A wavefront measurement method using a combined Hartmann system to improve spatial resolution

Abstract

The present invention discloses a wavefront measurement method that utilizes a combined Hartmann system to improve spatial resolution. The method uses two or more low-resolution wavefront detectors with different arrangements, and improves the spatial resolution of wavefront detection after performing a comprehensive wavefront restoration operation through a wavefront processor. The method utilizes two or more wavefront detectors, and with the help of the characteristics of different arrangements of the wavefront detectors, improves the spatial resolution of the combined wavefront detector by adding constraints in the restoration process, thereby achieving the purpose of high-resolution wavefront detection. The present invention achieves a high-resolution measurement effect by combining two or more low-resolution wavefront detectors, and has the characteristics of simple structure and strong real-time performance, and is particularly suitable for real-time high-resolution wavefront detection of low-contrast extended targets.

Description

Technical Field

[0001] The invention relates to a Hartmann wavefront measurement method, in particular to a wavefront measurement method utilizing a combined Hartmann system to improve spatial resolution. Background Art

[0002] The Hartmann wavefront detection method is an efficient means for measuring the wavefront distortion information of the incident light beam. It was initially used to detect the wavefront information of point targets, and then gradually extended to the detection of the wavefront information of extended targets. Compared with other extended target wavefront information detection methods, the Hartmann wavefront measurement method has the advantages of simple structure, high light energy utilization, and good real-time performance in the detection of extended target wavefront information.

[0003] The main problem with using a single Hartmann wavefront sensor to achieve wavefront detection of extended targets is the low spatial resolution of wavefront detection. Since high-contrast structural information of the target needs to be obtained within a single sub-aperture during extended target wavefront detection, more pixels are used in a single sub-aperture. At the same time, the high-speed sampling frequency makes it impossible for the detector target surface to achieve more sub-aperture measurements through infinite expansion. Therefore, in most cases, the spatial resolution of wavefront detection for extended targets is generally low.

[0004] In addition, under weak light conditions, more photons need to be received in a single sub-aperture to improve the signal-to-noise ratio of centroid detection. Therefore, the number of sub-aperture divisions is also small, making it difficult to obtain high-resolution wavefront information in a single measurement.

[0005] To this end, domestic and foreign peers have carried out a lot of research work. In order to obtain high-resolution wavefront information from low-resolution Hartmann, Guo Youming and other researchers used a set of Hartmann sensors with a resolution of only 19 sub-apertures to restore the wavefront aberration composed of 44 orders using deep learning methods; the non-wavefront control algorithm only uses a single far-field intensity information, and through multiple detection iterations, it can also achieve high-resolution detection and control of the target wavefront, but the convergence speed is relatively slow, and it is difficult to apply to rapidly changing dynamic aberrations; the phase difference algorithm only uses two far-field intensity distribution information to obtain high-resolution wavefront information, but it often takes a long iteration time. Through tools such as deep learning, some scholars have also achieved high-speed wavefront restoration, but its application in the field of extended targets has not yet been reported.

[0006] The above methods have solved the requirements of high-resolution wavefront detection to varying degrees, but it is also obvious that there are problems when using the above methods, such as the inability to be applied to extended targets or the low efficiency of wavefront detection. Summary of the invention

[0007] The technical problem to be solved by the present invention is: in view of the difficulties and contradictions mentioned above, a method for quickly restoring high-resolution wavefront information from a low-resolution wavefront is provided, wherein the method acquires high-resolution wavefront information in real time based on a combination of two or more low-resolution Hartmann wavefront detectors.

[0008] The essence of the method of combining low-resolution Hartmann detectors to obtain high-resolution wavefront information is to utilize the sampling differences between low-resolution Hartmann detectors. Since the sub-aperture collection areas corresponding to each low-resolution Hartmann detector are different, this difference will eventually be reflected in the sub-aperture slope. By solving the equation, this difference is solved to obtain high-resolution wavefront information. Since the entire wavefront restoration process is still a simple matrix solution, even if the alternating direction multiplier method (ADMM) solution method is used, it is only a small number of 2-3 iterations, and the amount of calculation is much smaller than iterative convergence algorithms such as phase difference. Therefore, this method has the characteristics of real-time detection; in addition, the optical path can be switched by a fast mirror, and the wavefront detection can be alternated between two low-resolution Hartmanns with different arrangements, and the high-resolution wavefront information can be obtained by combining the slope information of the previous and next frames.

