CN1556422A - Flexible X-ray reflection type multipayer film broad band poarizer and its preparation method - Google Patents

Abstract

Comparing with prior art, the disclosed wide band polarizer possesses advantages of higher luminous flux, degree of polarization, wider band, simple technique of preparation and easy of adjustment. The invention discloses designing thoughts for polarizer and concrete preparation method as well as optical property of the polarizer calculated under the designing thoughts. The invention is applicable to many polarization measurement areas such as soft X ray magnetic circular or linear dichromatic analysis and soft X ray resonance magnetic scattering.

Description

The reflective multilayer film of grenz ray broadband polarizer and preparation method thereof

Technical field

The present invention is a kind of grenz ray wave band multilayer film polarization optical element, is specially the reflective multilayer film of the grenz ray broadband polarizer, can be used for grenz ray magnetic circular dichroism (mcd), magnet-wire two colour analysiss, and many polarimetries field such as grenz ray resonance magnetic scattering.

Background technology

The grenz ray wave band polarizer is a kind of polarizer under accurate Brewster angle (because material has absorption, the Brewster angle that does not have P polarized light reflectivity to equal 0) incident condition, and Fig. 1 is the Mo/Si multilayer film R that wavelength is fixed, the cycle is slightly different _s, R _pAnd R _s/ R _pWith the variation of incident angle, (Fig. 1 reflection angle a) just in time mates with accurate Brewster angle the d=10.1nm multilayer film, R _sAnd R _s/ R _pAll reach higher value, the reflection angle and the accurate Brewster angle of d=10.5nm multilayer film (Fig. 1 b) do not match, because Rp is no longer forced down R fully _sAnd R _s/ R _pDo not reach maximum (R wherein simultaneously _s, R _pAnd R _s/ R _pThe reflectivity of representing the S polarized component of light respectively, the reflectivity of P component and degree of polarization).This shows that each multilayer film polarization optical element can only be used in a certain certain wavelengths place and reach optimum performance.For fear of this shortcoming, need design broadband polarizer.Traditional grenz ray wide waveband band polarizer generally has following two kinds:

1, the grenz ray gradient layers broadband polarizer

Gradient layers mainly is to utilize to be coated with different periodic thickness multilayer films at the substrate diverse location, make the polarizer of its corresponding different wave length, when using the gradient layers polarizer, only need to adjust incident light and incide the diverse location place, can reach certain degree of polarization, shown in Fig. 2 a, the multilayer film periodicity is 50, the normal incidence angle is 40.5 degree, at centre wavelength 16.0nm place, periodic thickness is 11.1nm, during corresponding different periodic thickness 10.2-11.8nm, the relation curve of Rs and lambda1-wavelength, top layer film thickness is 0.32 than (ratio of the thicknesses of layers on corresponding upper strata and periodic thickness in each cycle), roughness is 0nm, its advantage is to guarantee that the polarized light S component in a very wide wavelength coverage is all very big, but it is big that polarized light P component also and then becomes, make degree of polarization Rs/Rp reduce, shown in Fig. 2 b, the relation curve of Rp and lambda1-wavelength, and the preparation of gradient layers is very complicated, will accurately adjust the position at corresponding different wave length place in use through the gradient layers of demarcating, process is very complicated very, and permissible accuracy is also very high.

2, two multilayer film polarizers of grenz ray wave band angle adjustable

Two multilayer film polarizers of angle adjustable, utilize the multilayer film polarizer that higher degree of polarization is arranged when different-waveband correspondence different angles, use two parallel placements of the identical polarizer, simultaneously can guarantee the not deflection of outgoing beam direction, shown in Fig. 3 a, but such polarizer in the course of the work, corresponding different-waveband is wanted simultaneously accurately two polarizers of rotation, and remains parallel to each other, and adjusts inconvenience, and final luminous flux relative gradient multilayer film also will reduce, Fig. 3 b, 3c is depicted as the Mo/Si multilayer film, and the cycle is 50, and periodic thickness is 11.00nm, top layer film thickness ratio is 0.320, the polarized component R of multilayer film during corresponding different angles _sAnd R _pReflectivity and the relation curve of lambda1-wavelength.

Summary of the invention

The objective of the invention is to design a kind of both had high degree of polarization and luminous flux, simultaneously the reflective multilayer film of the grenz ray broadband polarizer of more convenient practicality in preparation and use.The reflective multilayer film of grenz ray broadband polarizer and preparation method thereof, it is simple to have manufacture craft, easy to adjust, inclined to one side earthquake degree height, but also can use at very wide wave band.

The calculating of the reflection characteristic of Soft X-Ray Multilayers system is to be starting point with the Fresnel formula, and drawing whole film is the complex amplitude reflectance formula.The reflective multilayer film of the grenz ray broadband polarizer in complex index of refraction is as shown in Figure 4 ${\tilde{n}}_o=n_o-{\mathrm{ik}}_o$ The infinite thickness substrate on, plating thickness successively is d _jThe isotropy homogeneous film of (j=1 ends to j=m), the complex index of refraction of material is ${\tilde{n}}_j=n_j-{\mathrm{ik}}_j.$ Wavelength is that the grenz ray parallel beam of λ incides film system surface with incident angle θ from vacuum.The incident angle θ of this patent must be at the accurate Brewster angle of centre wavelength correspondence.

