CN104111120B - Phase extraction method based on bright strange shearing interferometer - Google Patents

Abstract

A phase extraction method based on a Ronchi shearing interferometer. The Ronchi shearing interferometer structure used in the method includes a light source, a focusing lens, a scattering optical element, a one-dimensional diffraction grating plate, an optical system platform under test, a checkerboard grating, Two-dimensional photoelectric sensor and computer. Place a one-dimensional diffraction grating and a checkerboard grating on the object plane and image plane of the optical system under test, and calculate the phase by collecting 9 interference fringe patterns with a phase shift interval of π/4, eliminating the multi-level diffracted light interference in the Ronchi shear interference Influence on phase extraction accuracy. The phase extraction method of the present invention eliminates the influence of higher-order diffraction items other than 0th order and ±1st order, reduces the systematic error of phase extraction in wave aberration detection, and improves the wave aberration detection accuracy of the optical system.

Description

Phase Extraction Method Based on Ronchi Shearing Interferometer

technical field

The invention relates to a shearing interferometer, in particular to a phase extraction method based on the Ronchi shearing interferometer.

Background technique

Ronchi shearing interference is a shearing interference that uses an extended light source to modulate the spatial coherence of the light field. It has the advantages of not requiring a separate ideal reference wavefront, easy to achieve common optical path interference, no spatial optical path error, high detection accuracy, and high sensitivity. advantage. Ronchi shearing interferometry introduces the phase-shifting interferometry technology. By moving the grating laterally, a stable phase difference is introduced between the shearing wavefront and the 0th-order wavefront. By changing the phase shifting amount, multiple interferograms are obtained, and the measured phase distribution is calculated. Calculate the wave aberration of the measured optical system. In order to obtain the original wavefront, it is necessary to extract the phase of the interferogram. Phase extraction is an important step in interferometry, and the accuracy of phase extraction directly affects the final detection accuracy. Commonly used interferogram phase extraction methods include two types, namely the frequency domain method and the time domain method. The frequency domain method mainly uses the Fourier transform method, while the time domain method mainly uses the phase shift interferometry technique. The Ronchi shearing interferometer uses phase-shifting interferometry for phase extraction. Phase-shifting interferometry is simple, fast, and high-precision. Platform vibration, air disturbance, etc.; on the other hand, it comes from the inside of the interferometer, such as the calibration error and nonlinear error of the piezoelectric crystal of the phase shifter, the processing error of the optical system and the residual error after installation, and the nonlinear error of the photoelectric sensor. For the Ronchi shearing interferometer, when the shear rate is small, the shearing grating not only interferes with the ±1st order and the 0th order to obtain the required interference fringes, but also interferes with the 0th order light, and the higher order diffraction items also interfere with the 0th order light. Seriously affect the accuracy of phase extraction. The Ronchi shearing interferometer does not have high requirements for the phase shifter. The grating displacement is on the order of hundreds of nm, so the phase shift error is small. Under the condition of ensuring a good measurement environment, the interaction of the grating multi-level diffracted light The influence can be regarded as the main error source of the Ronchi shearing interferometer, so the elimination of multi-level diffraction errors is the prerequisite for the Ronchi shearing interferometer to be used in the detection of wave aberrations in high-precision optical systems.

Joseph Braat etc. proposed a Ronchi shearing interferometer improved with extended light sources (prior technology [1], Joseph Braat, Augustus J.E. Janssen, "Improved Ronchi test with extended source", Journal of the Optical Society of America A Vol. 16, No.1, 1999, pp:131-140). This interferometer uses the interference of +1 order and -1 order diffracted light to extract the phase, but does not consider the influence of high-order diffraction orders, which introduces a certain systematic error and reduces the measurement accuracy of displacement; and this method only It is suitable for optical systems with small numerical apertures, and a large number of measurement errors will be introduced in the detection process of optical systems with large numerical apertures.

