Intensity-wavefront-wavelength measuring instrument based on radial shear of metasurface

Abstract

The application relates to a strength-wavefront-wavelength measuring instrument based on a metasurface radial shear, which comprises a 1 / 4 wave plate, a metasurface radial shear interference plate, a CCD image sensor, a displacement device and a strength-wavefront-wavelength reconstruction unit. The reconstruction unit reconstructs the strength, the wavefront and the wavelength information of an incident light beam from an interference pattern, including obtaining an interference pattern intensity distribution expression by Rayleigh-Sommerfeld diffraction; obtaining an incident wavelength lambda by calculating the annular interval of interference fringes in the interference pattern intensity distribution expression; solving the wavefront phase difference according to the circular ring carrier frequency mode in the interference pattern; reconstructing the to-be-measured wavefront by adopting a mode wavefront reconstruction algorithm based on Zernike polynomials according to the similarity of the two beams with different apertures of the interference plate; and obtaining the strength distribution and the wavefront distribution by inversely obtaining the complex amplitude of the incident wavefront according to the path. The application has the advantages of high spatial resolution, high optical efficiency, adjustable shear rate and dynamic range, simple structure, small volume, high integration, high precision, high speed and being not easy to be disturbed by the environment.

Description

Technical Field

[0001] The present invention relates to the field of optical detection technology, and more particularly to an intensity-wavefront-wavelength measuring instrument based on radial shearing of a metasurface. Background Art

[0002] Laser weapons play a unique role in electro-optical countermeasures, air defense, and strategic defense, and are highly likely to transform future warfare. However, during operation, laser systems can experience wavefront distortion due to thermal effects on optical components or atmospheric disturbances, altering the intensity distribution of the focal spot and reducing the damage effectiveness. Correcting the laser wavefront based on beam quality is a key method for mitigating these adverse effects and improving equipment effectiveness. Therefore, accurate and rapid laser spot detection equipment is urgently needed.

[0003] Currently, beam quality testing primarily involves two categories: spot characterization and wavefront testing. Spot characterization primarily measures the intensity distribution of the spot and serves as a basis for evaluating laser focusing effectiveness. Wavefront testing, on the other hand, examines the wavefront information of the laser during propagation. Using algorithms, it not only reconstructs the focal spot size and energy distribution but, more importantly, provides a basis for laser wavefront compensation, supporting efficient laser focusing.

[0004] The spatial light field distribution E(r) can be composed of the real amplitude distribution A(r) and the phase distribution Description. From the electromagnetic field Helmholtz wave equation, we know that there is a mutual coupling relationship between amplitude and phase. It can also be seen that the intensity distribution only reflects the static energy distribution, and the wavefront It reflects the distribution of light field energy in space and the energy flow; the two together determine the propagation of the light beam. Therefore, a single intensity distribution test cannot accurately describe the beam quality.

[0005] The intensity distribution, wavefront, and instantaneous wavelength of a laser beam are crucial to laser applications. However, current spot detection and wavefront sensing technologies are unable to simultaneously obtain the intensity distribution, wavefront, and wavelength information of a laser beam:

[0006] 1. Beam profilers based on different measurement principles, such as CCD and CMOS cameras or rotating knife edges or slits, can only obtain beam intensity distributions on a limited, fixed plane within the permitted beam radius, optical power range, and wavelength. A typical example is the Beamon series CCD beam profiler from DUMA, an Israeli company. These methods can only obtain static energy distributions; and due to limitations in probe or pixel size, measurement resolution is limited. Detector noise and other factors also contribute to low measurement accuracy.

[0007] 2. Wavefront measurement techniques such as Hartmann wavefront sensing, phase inversion, curvature sensing, and interferometry can recover both the wavefront and the intensity distribution. However, these techniques currently perform wavefront recovery based on a given wavelength. Fluctuations in the wavelength of the light source can lead to significant errors in the intensity distribution and wavefront recovery results.

[0008] 3. Wavefront measurement methods based on shearing interferometry exploit the interference effect of light and offer higher accuracy than other detection methods. In particular, radial shearing interferometry offers advantages over point diffraction interferometry and transverse shearing interferometry, and has been a key research area in wavefront measurement in recent years. However, its complex structure, difficulty in adjusting the shear rate, and inability to account for dynamic wavelength variations remain significant limitations on its practical application.

[0009] Existing beam quality analysis primarily relies on intensity detection; wavefront is a key indicator of beam quality. Combining intensity and wavefront, leveraging their correlation and self-consistency, can reduce the impact of intensity noise and improve intensity detection accuracy and resolution. Therefore, combining intensity and wavefront detection is an effective way to improve spot detection accuracy and a prerequisite for precise beam control.

[0010] Therefore, it is urgent to develop a beam quality analysis equipment that can quickly and synchronously measure the beam intensity, wavefront and wavelength, provide a basis for the precise control of the laser beam, and provide solid support for significantly improving the combat effectiveness of laser weapon systems.

