Real-time single-frame wavefront measurement method and device

Abstract

The invention discloses a real-time single-frame wavefront measurement method and device, and relates to the technical field of optical measurement and imaging, and the method comprises the following steps: S1, carrying out an experiment on a wavefront to be measured according to a constructed displacement platform of a shearing interference structure, and obtaining a single-frame image containing a plurality of shearing interference fringes in any direction; s2, quickly extracting phase distribution information by adopting a method combining a two-dimensional variational mode decomposition algorithm and a four-step phase shift technology; and S3, according to the extracted phase distribution information, carrying out wavefront reconstruction by using a differential Zernike polynomial as a primary function. According to the method, a single interferogram containing a plurality of shearing interference fringes in any direction is allowed to be collected in one-time measurement, the measurement efficiency can be improved, and the application potential of the shearing interference method in wavefront analysis can be widened.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement and imaging technology, and in particular to a real-time single-frame wavefront measurement method and device. Background Art

[0002] Lateral shearing interferometry (LSI) technology uses the interference between the wavefront to be measured and its own wavefront after lateral translation. It does not require a reference wavefront and can overcome the defects in some off-axis interferometry structures. It is often used to measure wavefront aberrations. The most commonly used core optical components in LSI are glass plates, wedges, biprisms and Wollaston prisms. According to the different mechanisms of their generation, they can be divided into diffraction and non-diffraction methods. The diffraction method currently uses multi-wavefront shearing interference of composite gratings. The disadvantage is that the grating processing accuracy required to generate shear is high, resulting in high costs. The traditional non-diffraction lateral shearing method generally uses parallel plates, prisms, polarizers or some special optical path structures to generate lateral shearing. This method can generally only generate shear wavefronts in one direction at a time, and often requires methods such as rotating shearing devices to obtain shear wavefronts in orthogonal directions, so at least two interference images need to be taken to correctly obtain the wavefront.

[0003] In order to extract phase information from the captured interference image, fringe projection phase extraction methods can be divided into two categories: one is phase extraction based on a single fringe pattern, and the other is phase extraction based on multiple fringe patterns represented by the phase shift method. In the single-frame projection fringe phase extraction method, the method of extracting the corresponding wavefront is relatively complex, and this complexity is further amplified when dealing with factors such as noise, calibration errors, and precise alignment of optical components. Single-frame projection fringe phase extraction methods include techniques such as Fourier transform, continuous wavelet transform, and empirical mode decomposition using spatial carrier frequency. These algorithms have been improved in terms of robustness to noise and preservation of image edge details, but they still have disadvantages. Summary of the invention

[0004] The present invention solves the problem of low measurement efficiency of existing wavefront measurement methods and proposes a real-time single-frame wavefront measurement method and device. The above method allows the acquisition of a single interference pattern containing multiple shearing interference fringes in arbitrary directions in one measurement, which can not only improve the measurement efficiency, but also broaden the application potential of the shearing interferometry method in wavefront analysis.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: a real-time single-frame wavefront measurement method, comprising the following steps: S1, conduct experiments on the wavefront to be measured based on the translation stage of the shearing interference structure, and obtain a single frame containing multiple shearing interference fringe images in arbitrary directions; S2, uses a method combining a two-dimensional variational mode decomposition algorithm and a four-step phase shifting technique to quickly extract phase distribution information; S3, based on the extracted phase distribution information, the differential Zernike polynomial is used as the basis function to perform wavefront reconstruction.

[0006] In the present technical solution, a measuring device is constructed to simultaneously acquire two lateral shearing interference fringe images in arbitrary directions, and then the shearing interference fringe images are processed accordingly, and the gradient phase information is acquired by combining the effective method of two-dimensional variational mode decomposition and four-step phase shifting technology, and finally the wavefront is reconstructed based on the obtained gradient phase information; the above method can effectively separate a single original interference pattern with multiple arbitrary shearing directions, thereby improving flexibility and applicability.

