A Shack-Hartmann wavefront sensing system and method based on focal scanning

Abstract

The present invention discloses a Shack-Hartmann wavefront sensing system and method based on focus scanning. The detection light beam is conjugated with the scanning device through the first 4f system. The light beam after passing through the scanning device passes through the pinhole and the second 4f system, and finally enters the Shack-Hartmann wavefront sensor. During the focus scanning process, the scanning device deflects the light beam so that different positions of the focused light spot pass through the pinhole at the focal plane of the second 4f system respectively, and the light field phase gradient under different spectra is detected by the Shack-Hartmann wavefront sensor; during the reconstruction process, the light field phase gradient under different spectra is summed with the tilt phase compensated by the scanning device to obtain the corresponding real phase gradient. Finally, the real phase gradient under different spectra is synthesized into a complete phase gradient distribution by using the light spot synthesis method, thereby reconstructing a large dynamic range wavefront. The present invention can greatly improve the dynamic range of the Shack-Hartmann wavefront sensor and can effectively detect the wavefront of multiple guide stars.

Description

Technical Field

[0001] The invention relates to a wavefront sensing system and method in the field of wavefront measurement technology, and in particular to a Shack-Hartmann wavefront sensing system and method based on focus scanning. Background Art

[0002] In the fields of astronomy, visual science, and microscopy, adaptive optics detects the wavefront distortion of light waves passing through the atmosphere, the eyeball, or the sample through wavefront sensors, and eliminates these distortions by adjusting phase compensation devices to improve the quality of imaging. In the field of microscopy, especially in imaging systems such as multiphoton microscopy, confocal microscopy, and super-resolution microscopy, adaptive optics plays a huge role. In the wavefront detection process of adaptive optics, the Shack-Hartmann sensor is the most widely used wavefront sensing device. It consists of a microlens array and a camera. Each microlens forms a focused light spot in its corresponding camera area. The local phase gradient can be obtained by the relative displacement of the light spot behind each microlens, and the shape of the entire wavefront can be restored through the algorithm.

[0003] The dynamic range of wavefront detection of traditional Shack-Hartmann sensors is limited by the size of microlenses. When Shack-Hartmann sensors detect large dynamic range wavefronts, due to the limited size of microlenses, the light spot generated behind the microlenses will exceed the range of the microlenses, resulting in aliasing. Traditional Shack-Hartmann sensors cannot distinguish local light spots, and thus cannot effectively detect local phase gradients.

[0004] In previous work, holographic and algorithm-based wavefront sensing methods can improve the dynamic range without affecting the temporal resolution. However, when the wavefront changes too dramatically, the holographic generation or algorithm will be difficult to locate due to the aliasing of the holographic spots or will not be able to separate the aliased spots due to the search range of the algorithm. Although the previous scanning-based Hartmann sensing method can improve the dynamic range, it requires scanning and collecting the different spatial positions of the wavefront to be measured one by one, and the collection time is too long. Therefore, it can only be used for static wavefront detection. Summary of the invention

[0005] In order to solve the problems and needs in the background technology, the present invention proposes a Shack-Hartmann sensing system and method based on the Fourier stacking principle (focus scanning). The present invention scans the focus, collects the local phase gradient of the wavefront in different frequency domains, and synthesizes a complete large dynamic range wavefront gradient. The dynamic range is proportional to the scanning spectrum range. In the experiment, 49 point arrays were collected to synthesize a complete point array, which increased the dynamic range of the Shack-Hartmann wavefront sensor by 4 times. Therefore, the present invention can greatly improve the dynamic range of the Shack-Hartmann wavefront sensor and can effectively detect the wavefront of multiple guide stars.

[0006] The technical solution of the present invention is as follows:

[0007] 1. A Shack-Hartmann wavefront sensing system based on focal scanning

[0008] The Shack-Hartmann wavefront sensing system comprises a first 4f system, a scanning device, a pinhole, a second 4f system and a Shack-Hartmann sensor. The detection beam is located at the front focal plane of the first 4f system, the detection beam is conjugated with the scanning device through the first 4f system, the pinhole is located at the Fourier plane of the second 4f system, and the scanning device is conjugated with the Shack-Hartmann sensor through the second 4f system; the detection beam is incident on the scanning device after being transmitted by the first 4f system, and after being reflected by the scanning device, it passes through the second 4f system and the pinhole, and finally is incident on the Shack-Hartmann sensor.

[0009] The scanning device is one of a reflector, a galvanometer, a spatial light modulator, and an acousto-optic deflector.

[0010] The first 4f system includes a first lens and a second lens arranged along an optical axis, and the focal points of the first lens and the second lens coincide with each other.