[0011] Existing beam quality measurement systems can only obtain information related to light intensity distribution, and the accuracy of intensity measurement is easily affected by factors such as detector noise. Wavefront measurement can obtain the beam intensity distribution while obtaining wavefront information. Through the correlation and self-consistency between the two, it is expected to greatly improve the accuracy of intensity distribution measurement. However, existing wavefront measurement systems have problems such as large size, many components, low integration, low accuracy, slow speed, and inability to achieve dynamic wavefront and wavelength detection. The large size, many components, and low integration make wavefront measurement easily affected by environmental factors (such as temperature and vibration), making it difficult to achieve fast and high-precision wavefront and intensity distribution measurements in complex working environments; at the same time, the existing system cannot perform accurate wavelength measurement simultaneously during wavefront measurement (assuming the beam wavelength is known), so the fluctuation of the laser beam wavelength will inevitably cause great difficulties in accurate wavefront measurement. The above problems greatly limit the accuracy of beam quality measurement. Summary of the Invention

[0012] In response to the problems existing in the prior art, the present invention provides a high-precision beam intensity-wavefront-wavelength synchronous detection instrument. Based on the principle of metasurface radial shearing interferometry, the present invention adopts a metasurface structure radial shearing interferometer plate to replace traditional bulk optical elements, and combines intensity, wavefront and wavelength reconstruction algorithms to achieve rapid synchronous measurement of beam intensity, wavefront and wavelength.

[0013] The technical solutions of the present invention are as follows:

[0014] The present invention proposes an intensity-wavefront-wavelength measuring instrument based on metasurface radial shearing, comprising a quarter-wave plate, a metasurface radial shearing interferometer, a CCD image sensor, a displacement device, and an intensity-wavefront-wavelength reconstruction unit. The quarter-wave plate is used to convert incident laser light into circularly polarized light and feed it into the metasurface radial shearing interferometer. The metasurface radial shearing interferometer splits the circularly polarized light into two wavefronts with different apertures but identical surface shapes, forming an interference pattern on the CCD image sensor. The intensity-wavefront-wavelength reconstruction unit reconstructs the intensity, wavefront, and wavelength information of the incident light beam from the interference pattern. The displacement device is used to adjust the distance between the CCD image sensor and the metasurface radial shearing interferometer, thereby changing the shear rate.

[0015] In the present invention, a special structure of the metasurface radial shearing interferometer is adopted, which is composed of two metasurface optical lenses with different focal lengths integrated into one; the metasurface optical lens is based on a phase-controlled metasurface unit structure, and the phase-controlled metasurface unit structure is staggered according to two different phase control parameters to form a concentric ring structure with a width less than or equal to λ / 2. The two metasurface optical lenses occupy odd and even rings respectively to form the radial shearing interferometer.

[0016] In the present invention, the intensity-wavefront-wavelength reconstruction unit uses a special method to reconstruct the intensity, wavefront and wavelength information of the incident light beam from the interference pattern, including the following process:

[0017] Interference pattern analysis: From Rayleigh-Sommerfeld diffraction, we can get the expression for the intensity distribution of the interference pattern;

[0018] Wavelength reconstruction: The incident wavelength λ is calculated from the annular spacing of the interference fringes in the interference pattern intensity distribution expression;

[0019] Solve the wavefront difference: solve the wavefront phase difference based on the circular carrier frequency pattern in the interference pattern;

[0020] Reconstruct wavefront based on Zernike polynomials: Based on the similarity of the two wavefronts with different apertures separated by the radial shearing interferometer, the wavefront to be measured is reconstructed using the pattern wavefront reconstruction algorithm based on Zernike polynomials;

[0021] The complex amplitude of the incident wavefront is obtained by reverse calculation according to the path;

[0022] The wavefront and intensity distributions are reconstructed to obtain the intensity distribution and the wavefront distribution.

[0023] The present invention has the following advantages:

[0024] 1. The present invention utilizes a metasurface structure radial shearing interference plate to replace traditional bulk optical elements, and has the advantages of high spatial resolution, high optical efficiency, ultra-thinness, ultra-lightness, and easy integration.

[0025] 2. The present invention utilizes a displacement device to adjust the distance between the CCD image sensor and the metasurface radial shearing interference plate, thereby adjusting the shear rate, and the dynamic range of detection is high.

[0026] 3. The reconstruction method adopted by the intensity-wavefront-wavelength reconstruction unit of the present invention realizes the rapid synchronous measurement of light beam intensity, wavefront and wavelength. By utilizing the correlation and self-consistency of the three data, it can not only greatly improve the accuracy of light beam quality detection, but also simultaneously provide dynamic change information of the intensity, wavefront and wavelength of the detected light beam, providing more accurate and indispensable key parameters for laser beam quality measurement, and can meet the requirements of real-time and accurate dynamic measurement of laser beam quality in complex environments.

[0027] 4. The present invention has the advantages of simple structure, small size, high integration, high precision, high speed, and not susceptible to environmental interference. It can provide a basis for the precise control of laser beams and provide solid support for significantly improving the combat effectiveness of laser weapon systems.

