 <λf / d <a / 2, and represents each region of the 0th-order diffracted light and the ± 1st-order diffracted light. .

  The 0th-order diffracted light area incident on the condenser lens 36 is an area between the one-dot chain line X1 and the one-dot chain line X2, and the first-order diffracted light area is also an area on the right side of the one-dot chain line X2. As shown in FIG. 5, the light beams are parallel-shifted and superposed by the rhomboid prism 39, but the 0th-order diffracted light area reflected by the semi-transparent mirror 39A of the rhomboid prism 39 and the first-order reflected by the semi-transparent mirror 39B. There is a substantial optical path difference with the folding area. However, if the rhomboid prism 39 is made of a stable material such as glass that has a small thermal expansion, the optical path difference is constant, and this path difference is θ1.

  Therefore, the semicircular beam BA in the 0th-order diffracted light area is parallel-shifted by the rhomboid prism 39 and superimposed on the semicircular beam BB in the 1st-order diffracted light area. ). Specifically, the 0th-order diffracted light J0 shown in FIG. 9A is as shown in FIG. 10A because the 0th-order diffracted light area from 0 to a is shifted by a as a whole. Similarly, the −1st order diffracted light −J1 shown in FIG. 9C is also subjected to the same shift, and is as shown in FIG. 10D.

Since the first-order diffracted light J1 shown in FIG. 9B spans both the 0th-order diffracted light area and the first-order diffracted light area, it is divided into a portion that receives the shift and a portion that does not receive the shift. An optical path difference θ1 is added. This is as shown in FIGS. 10B and 10C. That is, the portion of the 0th-order diffracted light area in FIG. 9B is shifted by a, but the portion of the 1st-order diffracted light area remains the same.
In consideration of the overlapping part of these parts, the amplitude distribution E can be obtained from the following equation.

  Here, α and β in the above equation (11) are variables reflecting the phase of each delay element. That is, in the divided light receiving element 40A that receives the light in which the semicircular beam BA in the 0th-order diffracted light area is delayed by the delay element 43A and the semicircular beam BB in the 1st-order diffracted light area remains as it is, α = j and β = 1. Become. In the divided light receiving element 40B that receives light in which both the semicircular beam BA in the 0th-order diffracted light area and the semicircular beam BB in the 1st-order diffracted light area remain as they are, α = 1 and β = 1.

  In the divided light receiving element 50a that receives the light in which the semicircular beam BD in the first-order diffracted light area is delayed by the delay element 43B and the semicircular beam BC in the zero-order diffracted light area remains as it is, α = 1 and β = j. Become. In the divided light receiving element 50B that receives the light in which the semicircular beam BD in the first-order diffracted light area is delayed by the delay element 43C and the semicircular beam BC in the 0th-order diffracted light area remains as it is, α = 1 and β = −1. .

  Since the light receiving elements 40 and 50 receive the intensity information of the interference of light, the intensity of equation (11) may be calculated. When the intensity is I, the intensity I is obtained by the following equation in the divided light receiving element 40B and the divided light receiving element 50B (in the same composite order).

  Similarly, when the intensity is I, in the divided light receiving element 40A and the divided light receiving element 50A (in the same composite order), the intensity I is obtained by the following equation.

  Accordingly, the difference output ΔIb between the divided light receiving element 40B and the divided light receiving element 50B and the difference output ΔIa between the divided light receiving element 40A and the divided light receiving element 50A are as follows.

In general, since J0> J1 when the phase change is small, 2J1 ² sinθ0cos (θ0 + θ1) in the equations (12) and (13) can be ignored as the following equations (12) ′ and (13) ′. .

By obtaining the ratio of the expression (12) 'and the expression (13)', the phase θ can be measured from tanθ = tan (θ0 + θ1). This phase θ includes the phase difference of the delay element, but is an amount determined at the time of configuring the present embodiment as described above, and thus is equivalent to where the measurement origin is placed and can be ignored. Further, when the actual amplitude distribution is Eo and the phase is Θ, the following equation is obtained.

  When the pitch d of the sample S and the radius a of the objective lens, which is the irradiation beam radius, are associated with the above concept, the following relationship is obtained. However, as described above, J0> J1.

