JPS63298019A - Knife edge for measuring laser beam intensity distribution - Google Patents

Abstract

PURPOSE:To accurately measure a beam intensity distribution by equalizing two areas which are provided on a beam crossing direction about a boundary line in reflection factor to certain wavelength, and making the transmissivity of one area to other wavelength smaller than that of the other. CONSTITUTION:A focus servo mechanism performs focus servocontrol by utilizing a 1st area P in a knife edge 5. Then the knife edge 5 is sent laterally as shown by an arrow B to make a laser beam to be measured as an original knife edge cross the boundary line part between 1st and 2nd areas P and Q, thereby measuring the beam intensity distribution. At this time, the areas P and Q have nearly equal reflection factors P and Q to the laser beam (wavelength lambda1) for focus servocontrol, so even if the laser beam moves relatively from the area P to the area Q, the same focus servocontrol is performed. Transmitted light, on the other hand, decreases at the part of the area P, so output characteristics by laser beam (wavelength lambda2) for exposure decreases and the characteristic distribution is differentiated to obtain the laser beam intensity distribution of the beam waist part.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a knife for measuring laser light intensity distribution in, for example, an optical disk master exposure machine.

BACKGROUND OF THE INVENTION In general, an important factor during exposure of an optical disk master is the intensity distribution near the focal point of the laser beam that has passed through the objective lens. There are two known methods for measuring the intensity distribution of a laser beam, particularly the intensity distribution near the focal point of the laser beam under an objective lens: the intensity distribution measurement method on a cathode ray tube and the Knifezi method.

The former method of measuring the intensity distribution on a cathode ray tube magnifies the image at the beam waist with a microscope, photographs it with a solid-state camera, and digitizes the brightness and darkness on the cathode ray tube to understand the laser light intensity distribution ( “Optical Memory Symposium
86 Collected Papers” p. 157). However, in this measurement method, the resolution is limited by the resolving power of the cathode ray tube. Furthermore, it is difficult to understand the relationship between the brightness and darkness on the cathode ray tube and the laser light intensity distribution.

On the other hand, the latter Naifetsu method is rJuly 197
7/Vo1. l 6. 7/APPLIEDOPTIC
3J and "mastering of rVHD/AHD format video discs". Roughly speaking, the laser beam is blocked in the radial direction by a knife-shaped object, and the amount of light to the detector placed below is changed.The amount of light that reaches the detector is determined by the amount of movement of the knife This is to calculate the intensity distribution of .

Regarding the Naifetsuji method, according to Figures 3 to 5,
This will be explained in more detail. First, as shown in Fig. 3, the focus of the laser beam 2 under the objective lens 1 (beam waist 2a)
The knife 3 is traversed in the radial direction and passed through, and the laser light output on the detector 4 at that time is measured.

The laser light output on the detector 4 at this time is shown in Figure 4 (a
). That is, a characteristic is obtained in which the output decreases as the laser beam 2 is blocked by the knife 3. By differentiating such a characteristic distribution, the fourth
As shown in Figure (b), a laser light intensity distribution at the beam waist 2a is obtained.

However, it is actually extremely difficult to make the knife blade 3 cross accurately at the position of the beam waist 2a. Therefore, in reality, the position of the knife lens 3 should be moved closer to the objective lens 1 side near the beam waist 2a, or
The above measurement is repeated while moving away from the beam, and at each position, a laser beam intensity distribution as shown in Fig. 4(b) is obtained, and the one with the maximum center intensity is measured at the beam waist position 2a. I am trying to process it as a value.

However, even if the knife blade 3 is fed horizontally near the beam waist 2a in this way, it is difficult to feed it in a straight line because it is carried out using a step motor or the like. It tends to have a meandering trajectory with vertical vibrations like line A. Therefore, it is difficult to obtain an accurate measurement value at the beam waist 2a position.

OBJECTS The present invention has been made in view of the above points, and an object of the present invention is to provide a knife for measuring laser light intensity distribution that can accurately measure beam intensity distribution even if the lateral feed accuracy is somewhat poor.

Configuration In order to achieve the above object, the present invention provides a first region and a second region that are divided in the cross-beam direction along a boundary line,
The reflectance of the first region and the second region for a certain wavelength λ1 are set approximately equal, and the reflectance of the first region for a certain wavelength λ2 is set to be approximately equal.
This is characterized in that the transmittance of the region is set to be sufficiently smaller than the transmittance of the second region.

An embodiment of the present invention will be described below with reference to FIG.

This embodiment utilizes a focus servo mechanism in an optical disk master exposure machine.

First, FIG. 1 shows a knife 5 used in place of the knife 3 shown in FIG. 3, which consists of a first region P and a second region Q, which are divided into two along an assumed boundary line.

Note that the direction indicated by arrow B is the cross-beam direction, and the beam is divided into two in this direction.