Yucong Zhu et al. proposed a phase extraction algorithm for a two-dimensional grating phase-shifting interferometer (prior technology [2], Yucong Zhu, Satoru Odate, Ayako Sugaya, et al., "Method for designing phase-calculation algorithms for two-dimensional grating phase shifting interferometry”, Applied Optics, 2011, 50(18): p.2815-2822). The two-dimensional grating interferometer uses the object plane grating as the extended light source, and its period is the product of the image plane grating period and the imaging magnification of the optical system under test. Both the object plane grating and the image plane grating are orthogonal gratings, and the algorithm only uses 0-level Phase extraction is carried out by the interference of light with ±1 order, and the influence of unwanted ±3 order and ±5 order diffraction items of the grating is eliminated by phase shifting. However, this method uses an orthogonal grating as the object plane grating, and the modulation result of the spatial coherence of the light field is complicated, and many diffraction items outside the x-axis and y-axis appear, thereby introducing a large number of noise items, which seriously affect the detection accuracy.

Matthieu Visser et al. proposed an extended source interferometer for EUV lithography objective lens wave aberration detection (prior technology [3], Matthieu Visser, Martijn K.Dekker, Petra Hegeman, et al., "Extended source interferometry for at- wavelength test of EUV-optics", Emerging Lithographic Technologies Iii, Pts 1 and 2, 1999.3676: p.253-263). Both the object plane grating and the image plane grating of the interferometer use one-dimensional Ronchi gratings, and the 5-step phase shift method can reduce the influence on phase extraction caused by the interference of ±3-order and 0-order diffracted light, but it is difficult to eliminate other relatively The higher order diffraction terms interfere with the 0th order.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, and provide a phase extraction method based on the Ronchi shearing interferometer. The method eliminates the influence of the multi-level diffracted light of the image plane grating on the phase extraction accuracy during the detection process of the Ronchi shearing interferometer, and improves the wave aberration detection accuracy of the measured optical system.

Technical solution of the present invention is as follows:

A phase extraction method based on a Ronchi shearing interferometer. The detection device used in the method is a Ronchi shearing interferometer. The structure of the Ronchi shearing interferometer includes: along the output beam direction of a light source, a focusing lens, a scattering Optical elements, one-dimensional diffraction grating plate, measured optical system platform, checkerboard grating and two-dimensional photoelectric sensor; the one-dimensional diffraction grating plate is placed on the object plane grating displacement platform, and the checkerboard grating is placed on the image square grating On the displacement platform, the two-dimensional photoelectric sensor is connected with the computer;

The scattering optical element is an optical element such as frosted glass, a microlens array, etc., which can uniformly illuminate the illumination beam within the numerical aperture of the measured optical system;

The one-dimensional diffraction grating plate is composed of two object-plane one-dimensional diffraction gratings with a period P _o and a duty ratio of 50%, which are respectively the first grating with the grating lines along the y direction and the second grating with the grating lines along the x direction. raster.

The first grating and the second grating are phase gratings or amplitude gratings.

The period P _o of the one-dimensional diffraction grating on the object plane and the period P _i of the checkerboard grating on the image plane satisfy the following relationship,

P _o ＝P _i ·M

Among them, M is the imaging magnification of the optical system under test;

The numerical aperture of the measured optical system is NA, and the imaging magnification is M:1;

The checkerboard grating has a checkerboard layout, the light-transmitting unit and the light-shielding unit are squares of the same size, and each light-transmitting unit is surrounded by 4 light-shielding units, and each light-shielding unit is surrounded by 4 light-transmitting units; The period P _i of the checkerboard grating is equal to the diagonal length of the square; the diagonal direction of the checkerboard grating light-transmitting unit and the light-shielding unit is parallel to the x-axis and the y-axis direction; the size of the period P _i is determined by the wavelength λ of the light source , the numerical aperture NA and the shear rate s of the optical system under test are determined,

The object-plane grating displacement stage is a three-dimensional displacement stage that moves the first grating and the second grating into the object-side optical path of the optical system under test;

