Rapid detection method and system for tilting mirrors in ultra-high contrast imaging instruments

Abstract

This invention discloses a rapid detection method and system for a tilting mirror in an ultra-high contrast imaging instrument. The detection system includes a laser source, optical fiber, collimating lens, tilting mirror under test, imaging mirror, high-speed detector, image acquisition card, signal generator, and tilting mirror controller. This invention enables rapid and automated detection of the stabilization performance of the tilting mirror at different operating frequencies, and screens and records the actual resonant frequency of the tilting mirror under load conditions. This frequency can be avoided during mirror operation, ensuring normal image stabilization. Specifically designed and optimized for the detection needs of tilting mirrors in ultra-high contrast imaging instruments, it not only calibrates the tilting mirror's own response but also detects its image stabilization correction capability. Automatic calibration and image stabilization monitoring of the tilting mirror can be achieved through LabVIEW electronic control programs, reducing human interference. The compact optical path structure facilitates integration with pre-disturbance optical paths configured for different research needs, offering flexible and convenient application.

Description

Technical Field

[0001] This invention belongs to the field of exoplanet imaging and detection technology, and specifically relates to a rapid detection method and system for a pendulum mirror in an ultra-high contrast imaging instrument. Background Technology

[0002] Exoplanet detection is a cutting-edge and hot topic in contemporary astronomical research. Statistics show that over 5,400 exoplanets have been discovered and confirmed to date using various detection technologies, and the number continues to grow rapidly. Ultra-high contrast imaging instruments are crucial for exoplanet detection. During ground-based observations, to overcome the effects of atmospheric disturbances, key components of ultra-high contrast imaging instruments, such as the pendulum mirrors and deformable mirrors, typically require high-frequency calibration at kilohertz.

[0003] As the image stabilization unit in ultra-high contrast imaging instruments, the stabilization performance of the tilting mirror directly affects the working effect of subsequent core components (such as deformable mirrors and modulation filters). Therefore, the tilting mirror is one of the key components determining the overall performance of an ultra-high contrast imaging instrument, and its testing is crucial. When testing the tilting mirror:

[0004] On the one hand, considering the working characteristics of the oscillating mirror in ultra-high contrast imaging instruments, the complete process of self-calibration and image stabilization correction should be considered. Furthermore, the oscillating mirror needs to have the capability to detect a certain frequency bandwidth, allowing for the selection of the highest frequency achieved by the oscillating mirror during normal image stabilization in ultra-high contrast imaging instruments. In addition, the resonant frequency of the oscillating mirror should also be screened, as this frequency is related to the actual operating conditions of the oscillating mirror (e.g., the mass of the loaded mirror, the oscillating mirror's mounting structure and fixing method), and this frequency should be avoided during operation. On the other hand, the image stabilization accuracy of the oscillating mirror needs to be tested. Higher accuracy means less image drift, which helps the deformable mirror in ultra-high contrast imaging instruments achieve better correction results. Therefore, rapid and automated testing of the oscillating mirror in ultra-high contrast imaging instruments has significant research and application value. Summary of the Invention

[0005] To address the calibration and testing issues of the tilting mirror in ultra-high contrast imaging instruments, this invention proposes a rapid testing method and system for the tilting mirror in ultra-high contrast imaging instruments.

[0006] To achieve the above objectives, the present invention provides a rapid detection method for a tilting mirror in an ultra-high contrast imaging instrument, comprising the following steps:

[0007] Step 1: The laser source is coupled out through an optical fiber to form a point light source, which is then collimated by a collimating lens to become parallel light;

[0008] Step 2: Light rays are incident on the pendulum mirror to be tested and then reflected to the imaging mirror;

[0009] Step 3: After passing through the imaging mirror, the light enters the high-speed detector and receives the point spread function (PSF) image on the focal plane of the high-speed detector.

[0010] Step 4: The signal generator outputs the driving voltage of two channels, which is amplified and subdivided by the mirror controller and then pushed to the mirror under test with the median voltage to swing its two motion axes to the initial center position. The two motion axes are the X-axis and the Y-axis.

[0011] Furthermore, a high-speed detector is used to acquire PSF images and calculate the initial coordinates (x, y) of its centroid. PSF_0 ,y PSF_0 );

[0012] Step 5: The signal generator outputs the driving voltage of two channels, which is then amplified and subdivided by the mirror controller before being pushed to the X and Y axes of the mirror under test to calibrate the response relationship between the driving voltage and the mirror deflection.