Here, the optical properties of the first and second regions P and Q will be explained. First, when the reflectance of each area P and Q for a focus servo laser light source, for example, a He-Ne laser with a wavelength λ and 6328 people is P, Q,
The conditions are set such that P, Q, = R, and the two are approximately equal. On the other hand, when the transmittance of each region P and Q for an exposure laser light source, for example, an Ar laser with a wavelength λ = 4579 people (or λ2 = 488 nm) is P, , Q, the two are significantly different, and P ,
(It is set to satisfy the condition Q2.

That is, in this embodiment, the second area Q in the knife 5
The lens is provided with a light-shielding property to function as an original knife, while a first region P having reflective and light-transmitting properties for focus servo is added to the tip thereof. The first and second regions P and Q have such reflectance and transmittance characteristics.
can be formed using multilayer thin film technology.

The operation of measuring the laser light intensity distribution using such a knife 5 will be explained. Basically, this knife 5 is used in place of the knife 3 in FIG. Here, first, focus servo is applied by the focus servo mechanism using the first area P in the knife 5, and then the knife 5 is moved horizontally in the direction of arrow B, and the boundary line between the first and second areas P and Q is A laser beam, e.g. Ar
Cross the laser and measure the beam intensity distribution. At this time, the laser beam for focus servo, for example, the wavelength λ1
For a He-Ne laser, both the first and second regions P and Q have the same reflectance P,,Q.

Therefore, it acts regardless of the first and second regions P and Q.

As a result, even if the laser beam whose intensity is to be measured moves relatively from the first area P to the second area Q due to the lateral movement of the knife 5, the focus servo remains the same as in the first area P. becomes. This means that the distance from the objective lens 1 to the knife 5 is maintained constant when the knife 5 is moved laterally.

Therefore, as explained in the conventional example, even if the lateral movement of the knife 5 itself meanders due to vertical vibration, the distance between the objective lens 1 and the knife 5 is kept constant by the focus servo, so the knife 5 will be moved in a straight line relative to the beam. The effect of changing the amount of laser light 2 reaching the detector 4 is performed by the second region Q in the same manner as in the conventional case.

As described above, according to the laser beam intensity distribution measurement using the knife 5 of this embodiment, even if the cross-feeding accuracy of the knife 5 in the cross-beam direction is somewhat poor, it is possible to always maintain a linear movement state by the focus servo. This allows accurate beam intensity distribution to be obtained.

By the way, according to the knife 5 of this embodiment, the following applications are also possible. That is, conventionally, the true beam waist portion is searched for by moving the knife closer to or away from the objective lens near the beam waist, but when using the knife 5 of this embodiment, In this case, the beam waist can be found simply by changing the electrical offset value.

First, the focus error signal is generally expressed as a straight line passing through the 0 point (=beam waist position), as shown by the characteristic line E1 in FIG. If an offset voltage corresponding to π is applied to such a characteristic line E1 and the focus error signal is changed to follow the characteristic II E , then
The distance between the objective lens and the knife lens can be shifted from the beam waist by OD. Therefore, it is possible to replace the method by moving the knife itself far and near. In particular, compared to conventional mechanical movement methods, electrical offset processing can ensure a more stable movement distance.

In this embodiment, an example of beam intensity distribution measurement for an optical disk master exposure machine, that is, photoresist exposure is explained, but it can also be used as a knife for measuring the beam intensity distribution shape in an actual disk drive such as a compact disk. . In this case, both the recording/reproducing laser light source and the focus servo laser light source have a wavelength of 788 to 830.
It uses one nm semiconductor laser,
Wavelength λ1 that regulates the characteristics of the first and second regions P and Q described above
．． For λ2, λ, = λ, = 788nm or 830n
As m, the reflectance of each region P, Q is P, , Q.

and transmittance P, , Q, may be set.

Effects In the present invention, as described above, the 1.2 regions with the same reflectance and different transmittance characteristics are formed separately, so even if the accuracy of the knife's traverse in the beam transverse direction is somewhat poor when measuring the beam intensity distribution, By using a continuous focus servo from the first area to the second area, it is possible to control the beam so that it moves relatively linearly, so the beam intensity distribution is accurate without being affected by meandering. can be measured.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an embodiment of the present invention, Fig. 2 is a focus error signal characteristic diagram showing an applied example, Fig. 3 is a schematic side view of a conventional knife system, and Fig. 4 is a characteristic diagram. , FIG. 5 is an enlarged side view of the vicinity of the beam waist. 5... Naifetsuji, P... First area, Q... Second area, L... Boundary line, B... Beam crossing direction ratio. b) J55 diagram

Claims (1)

[Claims] A first region and a second region are provided which are divided in the cross-beam direction with the boundary line as a boundary, and the reflectance of the first region and the second region for a certain wavelength λ_1 are set to be approximately equal, and the reflectance for a certain wavelength λ_2 is set to be approximately equal. A knife edge for measuring laser light intensity distribution, characterized in that the transmittance of the first region is set to be sufficiently smaller than the transmittance of the second region.