[0028] In summary, the present invention offers the advantages of high spatial resolution, high optical efficiency, adjustable shear rate and dynamic range, simple structure, compact size, high integration, high precision, high speed, and low susceptibility to environmental interference. It not only significantly improves the accuracy of beam quality detection but also simultaneously provides information on the dynamic changes in the intensity, wavefront, and wavelength of the detected beam, providing more accurate and indispensable key parameters for laser beam quality measurement. It can meet the requirements for real-time, precise dynamic measurement of laser beam quality in complex environments and has broad application in fields such as laser weapons, inertial confinement fusion, laser guide stars, laser detection, laser processing, and adaptive optics. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Diagram of the structure of the intensity-wavefront-wavelength measuring instrument based on radial shear.

[0030] Figure 2 This is a schematic diagram of the working principle of the metasurface radial shearing interference plate.

[0031] Figure 3aPB phase optical metasurface unit structure diagram.

[0032] Figure 3b Phase and amplitude transmittance control curve of PB phase optical metasurface unit structure.

[0033] Figure 4 Schematic diagram of the metasurface structural unit array after partial enlargement of the metasurface radial shearing interference plate.

[0034] Figure 5 It is the interference fringe pattern under different shear ratios when using ideal plane wave illumination.

[0035] Figure 6 Flowchart of the intensity-wavefront-wavelength measurement method based on radial shearing of metasurfaces. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the accompanying drawings and examples:

[0037] The structure of the intensity-wavefront-wavelength measuring instrument based on radial shearing proposed by the present invention is as follows: Figure 1 As shown, it includes a 1 / 4 wave plate 2, a metasurface radial shearing interference plate 3, a CCD image sensor 6, a displacement device 7 and an intensity-wavefront-wavelength reconstruction unit 8.

[0038] The 1 / 4 wave plate 2, the metasurface radial shearing interferometer plate 3 and the CCD image sensor 6 are arranged in sequence on the optical path. The wavefront 1 of the detected light beam passes through the 1 / 4 wave plate 2 and enters the metasurface radial shearing interferometer plate 3. The metasurface radial shearing interferometer plate 3 divides the circularly polarized light into two wavefronts 4 and 5 with different apertures but consistent surface shapes, forming an interference pattern on the CCD image sensor 6.

[0039] The intensity-wavefront-wavelength reconstruction unit 8 is installed in the form of software on a computer terminal. The intensity-wavefront-wavelength reconstruction unit 8 processes and analyzes the interference pattern signal obtained from the CCD image sensor 6, and finally realizes the reconstruction of the incident light beam, wavefront and wavelength, and completes the extraction and analysis of beam quality related parameters.

[0040] The displacement device 7 is connected to the CCD image sensor 6. The displacement device 7 can be used to adjust the distance between the CCD image sensor 6 and the metasurface radial shearing interference plate 3, thereby adjusting the shear rate and improving the dynamic range of detection. In addition, different measurement distances can affect the contrast of the radial shearing interference pattern. When measuring wavefronts to be measured of different sizes, the distance between the shear plate and the detector can be adjusted so that the incident wavefront to be measured is within the measurement dynamic range. If the measurement distance increases, it will cause the energy of the reduced beam to increase and the energy of the expanded beam to decrease within the effective interference aperture, thereby reducing the contrast of the interference fringes. In addition, if the measurement distance is too small, the phase difference after the shearing of the reduced beam and the expanded beam will be too small, which will reduce sensitivity and reduce measurement accuracy. Therefore, the measurement distance must be accurately controlled (i.e., adjusting the shear rate). Reasonable setting of the shear rate can obtain interference fringes with better density and contrast.

[0041] The working principle of the measuring instrument is as follows: the light beam to be measured enters the radial shear module through a 1 / 4 wave plate, forming an interference pattern on the camera detection surface; according to the Sommerfeld-Rayleigh diffraction formula, the wavelength information is extracted from the diffraction spot pattern to obtain the interference pattern intensity distribution expression; the incident wavelength λ is calculated from the annular spacing of the interference fringes in the interference pattern intensity distribution expression; the wavefront phase difference is solved according to the circular carrier frequency pattern in the interference pattern; according to the similarity of the two beams of wavefronts with different apertures separated by the interference plate, the pattern wavefront reconstruction algorithm based on Zernike polynomials is used to reconstruct the wavefront to be measured; the complex amplitude of the incident wavefront is obtained by inversely deducing the path, thereby obtaining the intensity distribution and wavefront distribution, that is, the intensity-wavefront-wavelength reconstruction algorithm and deep learning algorithm are used to reconstruct the intensity and wavefront information of the incident light beam.

