Method for measuring stray light of spatial optical system based on time channel screening

Abstract

The present application belongs to the field of optical systems, and particularly relates to a stray light measurement method for a spatial optical system based on time channel screening. The method mainly solves the technical problem that the existing stray light measurement system cannot effectively distinguish target signals and background noise, and still has limitations in processing weak signals and high background noise. The system used in the method comprises a laser light source, a light splitting prism, a light delay device, an aperture, a collimation and beam expansion module, a turntable module, a time resolution detection module, a photoelectric detector and a data acquisition and processing module. The present application can effectively reduce the influence of environmental light and other interference factors, and can still accurately detect target signals in a high background noise environment, significantly improve the anti-interference ability of the system, and ensure the stability and reliability of the measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical system stray light measurement system and method, in particular to a spatial optical system stray light measurement system and method based on time channel screening. BACKGROUND

[0002] In a spatial optical system, stray light is a key factor affecting system performance and imaging quality. Stray light refers to the unintended light signal reaching the system image plane, forming background noise, leading to reduced image contrast, clarity and color restoration, and even causing data loss and task failure in severe cases. For example, the Hubble Space Telescope launched in 1990 suffered from spherical aberration caused by the primary mirror defect, resulting in reduced image quality and data loss. The GAIA space telescope launched in 2013 was interfered by stray light caused by the protrusion of the sunshade fiber shortly after launch, failing to achieve the expected effect. The future Laser Interferometer Space Antenna (LISA) project also faces the challenge of stray light interference on the extremely weak gravitational wave signal detection, which needs to strictly suppress the 10 -10 order of magnitude of backward stray light.

[0003] Currently, stray light measurement is a key link for evaluating and verifying the true stray light suppression capability of a spatial optical system. Existing stray light measurement systems mostly use vacuum tanks and double-column tanks to suppress air scattering and background stray light, but it is difficult to effectively distinguish between target signals and background noise, and there are still limitations in processing weak signals and high background noise. In addition, the construction cost of traditional stray light measurement systems is high and the site requirements are strict.

[0004] Therefore, there is an urgent need for a stray light measurement system that is efficient, low-cost and can effectively distinguish between target signals and background noise to improve the imaging quality and detection accuracy of spatial optical systems. SUMMARY

[0005] The purpose of the present application is to solve the technical problem that the existing stray light measurement system is difficult to effectively distinguish between target signals and background noise, and there are still limitations in processing weak signals and high background noise, and to provide a spatial optical system stray light measurement system and method based on time channel screening.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present application is:

[0007] A spatial optical system stray light measurement system based on time channel screening, characterized in that:

[0008] It comprises a laser light source, a beam splitter prism, a light delay device, an aperture, a collimation and beam expansion module, a turntable module, a time-resolved detection module, a photodetector and a data acquisition and processing module.

[0009] The light splitting prism is arranged on an exit light path of the laser light source;

[0010] The light delay device and the light barrier are arranged in sequence on a transmission light path of the light splitting prism;

[0011] The collimation and expansion module is used for collimating and expanding the delayed laser light, and an entrance of the collimation and expansion module is arranged on an exit light path of the light barrier;

[0012] An entrance pupil of the to-be-measured space optical system is arranged on an exit light path of the collimation and expansion module, and a detection end of the time-resolved detection module is arranged on an image plane of the to-be-measured space optical system, and is used for measuring photon numbers at the image plane and the entrance pupil of the to-be-measured space optical system;

[0013] The time-resolved detection module and the to-be-measured space optical system are arranged on a rotary table module respectively, and the rotary table module is used for adjusting a relative angle between the entrance pupil of the to-be-measured space optical system and the exit light path of the collimation and expansion module, so as to realize measurement of different off-axis angles;

[0014] The photoelectric detector is arranged on a reflection light path of the light splitting prism, and an output end of the photoelectric detector is electrically connected with an external trigger end of the time-resolved detection module, so as to realize external triggering of the time-resolved detection module;

[0015] The data acquisition and processing module is electrically connected with the time-resolved detection module, is used for receiving photon numbers at the image plane and the entrance pupil of the to-be-measured space optical system output by the time-resolved detection module, and is used for pre-processing the photon numbers, then screening the photon numbers according to a set time window, and finally calculating photon number densities of the image plane and the entrance pupil according to the screened photon numbers, and obtaining a point source transmittance value according to the photon number densities of the image plane and the entrance pupil.