[0011] The second 4f system includes a third lens and a fourth lens arranged along the optical axis, the focal points of the third lens and the fourth lens coincide, a pinhole is placed between the third lens and the fourth lens, and the pinhole is coaxially arranged with the third lens and the fourth lens.

[0012] The Shack-Hartmann sensor includes a connected microlens array and a camera.

[0013] The camera is a camera including a chip selected from the group consisting of CCD, EMCCD, COMS and sCMOS.

[0014] 2. A Shack-Hartmann wavefront sensing method based on focal scanning

[0015] 1) The detection light beam 1 is incident on the scanning device after passing through the first 4f system, and the scanning device scans the light beam; when the scanning device scans the light intensities of different spectra, the Shack-Hartmann sensor captures the light spot images corresponding to the light intensities of different spectra, which are used to synthesize the light spot images under the complete spectrum;

[0016] 2) After centroiding the spot images of different spectra and the calibration spot image (i.e., the spot image generated by the plane wavefront), the phase gradient of each sub-area is obtained, thereby obtaining the phase gradient map of different spectra;

[0017] 3) After summing the phase gradient maps of different spectra and the corresponding tilt phases generated by the scanning device, the effective phase gradient maps of the light spot under each spectrum are obtained;

[0018] 4) The effective phase gradient map of the light spot under different spectra is synthesized by the light spot synthesis method to obtain the phase gradient of all sub-areas of the detection beam.

[0019] In the above 1), when the scanning device scans light intensities of different spectra, the tilt phase compensation sequence of different angles generated by the scanning device is one of raster scanning, Lissajous scanning, and content-based random scanning.

[0020] In the focus scanning-based Shack-Hartmann wavefront sensing system, the limiting range of the pinhole is the dynamic range of an ordinary Shack-Hartmann wavefront sensor (ie, the microlens sub-region range) or the dynamic range supported by a wavefront reconstruction algorithm.

[0021] The light spot synthesis method is one of taking the strongest light intensity light spot displacement as the real phase gradient, taking any light spot displacement as the real phase gradient, and allocating the light spot displacement contribution of each spectrum according to the light intensity as the real phase gradient.

[0022] The beneficial effects of the present invention are:

[0023] (1) The traditional Shack-Hartmann sensor is limited by the inherent size of the microlens array, and the dynamic range of wavefront detection is limited. The present invention converts large dynamic range wavefront detection into wavefront detection within multiple dynamic ranges by adding a focal plane pinhole and scanning device phase compensation, greatly improving the dynamic range of the Shack-Hartmann wavefront sensor.

[0024] (2) For multi-guide star wavefront measurements, the present invention can avoid the aliasing of light spots caused by wavefront measurements of different guide stars by controlling the pinhole size and perform effective wavefront detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to explain the present invention in more detail and concretely, the following drawings are used for description: The drawings show the structure diagram of the system of the present invention, list the component numbers and give corresponding explanations.

[0026] Figure 1 It is a schematic diagram of the structure of the Shack-Hartmann wavefront sensor for focal scanning of the present invention.

[0027] Figure 2 Schematic diagram of the structure of the Shack-Hartmann wavefront sensor for focus scanning according to an embodiment of the present invention.

[0028] Figure 3 1 is an example schematic diagram of a light spot whose focal plane pinhole limit exceeds the dynamic range in an embodiment of the present invention, wherein (a) is a spherical aberration with a PV value of 400rad, (b) is a light spot image without pinhole limit, and (c) is a light spot image with pinhole limit.

[0029] Figure 4 These are spherical aberration spot images with a large dynamic range collected at different scanning angles according to an embodiment of the present invention.

[0030] Figure 5 It is a comparison diagram of the local phase gradient of the synthetic spot images with different spectra, where (a) is the PV value of 400rad spherical aberration, (b) is the local phase gradient distribution of the spherical aberration with a large dynamic range detected by the focus scanning Shack-Hartmann wavefront sensor under the spectrum with the galvanometer compensation phase of 0, and (c) is the complete large dynamic range spherical aberration phase gradient detection result of the focus scanning Shack-Hartmann wavefront sensor.

[0031] In the figure: detection beam 1, first lens 2, second lens 3, scanning device 4, third lens 5, pinhole 6, fourth lens 7, microlens array 8, camera 9, laser 10, fifth lens 11, sixth lens 12, spatial light modulator 13. DETAILED DESCRIPTION

[0032] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0033] The embodiments of the present invention and the specific process thereof are as follows: Example 1

[0034] The detection light beam 1 is a modulated light field generated by the spatial light modulator 13 .