The image plane grating displacement stage is a three-dimensional displacement stage that moves the checkerboard grating into the image square optical path of the optical system under test, and drives the image plane checkerboard grating to move stepwise along the x direction and along the y direction;

The two-dimensional photoelectric sensor is a camera, a CCD, a CMOS image sensor, or a two-dimensional photodetector array, and its detection surface receives the shearing interference fringes generated by the checkerboard grating;

The computer is used to control the wave aberration detection process, store measurement data, and process and analyze the interferogram;

Utilize the above-mentioned phase extraction method for eliminating the multi-order diffraction error of Ronchi shearing interferometer, it is characterized in that the method comprises steps as follows:

1) Place the optical system under test on the platform of the optical system under test, adjust the Ronchi shearing interferometer so that the light source is located on the object plane of the optical system under test, and the selection period is equal to the wavelength λ of the light source divided by An image plane checkerboard grating that is twice the product of the numerical aperture NA of the optical system under test and the shear rate s, and then select a one-dimensional diffraction grating whose period is the magnification at the working distance of the optical system under test multiplied by the period of the image plane grating; The one-dimensional diffraction grating plate is placed on the object-plane grating displacement stage, and adjusted to the object surface of the optical system under test, and the object-plane grating displacement stage is moved to move the first grating on the one-dimensional diffraction grating plate into the optical system under test. The position of the field of view on the object side; the checkerboard grating is placed on the image plane grating translation platform, and adjusted to the image plane of the optical system under test, and the image plane grating translation platform is moved to move the checkerboard grating into the image side optical path of the optical system under test;

2) Adjust the object plane grating displacement platform and the image plane grating displacement platform, align with the first grating and the checkerboard grating, and adjust the position of the two-dimensional photoelectric sensor to obtain an interference pattern with clear stripes on the detection surface;

3) The image plane grating translation stage moves the checkerboard grating along the x direction, moves 9 times, each time moves 1/8 grating period, after each movement, the two-dimensional photoelectric sensor collects a shearing interferogram I _xk , where k=1, 2,3...,9; According to the 9 interference fringe patterns, the phase is calculated according to the following formula:

in, is the phase of the measured wave front in the x direction, representing the gradient information of the measured wave front in the x direction;

4) moving the object-plane grating displacement stage, moving the second grating on the one-dimensional diffraction grating plate into the position of the object field of view of the optical system under test, readjusting the object-plane grating displacement stage and the image plane grating displacement platform, Align the second grating with the checkerboard grating;

5) The image plane grating translation stage moves the checkerboard grating along the y direction, and moves 9 times, each time moving 1/8 of the grating period. After each movement, the two-dimensional photoelectric sensor collects a shearing interferogram I _yk , where k=1, 2,3...,9; According to the 9 interference fringe patterns, the phase is calculated according to the following formula:

in, is the phase of the measured wave front in the y direction, representing the gradient information of the measured wave front in the y direction;

6) Unwrapping the above phase extraction results to obtain the differential wavefronts ΔW _x and ΔW _y in the x-direction and y-direction respectively. Perform shear interference wavefront reconstruction to obtain the wavefront of the optical system under test (see prior art 4, Harbers, G., PJ Kunst, and GWR Leibbrandt, Analysis of lateral shearing interferograms by use of Zernike polynomials. Applied Optics, 1996.35(31): p.6162-6172).

Compared with the prior art, the present invention has the following advantages:

1. Compared with the prior art [1], the influence of high-order diffraction orders is considered, the measurement accuracy of the wave aberration of the optical system is improved, and the accurate measurement of the wave aberration of the optical system with a large numerical aperture can be realized.

2. Compared with the prior art [2], the present invention uses a one-dimensional Ronchi grating on the object plane to modulate the spatial coherence of the light field, and there is no problem that other noise items overlap with 0-order and ±1-order interference fringes, and there are few error terms ,High precision.