[0016] Further, the data acquisition and processing module calculates the point source transmittance value PST(θ) according to the photon number densities of the image plane and the entrance pupil through the following formula:

[0017]

[0018] In the formula, E d (θ) and E i are the photon number densities of the image plane and the entrance pupil respectively; E d (θ) = N d (θ) / A d (θ); E i = N i / A i ; N d (θ) is the photon number at the image plane; A d (θ) is the area at the image plane; N i is the photon number at the entrance pupil; and A iA is the area at the entrance pupil; and θ is the off-axis angle.

[0019] Further, the collimating and expanding module comprises an off-axis parabolic mirror and a quadric mirror; the off-axis parabolic mirror is arranged on the exit light path of the diaphragm, the quadric mirror is arranged on the reflected light path of the off-axis parabolic mirror, and the entrance pupil of the to-be-measured spatial optical system is arranged on the exit light path of the quadric mirror.

[0020] Further, the collimating and expanding module comprises an off-axis parabolic mirror and a quadric mirror; the off-axis parabolic mirror is arranged on the exit light path of the diaphragm, the quadric mirror is arranged on the reflected light path of the off-axis parabolic mirror, and the entrance pupil of the to-be-measured spatial optical system is arranged on the exit light path of the quadric mirror.

[0021] Further, the time-resolved detection module is an IsCMOS image intensifier camera.

[0022] Further, the output end of the photoelectric detector is electrically connected to the external trigger end of the time-resolved detection module through a BNC cable.

[0023] Meanwhile, the application also provides a spatial optical system stray light measurement method based on time channel screening, which adopts the spatial optical system stray light measurement system based on time channel screening, and is characterized in that the method comprises the following steps:

[0024] Step 1: when the to-be-measured spatial optical system is not installed, the laser light source is started, the laser light beam emitted by the laser light source is divided into reflected light and transmitted light through the beam splitter prism, the reflected light is guided to the photoelectric detector, and the transmitted light is guided to the time-resolved detection module in sequence through the optical delay device, the diaphragm and the collimating and expanding module;

[0025] Step 2: the incident light path of the time-resolved detection module and the exit light path of the collimating and expanding module are adjusted to be parallel through the turntable module, and the state is taken as the initial state;

[0026] Step 3: the reflected light is photoelectrically detected by the photoelectric detector, an electrical signal is obtained, and the electrical signal is sent to the external trigger end of the time-resolved detection module to trigger the time-resolved detection module to start detection;

[0027] Step 4: the light signal output by the collimating and expanding module in the initial state is detected by the time-resolved detection module, the number of photons in the initial state is obtained, and the number of photons is taken as the number of photons at the entrance pupil of the to-be-measured spatial optical system;

[0028] Step 5, install the spatial optical system to be measured on the turntable module, and make the entrance pupil of the spatial optical system to be measured located on the output light path of the collimating beam expander module, and the image plane located on the detection end of the time-resolved detection module; the photon number in the initial state, i.e. the photon number under the 0th preset angle, is obtained in the same way as steps 3 to 4, and is taken as the 0th photon number at the image plane of the spatial optical system to be measured;

[0029] Step 6, adjust the axial direction of the entrance pupil of the spatial optical system to be measured to have the 1st preset angle with the output light path of the collimating beam expander module through the turntable module; the photon number under the 1st preset angle is obtained in the same way as steps 3 to 4, and is taken as the 1st photon number at the image plane of the spatial optical system to be measured;