[0042] The use of a metasurface radial shearing interferometer plate replaces traditional bulk optical elements, significantly reducing the instrument's size and improving its integration. Simultaneously, the combined intensity, wavefront, and wavelength reconstruction algorithms enable rapid, simultaneous measurement of beam intensity, wavefront, and wavelength. By leveraging the correlation and self-consistency of the three data, the instrument not only significantly improves beam quality detection accuracy but also simultaneously provides information on the dynamic changes in the intensity, wavefront, and wavelength of the detected beam, providing more accurate and essential key parameters for laser beam quality measurement. The instrument as a whole boasts a simple structure, small size, high integration, high precision, high speed, and resistance to environmental interference, meeting the requirements for real-time, accurate dynamic measurement of laser beam quality in complex environments.

[0043] This instrument differs from existing technologies in two aspects: first, it uses a specially structured metasurface radial shearing interferometer plate 3, and second, it uses a special reconstruction method in the intensity-wavefront-wavelength reconstruction unit 8. The specific structures and implementations of these two aspects are described in detail below.

[0044] Part I: Metasurface radial shear interference plate 3.

[0045] The metasurface radial shearing interferometer plate proposed in the present invention is constructed by integrating two metasurface optical lenses of different focal lengths. The two metasurface optical lenses are based on a phase-modulated metasurface unit structure. For example, in this embodiment, a transmission-type BP phase-modulated metasurface unit structure is specifically adopted. The transmission-type BP phase-modulated metasurface unit structure is arranged into a concentric ring structure with a width less than or equal to λ / 2 according to different phase control parameters. The two metasurface optical lenses are staggered, occupying odd and even rings, respectively, to form the radial shearing interferometer plate.

[0046] Because the annular band width of this metasurface radial shearing interferometer is less than λ / 2, and the sum of the annular band widths of two lenses with different focal lengths is less than the optical wavelength λ, its spatial wavefront control resolution is better than that of a single optical wavelength λ, thus enabling high-spatial-resolution wavefront control. This invention utilizes a metasurface radial shearing interferometer to replace traditional bulk optical elements, offering the advantages of high spatial resolution, high optical efficiency, ultrathinness, ultralightness, ease of integration, and high energy efficiency.

[0047] Specifically, the radial shearing interference plate can be of at least three types, as follows:

[0048] The two metasurface optical lenses of the first radial shearing interferometer are positive and negative lenses with focal lengths of +f and -f, respectively. The even-numbered and odd-numbered ring zones satisfy the phase conditions respectively. or, where r is the spatial polar coordinate on the metasurface optical lens, and λ is the incident wavelength.

[0049] The two metasurface optical lenses of the second radial shearing interferometer are positive lenses with focal lengths of f1 and f2, and the even-numbered and odd-numbered rings respectively meet the phase conditions or

[0050] The two metasurface optical lenses of the third radial shearing interferometer are negative lenses with focal lengths of -f1 and -f2, respectively. The even-numbered and odd-numbered rings satisfy the phase conditions respectively. or

[0051] The working principle of the radial shear interference plate can be found in Figure 2 , this figure corresponds to the first of the three types of radial shearing interference plates mentioned above, and the principle is as follows:

[0052] After the detected light beam wavefront 1 is incident on the radial shearing interferometer plate 3, since the radial shearing interferometer plate integrates a positive lens and a negative lens, a radially reduced wavefront 4 and a radially expanded wavefront 5 are generated. The two wavefronts are only different from the wavefront to be measured in aperture, but have the same surface shape. The reduced wavefront and the expanded wavefront interfere with each other in the overlapping area, converting the phase information in the wavefront into intensity information for subsequent detection. More specifically, the detected light beam wavefront 1 is focused by the metasurface integrated dual lenses on the radial shearing interferometer plate 3 into two light beams converging at z = f1 (real focus) and z = f2 (virtual focus); at z = z d At the intersection of the two beams, they partially overlap and interfere with each other, forming an interference pattern. The intensity distribution of the interference pattern is obtained by the detector array, and the wavefront distribution of the incident beam can be obtained through the reconstruction algorithm.

[0053] Of course, the radial shearing interference plate can be composed of two positive lenses or two negative lenses, such as the second or third type mentioned above. As long as the focal lengths of the two lenses are different, radial shearing interference will occur. However, a reasonable setting of the shear rate can obtain interference fringes with better density and contrast. The process of adjusting the shear rate is very simple in the optical path of the radial shearing interference plate of the present invention. It only requires moving the distance between the detector and the interference plate to change the distance Z between the imaging surface on the CCD image sensor 6 and the metasurface radial shearing interference plate 3. d This radial shearing interferometer plate, formed by integrating two lenses with different focal lengths, has the advantages of no need for reference light setting, no leakage of wavefront information, adjustable shear rate, simple structure, small size and high integration.

[0054] Figure 3a This is the unit structure diagram of the PB phase optical metasurface. Figure 3b This is the phase and amplitude transmittance control curve of the PB phase optical metasurface unit structure. Figure 2 The radial shearing interferometer plate adopts a continuous phase control metasurface design. Each metasurface optical lens is based on a transmission-type phase control metasurface unit structure. Here, the structure and principle of each control unit are illustrated by taking the PB phase optical metasurface unit as an example.