[0007] The present invention is further configured as follows: Step S2 comprises: S21, obtaining the light intensity distribution function of double lateral shearing interference in any direction; S22, using a two-dimensional variational mode decomposition algorithm, the decomposition process of multiple interference patterns obtained in a single shot is expressed as a constrained variational problem, and the characteristic mode function is calculated; S23, the amplitude distributions of the decomposed first and second stripes on four channels of the polarization array of the polarization camera are modulated by four-step phase shift to extract phase distribution information.

[0008] This technical solution specifically adopts a two-dimensional variational mode decomposition algorithm to express the decomposition process of multiple interference patterns as a constrained variational problem. Through the above algorithm, by minimizing the energy ubiquity of each component, the corresponding characteristic mode function can be obtained, and through four-step phase shift modulation, the phase distribution information can be quickly extracted to achieve real-time imaging.

[0009] The present invention is further configured as follows: Step S3 comprises: Determine the differential wavefront ΔW produced in the overlapping region; The relationship between the differential wavefront and the corresponding differential Zernike polynomial is established; the Zernike polynomial coefficients of the wavefront to be measured are determined by the least squares method, and finally the coefficients of the wavefront to be measured are solved.

[0010] In this technical solution, the wavefront reconstruction process can be completed through the above steps.

[0011] The present invention is further configured as follows: the light intensity distribution function is represented by the sum of the intensity distribution of the interference pattern, the modulation distribution of the incident wavefront and the interference pattern noise, and the modulation distribution of the incident wavefront is the product of the sum of the cosine values ​​of the two sets of shear wavefront phase differences and the modulation state of the incident wavefront.

[0012] In the technical solution, before using the two-dimensional variational modal decomposition algorithm, the light intensity distribution function of the double transverse shearing interference in any direction is expressed to facilitate the subsequent calculation process.

[0013] The present invention is further configured as follows: the objective function of the constrained variational problem is expressed as the Tikhonov regularization parameter and the gradient norm L 2 The minimum value of the product of the squares of , the constraint condition of the constrained variation problem is that the sum of the decomposed mode functions is equal to the interference pattern to be decomposed.

[0014] In the technical solution, the decomposition process of multiple interference patterns is represented as a constrained variational problem. By minimizing the energy generalization of each component through the above-mentioned two-dimensional variational mode decomposition algorithm, the corresponding characteristic mode function can be obtained.

[0015] The present invention is further configured as follows: the four channels on the polarization array of the polarization camera are respectively 0°, 45°, 90° and 135°.

[0016] The present invention is further configured such that: the wavefront to be measured is finally represented as the sum of products of a series of independent Zernike polynomials and related multiple weighted coefficients.

[0017] In this technical solution, the wavefront reconstruction process of this method is completed by solving the wavefront to be measured.

[0018] A real-time single-frame wavefront measurement device adopts the above-mentioned real-time single-frame wavefront measurement method, including a laser and a beam splitter, the output light path of the laser passes through a beam expander and a linear polarizer in sequence and then is emitted to a polarization beam splitter, and a first reflector and a first translation stage are respectively arranged on two output light paths of the polarization beam splitter; the beam splitter is arranged on one output light path of the polarization beam splitter, and a second reflector and a second translation stage are respectively arranged on two output light paths of the beam splitter, and an image acquisition device is also arranged on one side of the beam splitter.

[0019] In the present technical solution, a beam expander, a linear polarizer, and a polarization beam splitter are sequentially arranged on the output light path of the laser; a first reflector and a first translation stage are respectively located on two mutually perpendicular output light paths of the polarization beam splitter, and are respectively arranged tilted relative to the output light paths on which they are located; a beam splitter is located on the output light path of the polarization beam splitter, and similar to the polarization beam splitter, a second reflector and a second translation stage are provided, and the second reflector and the second translation stage are respectively located on two mutually perpendicular output light paths of the beam splitter; an image acquisition device is located on the output light path of the beam splitter.