[0030] The axial direction of the entrance pupil of the spatial optical system to be measured is adjusted to have the 2nd preset angle with the output light path of the collimating beam expander module through the turntable module; the photon number under the 2nd preset angle is obtained in the same way as steps 3 to 4, and is taken as the 2nd photon number at the image plane of the spatial optical system to be measured;

[0031] Similarly, the axial direction of the entrance pupil of the spatial optical system to be measured is adjusted to have the Xth preset angle with the output light path of the collimating beam expander module through the turntable module; the photon number under the Xth preset angle is obtained in the same way as steps 3 to 4, and is taken as the Xth photon number at the image plane of the spatial optical system to be measured; X≥2;

[0032] Step 7, pre-process all the obtained photon numbers through the data acquisition and processing module, eliminate abnormal values and noises, then screen the photon numbers according to the set time channel, and then obtain the photon number density of each according to the screened photon number at the entrance pupil and the screened photon number at the image plane under different preset angles, and finally obtain the point source transmittance value under different off-axis angles according to the photon number density at the entrance pupil and the photon number density at the image plane under different preset angles;

[0033] Step 8, compare the point source transmittance value under different off-axis angles with the corresponding standard value, judge whether the difference between the two is within the set range, verify the accuracy of the measurement, and complete the stray light measurement of the spatial optical system.

[0034] Further, before step 1, there is also a step of calibrating the measurement system, which is specifically:

[0035] Calibrate the output power and pulse frequency of the laser light source; calibrate the sensitivity and response time of the photodetector; calibrate the time resolution and photon counting accuracy of the time-resolved detection module; and calibrate the collimating beam expander module.

[0036] The beneficial effects of the present application are:

[0037] 1. High measurement accuracy

[0038] The application adopts single-photon time resolution technology, can realize picosecond-level time resolution, and greatly improves the measurement accuracy. The time resolution detection module can accurately capture and analyze weak light signals, thereby effectively detecting and distinguishing stray light signals and non-target signals, and greatly improving the accuracy of stray light measurement of the spatial optical system.

[0039] 2. Strong anti-interference capability

[0040] By using a single-photon detector and a time resolution detection method, the application effectively reduces the influence of environmental light and other interference factors. In a high background noise environment, the application can still accurately detect target signals, significantly improves the anti-interference capability of the system, and ensures the stability and reliability of the measurement.

[0041] 3. Wide application range and high cost-effectiveness

[0042] The application is suitable for stray light measurement of various spatial optical systems, including space telescopes, star sensors, imaging systems, etc. Whether in a ground laboratory environment or in a space environment, the measurement system of the application can work stably and efficiently. At the same time, the system and method of the application do not require high construction cost and harsh working environment, have high cost-effectiveness, and significantly reduce the system construction and operation cost. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a structural schematic diagram of a stray light measurement system of a spatial optical system based on time channel screening according to the application;

[0044] Figure 2 is a flowchart of a stray light measurement method of a spatial optical system based on time channel screening according to the application.

[0045] In the drawings:

[0046] 01 - spatial optical system;

[0047] 1 - laser light source, 2 - beam splitter prism, 3 - optical delay, 4 - diaphragm, 5 - mirror module, 51 - first mirror, 52 - second mirror, 6 - collimation and expansion module, 61 - off-axis parabolic mirror, 62 - quadratic surface mirror, 7 - turntable module, 8 - time resolution detection module, 9 - photodetector, 10 - BNC cable. DETAILED DESCRIPTION

[0048] In order to make the purpose, advantages and characteristics of the application more clear, the following combines the drawings and specific embodiments to make a further detailed description of a stray light measurement system and method of a spatial optical system based on time channel screening according to the application. The advantages and characteristics of the application will be clearer according to the following specific embodiments.

[0049] As shown in Figure 1 The embodiment of the application is a stray light measurement system of a spatial optical system based on time channel screening, mainly comprising a laser light source 1, a light splitting prism 2, a light delay device 3, an optical stop 4, a mirror module 5, a collimating and expanding module 6, a turntable module 7, a time-resolved detection module 8, a photoelectric detector 9 and a data acquisition and processing module.