[0013] Furthermore, the calibration involves the tilt vector S and the Zernike polynomial coefficient vector A, and their relationship is as follows:

[0014] S = [B]A, A = (a1, a2, ..., a K ) T (1)

[0015] In the formula, a1~a K These are the Zernike coefficients from the 1st to the Kth term, represented by the [B] matrix:

[0016]

[0017] In the formula, (x,y) are the coordinates of the PSF image after centroid offset;

[0018] The calibrated image-stabilized voltage V is:

[0019] V = DA, A = [B] + S (3)

[0020] In the formula, D is the voltage response function of the pendulum mirror;

[0021] Step 6: Set the starting frequency ν1, ending frequency ν2, and frequency interval Δν on the high-speed detector, which is the frequency range of the pendulum mirror detection. The total number of detections is p, where p = (ν2 - ν1) / Δν + 1.

[0022] The first test begins with the pendulum mirror operating at the initial frequency ν1. A high-speed detector is used to acquire PSF images and calculate their centroid coordinates (x). PSF ′,yPSF Then, its initial coordinates (x') are determined by its centroid. PSF_0 ,y PSF_0 The PSF drift was calculated as follows:

[0023]

[0024] Furthermore, the image stabilization effect of the tilting mirror is evaluated based on the PS value. The drift threshold Thres is set according to the research needs. When PS≤Thres, the image stabilization is considered normal. When PS>Thres, it is usually due to the resonance of the tilting mirror. This frequency is recorded and should be avoided when the tilting mirror is working in an ultra-high contrast imaging instrument.

[0025] Step 7: Detect the next working frequency ν = ν1 + sΔν, s = 1, 2, ..., p, and repeat step 6. When ν = ν2, the image stabilization detection of the tilting mirror in the set frequency range [ν1, ν2] is completed.

[0026] To achieve the above objectives, the present invention also provides a rapid detection system for a tilting mirror in an ultra-high contrast imaging instrument, comprising the following components: a laser source, an optical fiber, a collimating lens, a tilting mirror to be tested, an imaging mirror, a high-speed detector, an image acquisition card, a signal generator, and a tilting mirror controller. The high-speed detector is used to monitor PSF image drift, the image acquisition card is used to record the PSF image, the signal generator is used to output a driving voltage, and the tilting mirror controller is used to drive the tilting mirror to tilt and achieve image stabilization.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. The detection method and system proposed in this invention can realize rapid and automated detection of the image stabilization performance of the oscillating mirror at different operating frequencies, and screen and record the actual resonant frequency of the oscillating mirror under load conditions. When the oscillating mirror is working in an ultra-high contrast imaging instrument, this frequency can be avoided, ensuring that the image stabilization works normally.

[0029] 2. The detection method and system proposed in this invention are specifically designed and optimized for the detection requirements of tilting mirrors in ultra-high contrast imaging instruments. They not only enable the calibration of the tilting mirror's own response but also detect its image stabilization capability. Automatic calibration and image stabilization monitoring of the tilting mirror can be achieved through LabVIEW electronic control programming, reducing interference from human factors.

[0030] 3. The detection method and system proposed in this invention have a compact optical path structure, which is convenient to connect with the pre-perturbation optical path set up for different research needs, and is flexible and convenient to apply. Attached Figure Description

[0031] Figure 1 This is the flowchart of a rapid detection method for the tilting mirror in an ultra-high contrast imaging instrument proposed in this invention.

[0032] Figure 2 This is a schematic diagram of the detection system of the swing mirror in the ultra-high contrast imaging instrument proposed in the embodiment;

[0033] Figure labels: 1: Laser source; 2: Fiber optic cable; 3: Collimating lens; 4: Mirror to be tested; 5: Imaging lens; 6: High-speed detector; 7: Image acquisition card; 8: Signal generator; 9: Mirror controller. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] This invention is one of the results of the National Natural Science Foundation of China projects (Grant Nos. 11827804, U2031210, 11703058) and the Strategic Priority Research Program on Space Science (Phase II) of the Chinese Academy of Sciences (Grant No. XDA15072102).

[0036] The method described in this invention includes the design of a rapid detection method for a pendulum mirror in an ultra-high contrast imaging instrument, as well as a detection system. The detection method and system proposed in this invention can achieve rapid and automated detection of the image stabilization performance of the pendulum mirror at different operating frequencies, laying the foundation for subsequent ultra-high contrast imaging instruments to conduct exoplanet imaging and detection.

[0037] The rapid detection method for the oscillating mirror of the present invention is as follows: Figure 1 As shown, it includes the following steps:

[0038] Step 1: The laser source is coupled out through the optical fiber to form a point source. This point source is located at the focal point of the collimating lens and is collimated to form parallel light.