3. Compared with the prior art [3], the present invention can better eliminate the higher-order diffraction items except the 0th order and ±1 order, and can well eliminate the multi-order diffracted light interference in the Ronchi shear interference The impact on the phase extraction accuracy is caused.

Description of drawings

Fig. 1 is the Ronchi shear interferometer device schematic diagram that the present invention adopts;

Figure 2 is a schematic diagram of a one-dimensional diffraction grating plate on the object plane;

Fig. 3(a) is a schematic diagram of a checkerboard grating, and Fig. 3(b) is a distribution diagram of diffracted light intensity of a checkerboard grating.

Figure 4(a) is a schematic diagram of diffraction orders that can interfere after modulating the spatial coherence of the light field, and Figure 4(b) is a schematic diagram of shear interference.

detailed description

In order to make the content, implementation process and advantages of the present invention clearer, the present invention will be further described below in conjunction with the examples and drawings, but the examples should not limit the protection scope of the present invention.

The Ronchi shearing interferometer device used in the present invention is shown in schematic diagram 1. It can be seen from the figure that the detection device adopted in the present invention is a Ronchi shearing interferometer, and the structure of the Ronchi shearing interferometer includes: along the output beam direction of the light source 1, a focusing lens 2, a scattering optical element 3, and a one-dimensional diffraction grating Plate 4, measured optical system platform, checkerboard grating 7 and two-dimensional photoelectric sensor 9; the one-dimensional diffraction grating plate 4 is placed on the object plane grating displacement table 5, and the checkerboard grating 7 is placed on the image plane grating displacement On the platform 8, the two-dimensional photoelectric sensor 9 is connected with the computer 10;

The scattering optical element 3 is an optical element such as ground glass, a microlens array, etc. that make the illumination beam evenly illuminated within the numerical aperture of the measured optical system 6;

Described one-dimensional diffraction grating plate 4 (referring to Fig. 2) is made up of two object plane one-dimensional diffraction gratings of period P _o and duty cycle is 50%, is respectively the first grating 401 and grating line along y direction of grating Lines of the second grating 402 along the x-direction.

The first grating 401 and the second grating 402 are phase gratings or amplitude gratings.

The period P _o of the one-dimensional diffraction grating on the object plane and the period P _i of the checkerboard grating 7 satisfy the following relationship,

P _o ＝P _i ·M

Wherein, M is the imaging magnification of the optical system 6 under test.

The numerical aperture of the measured optical system 6 is NA, and the imaging magnification is M:1;

The checkerboard grating 7 has a checkerboard layout, the light-transmitting unit and the light-shielding unit are squares of the same size, and each light-transmitting unit is surrounded by 4 light-shielding units, and each light-shielding unit is surrounded by 4 light-transmitting units. For the amplitude checkerboard grating, the transmittance function is

Among them, P _i is the period of the grating along the x and y directions, and N is the period number of the grating.

The diffraction light intensity function of the checkerboard grating 7 in the far field is

I(ξ,η)=I ₀ |[sinc(ξ,η)]{1+exp[-j2π(ξ,η)]}×comb(2ξ,2η)*sinc(2Nξ,2Nη)| ²

Among them, I(ξ,η) is the far-field diffraction light intensity function, and I ₀ is the 0th order diffraction light intensity. In an ideal situation, the checkerboard grating has only 0 order and odd diffraction orders, and the light energy is mainly concentrated on the 0 order and ±1 order, and each odd diffraction order interferes with the 0 order in the far field. Affected by the checkerboard grating, the measured wave surface generates a shear wave surface at an angle of 45° to the x-axis direction in the overlapping area. The period of the equivalent grating in the shear direction is the length of the square side of each unit structure of the checkerboard grating times.

The checkerboard grating 7 is placed in a state where the diagonal direction of the light-transmitting unit and the light-shielding unit is parallel to the x-axis and y-axis directions (see FIG. 3(a)), and it is a Ronchi grating when viewed along the x-direction and y-direction , the duty cycle is 50%.