[0020] The present invention is further configured as follows: the image acquisition device is arranged on the outgoing light path of the beam splitter away from the second translation stage, and the image acquisition device includes a zoom lens and a polarization camera.

[0021] In the technical solution, the image acquisition device can simultaneously acquire the positions of two groups of transverse shearing interference light beams and simultaneously obtain two transverse shearing interference fringe images in arbitrary directions.

[0022] The present invention is further configured such that: a quarter wave plate is arranged between the image acquisition device and the beam splitter.

[0023] In this technical solution, the quarter wave plate and the image acquisition device are located on the outgoing light path of the beam splitter.

[0024] The present invention can bring the following beneficial effects: The present invention relates to a real-time single-frame wavefront measurement method, which can combine two-dimensional variational mode decomposition and four-step phase shifting technology to obtain gradient phase information, and can effectively separate a single original interference pattern with multiple arbitrary shear directions, thereby improving flexibility and applicability; The present invention relates to a real-time single-frame wavefront measurement device, which can collect a single interference image containing multiple shear interference fringes in any direction. The device integrates the interference characteristics of polarized light and adopts flexible and customizable shear settings, so that the device has high flexibility and can achieve real-time dynamic imaging through an image acquisition device under limited space. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of a real-time single-frame wavefront measurement device of the present application.

[0026] Figure 2 Schematic diagram of the geometric relationship of the wavefront shearing interferometer ray tracing to be measured in this application.

[0027] Figure 3 Schematic diagram of the double transverse shear wavefront pattern captured by the image acquisition device.

[0028] Figure 4 Schematic diagram of the interference fringe pattern of two packages in arbitrary shearing directions extracted by the phase extraction algorithm of the present application.

[0029] Reference numerals: 1. Laser 2. Beam expander 3. Linear polarizer 4. First translation stage 5. First reflector 6. Polarization beam splitter 7. Beam splitter 8. Quarter wave plate 9. Zoom lens 10. Polarization camera 11. Second translation stage 12. Second reflector. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation method described herein is only an optimal embodiment of the present invention, which is only used to explain the present invention and does not limit the scope of protection of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] Example 1 This embodiment provides a real-time single-frame wavefront measurement device. Figure 1 , which mainly includes a laser 1, a beam expander 2, a linear polarizer 3, a first translation stage 4, a first reflector 5, a polarization beam splitter 6, a beam splitter 7, a quarter wave plate 8, a zoom lens 9, a polarization camera 10, a second translation stage 11 and a second reflector 12.

[0032] Continue to refer Figure 1 The outgoing light path of the laser 1 passes through the beam expander 2 and the linear polarizer 3 in sequence and then is emitted to the polarization beam splitter 6. The first reflector 5 and the first translation stage 4 are respectively arranged on the two outgoing light paths of the polarization beam splitter 6; the beam splitter 7 is arranged on one outgoing light path of the polarization beam splitter 6, and the second reflector 12 and the second translation stage 11 are respectively arranged on the two outgoing light paths of the beam splitter 7. An image acquisition device is also arranged on one side of the beam splitter 7.

[0033] In more detail, the first reflector 5 and the first translation stage 4 are respectively arranged on two perpendicular outgoing light paths of the polarization beam splitter 6, and are respectively arranged to be inclined relative to the outgoing light paths where they are located.

[0034] The second reflecting mirror 12 and the second translation stage 11 are respectively arranged on two mutually perpendicular outgoing light paths of the beam splitter 7 .

[0035] The image acquisition device is specifically arranged on the outgoing light path of the beam splitter 7 away from the second translation stage 11 . The above-mentioned image acquisition device mainly includes a zoom lens 9 and a polarization camera 10 .

[0036] A quarter wave plate 8 is arranged between the image acquisition device and the beam splitter 7 .