[0050] The laser light source 1 adopts a solid-state pulsed laser, which can emit pulsed laser.

[0051] The mirror module 5 comprises a first mirror 51 and a second mirror 52, which can realize the turning of the laser light path.

[0052] The collimating and expanding module 6 comprises an off-axis parabolic mirror 61 and a quadric mirror 62, which can realize the expansion and collimation of the pulsed laser.

[0053] The time-resolved detection module 8 adopts an IsCMOS image intensifier camera, which comprises a photoelectric cathode, a microchannel plate (MCP) and a CMOS image sensor. Through photon counting and precise time-gating technology, high sensitivity and high time resolution detection can be realized. The single photon is converted into an electronic signal through the photoelectric cathode, and then multiplied through the microchannel plate, and finally the photon counting with high time resolution is realized on the CMOS image sensor. The precise time-gating technology is to selectively capture the light signal at a specific time point within a very short time window by using a high-speed time-gating circuit.

[0054] Specifically, the light splitting prism 2 is arranged on the light path of the laser light source 1, which can divide the pulsed laser emitted by the laser light source 1 into two paths, one of which is a reflection light path and the other of which is a transmission light path.

[0055] The light delay device 3 is arranged on the transmission light path, which can realize the delay of the light path through the light delay device 3, so as to ensure that the pulsed laser reaches the IsCMOS image intensifier camera at the same time.

[0056] The photoelectric detector 9 is arranged on the reflection light path, which can convert the received pulsed laser into an electrical signal. The output end of the photoelectric detector 9 is electrically connected to the external trigger end of the IsCMOS image intensifier camera through a BNC cable 10, so as to trigger the IsCMOS image intensifier camera synchronously through the electrical signal output by the output end of the photoelectric detector 9, thereby realizing the external trigger synchronization.

[0057] The optical stop 4 is arranged on the light path of the light delay device 3, which can control the size of the laser beam.

[0058] The first mirror 51 is arranged on the light path of the optical stop 4, and the second mirror 52 is arranged on the reflection light path of the first mirror 51.

[0059] The off-axis parabolic mirror 61 is arranged on the reflected light path of the second mirror 52, and the quadric mirror 62 is arranged on the reflected light path of the off-axis parabolic mirror 61.

[0060] The entrance pupil of the to-be-measured space optical system 01 is arranged on the exit light path of the quadric mirror 62, and the detection end of the IsCMOS image intensifier camera is arranged on the image plane of the to-be-measured space optical system 01, so as to detect the optical signal of the laser output by the to-be-measured space optical system 01, and the time-resolved detection module 8 and the to-be-measured space optical system 01 are arranged on the turntable module 7 respectively, so as to adjust the relative angle between the entrance pupil of the to-be-measured space optical system 01 and the exit light path of the collimating and expanding module 6 through the turntable module 7, so as to realize the measurement of different off-axis angles.

[0061] The data acquisition and processing module is electrically connected with the time-resolved detection module 8, so as to receive the photon numbers at the image plane and the entrance pupil of the to-be-measured space optical system 01 output by the time-resolved detection module 8, and to pre-process them, then to screen the photon numbers according to the set time window, and then to calculate the photon number densities of the image plane and the entrance pupil according to the screened photon numbers, and finally to obtain the point source transmittance value according to the photon number densities of the image plane and the entrance pupil.

[0062] Referring to Figure 2 , the measurement process of the point source transmittance stray light measurement system based on time channel screening is as follows:

[0063] 1) System calibration

[0064] The output power and pulse frequency of the laser light source 1 are calibrated to ensure its stability. The sensitivity and response time of the photodetector 9 are calibrated to ensure the accuracy of signal reception. The time resolution and photon counting accuracy of the IsCMOS image intensifier camera are calibrated to ensure high time resolution and high sensitivity of detection. The off-axis parabolic mirror 61 and the quadric mirror 62 are calibrated to ensure the collimation and parallelism of the laser beam.