[0009] The technical solution adopted by the present invention is:

[0010] A wavefront measurement method for improving spatial resolution by using a combined Hartmann system, the combined Hartmann system comprising a first Hartmann wavefront detector (1), a second Hartmann wavefront detector (2), a wavefront signal processing board (3), an input beam splitter (4) and a signal output interface (5), characterized in that the wavefront measurement method comprises the following steps:

[0011] Step 1): the input light beam containing the wavefront to be measured passes through the beam splitter (4) and enters the first Hartmann wavefront detector (1) and the second Hartmann wavefront detector (2) respectively, and the light spot array image data in the first Hartmann wavefront detector (1) and the second Hartmann wavefront detector (2) are collected through the wavefront signal processing board (3);

[0012] Step 2): Based on the spot array image data obtained in step 1), the measured wavefront slope distribution data S1 of the first Hartmann wavefront detector (1) and the measured wavefront slope distribution data S2 of the second Hartmann wavefront detector (2) are respectively calculated by a centroid calculation method;

[0013] Step 3): By solving the equation , obtain high-resolution wavefront distribution data C, where is the objective function of optimization. The optimization goal is to select different C so that The value of is the smallest; is the measured wavefront slope distribution data of the first Hartmann wavefront detector (1) obtained in step 2), is the measured wavefront slope distribution data of the second Hartmann wavefront detector (2) obtained in step 2), is the wavefront restoration matrix of the first Hartmann wavefront detector (1), is the wavefront restoration matrix of the second Hartmann wavefront detector (2), is a constraint or regularization term.

[0014] Furthermore, the sub-aperture arrangements of the first Hartmann wavefront detector (1) and the second Hartmann wavefront detector (2) are different, and the spatial resolution of wavefront detection can be improved by adding a beam splitter and using more than two Hartmann wavefront detectors.

[0015] Furthermore, the first Hartmann wavefront detector (1) and the second Hartmann wavefront detector (2) are formed by combining a microlens array and a CCD detector or a CMOS detector.

[0016] Furthermore, the centroid calculation method is a subaperture slope calculation method in an adaptive optical system, and the centroid calculation is performed specifically by the following expression:

[0017] ,

[0018] in, is the light intensity distribution of the light spot, S0 is the centroid position of the light spot when the incident beam does not contain aberration, D is the effective detection aperture, is the focal plane coordinate.

[0019] Furthermore, the Use quadratic norm, linear norm or weighted quadratic norm for constraints.

[0020] Furthermore, the solution of the equation is based on the regularization term Adjustments are made. When the regularization term is a quadratic norm, the least squares method is used to solve it; when the regularization term is a linear norm, the alternating direction multiplier method is used to solve it.

[0021] Compared with other super-resolution wavefront detection methods, the present invention has higher real-time performance and can be applied to beacon systems with different expansion degrees, and has wider applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the structure of the combined Hartmann system for measuring wavefront of the present invention;

[0023] Figure 2 It is a subaperture arrangement of two low-resolution Hartmann detectors;

[0024] Figure 3 In one embodiment, Figure 2 The restored wavefront using a combination of two low-resolution Hartmann detectors and the restored wavefront using a Hartmann subaperture of 11×11;

[0025] in, Figure 3 (a) shows the wavefront distribution and its restored residual restored by using 7×7 Hartmann array combined with 8×8 Hartmann array;

[0026] Figure 3 (b) is the wavefront distribution and its restored residual restored using the 11×11 Hartmann array;

[0027] Figure 3 (c) is the residual RMS comparison curve of the two restoration methods under different restoration mode conditions;

[0028] Figure 4 In another embodiment, when the input light intensity is weak and the signal-to-noise ratio of the light spot array is low, Figure 2 The restored wavefront using a combination of two low-resolution Hartmann detectors and the restored wavefront using a Hartmann subaperture of 11×11;

[0029] in, Figure 4 (a) shows the wavefront distribution and its restored residual restored by using 7×7 Hartmann array combined with 8×8 Hartmann array;

[0030] Figure 4 (b) is the wavefront distribution and its restored residual restored using the 11×11 Hartmann array;

[0031] Figure 4 (c) is the residual RMS comparison curve of the two restoration methods under different restoration mode conditions;

[0032] The meanings of the reference numerals in the figure are: 1 is the first Hartmann detector, 2 is the second Hartmann detector, 3 is the wavefront signal processing board, 4 is the beam splitter, and 5 is the wavefront data output interface. DETAILED DESCRIPTION

[0033] The specific implementation of the wavefront measurement method for improving spatial resolution by using a combined Hartmann system proposed in the present invention is described in detail below with reference to the accompanying drawings.