[0037] In the technical solution, the image acquisition device can simultaneously acquire the positions of two groups of transverse shearing interference light beams and simultaneously obtain two transverse shearing interference fringe images in arbitrary directions.

[0038] In this technical solution, the quarter wave plate 8 and the image acquisition device are located on the outgoing light path of the beam splitter 7 .

[0039] In the present technical solution, the beam expander 2, the linear polarizer 3, and the polarization beam splitter 6 are sequentially arranged on the outgoing light path of the laser 1; the first reflector 5 and the first translation stage 4 are respectively located on two mutually perpendicular outgoing light paths of the polarization beam splitter 6, and are respectively arranged tilted relative to the outgoing light paths where they are located; the beam splitter 7 is located on the outgoing light path of the polarization beam splitter 6, and similar to the polarization beam splitter 6, a second reflector 12 and a second translation stage 11 are provided, and the second reflector 12 and the second translation stage 11 are respectively located on two mutually perpendicular outgoing light paths of the beam splitter 6; the image acquisition device is located on the outgoing light path of the beam splitter 7.

[0040] In this embodiment, the distances from the direct light and the reflected light at the polarization beam splitter 6 to the first reflector 5 and the center of the first translation stage are 111 mm and 88 mm respectively; these distances may also be set separately according to actual needs.

[0041] In this embodiment, the distances from the direct light and the reflected light at the beam splitter 7 to the center of the second reflector 12 and the second translation stage 11 are 73 mm and 70 mm respectively, which may also be set separately according to actual needs.

[0042] In this embodiment, the angle between the first reflector 5 at the polarization beam splitter 6 and the horizontal direction is 68°.

[0043] In this embodiment, the angle between the second reflector 12 at the beam splitter 7 and the horizontal direction is 24°.

[0044] In this embodiment, the beam diameter of the laser 1 is 5 mm.

[0045] The working principle of a real-time single-frame wavefront measurement device is described as follows: the light emitted from the laser 1 is optimized at the front end, and uniformly distributed linear polarized light is obtained after passing through the linear polarizer 3. Then the linear polarized light source can be vertically incident on the polarization beam splitter 6, and then the direction with respect to the transmission axis is adjusted by the first translation stage 4, and then the polarization beam splitter 6 divides it into two, namely, reflected s-wave and transmitted p-wave, and then they meet again at the polarization beam splitter 6 to form the first lateral shearing interference; the interference light, namely the p-wave and the s-wave, will be divided into two p-waves and two s-waves after passing through the lateral shearing interference system composed of two translation stages and a non-polarizing beam splitter 7 again, and then the light beam will pass through a quarter-wave plate 8 whose fast axis is 45° to the polarization direction, and will be modulated into two left-handed circularly polarized lights and two right-handed circularly polarized lights, and the left-handed circularly polarized lights and the right-handed circularly polarized lights will interfere with each other.

[0046] Based on the above working principle, the wavefront to be measured is expressed as: E=Aexp[iW1] Where A represents the amplitude and W1 represents the phase delay of the p-wave.

[0047] Substitute each component in the device into the corresponding Jones matrix and vector expression for calculation, refer to the following formula for details: Where W1 and W2 represent the phase delay of p-wave and s-wave respectively; A represents the amplitude; E represents the Jones matrix representation of each element, where QWP represents a quarter wave plate, M1 and M2 represent a reflector and an adjustable reflector respectively; PBS represents a polarization beam splitter. The polarization states of E1 and E2 are orthogonal to each other, which conforms to the orthogonal polarization state.