[0035] like Figure 2 As shown, the detection beam 1 is generated by a beam generator, which includes a laser 10, a fifth lens 11, a sixth lens 12 and a spatial light modulator 13. The fifth lens 11 and the sixth lens 12 are coaxially arranged and their focal points coincide. The laser light emitted from the laser 10 passes through the fifth lens 11 and the sixth lens 12 in sequence, and then is reflected by the spatial light modulator 13 to generate the detection beam 1.

[0036] like Figure 1As shown, the Shack-Hartmann wavefront sensing system based on focus scanning of this embodiment includes a first 4f system, a scanning device 4, a pinhole 6, a second 4f system and a Shack-Hartmann sensor. The detection beam 1 is located at the front focal plane of the first 4f system (i.e., the first lens 2). The detection beam 1 is conjugated with the scanning device 4 through the first 4f system. The first 4f system is used to limit the high-frequency part of the detection beam 1 so that the dynamic range of the detection beam wavefront is within the dynamic range of the Shack-Hartmann. The pinhole 6 is located at the Fourier plane of the second 4f system. The scanning device 4 is conjugated with the microlens array 8 of the Shack-Hartmann sensor through the second 4f system. The detection beam 1 is incident on the scanning device 4 after being transmitted by the first 4f system, and then passes through the second 4f system and the pinhole 6 after being reflected by the scanning device 4, and finally incident on the Shack-Hartmann sensor. The pinhole 6 is used to limit the dynamic range of the detection beam wavefront. The light intensity exceeding the dynamic range is blocked by the pinhole 6 and will no longer be detected by the sensor, thereby eliminating the aliased light spot. During the scanning process of the scanning device 4, the wavefront of the detection beam is compensated by the tilt phase at different angles generated by the scanning device 4. The scanning device 4 deflects the beam so that the focused light spots at different positions pass through the pinhole 6 at the focal plane respectively, and the wavefront sensor detects the light field phase gradient in different frequency domains; during the reconstruction process, the light field phase gradient in different frequency domains is summed with the tilt phase gradient compensated by the scanning device 4 to obtain the real phase gradient. Finally, the phase gradients in different frequency domains are synthesized into a complete phase gradient distribution by using the spot synthesis method, and the large dynamic range wavefront is reconstructed accordingly.

[0037] The scanning device 4 is a galvanometer.

[0038] The first 4f system includes a first lens 2 and a second lens 3. The first lens 2 and the second lens 3 are coaxially arranged and their focal points coincide with each other.

[0039] The second 4f system includes a third lens 5 and a fourth lens 7, which are coaxially arranged and have the same focal points. A pinhole 6 is placed between the third lens 5 and the fourth lens 7, and the pinhole 6 is coaxially arranged with the third lens 5 / the fourth lens 7.

[0040] The Shack-Hartmann sensor comprises a connected microlens array 8 and a camera 9. The camera 9 is a camera using sCMOS as a chip.

[0041] The implementation process is as follows:

[0042] 1) The laser 10 emits a laser beam, which is expanded to the size of the spatial light modulator 13 through the fifth lens 11 and the sixth lens 12. For example, the beam diameter is expanded from 2 mm to about 8 mm. The spatial light modulator 13 generates a wavefront with a large dynamic range through phase wrapping. For example Figure 3In (a), the spherical aberration phase is loaded. The laser 10 is ALCOR 920-4 from Spark of France. The spatial light modulator 13 is 1920x1200, 850-1300nm from Meadowlark Optics of the United States.

[0043] 2) The modulated light beam passes through the first 4f system to control the beam size within the range of the galvanometer. The galvanometer is located at the rear focal plane of the second lens 3 and maintains a conjugate relationship with the spatial light modulator 13 to ensure the effectiveness of the galvanometer tilt phase compensation. The galvanometer is a 6215h galvanometer from CTI of the United States.

[0044] 3) The light beam passing through the galvanometer is focused by the third lens 5, and the light intensity distribution at the focal plane is the Fourier transform of the light beam at the galvanometer. The larger the phase gradient of the light beam, the more the light intensity of this part deviates from the optical axis at the focal plane. The pinhole 6 located at the focal plane filters out the light intensity that exceeds a certain dynamic range and has a large phase gradient, such as Figure 3 The spot image without pinhole restriction is shown in (c). Figure 3 As shown in (b), the filtering range of the pinhole 6 is the dynamic range of the Shack-Hartmann wavefront sensor.

[0045] 4) The light passing through the pinhole 6 passes through the fourth lens 7 and is incident on the Shack-Hartmann wavefront sensor composed of the microlens array 8 and the scientific camera. The galvanometer compensates for the tilt phase in all directions through two-dimensional scanning, moves the light intensity with a larger phase gradient to the low-frequency part closer to the optical axis, and the phase distribution of the beams with different spatial frequencies is collected by the Shack-Hartmann wavefront sensor, such as Figure 4 As shown in FIG. 8 , the microlens array 8 is 64-483 from Edmund of the United States, and the scientific research camera is 400BSI from Xintu Optoelectronics of China. The scanning method of the galvanometer is Lissajous scanning.