Example:

In the Ronchi shearing interferometer, the wavelength of light output by the light source 1 is 193nm, the numerical aperture of the measured optical system 6 is 0.75, the imaging magnification is 4×, the shear rate is set to 1/30, and the period of the checkerboard grating 7 is selected P _i is 3.86 μm, and the object plane one-dimensional diffraction grating period is P _o is 15.44 μm.

The object plane grating translation stage 5 is a three-dimensional translation stage that moves the first grating 401 and the second grating 402 into the optical path of the measured optical system 6 objects;

The image plane grating displacement stage 8 is a three-dimensional displacement stage that moves the checkerboard grating 7 into the image square optical path of the measured optical system 6, and drives the checkerboard grating 7 to move along the x direction and along the 1/8 grating period of the y direction. ;

The two-dimensional photoelectric sensor 9 is a camera, a CCD, a CMOS image sensor, or a two-dimensional photodetector array, and its detection surface receives the shearing interference fringes generated by the checkerboard grating 7;

The computer 10 is used to control the wave aberration detection process, store measurement data, and process and analyze the interferogram.

Utilize the above-mentioned phase extraction method for eliminating the Ronchi shearing interferometer multi-order diffraction error, it is characterized in that the method comprises the following steps:

1) Place the optical system under test 6 on the platform of the optical system under test, adjust the Ronchi shearing interferometer so that the light source 1 is located on the object plane of the optical system under test 6, and the selection period is equal to that of the light source 1 The wavelength λ is divided by twice the numerical aperture NA of the measured optical system 6 and the shear rate s of the checkerboard grating 7, and then the selected period is the magnification at the working distance of the measured optical system 6 multiplied by one period of the checkerboard grating 7 One-dimensional diffraction grating plate 4; the one-dimensional diffraction grating plate 4 is placed on the object plane grating displacement table 5, and adjusted to the object plane of the measured optical system 6, the object plane grating displacement table 5 is moved, and the one-dimensional diffraction grating plate 4 The first grating 401 on the top moves into the position of the object field of view of the optical system under test 6; the checkerboard grating 7 is placed on the image plane grating displacement table 8, and adjusted to the image plane of the optical system under test 6, and the image plane grating is moved The displacement stage 8 moves the checkerboard grating 7 into the image square optical path of the measured optical system 6;

2) Adjust the object plane grating displacement stage 5 and the image plane grating displacement stage 8, align the first grating 401 and the checkerboard grating 7, and adjust the position of the two-dimensional photoelectric sensor 9, so that the interference pattern with clear stripes is obtained on the detection surface;

3) The image plane grating displacement stage 8 moves the checkerboard grating 7 along the x direction, moves 9 times, and moves 1/8 grating period each time, after each movement, the two-dimensional photoelectric sensor 9 collects a shearing interferogram I _xk , where k ＝1,2,3...,9; According to 9 interference fringe patterns, the phase is calculated according to the following formula:

in, is the phase of the measured wave front in the x direction, representing the gradient information of the measured wave front in the x direction;

4) Move the object plane grating displacement stage 5, move the second grating 402 on the one-dimensional diffraction grating plate 4 into the object side field of view point position of the measured optical system 6, readjust the object plane grating displacement stage 5 and the image Surface grating translation stage 8, aligned with second grating 402 and checkerboard grating 7;

5) The image plane grating displacement table 8 moves the checkerboard grating 7 along the y direction, and moves 9 times, each time moving 1/8 grating period, after each movement, the two-dimensional photoelectric sensor 9 collects a shearing interferogram I _yk , where k ＝1,2,3...,9; According to 9 interference fringe patterns, the phase is calculated according to the following formula:

in, is the phase of the measured wave front in the y direction, representing the gradient information of the measured wave front in the y direction;

6) Unpack the above phase extraction results to obtain the differential wavefronts ΔW _x and ΔW _y in the x-direction and y-direction respectively, and perform shearing interference wavefront reconstruction to obtain 6 wavefronts of the optical system under test.