[0048] Since orthogonal polarization states do not produce interference patterns, the light beam needs to pass through the image sensor array of the polarization camera 10 to produce interference. The basic principle of the polarization camera 10 used in this application is to cover the mask plate made by a special process on its imaging array surface, and the 2×2 array is composed of 4 polarization pixels. The polarization angle of adjacent polarization pixels is 45°. The light beam will interfere in four directions, and four interference fringes with obvious phase shift can be observed on the polarization camera 10. The Jones vectors of E1 and E2 after passing through the imaging array surface of the polarization camera are specifically expressed as: Where W1 and W2 represent the phase delays of the p-wave and s-wave, respectively; α represents the polarization angle of the polarization camera imaging array, which are 0°, 45°, 90°, and 135°, respectively.

[0049] Therefore, the intensity distribution of the final light beam falling on the camera polarization array is specifically expressed as: ΔW1 is used to represent the differential phase W1-W2, and the intensity distribution of the other two beams of left-right circularly polarized light that interfere with I a_1 Finally, the intensity distribution of the double interference fringes received by the polarization camera is shown below. When α is 0°, 45°, 90°, and 135°, phase shifts of 0, π / 2, π, and 3π / 2 can be generated simultaneously on the polarization camera imaging array plane, achieving four-step phase shift, quickly extracting phase distribution information, and realizing real-time imaging. Where A represents amplitude; ΔW1 represents differential phase W1-W2; NOISE represents noise; and α represents the polarization angle of the polarization camera imaging array.

[0050] Example 2 This embodiment proposes a real-time single-frame wavefront measurement device, which mainly includes a laser 1, a beam expander 2, a linear polarizer 3, a first translation stage 4, a first reflector 5, a polarization beam splitter 6, a beam splitter 7, a quarter wave plate 8, a zoom lens 9, a polarization camera 10, a second translation stage 11 and a second reflector 12. Figure 1 The outgoing light path of the laser 1 passes through the beam expander 2 and the linear polarizer 3 in sequence and then is emitted to the polarization beam splitter 6. The first reflector 5 and the first translation stage 4 are respectively arranged on the two outgoing light paths of the polarization beam splitter 6; the beam splitter 7 is arranged on one outgoing light path of the polarization beam splitter 6, and the second reflector 12 and the second translation stage 11 are respectively arranged on the two outgoing light paths of the beam splitter 7. An image acquisition device is also arranged on one side of the beam splitter 7.

[0051] In more detail, the first reflector 5 and the first translation stage 4 are respectively arranged on two perpendicular outgoing light paths of the polarization beam splitter 6, and are respectively arranged to be inclined relative to the outgoing light paths where they are located.

[0052] The second reflecting mirror 12 and the second translation stage 11 are respectively arranged on two mutually perpendicular outgoing light paths of the beam splitter 7 .

[0053] The image acquisition device is specifically arranged on the outgoing light path of the beam splitter 7 away from the second translation stage 11 . The above-mentioned image acquisition device mainly includes a zoom lens 9 and a polarization camera 10 .

[0054] A quarter wave plate 8 is arranged between the image acquisition device and the beam splitter 7 .

[0055] In the technical solution, the image acquisition device can simultaneously acquire the positions of two groups of transverse shearing interference light beams and simultaneously obtain two transverse shearing interference fringe images in arbitrary directions.

[0056] In this technical solution, the quarter wave plate 8 and the image acquisition device are located on the outgoing light path of the beam splitter 7 .

[0057] In the present technical solution, the beam expander 2, the linear polarizer 3, and the polarization beam splitter 6 are sequentially arranged on the outgoing light path of the laser 1; the first reflector 5 and the first translation stage 4 are respectively located on two mutually perpendicular outgoing light paths of the polarization beam splitter 6, and are respectively arranged tilted relative to the outgoing light paths where they are located; the beam splitter 7 is located on the outgoing light path of the polarization beam splitter 6, and similar to the polarization beam splitter 6, a second reflector 12 and a second translation stage 11 are provided, and the second reflector 12 and the second translation stage 11 are respectively located on two mutually perpendicular outgoing light paths of the beam splitter 6; the image acquisition device is located on the outgoing light path of the beam splitter 7.