[0055] Existing research shows that the use of metasurface structures can achieve continuous wavefront control of incident light waves at a scale of less than half a wavelength in a plane, which provides a new way to flexibly realize various types of planar optical devices. The metasurface structure is a periodic subwavelength structure formed by micro-nano processing on a planar substrate. Its functional structural period can be less than half a wavelength and its thickness is about the wavelength scale. It can realize optical lenses with high spatial resolution, high optical efficiency, ultra-thinness, ultra-lightness, and easy integration. The radial shearing interferometer plate involved in the present invention adopts a PB phase optical metasurface unit structure with continuous phase control function. Its structural units are as follows: Figure 3a As shown, for the wavelength working range [λ min ,λ max ] incident light, a full dielectric (e.g., TiO2, α-Si, etc.) cubic metasurface structure 32 is fabricated on a glass substrate 31. Within the plane of the glass substrate 31, the TiO2 cubic metasurface structure is rotated to achieve continuous control of the incident light wavefront (within the range of 0-2π). The control efficiency depends mainly on the length L, width W, height t, and period T of the structure. Taking the TiO2 cubic structure as an example, when L = 120nm, W = 60nm, t = 320nm, and T = 260nm, as shown in FIG. Figure 3b As shown in Figure 2, its amplitude transmittance can reach over 90%. Further improving the aspect ratio can achieve an amplitude transmittance close to 100%. By rotating the cubic unit structure, the wavefront of the output light can be controlled at a sub-wavelength scale. When the rotation angle is When , the corresponding phase shift is More importantly, the PB phase optical metasurface unit structure has excellent broadband characteristics, with a bandwidth of more than 400nm. It can be used to realize broadband metasurface radial shearing interferometers to meet the needs of broadband wavefront measurement.

[0056] Figure 4 The radial shearing interference metasurface proposed in this invention is a metasurface optical lens that integrates two different focal lengths. Its basic unit structure is as follows: Figure 3a The positive and negative lenses are arranged in a specific way by a transmissive phase-modulated metasurface structure according to the phase-modulation parameters, and the even-numbered and odd-numbered rings respectively meet the phase space distribution conditions:

[0057] r i ≤r<r i +T

[0058] r i+1 ≤r<r i+1 +T

[0059] or

[0060] r i ≤r<r i +T

[0061] r i+1 ≤r<r i+1 +T

[0062] where r is the spatial polar coordinate on the metasurface optical lens, f and-f are the focal lengths of the two lenses respectively, λ is the wavelength of light, T is the period of the metasurface structure unit, r i = i x T (i is an integer). The entire metasurface is divided into several annular regions with a width of T by the center of the circle i ≤ r < r i + T, where T ≤ λ / 2. In the adjacent two annular regions, the corresponding phases are described by the above two formulas respectively. Thus, two metasurface lenses with focal lengths of f and-f are integrated in the same planar structure, and the optimal shear rate required can be obtained by optimizing f and-f, thereby meeting the requirements of large dynamic range of beam quality detection. Since the annular width is less than or equal to λ / 2, the sum of the annular widths of the two lenses with different focal lengths is less than the wavelength λ, so the resolution of the spatial wavefront control is better than one wavelength λ, thereby realizing high spatial resolution of the wavefront control. At the same time, since the annular width is less than the wavelength, only zero-order diffraction exists, and there is no any high-order diffraction beam, thereby realizing high energy utilization rate and avoiding the interference caused by high-order diffraction.

[0063] The odd annular zones in the radial shear interferometric plate have converging effect on the incident left circularly polarized light, and have diverging effect on the incident right circularly polarized light. Similarly, the even annular zones have opposite effects on the left and right circularly polarized light. Thus, whether the incident light is LCP (left circularly polarized light) or RCP (right circularly polarized light), the incident light is always divided into a converging wave surface and a diverging wave surface, and then forms the same interference pattern. Since any polarized light can be decomposed into a linear superposition of LCP light and RCP light, the radial shear interferometric plate has polarization independence, and can be applied to wavefront detection of any polarized light.

[0064] Figure 5 In the formula, a, b, c and d give the simulated interference patterns of the imaging surface under ideal plane wave illumination, and the shear rates are 0.9, 0.8, 0.7 and 0.6 respectively. It can be seen that the shear rate can be adjusted by only adjusting the distance between the radial shear interferometric plate and the camera.

[0065] As can be seen from the above embodiments, the present invention utilizes a metasurface structure to continuously control phase, amplitude, etc., and at the same time has the characteristics of high spatial resolution, high optical efficiency, ultra-thinness, ultra-lightness, easy integration, and broadband control, and proposes a radial shearing interferometer based on a metasurface structure. By integrating two metasurface optical lenses with different focal lengths, its basic unit structure is a transmission-type phase-control metasurface unit structure, which is arranged with annular bands less than or equal to half a wavelength according to specific phase requirements, achieving polarization independence, high energy utilization, no need for reference light setting, no leakage of wavefront information, simple structure, easy adjustment of shear rate, and not susceptible to environmental interference. The advantages of this technology's high degree of integration can overcome the weaknesses of existing radial shearing interferometer wavefront detection devices, such as large size, many components, low integration, low precision, slow speed, and difficulty in adjusting shear rate, and can meet the requirements of real-time and accurate laser wavefront detection.