  When the horizontal axis is λf / d and the vertical axis is the modulation amount, a characteristic curve C of the present embodiment according to the MTF curve can be obtained as shown in FIG. In the normal MTF curve, the cutoff frequency of the objective lens is 2a. In this embodiment, it is possible to obtain a frequency up to 3a higher than this frequency. I understand more.

  Although it was originally difficult to distinguish the first-order diffracted light component contained in the 0th-order diffracted light area from the 0th-order diffracted light, it is possible to calculate and distinguish the first-order diffracted light in the 0th-order diffracted light area according to this embodiment. It becomes possible. That is, the spatial frequency is converted into an electrical modulation signal by scanning the laser beam as in the optical system shown in FIGS. 1 and 4, whereas this is detected by heterodyne detection or analysis of the modulation frequency itself. Spatial frequency information can be converted to electrical frequency.

  Therefore, the original magnitude of the first-order diffracted light can be automatically extracted from the above-described series of spatial frequency modulation factors by an electrical frequency filter. In FIG. 11, the gain can be made constant by changing the gain in a hyperbola with respect to the fluctuation of the frequency in the range of 0a, 2a-3a that linearly changes along the horizontal axis. On the other hand, if the flat portion CF from a to 2a where the modulation amount is constant is set to a constant gain, it is effectively frequency independent, that is, a constant modulation degree independent of the spatial frequency. The range of 0-3a can be corrected.

  As described above, the spatial frequency drop due to the conventional lens can be corrected by correcting the spatial frequency dependence of ε. Accordingly, the amount of the first-order diffracted light substantially included in the 0th-order diffracted light area can be estimated, and as a result, γ = J1 / J0 can be correctly evaluated. Further, according to the present embodiment, it is possible to increase the information on the acquired spatial frequency. In other words, since it is possible to acquire even spatial frequencies that could not be obtained with conventional lenses, phase information can be calculated correctly, and effective super-resolution can be realized for phase information of transparent bodies such as cells. it can.

  In addition, as long as the 0th-order diffracted light is substantially incident as the light in the 0th-order diffracted light area incident on the condenser lens 36, the optical axis L3 may be inclined in any way. For example, when the 0th-order diffracted light is set to be slightly incident, the range of interference with the first-order diffracted light is effectively expanded, so that the spatial frequency can be made larger than that described above. In this case, since the flat portion CF in the characteristic curve C of FIG. 11 is effectively increased, the characteristic can be flattened over almost the entire range where the spatial frequency can be acquired except for the low frequency portion and the high frequency portion of the spatial frequency. Therefore, it is not necessary to use the frequency filter as described above.

  However, in this case, since the degree of interference with the 0th-order diffracted light is reduced, it is necessary to increase the gain of the light receiving element, resulting in degradation of the SN ratio. On the other hand, when the 0th-order diffracted light area is enlarged, the spatial frequency region to be acquired and the flat portion of the spatial frequency are reduced. Therefore, better characteristics can be obtained by applying a frequency filter. In this case, the SN ratio of the acquired signal is also good. On the other hand, there is not much influence by the objective lens 31, and the resolution is determined by the condensing lens 36. Therefore, according to the present embodiment, an optical system having a wide visual field range and high lateral resolution can be realized. This is one of the major features that cannot be seen in a normal imaging optical system. The role of the light receiving element 41 in FIG. 5 is the same as that of the light receiving element 40, and is used for effective use of light.

  Here, a modification shown in FIG. 12 can be considered as a modification of the present embodiment, and this modification will be described below. In this modification, instead of the prisms 39 and 49, a beam splitter 60 in which two cube-type beam splitters 60A and 60B are arranged is employed. Thus, the two beam splitters 60A and 60B constitute the functions of the semi-transparent mirror 39A and the semi-transparent mirror 39B of the prism 39 shown in FIG. 5, for example. Similarly, a beam splitter 61 in which two cube-type beam splitters 61A and 61B are arranged constitutes the function of the semi-transparent mirror 49A and the semi-transparent mirror 49B of the prism 49. Therefore, the present modification also exhibits the same operational effects as the embodiment described above.