[0046] 5) Through the different spectrum spot images collected by the Shack-Hartmann wavefront sensor, the local phase gradient under the corresponding spectrum is obtained through the centroid positioning algorithm, such as Figure 5 As shown in (b), Figure 5 (b) is Figure 5 (a) shows the local phase gradient distribution of the large dynamic range spherical aberration under the spectrum with the galvanometer compensation phase of 0. After fitting the relationship between the galvanometer compensation phase and the phase gradient detected by the Shack-Hartmann wavefront detector, the galvanometer compensation phase gradient is summed with the centroid positioning local phase gradient to obtain the true phase gradient. Finally, the local phase gradients under all spectra are summarized to obtain the complete phase gradient distribution, as shown in Figure 5 As shown in (c), when summarizing the local gradients, the repeated spot position retention method is to retain the spot in any frequency domain.

[0047] like Figure 3This is the distribution of the spot image of the large dynamic range spherical aberration in the ordinary Shack-Hartmann wavefront sensor and the wavefront sensor with pinhole filter under simulation. In the ordinary sensor, the distribution of the spot will disappear or alias in the phase part beyond the dynamic range, while the pinhole 6 effectively retains the spot within the dynamic range. Figure 4 It is the distribution of the spot image obtained by the wavefront sensor at different scanning angles of the scanning device corresponding to the spherical aberration. Large gradient phases in different directions are detected at opposite scanning angles. Figure 5 The results of the phase gradient detection of the spherical aberration by the common wavefront sensor and the phase synthesis gradient detection effect after focus scanning are shown in the figure. The effectiveness of the present invention in the case of large dynamic range wavefront detection can be found from the figure. Example 2

[0048] The detection light beam 1 is a modulated light field generated by the spatial light modulator 13 .

[0049] like Figure 2 As shown, the detection beam 1 is generated by a beam generator, which includes a laser 10, a fifth lens 11, a sixth lens 12 and a spatial light modulator 13. The fifth lens 11 and the sixth lens 12 are coaxially arranged and their focal points coincide. The laser light emitted from the laser 10 passes through the fifth lens 11 and the sixth lens 12 in sequence, and then is reflected by the spatial light modulator 13 to generate the detection beam 1.

[0050] The Shack-Hartmann wavefront sensing system based on focal scanning of this embodiment includes a first 4f system, a scanning device 4, a pinhole 6, a second 4f system and a Shack-Hartmann sensor. The detection beam 1 is located at the front focal plane of the first 4f system (i.e., the first lens 2). The detection beam 1 is conjugated with the scanning device 4 through the first 4f system. The first 4f system is used to limit the high-frequency part of the detection beam 1 so that the dynamic range of the detection beam wavefront is within the dynamic range of the Shack-Hartmann. The pinhole 6 is located at the Fourier plane of the second 4f system. The scanning device 4 is conjugated with the microlens array 8 of the Shack-Hartmann sensor through the second 4f system. The detection beam 1 is incident on the scanning device 4 after being transmitted by the first 4f system, and is incident on the Shack-Hartmann sensor through the second 4f system and the pinhole 6 after being reflected by the scanning device 4. The pinhole 6 is used to limit the dynamic range of the detection beam wavefront. The light intensity exceeding the dynamic range is blocked by the pinhole and will no longer be detected by the sensor, thereby eliminating the aliased light spot. During the scanning process of the scanning device, the wavefront of the detection beam is compensated by the tilt phase of different angles generated by the scanning device 4. The scanning device 4 deflects the beam so that the focused light spots at different positions pass through the pinhole 6 at the focal plane respectively, and the wavefront sensor detects the light field phase gradient in different frequency domains; during the reconstruction process, the light field phase gradient in different frequency domains is summed with the tilt phase gradient compensated by the scanning device 4 to obtain the real phase gradient. Finally, the phase gradients in different frequency domains are synthesized into a complete phase gradient distribution by the spot synthesis method, and the large dynamic range wavefront is reconstructed accordingly.

[0051] The scanning device 4 is a first spatial light modulator.

[0052] The first 4f system includes a first lens 2 and a second lens 3. The first lens 2 and the second lens 3 are coaxially arranged and their focal points coincide with each other.

[0053] The second 4f system includes a third lens 5 and a fourth lens 7, which are coaxially arranged and have the same focal points. A pinhole 6 is placed between the third lens 5 and the fourth lens 7, and the pinhole 6 is coaxially arranged with the third lens 5 / the fourth lens 7.