[0066] The second part is the intensity-wavefront-wavelength reconstruction unit 8.

[0067] Figure 6 This is a flow chart of the reconstruction method of the intensity-wavefront-wavelength reconstruction unit 8. In short, the incident wavelength λ is calculated from the annular spacing of the interference fringes in the interference pattern intensity distribution expression; the wavefront phase difference is solved according to the annular carrier frequency pattern in the interference pattern; according to the similarity of the two wavefronts with different apertures separated by the interference plate, the pattern wavefront reconstruction algorithm based on Zernike polynomials is used to reconstruct the wavefront to be measured; the complex amplitude of the incident wavefront is obtained by reverse deduction according to the path, thereby obtaining the intensity distribution and wavefront distribution. Specifically, the interference pattern expression is analyzed through the following steps (1):

[0068] Assume that the complex amplitude of the incident wavefront is

[0069] U i (r,θ)=A(r,θ)exp[jkW(r,θ)]

[0070] Where A(r,θ) is the amplitude, W(r,θ) is the wavefront to be measured, and k = 2π / λ is the beam. The transmittance function formula of the measured beam passing through the metasurface structure lens, the converging lens and the diverging lens is:

[0071]

[0072] Where d = λf. Let α = f / (fz) be the ratio of the incident beam aperture to the reduced beam aperture, and β = f / (f+z). From Rayleigh-Sommerfeld diffraction, the expression for the interference pattern intensity distribution is obtained:

[0073]

[0074] (2) Wavelength reconstruction: In the interference pattern, -απr 2 / d-βπr2 / d is r 2 function, which represents the annular interference fringes.

[0075]

[0076] There are only two unknowns in the formula, λ and f, and the incident wavelength λ and the design focal length f are in a fixed functional relationship. Therefore, the specific value of the incident wavelength λ can be obtained from the annular spacing of the interference fringes.

[0077] (3) Solve the wavefront error:

[0078]

[0079] The interference intensity pattern on the image plane can be simply expressed as

[0080]

[0081] In order to extract the wavefront phase difference ΔW(r,θ,z)=W(αr,θ)-W(βr,θ), a corresponding reference interferogram is introduced.

[0082]

[0083] Make its carrier frequency -απr 2 / d-βπr 2 / d is consistent with the interference fringe carrier frequency, while the phase Set to specific four phases. After multiplying and superimposing the interference pattern to be solved with the reference interference pattern, a new fringe pattern can be obtained. The corresponding light intensity distribution is

[0084]

[0085] By properly selecting filters and filtering out high-frequency components, information containing shear phase differences can be extracted, i.e., the first and second terms in the formula, corresponding to the four phase representation intensity distributions are:

[0086]

[0087] So the wavefront phase difference at the image plane is solved as

[0088]

[0089] (4) Reconstructing the wavefront based on Zernike polynomials: The wavefront can be corrected by the phase unwrapping algorithm, and then the wavefront can be reconstructed to extract the original wavefront from the phase difference between the expanded wavefront and the reduced wavefront. Here, the pattern wavefront reconstruction algorithm based on Zernike polynomials can be used. The reduced wavefront and the expanded wavefront of the beam to be measured can be written as follows

[0090]

[0091]

[0092] When the shear rate (ratio of the aperture of the reduced beam to that of the expanded beam in radial shear interference (fz) / (f+z)) is determined, the relationship between the two can be obtained, then we have So the expression of phase difference can be obtained as

[0093]

[0094] Where A={a1,a2,…,a N} is the Zernike polynomial coefficient vector of the wavefront to be measured,

[0095] Z={Z1,Z2,…,Z N} T is the column vector of Zernike polynomials, and B is the coefficient matrix.

[0096]

[0097] In addition, the known phase difference ΔW(r,θ) obtained from the interference pattern is expanded according to the orthogonal Zernike polynomials in the interference region

[0098] ΔW(r,θ)=CZ,

[0099] Correspondingly, the coefficient vector A of the Zernike polynomial of the wavefront to be measured is obtained

[0100] A=CB +

[0101] Therefore, the reduced wavefront W1(r,θ) and the magnified wavefront W2(r,θ) of the wavefront to be measured on the image plane can be reconstructed according to the Zernike orthogonal decomposition expansion.