The specific theoretical discussion of the above phase extraction method to eliminate the multi-level diffraction error of the Ronchi shearing interferometer is as follows:

According to the principle of the Ronchi shearing interferometer, when the modulation of the spatial coherence by the one-dimensional diffraction grating on the object plane is not considered, the checkerboard grating 7 is used, and the light intensity on the detection plane is

Among them, a ₀ is the background light intensity, a _ij is the interference fringe contrast between the i-th order diffracted by the grating in the x-axis direction and the j-th order diffracted in the y-axis direction, is the phase difference corresponding to two diffraction orders; i is the 0th, m or m' diffraction order along the x-axis direction, j is the 0th, n or n' diffraction order along the y-axis direction, k, k ', l, l' are all non-zero integers.

According to the "Van Sittert-Zernik Theorem", the spatial coherence of the light field is equal to the Fourier transform of the intensity distribution of the light source, so it is modulated by the one-dimensional diffraction grating on the object surface. When the one-dimensional diffraction grating on the object surface When the grating is the first grating 401 whose grating lines are along the y direction and the duty ratio is 50%, the spatial coherence in the x direction is the Fourier transform corresponding value of the first grating 401; while the light field in the y direction is still incoherent , so there is no interference in the y direction (see Figure 4), then the expression of light intensity is rewritten as

Among them, a ₀ is the background light intensity, a _m0 is the contrast ratio between the mth order diffraction and the 0th order interference fringe diffracted by the grating in the x direction, is the phase difference between the mth order diffraction and the 0th order of the grating in the x direction. where the phase difference is

Among them, W(x,y) is the wavefront function, λ is the wavelength, and S is the shear amount. When considering the phase shift, the light intensity expression can be rewritten as

Among them, δ is the phase shift amount of the first-order diffraction caused by each step of the checkerboard grating 7 moving along the shear direction in the phase-shift interference, and then mδ represents the phase shift amount of the m-th order diffraction when the grating moves along the shear direction, is the phase difference between the mth order diffraction and the 0th order in the x direction. Since the intensity of the diffraction light above the 5th order of the checkerboard grating is less than 1% of the 0th order light, it basically does not affect the measurement results, so the influence of the diffraction light above the 5th order can be ignored. The light intensity expression can be written as

Among them, k=1,2,3...,N, represents the phase shift of the kth step, and N is the total number of phase shift steps; is the phase difference between the mth order diffraction and the 0th order in the x direction, m=±1,±3,±5; δ _k is the amount of phase shift.

In order to suppress the influence of grating multi-level diffracted light on the phase extraction accuracy, the phase shift interval The interferogram of , that is, the phase shift of each step is 9 interferograms of , where j=0,1,2...8. Then the light intensity of each step is

According to formulas (6)~(14), it can be obtained:

Since when the phase shift is not considered, the condition of small shear amount satisfies

And the coefficients a ₁ and a _-1 are equal to the spatial coherence of the light field. For the Ronchi shearing interferometer, a ₁ = a _-1 , then the phase of the measured optical system 6 along the x direction

In order to restore the two-dimensional original wavefront of the optical system under test 6, the one-dimensional diffraction grating on the object plane is switched to the second grating 402 whose grating lines are along the x direction, and the phase of the optical system under test 6 along the y direction is calculated similarly with Represent the gradient information of the measured wavefront in the x direction and y direction, respectively. Unpack the above phase extraction results to obtain the differential wavefronts ΔW _x and ΔW _y in the x-direction and y-direction respectively, and perform shearing interference wavefront reconstruction to obtain 6 wavefronts of the optical system under test.

The invention is applied to the Ronchi shearing interferometer to detect the wave aberration of the measured optical system, can effectively eliminate the influence of grating multi-level diffracted light interference on the phase extraction accuracy, and improve the wave aberration detection accuracy of the measured optical system.

Those of ordinary skill in the art should recognize that the above embodiments are only used to illustrate the present invention, rather than as a limitation of the present invention, as long as within the scope of the spirit of the present invention, the changes and The deformations all belong to the scope of the claims of the present invention.