Next, Embodiment 2 of the optical distance measuring apparatus according to the present invention will be described below with reference to FIG. In this embodiment, an optical system for quantifying phase information with one condenser lens 36 will be described with reference to FIG.
As shown in FIG. 13, also in this embodiment, the laser light source 21 is arranged to face the objective lens 31 via an optical device (not shown), and the laser beam that has passed through the objective lens 31 is a sample of a transmission material. Irradiates with convergence to S. The laser light applied to the sample S is condensed by a condensing lens 36 located on the optical axis L0 to be a parallel light beam.

  A beam splitter 71 is disposed at a position directly below the condenser lens 36 on the optical axis L0 of the laser light. The beam splitter 71 has a structure in which two beam splitters 71A and 71B for separating light beams in opposite directions are arranged in the left-right direction in FIG. Accordingly, the beam splitter 71 separates the light flux into a total of four paths in two opposite directions and two transmission directions with the optical axis L0 as a boundary.

An optical system combining the block 1 and the block 2 is disposed on the right side with the optical axis L0 shown in FIG. 13 as a boundary. Each of the blocks 1 and 2 includes beam splitters 72 and 73, light receiving elements 81 and 82, delay elements 43A, 43B, and 43C. These blocks 1 and 2 include a 0th-order diffracted light area and a 1st-order diffracted light area, and the combination of these blocks 1 and 2 is substantially the same as the optical system after being separated by the beam splitter 38 shown in FIG. It has become.
On the other hand, the block 3 and the block 4 include a 0th-order diffracted light area and a −1st-order diffracted light area, are arranged in a symmetrical system of the block 1 and the block 2, and have the same configuration as the blocks 1 and 2. For this reason, the combination of these blocks 3 and 4 is an optical system including a −1st order diffracted light area not shown in the embodiment shown in FIG. 5, but functions in substantially the same manner as in the embodiment of FIG. 5. To do.

  As described above, each of the blocks 1 to 4 has the same effect as the embodiment shown in FIG. According to the present embodiment, information having an extremely high spatial frequency as in the first embodiment shown in FIG. 5 cannot be obtained, but phase information can be quantified with a very simple configuration. Therefore, in the present embodiment, the characteristic is such that the flat portion CF of the characteristic curve C shown in FIG. 11 is eliminated, but the frequency filter based on the electrical frequency conversion of the spatial frequency accompanying the scanning of the laser light described above is extremely effective. It is possible to reproduce missing information due to the MTF that the condenser lens 36 essentially has.

  As described above, in this embodiment, it is possible to obtain a measurement value that correctly reflects the phase information of the sample S that the condenser lens 36 originally has. Further, each of the blocks 1 to 4 includes beam splitters 72 and 73, light receiving elements 81 and 82, delay elements 43A, 43B, and 43C. Although not shown, the light receiving elements 81 and 82 of the blocks 1 to 4 are connected to the above-described comparator 7, and the comparator 7 is connected to the data processing unit 8. From this, the same effect as Example 1 shown in FIG. 5 can be obtained also in this example. Further, it is conceivable to arrange the optical systems of the blocks 1 to 4 in a plurality of directions such as a direction perpendicular to the paper surface of FIG. 13 while shifting the beam splitters 71A and 71B by an appropriate amount. By arranging a plurality of blocks 1 to 4 in this way, it is possible to obtain measurement values relating to a plurality of directions when the sample S is viewed from the objective lens 31 side.

A third embodiment of the optical distance measuring device according to the present invention will be described below with reference to FIG.
FIG. 14 is a schematic diagram showing the configuration of the optical distance measuring device of the present embodiment. In the present embodiment, as shown in FIG. 14, as a means for giving a phase difference of ± π / 2 or π between 0th-order diffracted light and 1st-order diffracted light, a diffraction grating 54 which is a grating formed in a sine wave shape. Are arranged at the focal point of the lens 52.

  Specifically, in this embodiment, as shown in FIG. 14, a condensing lens 36 is disposed on an inclined optical axis L3, and a light beam including 0th-order diffracted light and 1st-order diffracted light is made into a parallel light beam. A beam splitter 38 similar to that shown in FIG. 5 is disposed below the condenser lens 36, and the beam splitter 38 divides the parallel light flux. Further, the light beam including the 0th-order diffracted light and the 1st-order diffracted light, which is one of the branched parallel light beams, is stopped by the lens 52 positioned below the beam splitter 38, and the diffraction grating 54 is disposed near the focal plane. However, the diffraction grating 54 is a phase type grating which is a sine wave phase diffraction grating.