[0102] (5) Perform Fresnel diffraction integration along the propagation path to obtain the complex amplitude distribution expression of any cross section: Substitute the reduced wavefront W1(r,θ) and the magnified wavefront W2(r,θ) on the image plane into the image plane interference intensity expression I r In (r,θ), the Fresnel diffraction integral can be reversed according to the path to obtain the complex amplitude of the incident wavefront at any section before the incident shear plate

[0103] U i (r,θ)=A(r,θ)exp[jkW(r,θ)]

[0104] (6) Reconstruction of wavefront and intensity distribution: The wavefront distribution is W(r,θ) from the complex amplitude expression of the incident wavefront, and the intensity distribution can be obtained from the square of the complex amplitude and its conjugate

[0105] I(r,θ)=U i (r,θ)*U i (r,θ) * =A 2 (r,θ)

[0106] At this point, this measurement method has achieved the simultaneous calculation of intensity, wavefront and wavelength from an interference pattern. The settlement process utilizes the correlation between the three to promote each other and cooperate with the algorithm to solve, and keeps the three self-consistent.

[0107] As can be seen from the above embodiments, the present invention utilizes a metasurface structure radial shearing interferometer plate to replace traditional bulk optical elements, and has the advantages of high spatial resolution, high optical efficiency, ultra-thinness, ultra-lightness, ease of integration, high energy utilization, simple structure, small size, high integration, high precision, high speed, and not susceptible to environmental interference. The displacement device can be used to adjust the distance between the CCD image sensor and the metasurface radial shearing interferometer plate, thereby adjusting the shear rate, with a high dynamic range of detection, fewer instrument components, high integration, and a simple overall structure. The instrument of the present invention is combined with a measurement method that utilizes the correlation and self-consistency of the intensity, wavefront, and wavelength data, which can not only greatly improve the accuracy of beam quality detection, but also can simultaneously provide information on the dynamic changes in the intensity, wavefront, and wavelength of the detected light beam, providing more accurate and indispensable key parameters for laser beam quality measurement, and can meet the requirements of real-time and accurate dynamic measurement of laser beam quality in complex environments.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention.

Claims

1. An intensity-wavefront-wavelength measuring instrument based on radial shear of a metasurface, characterized by: The invention comprises a quarter-wave plate, a metasurface radial shearing interferometer plate, a CCD image sensor, a displacement device, and an intensity-wavefront-wavelength reconstruction unit; the quarter-wave plate is used to convert an incident laser into circularly polarized light and send it into the metasurface radial shearing interferometer plate; the metasurface radial shearing interferometer plate divides the circularly polarized light into two wavefronts with different apertures but the same surface shape, forming an interference pattern on the CCD image sensor; the intensity-wavefront-wavelength reconstruction unit reconstructs the intensity, wavefront and wavelength information of the incident light beam from the interference pattern; the displacement device adjusts the distance between the CCD image sensor and the metasurface radial shearing interferometer plate, thereby changing the shear rate; The metasurface radial shearing interferometer is composed of two metasurface optical lenses with different focal lengths integrated into one; the metasurface optical lens is based on a phase-modulated metasurface unit structure, and the phase-modulated metasurface unit structure is staggered into a concentric ring structure with a width less than or equal to λ / 2 according to two different phase control parameters, where λ is the incident wavelength, and the two metasurface optical lenses occupy odd and even rings respectively to form the radial shearing interferometer; The intensity-wavefront-wavelength reconstruction unit reconstructs the intensity, wavefront and wavelength information of the incident light beam from the interference pattern, including: Interference pattern analysis: From Rayleigh-Sommerfeld diffraction, we can get the expression for the intensity distribution of the interference pattern; Wavelength reconstruction: The incident wavelength λ is calculated from the annular spacing of the interference fringes in the interference pattern intensity distribution expression; Solve the wavefront difference: solve the wavefront phase difference based on the circular carrier frequency pattern in the interference pattern; Reconstruct wavefront based on Zernike polynomials: Based on the similarity of the two wavefronts with different apertures separated by the radial shearing interferometer, the wavefront to be measured is reconstructed using the pattern wavefront reconstruction algorithm based on Zernike polynomials; The complex amplitude of the incident wavefront is obtained by reverse calculation according to the path; Wavefront and intensity distribution reconstruction; The two metasurface optical lenses are positive and negative lenses with focal lengths of +f and -f, respectively. The even-numbered rings and odd-numbered rings satisfy the phase conditions respectively. , or, , ; Where r is the spatial polar coordinate diameter on the metasurface optical lens; Alternatively, the two metasurface optical lenses are positive lenses with focal lengths f1 and f2, respectively, and the even-numbered rings and the odd-numbered rings satisfy the phase conditions , or , ; Alternatively, the two metasurface optical lenses are negative lenses with focal lengths of -f1 and -f2, respectively, and the even-numbered rings and the odd-numbered rings satisfy the phase conditions , or , .

2. The intensity-wavefront-wavelength measuring instrument based on metasurface radial shearing according to claim 1, characterized in that: The phase-control metasurface unit structure has a continuous phase control function, including a substrate and an all-dielectric cubic metasurface structure thereon. By rotating the all-dielectric cubic metasurface structure, the wavefront of the outgoing light can be controlled on a subwavelength scale.