The amplitude reflectivity R of j layer multi-layer film system _jFor:

$R_j=\frac{r_j(1-r_j{R}_{j-1})+(R_{j-1}-r_j)\exp (-{\mathrm{i\δ}}_j)}{1-r_j{R}_{j-1}+r_j(R_{j-1}-r_j)\exp (-{\mathrm{i\δ}}_j)}$

R wherein _j, R _J-1Be the j layer, the amplitude reflectivity of j-1 layer multi-layer film system, r _jBe the Fresnel reflection coefficient of j layer medium with respect to the vacuum medium:

$r_j=\frac{\cos \mathrm{\θ}-{\tilde{n}}_j{\cos \mathrm{\θ}}_j}{\cos \mathrm{\θ}+{\tilde{n}}_j\cos {\mathrm{\θ}}_j}$ (s polarization)

$r_j\frac{{\tilde{n}}_j\cos \mathrm{\θ}-\cos \mathrm{\θ}}{{\tilde{n}}_j\cos \mathrm{\θ}+{\cos \mathrm{\θ}}_j}$ (p polarization)

From j=1 (R _o=r _o) beginning, carry out iterative computation up to j=m, obtain the amplitude reflectivity R of m layer multi-layer film system _m, and the light intensity reflectivity of multilayer film system | R _m| ²(reflectivity of s polarization and p polarization is respectively Rs, Rp).The degree of polarization P of multilayer film is defined as P=R _s/ R _p, utilize the simple form optimized Algorithm to be optimized design then, obtain the minimal value of evaluation function, evaluation function is defined as

$F={\left(\underset{\mathrm{\λ}}{\mathrm{\Σ}}{(R_0-R_s+\mathrm{\τ}\×(R_p/R_s))}^2\right)}^{1/2}$

Wherein Rs represents S polarized component, R _pExpression P polarized component, R ₀Be target R _sFunction, τ is one and adjusts coefficient, guarantees that luminous flux and degree of polarization are optimized to maximal value simultaneously.Fig. 4 utilizes the Rs that non-periodic, assembly of thin films was optimized and the funtcional relationship of Rp corresponding wavelength, wavelength from 13 nanometers in the wide scope of 25 nanometers, the value of corresponding Rs is all greater than 10%, and R _pValue is all less than 1%, and degree of polarization reaches 10 to 10 ⁴Magnitude can guarantee all to guarantee very big degree of polarization in very wide wavelength coverage.

Description of drawings

Fig. 1 a is 13.9 nanometers for the prior art wavelength, and the cycle is 50, and periodic thickness is 10.1 nanometers, and top layer film thickness ratio is 0.4, when roughness is 0 nanometer, and Mo/Si multilayer film R _s, R _pAnd R _s/ R _pChange curve with incident angle;

Fig. 1 b is 13.9 nanometers for the prior art wavelength, and the cycle is 50, and periodic thickness is 10.5 nanometers, and top layer film thickness ratio is 0.4, when roughness is 0 nanometer, and Mo/Si multilayer film R _s, R _pAnd R _s/ R _pChange curve with incident angle;

Fig. 2 a is a prior art Mo/Si gradient layers broadband polarizer synoptic diagram, the multilayer film periodicity is 50, the normal incidence angle is 40.5 degree, in centre wavelength 16.0 nanometers, periodic thickness is 11.1 nanometers, and top layer film thickness ratio is 0.32, corresponding different periodic thickness 10.2-11.8 nanometers, top layer film thickness ratio is 0.32, when roughness is 0 nanometer, and the relation curve of Rs and lambda1-wavelength;

Fig. 2 b is a prior art Mo/Si gradient layers, the multilayer film periodicity is 50, the normal incidence angle is 40.5 degree, in centre wavelength 16.0 nanometers, periodic thickness is 11.1 nanometers, and top layer film thickness ratio is 0.32, corresponding different periodic thickness 10.2-11.8 nanometers, top layer film thickness ratio is 0.32, when roughness is 0 nanometer, and the relation curve of Rp and lambda1-wavelength;

Fig. 3 a is two multilayer film polarizer synoptic diagram of prior art angle adjustable, P1 wherein, and P2 is the polarizer, D is a detector, in the course of the work according to different wavelength requirements, reaches wideband polarization by the position and the angle of regulating P1 and P2;

Fig. 3 b is a prior art Mo/Si multilayer film, and the cycle is 50, and periodic thickness is 11.00 nanometers, and the thickness of Mo rete and periodic thickness ratio are 0.320, the reflectivity of the polarized component Rs of multilayer film and the relation curve of lambda1-wavelength during corresponding different angles;

Fig. 3 c is a prior art Mo/Si multilayer film, and the cycle is 50, and periodic thickness is 11.00nm, Gamma=0.320, the reflectivity of the polarized component Rp of multilayer film and the relation curve of lambda1-wavelength during corresponding different angles;

Fig. 4 is a reflective multilayer film of the present invention broadband polarizer structural representation;

Fig. 5 a utilizes assembly of thin films design reflectivity formula multilayer film broadband polarizer non-periodic for the present invention, Rs, Rp are with the change curve of lambda1-wavelength and the corresponding thicknesses of layers optimization result with the reflective multilayer film of the relation curve of the rete sequence number broadband polarizer, at wavelength from 11nm to 19nm in the wide scope, the value of corresponding Rs is generally greater than 10%, and the Rp value is generally less than 1%, and degree of polarization reaches 10 to 104 magnitudes;

Fig. 5 b is the reflective multilayer film of the relation curve broadband polarizer structural representation between the reflective multilayer film of the present invention broadband polarizer thicknesses of layers and the number of plies.