  Then, each of the 0th order diffracted light and the 1st order diffracted light diffracted by the sample S included in the 0th order diffracted light area is caused to interfere with each other by the diffraction grating 54, and the first time diffracted by the sample S included in the 1st order diffracted light area. Each of the folded light and the 0th-order diffracted light is caused to interfere by the diffraction grating 54. Thus, the 0th-order diffracted light and the 1st-order diffracted light diffracted by the sample S are effectively interfered with each other. In FIG. 14, the hatched portion is the interference portion K where the 0th-order diffracted light and the 1st-order diffracted light overlap, but a similar interference portion K exists on the opposite side of the optical axis L3. Further, the light receiving element 50 receives the interfered light beam. The light receiving element 50 is connected to the above-described comparator 7 (not shown), and the comparator 7 is connected to the data processing unit 8.

  On the other hand, in the direction orthogonal to the optical axis L3 at the position of the beam splitter 38, the same lens 52, diffraction grating 54A, and light receiving element 50 are similarly arranged and operate in the same manner as described above. However, the diffraction grating 54A is an intensity type grating which is a sine wave amplitude diffraction grating.

Here, the values of the amplitude E of the sine wave amplitude diffraction grating and the amplitude E of the sine wave phase diffraction grating are obtained by the following equations. However, in the following formula, the phase is represented by θ.
In the sine wave amplitude diffraction grating, the following amplitude E is set.
E = E ₀ sin (2πx / d-θ)
In the sine wave phase diffraction grating, the following amplitude E is set.

  As described above, in this embodiment, as shown in FIG. 14, the parallel light beam including the 0th-order diffracted light and the 1st-order diffracted light is stopped by the lens 52, and the diffraction gratings 54 and 54A are arranged near the focal plane. At this time, the above-described sine wave amplitude diffraction grating causes a phase shift of ± π / 2, and the sine wave phase diffraction grating causes a phase shift of 0 or π, which is a phase shift of in-phase or anti-phase. If the combination is applied to the relationship of the delay elements shown in FIG. 5, an optical system similar to that of the first embodiment shown in FIG. 5 can be formed.

  Further, when the pitch of the diffraction gratings 54 and 54A is about the same as the beam diameter narrowed by the lens 52, it becomes sensitive to the phase θ of the above formula. Accordingly, the phase θ is determined by relatively adjusting the focal position of the beam and the positions of the diffraction gratings 54 and 54A. For example, in the sine wave amplitude diffraction grating, if the phase θ = 0, it becomes ± π / 2 between the 0th order diffracted light and the ± 1st order diffracted light, and if the phase θ = −π / 2, then the 0th order diffracted light and ± 1 The phase is reversed between the next diffracted lights. As a result, a phase difference of ± π / 2 or π is generated between the 0th order diffracted light and the 1st order diffracted light, as in the first embodiment shown in FIG.

  Here, a modification of the present embodiment will be described with reference to FIG. For example, the diffraction grating 54 irradiated with one branched light beam is a phase type grating, and for this one light beam, the 0th order diffracted light and the ± 1st order diffracted light are in phase or out of phase with the optical axis L3 as the center. The diffraction grating 54 is arranged with its position adjusted. Separately, the diffraction grating 54A irradiated with the other branched light beam is an intensity type grating, and the diffraction grating 54A is shifted by ± 1/4 pitch with respect to the other light beam. As a result, in this modification, a phase difference of π / 4 or 3π / 4 is generated between the 0th order diffracted light and the 1st order diffracted light.

A fourth embodiment of the optical distance measuring device according to the present invention will be described below with reference to FIG.
FIG. 15 is a schematic diagram showing the configuration of the optical distance measuring device of the present embodiment. As shown in FIG. 15, in this embodiment, the condensing lens 36 is inclined with respect to the optical axis L0 of the 0th-order diffracted light. As a result, not only a part of the 0th-order diffracted light but also a part of the 1st-order diffracted light having a higher spatial frequency compared to the case where the same lens is used, and interference is realized in the imaging optical system. ing. Although not shown, in the present embodiment, a similar optical system is disposed at a target position with respect to the axis L0.