[0034] like Figure 1 As shown, the input beam with distortion aberration is decomposed into two beams with the same wavefront distribution after passing through the beam splitter 4, and enters the first Hartmann wavefront detector 1 and the second Hartmann wavefront detector 2 respectively (the sub-aperture center position of the first Hartmann detector 1 is arranged by Figure 2Zhongxing said that the position of the center point of the second sub-aperture of the second Hartmann wavefront detector is Figure 2 The circle in the figure indicates that the first Hartmann detector 1 has an array number of 7×7 and is arranged on four sides; the second Hartmann detector 2 has an array number of 8×8 and is arranged on four sides), and forms a light spot array. The wavefront signal processing board 3 collects detector image data and calculates the sub-aperture slope data using the centroid algorithm or image correlation algorithm. and By solving the equation , and the wavefront distribution is obtained ,in, is the optimization objective function, is the wavefront restoration matrix of the first Hartmann wavefront detector 1, is the wavefront restoration matrix of the second Hartmann wavefront detector 2, λ is the coefficient of the second norm constraint term, and I is the unit matrix.

[0035] Figure 3 (a)-(c) in the figure show the wavefront distribution of a 100th-order Zernike aberration combination detected by a 7×7 Hartmann array combined with an 8×8 Hartmann array, and the wavefront distribution restored by an 11×11 Hartmann array. It can be seen that the detection error of the combined Hartmann array is equivalent to that of the 11×11 Hartmann array. Among them, Figure 3 The three small figures in (a) and (b) correspond from left to right to: input wavefront distribution, reconstructed wavefront distribution and the difference between the two.

[0036] Figure 4 (a)-(c) in the figure show the wavefront distribution of a combination of 100-order Zernike aberrations detected by a 7×7 Hartmann array combined with an 8×8 Hartmann array under weak input light intensity, as well as the wavefront distribution restored by an 11×11 Hartmann array. It can be seen that the detection error of the combined Hartmann array is significantly better than that of the 11×11 Hartmann array. Among them, the detection error of the 11×11 Hartmann array is increased to more than 0.3 wavelengths, but the root mean square value of the combined Hartmann restoration error remains at around 0.14 wavelengths.

[0037] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any modification, equivalent replacement, improvement, etc. made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A wavefront measurement method for improving spatial resolution using a combined Hartmann system, the combined Hartmann system comprising a first Hartmann wavefront detector (1), a second Hartmann wavefront detector (2), a wavefront signal processing board (3), an input beam splitter (4) and a signal output interface (5), characterized in that: The wavefront measurement method comprises the following steps: Step 1): the input light beam containing the wavefront to be measured passes through the beam splitter (4) and enters the first Hartmann wavefront detector (1) and the second Hartmann wavefront detector (2) respectively, and the light spot array image data in the first Hartmann wavefront detector (1) and the second Hartmann wavefront detector (2) are collected through the wavefront signal processing board (3); Step 2): Based on the spot array image data obtained in step 1), the measured wavefront slope distribution data S1 of the first Hartmann wavefront detector (1) and the measured wavefront slope distribution data S2 of the second Hartmann wavefront detector (2) are respectively calculated by a centroid calculation method; Step 3): By solving the equation , obtain high-resolution wavefront distribution data C, where is the objective function of optimization. The optimization goal is to select different C so that The value of is the smallest; is the measured wavefront slope distribution data of the first Hartmann wavefront detector (1) obtained in step 2), is the measured wavefront slope distribution data of the second Hartmann wavefront detector (2) obtained in step 2), is the wavefront restoration matrix of the first Hartmann wavefront detector (1), is the wavefront restoration matrix of the second Hartmann wavefront detector (2), is a constraint or regularization term; The sub-aperture arrangements of the first Hartmann wavefront detector (1) and the second Hartmann wavefront detector (2) are different; by utilizing the sampling difference between the low-resolution Hartmann detectors, since the sub-aperture acquisition areas corresponding to each low-resolution Hartmann detector are different, this difference will eventually be reflected in the sub-aperture slope. By solving the equation, this difference is solved to obtain high-resolution wavefront information.

2. A wavefront measurement method for improving spatial resolution using a combined Hartmann system according to claim 1, characterized in that: The first Hartmann wavefront detector (1) and the second Hartmann wavefront detector (2) are formed by combining a microlens array and a CCD detector or a CMOS detector.

3. A wavefront measurement method for improving spatial resolution using a combined Hartmann system according to claim 1, characterized in that: The centroid calculation method is a subaperture slope calculation method in an adaptive optical system, and the centroid calculation is performed specifically by the following expression: in, is the light intensity distribution of the light spot, S0 is the centroid position of the light spot when the incident beam does not contain aberration, D is the effective detection aperture, is the focal plane coordinate.

4. A wavefront measurement method for improving spatial resolution using a combined Hartmann system according to claim 1, characterized in that: Said Use quadratic norm, linear norm or weighted quadratic norm for constraints.

5. The wavefront measurement method for improving spatial resolution by using a combined Hartmann system according to claim 1, characterized in that: The equation The solution is based on the regularization term Adjustments are made. When the regularization term is a quadratic norm, the least squares method is used to solve it; when the regularization term is a linear norm, the alternating direction multiplier method is used to solve it.

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