[0058] In this embodiment, the distances from the direct light and the reflected light at the polarization beam splitter 6 to the first reflector 5 and the center of the first translation stage are 111 mm and 88 mm respectively; these distances may also be set separately according to actual needs.

[0059] In this embodiment, the distances from the direct light and the reflected light at the beam splitter 7 to the center of the second reflector 12 and the second translation stage 11 are 73 mm and 70 mm respectively, which may also be set separately according to actual needs.

[0060] In this embodiment, the angle between the first reflector 5 at the polarization beam splitter 6 and the horizontal direction is 68°.

[0061] In this embodiment, the angle between the second reflector 12 at the beam splitter 7 and the horizontal direction is 24°.

[0062] In this embodiment, the beam diameter of the laser 1 is 5 mm.

[0063] Based on Example 1, this example proposes a real-time single-frame wavefront measurement method, which mainly includes the following steps.

[0064] Step S1, conducting an experiment on the wavefront to be measured by using a translation stage with a shearing interference structure that has been constructed, and obtaining a single-frame shearing interference fringe image including multiple arbitrary directions.

[0065] Step S2, after obtaining the shearing interference fringe image, the phase distribution information is extracted quickly by combining the two-dimensional variational mode decomposition algorithm and the effective method of the four-step phase shifting technology.

[0066] Step S3, reconstructing the wavefront according to the phase distribution information obtained in step S2 and using differential Zernike polynomials as basis functions.

[0067] For step S1, the translation stage involved mainly includes a first translation stage 4 and a second translation stage 11. The translation stage is mainly composed of a rotation translation stage and an angle translation stage, which can realize 360° rotation and ±5° pitch adjustment of the reflector, and can be adjusted by a differential head. By adjusting the differential head, the reflector can be precisely adjusted, see Figure 2 , the shearing amount can be calculated according to the geometric relationship of the wavefront shearing interference ray tracing to be measured; in addition, the shearing direction can be obtained by edge detection of the two fringe images obtained by decomposition. Among them, oo1 and α are the distance from the direct light reflector to the center of the beam splitter prism and x The angle between the deflecting light reflector and the x-axis; oo2 and β are the distance from the deflecting light reflector to the center of the beam splitter prism and the angle with the x-axis.

[0068] Step S2 mainly includes the following sub-steps.

[0069] Step S21, first, obtain the light intensity distribution function of double lateral shearing interference in any direction; for the above-mentioned light intensity distribution function, it is specifically the sum of the modulation distribution of the incident wavefront, the interference pattern noise and the intensity distribution of the interference pattern, wherein the modulation distribution of the incident wavefront is the product of the sum of the cosine values ​​of the phase difference of the two sets of shear wavefronts and the modulation state of the incident wavefront.

[0070] In the technical solution, before using the two-dimensional variational modal decomposition algorithm, the light intensity distribution function of the double transverse shearing interference in any direction is expressed to facilitate the subsequent calculation process.

[0071] In this embodiment, the light intensity distribution function can be specifically expressed as: I(x,y)=I a (x,y)+I b (x,y){cos[ΔW1(x,y)]+cos[ΔW2(x,y)]}+n Among them, I a (x, y) represents the intensity distribution of the interference pattern, I b (x, y) represents the modulation state of the incident wavefront; ΔW1(x, y) and ΔW2(x, y) are the phase differences between the two sets of shear wavefronts, and n is the interference pattern noise.

[0072] Step S22, secondly, a two-dimensional variational mode decomposition algorithm is specifically used to express the decomposition process of multiple interference patterns obtained in a single shot as a constrained variational problem, and obtain the characteristic mode function. Specifically, the objective function of the constrained variational problem is expressed as the Tikhonov regularization parameter and the gradient norm L 2 The minimum value of the product of the squares of , the constraint condition of the constrained variation problem is that the sum of the decomposed mode functions is equal to the interference pattern to be decomposed.