[0054] The Shack-Hartmann sensor comprises a microlens array 8 and a camera 9 which are connected.

[0055] The camera 9 is a camera using a CMOS chip.

[0056] The implementation process is as follows:

[0057] 1) The laser 10 emits a laser beam, which is expanded to the size of the spatial light modulator 13 through the fifth lens 11 and the sixth lens 12. For example, the beam diameter is expanded from 2 mm to about 8 mm. The spatial light modulator 13 generates a wavefront with a large dynamic range through phase wrapping. For example Figure 3In (a), the spherical aberration phase is loaded. The laser 10 is ALCOR 920-4 from Spark of France. The spatial light modulator 13 is 1920x1200, 850-1300nm from Meadowlark Optics of the United States.

[0058] 2) The modulated light beam passes through the first 4f system to control the light beam size within the range of the first spatial light modulator. The first spatial light modulator is located at the rear focal plane of the second lens 3 and maintains a conjugate relationship with the spatial light modulator 13 to ensure the effectiveness of the tilt phase compensation of the first spatial light modulator. The first spatial light modulator can be 1920x1200, 850-1300nm from MeadowlarkOptics of the United States.

[0059] 3) The light beam passing through the first spatial light modulator is focused by the third lens 5, and the light intensity distribution at the focal plane is the Fourier transform of the light beam at the first spatial light modulator. The larger the phase gradient of the light beam, the more the light intensity of this part deviates from the optical axis at the focal plane. The pinhole 6 located at the focal plane filters out the light intensity that exceeds a certain dynamic range and has a large phase gradient, such as Figure 3 The spot image without pinhole restriction is shown in (c). Figure 3 As shown in (b), the filtering range of the filter pinhole is the dynamic range supported by the wavefront reconstruction algorithm, that is, the frequency domain range supported by the algorithm.

[0060] 4) The light passing through the pinhole 6 passes through the fourth lens 7 and is incident on the Shack-Hartmann wavefront sensor composed of the microlens array 8 and the camera 9. The first spatial light modulator generates grating phases of different spatial frequencies to compensate for the tilted phases in all directions, and moves the light intensity with a larger phase gradient to the low-frequency part closer to the optical axis. The phase distribution of the light beams with different spatial frequencies is collected by the Shack-Hartmann wavefront sensor, such as Figure 4 The microlens array 8 is 64-483 from Edmund, USA, and the camera is CC126MU from Thorlabs, USA. The scanning sequence of the first spatial light modulator is grid sequential scanning.

[0061] 5) Through the different spectrum spot images collected by the Shack-Hartmann wavefront sensor, the local phase gradient under the corresponding spectrum is obtained through the centroid positioning algorithm, such as Figure 5 As shown in (b), Figure 5 (b) is Figure 5 (a) The local phase gradient distribution of the large dynamic range spherical aberration under the spectrum with the galvanometer compensation phase of 0. After fitting the relationship between the galvanometer compensation phase and the phase gradient detected by the Shack-Hartmann wavefront detector, the galvanometer compensation phase gradient is summed with the local phase gradient of the centroid positioning to obtain the true phase gradient. Finally, the local phase gradients under all spectra are summarized to obtain the complete phase gradient distribution, as shown in Figure 5As shown in (c), when summarizing the local gradients, the repeated spot position retention method is to retain the spot with the strongest light intensity in different frequency domains.

[0062] like Figure 3 This is the distribution of the spot image of the large dynamic range spherical aberration in the ordinary Shack-Hartmann wavefront sensor and the wavefront sensor with pinhole filter under simulation. In the ordinary sensor, the distribution of the spot will disappear or alias in the phase part exceeding the dynamic range, while the pinhole 6 effectively retains the spot within the dynamic range. Figure 4 It is the distribution of the spot image obtained by the wavefront sensor at different scanning angles of the scanning device corresponding to the spherical aberration. Large gradient phases in different directions are detected at opposite scanning angles. Figure 5 The results of the phase gradient detection of the spherical aberration by the common wavefront sensor and the phase synthesis gradient detection effect after focus scanning are shown in the figure. The effectiveness of the present invention in the case of large dynamic range wavefront detection can be found from the figure. Example 3

[0063] The detection light beam 1 is a modulated light field generated by the spatial light modulator 13 .

[0064] like Figure 2 As shown, the detection beam 1 is generated by a beam generator, which includes a laser 10, a fifth lens 11, a sixth lens 12 and a spatial light modulator 13. The fifth lens 11 and the sixth lens 12 are coaxially arranged and their focal points coincide. The laser light emitted from the laser 10 passes through the fifth lens 11 and the sixth lens 12 in sequence, and then is reflected by the spatial light modulator 13 to generate the detection beam 1.