  The process up to obtaining the part of the 0th-order diffracted light and the part of the 1st-order diffracted light by tilting the condenser lens 36 is the same as that of the embodiment of FIGS. In the present embodiment, the diffracted lights that have been converted into parallel light beams by the condenser lens 36 are condensed by the lens 52. The lens 52 causes the diffracted lights to overlap in the vicinity of the focal point and substantially interfere. However, since it is not interference between the 0th order diffracted light and the ± 1st order diffracted light, it is different from the image formation of the sample S itself.

  On the other hand, also in the present embodiment, a beam splitter 38 is disposed between the condenser lens 36 and the lens 52 as in the third embodiment of FIG. However, in the present embodiment, a beam splitter 38A is further arranged, and the parallel light beam branched by the beam splitter 38 is further branched by this beam splitter 38A.

  On the lower side of FIG. 15 of the beam splitter 38A, not only the delay element 43A but also the lens 52, the magnifying optical system 53, and the light receiving element 50 are similarly arranged. Further, not only the delay elements 43B and 43C are disposed on the right side of FIG. 15 of the beam splitter 38A, but also the lens 52, the magnifying optical system 53, and the light receiving element 50 are similarly disposed. These magnifying optical systems 53 have a function of enlarging the interference fringes and the like by increasing the effective focal length of the lens 52. That is, by increasing the effective focal length of the lens 52, the pitch of the interference fringes can be increased.

  According to the present embodiment, the lens 52, the magnifying optical system 53, and the light receiving element 50 along the optical axis L3 are provided. Along with this, if the interference fringes themselves are enlarged by this magnifying optical system 53 and made substantially equal to the size of the light receiving element 50, the first-order diffracted light will naturally have an opposite phase, so that the zero-order diffracted light becomes a bias. Light and dark are reversed in shape. In this way, information can be acquired very easily up to a region having a high spatial frequency. In this embodiment, since the lens 52 is used, a wavefront aberration that allows the phase difference between the 0th-order diffracted light and the 1st-order diffracted light incident on the lens 52 to be reflected as it is is allowed. Therefore, it is not necessary to use an expensive lens.

  Furthermore, according to the present embodiment, the beam splitters 38 and 38A, the delay elements 43A, 43B, and 43C, the lens 52, the magnifying optical system 53, and the light receiving element 50 are arranged, and the light beams are branched by these beam splitters 38 and 38A. Finally, the two light receiving elements 50 each receive the light flux. Although not shown, the two light receiving elements 50 are connected to the above-described comparator 7, and the comparator 7 is connected to the data processing unit 8. From this, the same effect as Example 1 shown in FIG. 5 can be obtained also in this example.

Embodiment 5 of the optical distance measuring device according to the present invention will be described below with reference to FIG.
FIG. 16 is a schematic diagram illustrating the configuration of the optical distance measuring device according to the present embodiment.
As shown in FIG. 16, in this embodiment, the converged light is not incident on the sample S, but a parallel light beam having a relatively large diameter is incident. In this case, the condenser lens 36 is installed to be inclined with respect to the optical axis L0 of the 0th-order diffracted light. Thus, not only a part of the 0th-order diffracted light but also a part of the 1st-order diffracted light having a higher spatial frequency compared to the case where the same lens is used can be incorporated. Although not shown, in the present embodiment, a similar optical system is disposed at a target position with respect to the optical axis L0.

  In this embodiment, the 0th-order diffracted light and the 1st-order diffracted light are respectively used as the condensed light beams. However, separate lenses 64 and 65 having focal points are arranged at the respective focal positions of the condensing lens 36, and these lenses 64 and 65 are arranged. Thus, the condensed light beam is changed to a parallel light beam. After the collimated light beam is made in this way, a part of the 0th-order diffracted light and a part of the 1st-order diffracted light are caused to interfere with each other using the optical system of the embodiment shown in FIG. That is, according to the present embodiment, as shown in FIG. 16, the beam splitters 38B and 38C, the beam splitters 72 and 73, the delay elements 43A, 43B and 43C, the light receiving elements 40 and 50, the comparator 7, and the data processing unit 8 Etc. From this, the same effect as Example 1 shown in FIG. 5 can be obtained also in this example.