[0039] Step 2: Light rays are incident on the pendulum mirror to be tested and then reflected to the imaging mirror;

[0040] Step 3: After passing through the imaging mirror, the light enters the high-speed detector and receives the PSF image on the focal plane of the high-speed detector;

[0041] Step 4: The signal generator outputs two channels of driving voltage (5V, 5V), which are amplified and subdivided by the mirror controller and then pushed to the mirror under test with the median voltage to swing its two motion axes to the initial center position. The two motion axes are the X-axis and the Y-axis.

[0042] Furthermore, a high-speed detector is used to acquire PSF images and calculate the initial coordinates (x, y) of its centroid. PSF_0 ,y PSF_0 );

[0043] Step 5: Output the driving voltage (0.01~0.3V, 0.01~0.3V) of two channels through the signal generator. After the signal is amplified and subdivided by the mirror controller, the bias voltage is pushed to the X-axis and Y-axis of the mirror to be tested to calibrate the response relationship between the driving voltage and the mirror deflection.

[0044] Furthermore, in the calibration, the second and third Zernike coefficients (representing the X-axis tilt and Y-axis tilt, respectively) are taken. The tilt vector S and the Zernike polynomial coefficient vector A are related as follows:

[0045] S = [B]A, A = (a2, a3) T (5)

[0046] In the formula, a2 and a3 are the Zernike coefficients of the second and third terms, respectively, and the [B] matrix is ​​represented as:

[0047]

[0048] In the formula, (x,y) are the coordinates after the centroid of the sub-aperture is offset;

[0049] The calibrated image-stabilized voltage V is:

[0050] V = DA, A = [B] + S (7)

[0051] In the formula, D is the voltage response function of the pendulum mirror;

[0052] Step 6: Set the starting frequency ν1 = 800Hz, the ending frequency ν2 = 1200Hz, and the frequency interval Δν = 10~20Hz on the high-speed detector for the pendulum mirror detection, and perform a total of p = 21~41 detections.

[0053] The first test began with the pendulum mirror operating at an initial frequency ν1 = 800 Hz. A high-speed detector was used to acquire PSF images and calculate its centroid coordinates (x). PSF ′,y PSF Then, its initial coordinates (x') are determined by its centroid. PSF_0 ,y PSF_0 The PSF drift was calculated as follows:

[0054]

[0055] Furthermore, the image stabilization effect of the mirror is evaluated based on the PS value. The PSF drift threshold Thres is set according to the research needs. For example, the drift threshold Thres is set to 5 to 10 pixels. When PS ≤ Thres, the image stabilization is considered normal. When PS > Thres, it is usually due to mirror resonance. This frequency is recorded and should be avoided when the mirror is working in an ultra-high contrast imaging instrument.

[0056] Step 7: Detect the next working frequency ν = ν1 + sΔν, s = 1, 2, ..., p, and repeat step 6. When ν = ν2 = 1200Hz, the image stabilization test of the tilting mirror in the frequency range of 800 to 1200Hz is completed.

[0057] In this embodiment, the specific structure of the tilting mirror detection system is as follows: Figure 2 As shown, the detection system includes a laser source 1, an optical fiber 2, a collimating lens 3, a mirror under test 4, an imaging lens 5, a high-speed detector 6, an image acquisition card 7, a signal generator 8, and a mirror controller 9. The high-speed detector monitors PSF image drift, the image acquisition card records the PSF image, the signal generator outputs the driving voltage, and the mirror controller drives the mirror to tilt and stabilize the image.

[0058] Laser source 1 is a fiber-coupled Fabry-Perot laser source with a working wavelength of 637nm and an adjustable output power of 0-8mW. It is output through single-mode fiber 2 to form a point source.

[0059] Collimating lens 3 has an aperture of 25.4–50.8 mm and a focal length range of 150–500 mm. It is used to collimate a point light source into parallel light.

[0060] The swing angle of the two motion axes (X-axis and Y-axis) of the pendulum mirror 4 to be tested is ≤3.5mrad / 2mrad (open loop / closed loop), the resolution is 2nrad / 5nrad (open loop / closed loop), the diameter of the reflector installed on the pendulum mirror is 30mm, and the mass is 11.8g (including the mirror fixing structure).

[0061] Imaging mirror 5 has an aperture of 25.4–50.8 mm and a focal length range of 900–1500 mm, and is used for imaging a stable beam.

[0062] The high-speed detector 6 preferably uses an EMCCD detector with a resolution of 64×64 (windowed mode, maximum resolution 512×512), a frame rate >1300Hz, a pixel size of 16μm×16μm, a quantum efficiency >95%, a dark current of 0.0003e- / pixel / s@-80℃, and readout noise <1e-with EM. This detector receives PSF images and monitors their position to analyze the stabilization of the tilting mirror.

[0063] The image acquisition card 7 uses a single port output, a pixel frequency of 80MHz, and a CameraLink data interface.