[0065] like Figure 1As shown, a Shack-Hartmann wavefront sensing system based on focus scanning includes a first 4f system, a scanning device 4, a pinhole 6, a second 4f system and a Shack-Hartmann sensor. The detection beam 1 is located at the front focal plane of the first 4f system (i.e., the first lens 2). The detection beam 1 is conjugated with the scanning device 4 through the first 4f system. The first 4f system is used to limit the high-frequency part of the detection beam 1 so that the dynamic range of the detection beam wavefront is within the dynamic range of the Shack-Hartmann. The pinhole 6 is located at the Fourier plane of the second 4f system. The scanning device 4 is conjugated with the microlens array 8 of the Shack-Hartmann sensor through the second 4f system. The detection beam 1 is incident on the scanning device 4 after being transmitted by the first 4f system, and is incident on the Shack-Hartmann sensor through the second 4f system and the pinhole 6 after being reflected by the scanning device 4. The pinhole 6 is used to limit the dynamic range of the detection beam wavefront. The light intensity exceeding the dynamic range is blocked by the pinhole and will no longer be detected by the sensor, thereby eliminating the aliased light spot. During the scanning process of the scanning device 4, the wavefront of the detection beam is compensated by the tilt phase at different angles generated by the scanning device 4. The scanning device 4 deflects the beam so that the focused light spots at different positions pass through the pinhole 6 at the focal plane respectively, and the wavefront sensor detects the light field phase gradient in different frequency domains; during the reconstruction process, the light field phase gradient in different frequency domains is summed with the tilt phase gradient compensated by the scanning device 4 to obtain the real phase gradient. Finally, the phase gradients in different frequency domains are synthesized into a complete phase gradient distribution by using the spot synthesis method, and the large dynamic range wavefront is reconstructed accordingly.

[0066] The scanning device 4 is an acousto-optic deflector.

[0067] The first 4f system includes a first lens 2 and a second lens 3. The first lens 2 and the second lens 3 are coaxially arranged and their focal points coincide with each other.

[0068] The second 4f system includes a third lens 5 and a fourth lens 7, which are coaxially arranged and have the same focal points. A pinhole 6 is placed between the third lens 5 and the fourth lens 7, and the pinhole 6 is coaxially arranged with the third lens 5 / the fourth lens 7.

[0069] The Shack-Hartmann sensor comprises a connected microlens array 8 and a camera 9. The camera 9 is a camera using a CMOS chip.

[0070] The implementation process is as follows:

[0071] 1) The laser 10 emits a laser beam, which is expanded to the size of the spatial light modulator 13 through the fifth lens 11 and the sixth lens 12. For example, the beam diameter is expanded from 2 mm to about 8 mm. The spatial light modulator 13 generates a wavefront with a large dynamic range through phase wrapping.

[0072] 2) The modulated light beam passes through the first 4f system to control the beam size within the range of the acousto-optic deflector. The acousto-optic deflector is located at the rear focal plane of the second lens 3 and maintains a conjugate relationship with the spatial light modulator 13 to ensure the effectiveness of the tilt phase compensation of the acousto-optic deflector.

[0073] 3) The light beam passing through the acousto-optic deflector is focused by the third lens 5, and the light intensity distribution at the focal plane is the Fourier transform of the light beam at the acousto-optic deflector. The larger the phase gradient of the light beam, the more the light intensity of this part deviates from the optical axis at the focal plane. The pinhole 6 located at the focal plane filters out the light intensity that exceeds a certain dynamic range and has a large phase gradient.

[0074] 4) The light passing through the pinhole 6 passes through the fourth lens 7 and is incident on the Shack-Hartmann wavefront sensor composed of a microlens array 8 and a scientific camera. The acousto-optic deflector compensates for the tilt phase in all directions through two-dimensional scanning, moves the light intensity with a large phase gradient to the low-frequency part closer to the optical axis, and the phase distribution of the beams of different spatial frequencies is collected by the Shack-Hartmann wavefront sensor.

[0075] 5) Through the different spectrum spot images collected by the Shack-Hartmann wavefront sensor, the local phase gradient under the corresponding spectrum is obtained through the centroid positioning algorithm. After fitting the relationship between the compensation phase of the acousto-optic deflector and the phase gradient detected by the Shack-Hartmann wavefront detector, the compensation phase gradient of the acousto-optic deflector and the local phase gradient of the centroid positioning are summed to obtain the real phase gradient. Finally, the local phase gradients under all spectra are summarized to obtain the complete phase gradient distribution. Example 4

[0076] The detection light beam 1 is a modulated light field generated by the spatial light modulator 13 .