[0065] 2) Laser beam modulation

[0066] When the to-be-measured space optical system 01 is not installed, the laser light source 1 is started, and the laser beam emitted by the laser light source 1 is divided into two paths by the beam splitter prism 2, which are reflected light and transmitted light respectively. The reflected light is received by the photodetector 9, and the transmitted light is delayed by the optical delay device 3. After the delayed laser beam passes through the diaphragm 4, it reaches the first mirror 51. The laser beam is turned by the first mirror 51 and the second mirror 52 in turn, and then collimated and expanded by the off-axis parabolic mirror 61 and the quadric mirror 62, so as to ensure the parallelism of the laser beam.

[0067] 3) Adjust the incident light path of the time resolution detection module 8 and the exit light path of the collimation and beam expansion module 6 to be parallel by the rotary table module 7, and take this state as the initial state.

[0068] 4) Photoelectrically detect the light signal of the reflected light path by the photodetector 9, obtain an electrical signal, and send it to the external trigger end of the IsCMOS image intensifier camera through the BNC cable 10 to trigger the IsCMOS image intensifier camera to start detection.

[0069] 5) Detect the laser beam emitted by the secondary curved mirror 62 in the initial state by the IsCMOS image intensifier camera, obtain the photon number in the initial state, and take it as the photon number at the entrance pupil of the spatial optical system 01 to be measured.

[0070] 6) Off-axis angle adjustment and signal acquisition

[0071] Install the spatial optical system 01 to be measured on the rotary table module 7, and make the entrance pupil of the spatial optical system 01 to be measured located on the exit light path of the collimation and beam expansion module 6, and the detection end of the IsCMOS image intensifier camera located at the image plane of the spatial optical system 01 to be measured; obtain the photon number in the initial state, i.e. the photon number at the 0th preset angle, in the same way as steps 4 to 5, and take it as the 0th photon number at the image plane of the spatial optical system 01 to be measured.

[0072] 7) Adjust the spatial optical system 01 to be measured to have a 1st preset angle between the axial direction of the entrance pupil and the exit light path of the collimation and beam expansion module 6 by the rotary table module 7, and take 10° as an example in this embodiment, and other angles can also be set according to actual needs in other embodiments of the present application; obtain the photon number at the 1st preset angle in the same way as steps 4 to 5, and take it as the 1st photon number at the image plane of the spatial optical system 01 to be measured.

[0073] Adjust the spatial optical system 01 to be measured to have a 2nd preset angle between the axial direction of the entrance pupil and the exit light path of the collimation and beam expansion module 6 by the rotary table module 7, and take 20° as an example in this embodiment; obtain the photon number at the 2nd preset angle in the same way as steps 4 to 5, and take it as the 2nd photon number at the image plane of the spatial optical system 01 to be measured.

[0074] Adjust the spatial optical system 01 to be measured to have a 3rd preset angle between the axial direction of the entrance pupil and the exit light path of the collimation and beam expansion module 6 by the rotary table module 7, and take 30° as an example in this embodiment; obtain the photon number at the 3rd preset angle in the same way as steps 4 to 5, and take it as the 3rd photon number at the image plane of the spatial optical system 01 to be measured.

[0075] In the embodiment, the number of photons at the image plane under 4 different preset angles is obtained for illustration. In other embodiments of the application, more preset angles can be obtained by those skilled in the art according to actual needs. The more the number of measurements, the more accurate the measurement results, but the more time and calculation are required.

[0076] 8) Data processing

[0077] All the obtained numbers of photons are preprocessed by the data acquisition and processing module to eliminate abnormal values and noises, then the numbers of photons are screened according to the set time channel, and then the number of photons at the pupil and the number of photons at the image plane under different preset angles are screened to obtain the number of photons at the image plane under different preset angles, and finally the point source transmittance value under different off-axis angles is obtained according to the number of photons at the pupil and the number of photons at the image plane under different preset angles.