Claims (1)

1. A phase extraction method based on a Ronchi shearing interferometer, the detection device used in the method is a Ronchi shearing interferometer, and the structure of this Ronchi shearing interferometer comprises: along the output beam direction of the light source (1) sequentially It is a focusing lens (2), a scattering optical element (3), a one-dimensional diffraction grating plate (4), a measured optical system platform, a checkerboard grating (7) and a two-dimensional photoelectric sensor (9); the one-dimensional diffraction grating The plate (4) is placed on the object plane grating displacement platform (5), the checkerboard grating (7) is placed on the image plane grating displacement platform (8), and the two-dimensional photoelectric sensor (9) and the computer (10 ) is connected; it is characterized in that the steps of the method are as follows: ① Place the measured optical system (6) on the measured optical system platform, adjust the Ronchi shearing interferometer so that the described light source (1) is located on the object side of the measured optical system (6), select The period is equal to the wavelength λ of the light source (1) divided by the image plane checkerboard grating (7) of the product of twice the numerical aperture NA of the optical system under test (6) and the shear rate s, and then the period is selected as the optical system under test (6 ) multiply the magnification at the working distance by the one-dimensional diffraction grating plate (4) of the period of the image plane grating (7); the one-dimensional diffraction grating plate (4) is placed on the object plane grating displacement stage (5), and adjusted to On the object plane of the measuring optical system (6), move the object plane grating displacement stage (5), and move the first grating (401) on the one-dimensional diffraction grating plate (4) into the object side view of the measured optical system (6). Field point position; the checkerboard grating (7) is placed on the image plane grating displacement platform (8), and is adjusted to the image plane of the measured optical system (6), and the image plane grating displacement platform (8) is moved, and the checkerboard grating ( 7) Move into the optical path of the image side of the measured optical system (6), the one-dimensional diffraction grating plate is composed of two object plane one-dimensional diffraction gratings with a period P _o and a duty ratio of 50%. The first grating (401) in the y direction and the second grating (402) whose grating lines are along the x direction, the checkerboard grating (701) is placed so that the diagonal direction of the light-transmitting unit and the light-shielding unit is parallel to the x-axis and y-axis The state in the axial direction is a Ronchi grating viewed along the x and y directions, with a duty cycle of 50%; ②Adjust the object plane grating translation stage (5) and the image plane grating translation stage (8), align with the first grating (401) and checkerboard grating (701), and adjust the position of the two-dimensional photoelectric sensor (9) so that the detection surface Interferograms with clear fringes are obtained; ③The image plane grating translation stage (8) moves the checkerboard grating (701) along the x direction, moving 9 times, each time moving 1/8 grating period, after each movement, the two-dimensional photoelectric sensor (9) collects a shearing interferogram I _xk , where According to the 9 interference fringe images, the phase is calculated according to the following formula: in, is the phase of the measured wave front in the x direction, representing the gradient information of the measured wave front in the x direction; ④ Move the object plane grating displacement stage (5), move the second grating (402) on the one-dimensional diffraction grating plate (4) into the object field point position of the measured optical system (6), and readjust the object position. The surface grating displacement platform (5) and the image plane grating displacement platform (8) are aligned with the second grating (402) and the checkerboard grating (701); ⑤The image plane grating translation stage (8) moves the checkerboard grating (701) along the y direction, moving 9 times, each time moving 1/8 grating period, after each movement, the two-dimensional photoelectric sensor (9) collects a shearing interferogram I _yk , where According to the 9 interference fringe images, the phase is calculated according to the following formula: in, is the phase of the measured wave front in the y direction, representing the gradient information of the measured wave front in the y direction; ⑥ Unwrap the above phase extraction results to obtain the differential wavefronts ΔW _x and ΔW _y in the x-direction and y-direction respectively, and perform shearing interference wavefront reconstruction to obtain the wavefront of the optical system under test (6).