[0064] Signal generator 8 is a multi-channel signal generation source. It outputs driving voltages for two channels, with each channel having a voltage range of 0 to 10V.

[0065] The position servo control module of the tilting mirror controller 9 has a maximum of three channels and a maximum power of 400W. This controller amplifies and subdivides the drive voltage output by the signal generator 8 to drive the two motion axes (X-axis and Y-axis) of the tilting mirror to swing.

[0066] Starting from the set detection start frequency ν1 = 800Hz on the high-speed detector 6, the frequency is increased at a certain frequency interval Δν = 10~20Hz. The image stabilization results of the swing mirror at different working frequencies are detected sequentially using formula (4). The above steps are repeated until the set termination frequency ν2 = 1200Hz is detected, thus completing the rapid and automated detection of the swing mirror in the set frequency range.

[0067] This embodiment only illustrates the detection process using a detection wavelength of 637nm, a 30mm diameter mirror loaded on the pendulum mirror, and a detection frequency in the range of 800-1200Hz. However, those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rapid detection method for a tilting mirror in an ultra-high contrast imaging instrument, characterized in that, Includes the following steps: Step 1: The laser source is coupled out through an optical fiber to form a point light source, which is then collimated by a collimating lens to become parallel light; Step 2: Light rays are incident on the pendulum mirror to be tested and then reflected to the imaging mirror; Step 3: After passing through the imaging mirror, the light enters the high-speed detector and receives the point spread function image on the focal plane of the high-speed detector; Step 4: The signal generator outputs the driving voltage of two channels, which is amplified and subdivided by the mirror controller and then pushed to the mirror under test with the median voltage to swing its two motion axes to the initial center position. The two motion axes are the X-axis and the Y-axis. Step 5: The signal generator outputs the driving voltage of two channels, which is then amplified and subdivided by the mirror controller before being pushed to the X and Y axes of the mirror under test to calibrate the response relationship between the driving voltage and the mirror deflection. Step 6: Set the starting frequency, ending frequency, and frequency interval for the pendulum mirror detection on the high-speed detector; begin the first detection, with the pendulum mirror operating at the starting frequency. Use the high-speed detector to acquire the PSF image and calculate its centroid, then calculate the PSF drift amount using its initial centroid coordinates; set the drift amount threshold according to research needs. When the PSF drift amount ≤ the drift amount threshold, the pendulum mirror is considered to be normally stabilized; when the PSF drift amount > the drift amount threshold, it is usually due to pendulum mirror resonance, and record the frequency at this time. Step 7: Detect the next operating frequency and repeat Step 6 to finally complete the image stabilization detection of the tilting mirror within the set frequency range.

2. The rapid detection method for the tilting mirror in the ultra-high contrast imaging instrument according to claim 1, characterized in that, In step 4, a high-speed detector is used to acquire PSF images and calculate the initial coordinates of its centroid. , ).

3. The rapid detection method for the tilting mirror in the ultra-high contrast imaging instrument according to claim 1, characterized in that, In step 5, the calibration involves the tilt vector S and the Zernike polynomial coefficient vector A, and their relationship is as follows: , (1) In the formula, ~ These are the Zernike coefficients from the 1st to the Kth term. The matrix is ​​represented as: (2) In the formula, (x, y) are the coordinates after the centroid of the sub-aperture is offset; The calibrated image-stabilized voltage V is: , (3) In the formula, D is the voltage response function of the pendulum mirror.

4. The rapid detection method for the tilting mirror in the ultra-high contrast imaging instrument according to claim 1, characterized in that, In step 6, the first test begins, with the pendulum mirror operating at the initial frequency. High-speed detectors are used to acquire PSF images and calculate their centroid coordinates. , ), and then with its initial centroid coordinates ( , The PSF drift was calculated as follows: (4) based on Numerical evaluation of the image stabilization effect of the pendulum mirror, setting the drift threshold according to research needs. ,when When the image is stable, it is determined to be normal; when At this time, it is usually due to the resonance of the pendulum mirror. Record the frequency at this time. Avoid using this frequency when the pendulum mirror is working in an ultra-high contrast imaging instrument.

5. A rapid detection system for a tilting mirror in an ultra-high contrast imaging instrument based on the rapid detection method described in any one of claims 1-4, characterized in that, The system includes a laser source, an optical fiber, a collimating lens, a mirror to be tested, and an imaging lens arranged sequentially along the optical path. The PSF image is received by a high-speed detector connected to a computer. The rapid detection system also includes an image acquisition card, a signal generator, and a mirror controller connected to the computer. The high-speed detector is used to monitor PSF image drift, the image acquisition card is used to record PSF images, the signal generator is used to output driving voltage, and the mirror controller is used to drive the mirror to tilt and stabilize the image.

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