[0078] The point source transmittance value PST is defined as the ratio of the point source target radiation of the off-axis angle θ outside the field of view to the pupil irradiance E d (θ) and the pupil irradiance E i , and the expression is:

[0079]

[0080] The formula of the photon energy e is e = hv, where h is the Planck constant and v is the frequency of light. Assuming that the radiation source emits N photons per second, and the energy of each photon is e, then the radiant flux can be expressed as Then the irradiance can be expressed as:

[0081]

[0082] Where A is the irradiation area. If N / A is used to represent the number of photons per unit area, then the point source transmittance value PST can be converted into the ratio of the number of photons at the image plane to the number of photons at the pupil, and the expression is:

[0083]

[0084] In the formula, E d (θ) and E i are the number of photons at the image plane and the number of photons at the pupil, respectively;

[0085] E d (θ) = N d (θ) / A d (θ); E i = N i / A i ; N d (θ) is the number of photons at the image plane; and A d(θ) is the area at the image plane; N i is the number of photons at the entrance pupil; A i is the area at the entrance pupil.

[0086] 9) Result comparison

[0087] The point source transmittance values at different off-axis angles are compared with the corresponding standard values to determine whether the difference between the two is within the set range, verify the accuracy and reliability of the measurement, ensure the credibility of the measurement results, and complete the stray light measurement of the spatial optical system.

Claims

1. A stray light measurement method for a space optical system based on time channel filtering, comprising a stray light measurement system for a space optical system based on time channel filtering, the system including a laser source (1), a beam splitter (2), an optical delayer (3), an aperture (4), a collimation and beam expansion module (6), a turntable module (7), a time-resolved detection module (8), a photodetector (9), and a data acquisition and processing module; the beam splitter (2) is disposed on the outgoing light path of the laser source (1); the optical delayer (3) and the aperture (4) are disposed sequentially on the transmission light path of the beam splitter (2); the collimation and beam expansion module (6) is used to collimate and expand the delayed laser beam, and its entrance is disposed on the outgoing light path of the aperture (4); the space optical system under test (0 1) The entrance pupil of the collimating beam expander (6) is set on the output optical path of the collimating beam expander (6), and the detection end of the time-resolved detection module (8) is set on the image plane of the space optical system (01) under test; the time-resolved detection module (8) and the space optical system (01) under test are respectively set on the turntable module (7), and the turntable module (7) is used to adjust the relative angle between the entrance pupil of the space optical system (01) under test and the output optical path of the collimating beam expander (6) to realize the measurement of different off-axis angles; the photodetector (9) is set on the reflected optical path of the beam splitter (2), and the output end of the photodetector (9) is electrically connected to the external trigger end of the time-resolved detection module (8); the data acquisition and processing module is electrically connected to the time-resolved detection module (8); The time-resolved detection module (8) uses an IsCMOS image intensifier camera and a high-speed time-gating circuit to selectively capture light signals at specific time points within an extremely short time window. Then, the single photon is converted into an electronic signal through a photocathode, which is multiplied by a microchannel plate to achieve high time-resolution photon counting on the CMOS image sensor. Its features are, Includes the following steps: Step 1: When the space optical system under test (01) is not installed, start the laser source (1), and split the laser beam emitted by it into reflected light and transmitted light through the beam splitter (2). Guide the reflected light to the photodetector (9), and guide the transmitted light to the time-resolved detection module (8) through the optical delay unit (3), the aperture (4) and the collimation and beam expansion module (6) in sequence. Step 2: Adjust the incident light path of the time-resolved detection module (8) and the output light path of the collimation and beam expansion module (6) to be parallel through the turntable module (7), and take this state as the initial state; Step 3: The reflected light is photoelectrically detected by the photodetector (9) to obtain an electrical signal, and then sent to the external trigger terminal of the time-resolved detection module (8) to trigger the time-resolved detection module (8) to start detection. Step 4: Detect the light signal output by the collimation and beam expansion module (6) in the initial state through the time-resolved detection module (8), obtain the number of photons in the initial state, and use it as the number of photons at the entrance pupil of the space optical system (01) under test; Step 5: Install the space optical system under test (01) onto the turntable module (7), and make the entrance pupil of the space optical system under test (01) located on the output optical path of the collimation and beam expansion module (6), and the image plane located at the detection end of the time-resolved detection module (8); obtain the number of photons in the initial state, i.e. the number of photons at the 0th preset angle, in the same way as steps 3 to 4, and take it as the 0th photon number at the image plane of the space optical system under test (01); Step 6: Adjust the axis at the entrance pupil of the space optical system under test (01) to have a first preset angle with the output optical path of the collimating beam expanding module (6) by using the turntable module (7); obtain the number of photons at the first preset angle in the same way as steps 3 to 4, and take it as the first photon number at the image plane of the space optical system under test (01); The axis at the entrance pupil of the space optical system under test (01) is adjusted by the turntable module (7) to have a second preset angle with the output optical path of the collimating beam expanding module (6); the number of photons at the second preset angle is obtained in the same way as steps 3 to 4, and is used as the second photon number at the image plane of the space optical system under test (01); Similarly, the axis at the entrance pupil of the space optical system under test (01) is adjusted by the turntable module (7) to have a preset angle X between it and the outgoing light path of the collimating and expanding module (6); the number of photons at the preset angle X is obtained in the same way as steps 3 to 4, and is taken as the number of photons X at the image plane of the space optical system under test (01); X≥2; Step 7: Preprocess all the acquired photon counts through the data acquisition and processing module to remove outliers and noise. Then, filter the photon counts according to the set time channel. Next, obtain the photon count density of each photon count based on the photon count at the entrance pupil after filtering and the photon count at the image plane after filtering at different preset angles. Finally, obtain the point source transmittance value at different off-axis angles based on the photon count density at the entrance pupil and the photon count density at the image plane at different preset angles. The data acquisition and processing module calculates the point source transmittance value PST(θ) based on the photon number density at the image plane and the photon number density at the entrance pupil using the following formula: In the formula: E d (θ) and E i These are the photon number density at the image plane and the photon number density at the entrance pupil, respectively; E d (θ)=N d (θ) / A d (θ); E i =N i / A i N d (θ) represents the number of photons at the image plane; A d (θ) is the area at the image plane; N i A is the number of photons at the entrance pupil; i θ is the area at the entrance pupil; θ is the off-axis angle. Step 8: Compare the point source transmittance values ​​at different off-axis angles with the corresponding standard values, determine whether the difference between the two is within the set range, verify the accuracy of the measurement, and complete the stray light measurement of the space optical system.