Embodiment

The selection principle of the reflective multilayer film of the grenz ray of the present invention broadband polarizer is from the angle of optics own, the material that mainly is two kinds of material refringence maximums of searching is right, at given wave band minimum absorption is arranged all simultaneously, what the present invention chose is molybdenum (Mo), two kinds of materials of silicon (Si), utilize the program of said method compiling, calculate the thickness of the every tunic of the required multilayer film of corresponding wave band, thickness be 0.5 nanometer between 8.5 nanometers, concrete thickness parameter is shown in Fig. 5 b.The present invention also be applicable to the grenz ray wave band other material to the combination, as tungsten/carbon, tungsten/silicon etc.

The reflective multilayer film of the preparation grenz ray broadband polarizer uses the magnetron sputtering embrane method.What use in experiment is JGP560C6 type high vacuum multifunctional magnetic control sputtering film plating equipment, before plated film begins, with the alcohol ether polarizer substrate (ultra-smooth silicon chip) is cleaned, and with absorbent cotton the surface is wiped clean, and is lower than 5.0 * 10 at the base vacuum degree ^-5Pa, vacuum tightness remains on 250Pa during plated film, to molybdenum, two kinds of target material surface applying argon gas of silicon, flow control is at 15.5SCCM, must spatter half an hour in advance to clean target by build-up of luminance before the plated film, revolution and rotation with step motor control polarizer substrate, the signal of stepper motor is by computation, when finishing to molybdenum, after two kinds of material sputter rates of silicon are demarcated, according to theory calculate the molybdenum with the 0.5-8.5 nano thickness, silicon film (seeing Fig. 5 b), the corresponding time input computer that is coated with, during program run, polarizer substrate is at two kinds of molybdenums, rotate back and forth stop between silicon, make molybdenum, silicon alternately is coated on the polarizer substrate, after program run finishes, take out the polarizer that is coated with.Preparation method of the present invention also is applicable to other wavelength coverage of grenz ray wave band.The present invention can be applicable to many polarimetries fields such as grenz ray magnetic circular dichroism (mcd), magnet-wire two colour analysiss and grenz ray resonance magnetic scattering.

Claims (4)

1, the reflective multilayer film of a kind of grenz ray broadband polarizer is characterized in that:

Right by molybdenum, two kinds of materials of silicon, the thickness of the required every tunic of multilayer film in calculating from 13 nanometers to 25 nanometer wavelength range and the multilayer film broadband polarizer that forms, the value of corresponding s component reflectivity Rs is all greater than 10%, and the reflectivity R of p component _pValue is all less than 1%, and degree of polarization Rs/Rp reaches 10 to 10 ⁴Magnitude guarantees all to guarantee very big degree of polarization in very wide wavelength coverage.

2, the reflective multilayer film of the grenz ray according to claim 1 broadband polarizer is characterized in that:

Described multilayer film thickness, thickness are between 0.5 nanometer～8.5 nanometers, and this thickness can be prepared with equipment for producing thin film.

3, the reflective multilayer film of the grenz ray according to claim 1 broadband polarizer is characterized in that:

Molybdenum of the present invention, two kinds of materials of silicon are right, also are applicable at other material of grenz ray wave band to combination, as tungsten/carbon, tungsten/silicon etc.

4, the preparation method of the reflective multilayer film of a kind of grenz ray broadband polarizer is characterized in that:

To polarizer plated film, use the alcohol ether to polarizer substrate with high vacuum multifunctional magnetic control sputtering film device earlier, the ultra-smooth silicon chip cleans, and the surface is wiped clean, and is lower than 5.0 * 10 in this vacuum tightness ^-5Pa, vacuum remains on 250Pa during plated film, to molybdenum, two kinds of target material surface applying argon gas of silicon, flow control is at 15.5SCCM, must spatter half an hour in advance to clean target by build-up of luminance before the plated film, revolution and rotation with step motor control polarizer substrate, the signal of stepper motor is by computation, to molybdenum, after two kinds of material sputter rates of silicon are demarcated, molybdenum with 0.5 nanometer～8.5 nano thickness, silicon materials are imported computer to the time that correspondence is coated with, during program run, polarizer substrate is at two kinds of molybdenums, rotate back and forth stop between silicon, make molybdenum, silicon alternately is coated on the polarizer substrate; And this method also is applicable to other wavelength coverage of grenz ray wave band.

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