[0077] like Figure 2 As shown, the detection beam 1 is generated by a beam generator, which includes a laser 10, a fifth lens 11, a sixth lens 12 and a spatial light modulator 13. The fifth lens 11 and the sixth lens 12 are coaxially arranged and their focal points coincide. The laser light emitted from the laser 10 passes through the fifth lens 11 and the sixth lens 12 in sequence, and then is reflected by the spatial light modulator 13 to generate the detection beam 1.

[0078] like Figure 1As shown, a Shack-Hartmann wavefront sensing system based on focus scanning includes a first 4f system, a scanning device 4, a pinhole 6, a second 4f system and a Shack-Hartmann sensor. The detection beam 1 is located at the front focal plane of the first 4f system (i.e., the first lens 2). The detection beam 1 is conjugated with the scanning device 4 through the first 4f system. The first 4f system is used to limit the high-frequency part of the detection beam 1 so that the dynamic range of the detection beam wavefront is within the dynamic range of the Shack-Hartmann. The pinhole 6 is located at the Fourier plane of the second 4f system. The scanning device 4 is conjugated with the microlens array 8 of the Shack-Hartmann sensor through the second 4f system. The detection beam 1 is incident on the scanning device 4 after being transmitted by the first 4f system, and is incident on the Shack-Hartmann sensor through the second 4f system and the pinhole 6 after being reflected by the scanning device 4. The pinhole is used to limit the dynamic range of the detection beam wavefront. The light intensity exceeding the dynamic range is blocked by the pinhole and will no longer be detected by the sensor, thereby eliminating the aliased light spot. During the scanning process of the scanning device 4, the wavefront of the detection beam is compensated by the tilt phase at different angles generated by the scanning device 4. The scanning device 4 deflects the beam so that the focused light spots at different positions pass through the pinhole 6 at the focal plane respectively, and the wavefront sensor detects the light field phase gradient in different frequency domains; during the reconstruction process, the light field phase gradient in different frequency domains is summed with the tilt phase gradient compensated by the scanning device 4 to obtain the real phase gradient. Finally, the phase gradients in different frequency domains are synthesized into a complete phase gradient distribution by using the spot synthesis method, and the large dynamic range wavefront is reconstructed accordingly.

[0079] The scanning device 4 is a reflection mirror.

[0080] The first 4f system includes a first lens 2 and a second lens 3. The first lens 2 and the second lens 3 are coaxially arranged and their focal points coincide with each other.

[0081] The second 4f system includes a third lens 5 and a fourth lens 7, which are coaxially arranged and have the same focal points. A pinhole 6 is placed between the third lens 5 and the fourth lens 7, and the pinhole 6 is coaxially arranged with the third lens 5 / the fourth lens 7.

[0082] The Shack-Hartmann sensor comprises a connected microlens array 8 and a camera 9. The camera 9 is a camera using a CCD as a chip.

[0083] The implementation process is as follows:

[0084] 1) The laser 10 emits a laser beam, which is expanded to the size of the spatial light modulator 13 through the fifth lens 11 and the sixth lens 12. For example, the beam diameter is expanded from 2 mm to about 8 mm. The spatial light modulator 13 generates a wavefront with a large dynamic range through phase wrapping.

[0085] 2) The modulated light beam passes through the first 4f system to control the beam size within the range of the acousto-optic deflector. The acousto-optic deflector is located at the rear focal plane of the second lens 3 and maintains a conjugate relationship with the spatial light modulator 13 to ensure the effectiveness of the tilt phase compensation of the acousto-optic deflector.

[0086] 3) The light beam passing through the acousto-optic deflector is focused by the third lens 5, and the light intensity distribution at the focal plane is the Fourier transform of the light beam at the acousto-optic deflector. The larger the phase gradient of the light beam, the more the light intensity of this part deviates from the optical axis at the focal plane. The pinhole 6 located at the focal plane filters out the light intensity that exceeds a certain dynamic range and has a large phase gradient.

[0087] 4) The light passing through the pinhole 6 passes through the fourth lens 7 and is incident on the Shack-Hartmann wavefront sensor composed of a microlens array 8 and a scientific camera. The acousto-optic deflector compensates for the tilt phase in all directions through two-dimensional scanning, moves the light intensity with a large phase gradient to the low-frequency part closer to the optical axis, and the phase distribution of the beams of different spatial frequencies is collected by the Shack-Hartmann wavefront sensor.

[0088] 5) Through the different spectrum spot images collected by the Shack-Hartmann wavefront sensor, the local phase gradient under the corresponding spectrum is obtained through the centroid positioning algorithm. After fitting the relationship between the compensation phase of the acousto-optic deflector and the phase gradient detected by the Shack-Hartmann wavefront detector, the compensation phase gradient of the acousto-optic deflector and the local phase gradient of the centroid positioning are summed to obtain the real phase gradient. Finally, the local phase gradients under all spectra are summarized to obtain the complete phase gradient distribution.