3. The intensity-wavefront-wavelength measuring instrument based on metasurface radial shearing according to claim 2, characterized in that: The period of the phase-controlled metasurface unit structure is less than or equal to half a wavelength, and there is only zero-order diffraction. The odd and even ring bands produce double-beam interference, which can improve energy utilization. By changing the length, width, height and period of the all-dielectric cubic metasurface structure, the light control efficiency is changed. Among the even-numbered and odd-numbered ring bands, any adjacent ring bands can focus and diverge left-handed circularly polarized light and right-handed polarized light respectively, so that the radial shearing interferometer plate has polarization independence.

4. The intensity-wavefront-wavelength measuring instrument based on metasurface radial shearing according to claim 1, 2 or 3, characterized in that: The method for the intensity-wavefront-wavelength reconstruction unit to perform interference pattern expression analysis includes: Assume that the complex amplitude of the incident wavefront is: ， in, is the amplitude, is the wavefront to be measured, is the wave number, and the transmittance function formula of the measured light beam passing through the metasurface structure lens, the converging lens and the diverging lens combined together is: ， in, , j is the symbol of the complex imaginary part; Let 𝛼=𝑓 / (𝑓−𝑧) be the ratio of the incident beam aperture to the reduced beam aperture, , from Rayleigh-Sommerfeld diffraction, the interference pattern intensity distribution expression is obtained: ， Where r is the polar diameter of the spatial polar coordinate on the metasurface optical lens, θ is the polar angle, and the distance coordinate from the metasurface radial shearing interferometer plate to the imaging surface of the CCD image sensor in the z optical axis direction.

5. The intensity-wavefront-wavelength measuring instrument based on metasurface radial shearing according to claim 1, 2 or 3, characterized in that: The method for the intensity-wavefront-wavelength reconstruction unit to perform wavelength reconstruction: In the interference pattern, It is 𝑟 2 function, which represents the annular interference fringes. There are only two unknowns in the formula: λ and 𝑓. The incident wavelength λ and the design focal length 𝑓 have a fixed functional relationship. Therefore, the specific value of the incident wavelength λ is obtained from the annular spacing of the interference fringes.

6. The intensity-wavefront-wavelength measuring instrument based on metasurface radial shearing according to claim 1, 2 or 3, characterized in that: The method for the intensity-wavefront-wavelength reconstruction unit to solve the wavefront phase difference at the image plane is as follows: life: ， ， The interference intensity diagram on the image plane is abbreviated as: ， In order to extract the wavefront phase difference, a corresponding reference interference pattern is introduced: ， Make its carrier frequency The carrier frequency is consistent with the interference fringe, while the phase By setting the four specific phases and performing multiplication and superposition operations on the interference pattern to be solved and the reference interference pattern, a new fringe pattern can be obtained. The corresponding light intensity distribution is: ， By selecting a filter, the high-frequency components are filtered out and the information containing the shear phase difference is extracted, that is, the first and second terms in the formula, corresponding to the four phase representation intensity distributions are: ， So the wavefront phase difference at the image plane is solved as: 。 7. The intensity-wavefront-wavelength measuring instrument based on metasurface radial shearing according to claim 1, 2 or 3, characterized in that: The intensity-wavefront-wavelength reconstruction unit reconstructs the wavefront based on the Zernike polynomial as follows: The reduced wavefront and expanded wavefront of the beam to be measured are written as follows: ， When the shear rate is , the ratio of the aperture of the narrowed beam to that of the expanded beam in radial shearing interferometry is When it is determined, the relationship between the two can be obtained, then there is , so the expression of phase difference can be obtained as: ， in, is the Zernike polynomial coefficient vector of the wavefront to be measured, is the column vector of Zernike polynomials, B is the coefficient matrix, ， In addition, the known phase difference Δ𝑊(𝑟,𝜃) obtained from the interference pattern is expanded according to the orthogonal Zernike polynomials in the interference region Δ𝑊(𝑟,𝜃)=𝐶𝑍, Correspondingly, the coefficient vector A of the Zernike polynomial of the wavefront to be measured is obtained. ， Thus, the reduced wavefront of the wavefront to be measured on the image plane can be reconstructed according to the Zernike orthogonal decomposition expansion and amplified wavefront .

8. The intensity-wavefront-wavelength measuring instrument based on radial shearing of a metasurface according to claim 1, 2 or 3, characterized in that: The intensity-wavefront-wavelength reconstruction unit performs Fresnel diffraction integration along the propagation path to obtain the complex amplitude distribution expression of any cross section as follows: The reduced wavefront on the image plane and amplified wavefront Substitute into the image plane interference intensity expression The Fresnel diffraction integral can be reversed according to the path to obtain the complex amplitude of the incident wavefront at any section before the incident shear plate. 。 9. The intensity-wavefront-wavelength measuring instrument based on metasurface radial shearing according to claim 1, 2 or 3, characterized in that: The method for the intensity-wavefront-wavelength reconstruction unit to reconstruct the wavefront and intensity distribution is as follows: The wavefront distribution is obtained from the complex amplitude expression of the incident wavefront: , the intensity distribution is obtained by the square of the complex amplitude and its conjugate 。

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