[0073] More specifically, two-dimensional variational mode decomposition (2DVMD) is a newly proposed adaptive signal analysis method based on the variational method and Wiener filtering. It can adaptively separate several signals with different modes, that is, it can obtain band-limited intrinsic mode functions. First, for each intrinsic mode u k , the corresponding analytical signal is calculated by Hilber transform, and the single-sided spectrum is obtained. Secondly, for each single-sided spectrum mode, by mixing a center frequency w k The exponential modulation term moves each spectrum to the "baseband". Finally, the H 1 Gaussian smoothness (the gradient L 2 norm) to estimate the bandwidth.

[0074] Use Fourier properties to define the 2D analytical signal u k , see the following formula for details: Among them, * represents convolution, δ(t) represents the Dirac function, is the partial derivative with respect to time t, is the center frequency.

[0075] Using a 2D variational mode decomposition algorithm, the decomposition process of multiple interferograms captured in a single shot is formulated as a constrained variational problem: where α k is the Tikhonov regularization parameter, is the gradient norm L 2 The square of u k =(u1,u2,…u k ) is the decomposed mode function; U AS,K (x) represents the k and its Hilbert transform composed of complex analytical signals, 〈w k ,X〉 represents the frequency-wavenumber domain, and f represents the interference pattern to be decomposed.

[0076] First, solve for u k The minimization problem of Where α is the regularization function and λ is the Lagrange multiplier. This will produce the following Wiener-Filter result: in, and are the Fourier transforms of f(w), u(w) and λ(w) respectively, and n is the iteration time.

[0077] Secondly, solve the problem about The minimization problem is as follows: In the Fourier frequency domain it is expressed as: The solution is: in, is the mode power In the half plane Ω k The Lagrange multiplier λ is updated by standard gradient ascent with a fixed time step γ: After several iterations, the energy functional can be minimized and each modal component can be obtained.

[0078] Using the above algorithm, by minimizing the energy generalization of each component, the corresponding characteristic mode function u can be obtained k , specifically:

[0079] Step S23, finally, the amplitude distribution of the decomposed first fringe and the second fringe on the four channels of the polarization array of the polarization camera is modulated by four-step phase shift to extract the phase distribution information. Specifically, the amplitude distribution of the decomposed first fringe and the second fringe falling on the four channels of 0°, 45°, 90° and 135° on the polarization array of the polarization camera is further modulated by four-step phase shift, which can be specifically referred to the following formula:

[0080] As for step S3, the wavefront to be measured can be finally represented as the sum of products of a series of independent Zernike polynomials and related multiple weighting coefficients.

[0081] More specifically, the differential wavefront ΔW generated in the overlapping area can be specifically referred to the following formula: Wherein, θ is the shear direction (the angle between the shear wavefront defined by the wavefront to be measured and the z-axis), S is the shear amount; ΔZ is the expression of the differential Zernike basis function.

[0082] The shear direction θ and the shear amount S are determined as known quantities by the above geometric calculations. Then, by solving the wavefront coefficient to be measured, the relationship between the differential wavefront and the corresponding differential Zernike polynomial can be established. For details, refer to the following formula: Among them, each column of ΔZ1 and ΔZ2 represents N 2 The value of the Zernike difference polynomial of ×1.

[0083] The least squares method is used to determine the Zernike polynomial coefficients of the wavefront to be measured, which can be specifically expressed as:

[0084] The wavefront to be measured can be expressed as the sum of a series of independent Zernike polynomials and related multi-weighted coefficients, and its formula is specifically expressed as: Where Z j (x,y) is the jth term of the Zernike polynomial, and the vector a j Represents the relevant polynomial weight coefficient.

[0085] refer to Figure 3 , a schematic diagram of a double transverse shear wavefront pattern captured by an image acquisition device, in this embodiment, a single frame interference fringe image containing any two shear directions is displayed by the image acquisition device.