  In the case of the present embodiment, since the diameter of the light beam incident on the sample S is large, the in-plane information is averaged. Therefore, by providing a restriction aperture (not shown) in the incident parallel light beam, it can be interpreted as information on that portion, or an irregular pattern in a regular pattern can be detected. That is, since the direction of the regular first-order diffracted light is known in advance by design, the direction of the first-order diffracted light can be suppressed by masking the focal point of the condenser lens 36.

  On the other hand, since the other components are incident on the lenses 64 and 65, information from the defective portion can be detected. For example, the present invention can be applied to defect inspection on a semiconductor wafer, non-uniformity inspection of nanostructures, and the like.

  The embodiments according to the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

The optical distance measuring device of the present invention can be applied not only to the distance to the sample and the shape of the sample, but also to various types of measuring instruments such as a microscope.
The optical distance measuring device of the present invention can be applied not only to a microscope but also to various types of optical devices and measuring devices using electromagnetic waves having waves, and these optical devices and measuring devices using electromagnetic waves having waves. Resolution can be improved.

DESCRIPTION OF SYMBOLS 7 Comparator 8 Data processing part 21 Laser light source 30 Pupil transmission lens system 31 Objective lens 36 Condensing lens 38 Beam splitter 39 Ronoid prism 40 Light receiving element 40A, 40B Division | segmentation light receiving element 43A Delay element 43B, 43C Delay element 49 Ronoid prism 50 Light receiving element 50A, 50B Split light receiving element 52 Lens 53 Magnifying optical system 54 Grating 55, 56 Lens 57, 58 Light receiving element 64, 65 Lens B1, B2 Optical path BA, BB Semicircular beam BC, BD Semicircular beam S Sample L0, L1, L2, L3 Optical axis

Claims (6)

A light source for irradiating a measurement object with a light beam;
A separation element that converts a light beam including the 0th-order diffracted light and the 1st-order diffracted light generated by being diffracted by the measurement object as the light beam is incident into two light beams;
A first delay element that delays the travel of a part of the diffracted light beams constituting each of the light beams divided by the separation element;
A first light-receiving element comprising a pair of divided light-receiving elements that are detected in two parts in a state where the zero-order diffracted light and the first-order diffracted light partially delayed by the first delay element are caused to interfere with each other;
A second delay element for delaying the progress of a part of the diffracted light beams constituting each of the other light beams divided by the separation element with a phase different from that of the first delay element;
A second light-receiving element comprising a pair of divided light-receiving elements that are detected in two parts in a state in which the zero-order diffracted light and the first-order diffracted light partially delayed by the second delay element are caused to interfere with each other;
The phase of the pair of divided light receiving elements of the second light receiving element is different from each other between the electric signals of the two kinds of light receiving outputs detected while the phases of the pair of divided light receiving elements of the first light receiving element are different from each other. An output sum / difference detection unit for detecting an output value of a sum or a difference between electrical signals of two types of detected light reception outputs;
An optical distance measuring device.   The optical distance measuring device according to claim 1, wherein the separation element is disposed on an inclined optical axis having an inclination with respect to an irradiation optical axis of a light beam. The separation element is
A lens that converts a light beam including zeroth-order diffracted light and first-order diffracted light diffracted as it passes through the measurement object into a parallel light beam;
A beam splitter that divides the luminous flux into two luminous fluxes;
The optical distance measuring device according to claim 1 or 2, comprising:   4. The device according to claim 1, wherein the first delay element and the second delay element are quarter-wave plates or half-wave plates, and delay the phase of the light beam by 90 degrees or 180 degrees. 5. Optical distance measuring device.   4. The optical distance measuring device according to claim 1, wherein the first delay element and the second delay element are diffraction gratings and delay the phase of the light beam by 90 degrees or 180 degrees. 5. Prisms are respectively disposed between the first delay element and the first light receiving element and between the second delay element and the second light receiving element,
6. The zero-order diffracted light and the first-order diffracted light are caused to interfere with each other by the prism before the first and second light-receiving elements detect the zero-order diffracted light and the first-order diffracted light, respectively. The optical distance measuring device described.

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