[0089] In summary, the present invention avoids the aliasing of the light spot under the large dynamic range wavefront through the pinhole at the focal plane. By focusing scanning, the tilt phase exceeding the dynamic range is compensated. The aliased light spot image is converted into multiple light spot images corresponding to the microlens sub-areas in different frequency domains. The wavefront detection exceeding the original dynamic range is obtained before and after the synthetic wave; and the wavefront of multiple guide stars can be effectively detected.

[0090] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0091] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0092] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A Shack-Hartmann wavefront sensing system based on focal scanning, characterized in that: The invention comprises a first 4f system, a scanning device (4), a pinhole (6), a second 4f system and a Shack-Hartmann sensor. The detection light beam (1) is located at the front focal plane of the first 4f system, the detection light beam (1) is conjugated with the scanning device (4) through the first 4f system, the pinhole (6) is located at the Fourier plane of the second 4f system, and the scanning device (4) is conjugated with the Shack-Hartmann sensor through the second 4f system. The detection light beam (1) is incident on the scanning device (4) after being transmitted by the first 4f system, and after being reflected by the scanning device (4), it passes through the second 4f system and the pinhole (6) and finally is incident on the Shack-Hartmann sensor.

2. The Shack-Hartmann wavefront sensing system based on focal scanning according to claim 1, characterized in that: The scanning device (4) is one of a reflector, a galvanometer, a spatial light modulator, and an acousto-optic deflector.

3. The Shack-Hartmann wavefront sensing system based on focal scanning according to claim 1, characterized in that: The first 4f system comprises a first lens (2) and a second lens (3), wherein the first lens (2) and the second lens (3) are coaxially arranged and their focal points coincide with each other.

4. The Shack-Hartmann wavefront sensing system based on focal scanning according to claim 1, characterized in that: The second 4f system comprises a third lens (5) and a fourth lens (7), wherein the third lens (5) and the fourth lens (7) are coaxially arranged and the focal points of the third lens (5) and the fourth lens (7) coincide with each other, and a pinhole (6) is disposed between the third lens (5) and the fourth lens (7), and the pinhole (6) is coaxially arranged with the third lens (5) and the fourth lens (7).

5. The Shack-Hartmann wavefront sensing system based on focal scanning according to claim 1, characterized in that: The Shack-Hartmann sensor comprises a connected microlens array (8) and a camera (9).

6. The Shack-Hartmann wavefront sensing system based on focal scanning according to claim 5, characterized in that: The camera (9) is a camera comprising a chip selected from the group consisting of CCD, EMCCD, COMS and sCMOS.

7. A Shack-Hartmann wavefront sensing method based on focus scanning, characterized in that: The sensing method adopts the Shack-Hartmann wavefront sensing system based on focus scanning as described in claim 1, and the sensing method comprises the following steps: 1) The detection light beam (1) is incident on the scanning device (4) after passing through the first 4f system, and the scanning device (4) scans the light beam; when the scanning device (4) scans light intensities of different spectra, the Shack-Hartmann sensor captures and obtains light spot images corresponding to the light intensities of different spectra; 2) After centroiding the spot images of different spectra and the calibration spot images, the phase gradient of each sub-area is obtained, thereby obtaining the phase gradient map of different spectra; 3) After summing the phase gradient images of different spectra and the corresponding tilt phases generated by the scanning device (4), an effective phase gradient image of the light spot under each spectrum is obtained; 4) The effective phase gradient map of the light spot under different spectra is synthesized by the light spot synthesis method to obtain the phase gradient of all sub-areas of the detection beam (1).

8. The Shack-Hartmann wavefront sensing method based on focus scanning according to claim 7, characterized in that: In the step 1), when the scanning device (4) scans light intensities of different spectra, the scanning method of the scanning device (4) in the compensation process is one of raster scanning, Lissajous scanning, and content-based random scanning.

9. The Shack-Hartmann wavefront sensing method based on focus scanning according to claim 7, characterized in that: In the Shack-Hartmann wavefront sensing system based on focus scanning, the limiting range of the pinhole (6) is the dynamic range of a common Shack-Hartmann wavefront sensor or the dynamic range supported by a wavefront reconstruction algorithm.

10. The Shack-Hartmann wavefront sensing method based on focus scanning according to claim 7, characterized in that: The light spot synthesis method is one of taking the strongest light intensity light spot displacement as the real phase gradient, taking any one of the light spot displacements as the real phase gradient, and distributing the light spot displacement contribution of each spectrum according to the light intensity as the real phase gradient.

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