[0086] See also Figure 4 , through Figure 3Phase extraction is performed on the interference fringe image, and a schematic diagram of the interference fringe pattern and image background of two packages in arbitrary shearing directions are obtained by decomposing the algorithm of this embodiment.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A real-time single-frame wavefront measurement method, characterized in that: The following steps are involved: S1, conduct experiments on the wavefront to be measured based on the translation stage of the shearing interference structure, and obtain a single frame containing multiple shearing interference fringe images in arbitrary directions; S2, uses a method combining a two-dimensional variational mode decomposition algorithm and a four-step phase shifting technique to quickly extract phase distribution information; S3, based on the extracted phase distribution information, the differential Zernike polynomial is used as the basis function to perform wavefront reconstruction.

2. A real-time single-frame wavefront measurement method according to claim 1, characterized in that: The step S2 comprises: S21, obtaining the light intensity distribution function of double lateral shearing interference in any direction; S22, using a two-dimensional variational mode decomposition algorithm, the decomposition process of multiple interference patterns obtained in a single shot is expressed as a constrained variational problem, and the characteristic mode function is calculated; S23, the amplitude distributions of the decomposed first and second stripes on four channels of the polarization array of the polarization camera are modulated by four-step phase shift to extract phase distribution information.

3. A real-time single-frame wavefront measurement method according to claim 2, characterized in that: The step S3 comprises: Determine the differential wavefront ΔW produced in the overlapping region; The relationship between the differential wavefront and the corresponding differential Zernike polynomial is established; the Zernike polynomial coefficients of the wavefront to be measured are determined by the least squares method, and finally the coefficients of the wavefront to be measured are solved.

4. A real-time single-frame wavefront measurement method according to claim 2, characterized in that: The light intensity distribution function is represented by the sum of the intensity distribution of the interference pattern, the modulation distribution of the incident wavefront and the interference pattern noise. The modulation distribution of the incident wavefront is the product of the sum of the cosine values ​​of the phase differences of the two sets of shear wavefronts and the modulation state of the incident wavefront.

5. A real-time single-frame wavefront measurement method according to claim 2, characterized in that: The objective function of the constrained variational problem is expressed as the Tikhonov regularization parameter and the gradient norm L 2 The minimum value of the product of the squares of , the constraint condition of the constrained variation problem is that the sum of the decomposed mode functions is equal to the interference pattern to be decomposed.

6. A real-time single-frame wavefront measurement method according to claim 2, characterized in that: The four channels on the polarization array of the polarization camera are 0°, 45°, 90° and 135° respectively.

7. A real-time single-frame wavefront measurement method according to claim 1, characterized in that: The wavefront to be measured is finally expressed as the sum of products of a series of independent Zernike polynomials and related multiple weighting coefficients.

8. A real-time single-frame wavefront measurement device, using a real-time single-frame wavefront measurement method according to any one of claims 1 to 7, characterized in that: The invention comprises a laser (1) and a beam splitter (7), wherein the output light path of the laser (1) passes through a beam expander (2) and a linear polarizer (3) in sequence and then is emitted to a polarization beam splitter (6), and a first reflector (5) and a first displacement stage (4) are respectively arranged on two output light paths of the polarization beam splitter (6); the beam splitter (7) is arranged on one output light path of the polarization beam splitter (6), and a second reflector (12) and a second displacement stage (11) are respectively arranged on two output light paths of the beam splitter (7), and an image acquisition device is also arranged on one side of the beam splitter (7).

9. A real-time single-frame wavefront measurement device according to claim 8, characterized in that: The image acquisition device is arranged on an outgoing light path of the beam splitter (7) away from the second displacement stage (11), and the image acquisition device comprises a zoom lens (9) and a polarization camera (10).

10. A real-time single-frame wavefront measurement device according to claim 8 or 9, characterized in that: A quarter wave plate (8) is also provided between the image acquisition device and the beam splitter (7).

Images