2. The method for measuring stray light in a spatial optical system based on time-channel filtering according to claim 1, characterized in that, Before step 1, there is also a step of calibrating the measurement system, specifically: The output power and pulse frequency of the laser source (1) are calibrated; the sensitivity and response time of the photodetector (9) are calibrated; the time resolution and photon counting accuracy of the time-resolved detection module (8) are calibrated; and the collimation and beam expansion module (6) is calibrated.

3. The method for measuring stray light in a spatial optical system based on time-channel filtering according to claim 2, characterized in that: The collimation and beam expanding module (6) includes an off-axis parabolic mirror (61) and a quadric mirror (62); The off-axis parabolic mirror (61) is set on the outgoing light path of the aperture (4), the quadric mirror (62) is set on the reflected light path of the off-axis parabolic mirror (61), and the entrance pupil of the space optical system (01) under test is set on the outgoing light path of the quadric mirror (62).

4. The method for measuring stray light in a spatial optical system based on time-channel filtering according to claim 3, characterized in that: It also includes a reflector module (5); The reflector module (5) includes a first reflector (51) and a second reflector (52); The first reflector (51) is disposed on the outgoing light path of the aperture (4), the second reflector (52) is disposed on the reflected light path of the first reflector (51), and the off-axis parabolic mirror (61) is disposed on the reflected light path of the second reflector (52).

5. The method for measuring stray light in a spatial optical system based on time-channel filtering according to claim 4, characterized in that: The output terminal of the photodetector (9) is electrically connected to the external trigger terminal of the time-resolved detection module (8) via a BNC cable (10).

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