Space optical system stray light measurement system and method based on time channel screening

Abstract

The invention belongs to the field of optical systems, and particularly relates to a space optical system stray light measuring system and method based on time channel screening. The stray light measuring system mainly solves the technical problems that an existing stray light measuring system is difficult to effectively distinguish target signals and background noise, and limitation still exists when weak signals and high background noise are processed. The system comprises a laser light source, a beam splitter prism, a light delayer, a diaphragm, a collimation and beam expansion module, a turntable module, a time resolution detection module, a photoelectric detector and a data acquisition and processing module. According to the invention, the influence of ambient light and other interference factors can be effectively reduced, the target signal can still be accurately detected in a high background noise environment, the anti-interference capability of the system is obviously improved, and the stability and reliability of measurement are ensured.

Description

Technical Field

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

[0002] In space optical systems, the stray light problem is a key factor affecting system performance and imaging quality. Stray light refers to unexpected light signals that reach the system image plane, forming background noise, resulting in reduced image contrast, clarity and color reproduction. In severe cases, it may even lead to data loss and mission failure. For example, the Hubble Space Telescope launched in 1990 suffered from spherical aberration problems caused by defects in the primary mirror, resulting in degraded image quality and data loss. The GAIA space telescope launched in 2013 suffered from stray light interference from protruding fibers of the sunshade shortly after its launch and failed to achieve the expected results. The Laser Interferometer Space Antenna (LISA) project to be launched in the future also faces the huge challenge of stray light interference in the detection of extremely weak gravitational wave signals, and it needs to be tested for 10 -10 The backward stray light of the order of magnitude is strictly suppressed.

[0003] At present, stray light measurement is a key link in evaluating and verifying the true stray light suppression capability of space optical systems. 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 target signals from background noise, and there are still limitations when dealing with 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 an efficient, low-cost stray light measurement system that can effectively distinguish target signals from background noise, so as to improve the imaging quality and detection accuracy of space optical systems. Summary of the invention

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

[0006] To achieve the above purpose, the technical solution adopted by the present invention is: A stray light measurement system for a spatial optical system based on time channel screening, which is special in that: It includes a laser light source, a beam splitter, an optical delay device, an aperture, a collimation and beam expansion module, a turntable module, a time-resolved detection module, a photoelectric detector and a data acquisition and processing module; The beam splitter prism is arranged on the outgoing light path of the laser light source; The optical retarder and the aperture are sequentially arranged on the transmission light path of the beam splitter prism; The collimation and beam expansion module is used to collimate and expand the delayed laser, and its light inlet is set on the exit light path of the aperture; The entrance pupil of the spatial optical system to be measured is arranged on the exit light path of the collimating beam expansion module, and the detection end of the time-resolved detection module is arranged at the image plane of the spatial optical system to be measured, so as to measure the number of photons at the image plane and the number of photons at the entrance pupil of the spatial optical system to be measured; The time-resolved detection module and the spatial optical system to be measured are respectively arranged on a turntable module, and the turntable module is used to adjust the relative angle between the entrance pupil of the spatial optical system to be measured and the exit light path of the collimating beam expansion module to achieve measurement of different off-axis angles; The photodetector is arranged on the reflected light path of the beam splitter prism, and the output end of the photodetector is electrically connected to the external trigger end of the time-resolved detection module, so as to realize the external trigger of the time-resolved detection module; The data acquisition and processing module is electrically connected to the time-resolved detection module, and is used to receive the number of photons at the image plane and the number of photons at the entrance pupil of the spatial optical system to be measured output by the time-resolved detection module, and pre-process the received photons. The number of photons is then screened according to a set time window, and the respective photon number densities are calculated based on the screened number of photons at the image plane and the number of photons at the entrance pupil. Finally, the point source transmittance value is obtained based on the image plane photon number density and the photon number density at the entrance pupil.

[0007] Furthermore, the data acquisition and processing module calculates the point source transmittance value according to the photon number density at the image plane and the photon number density at the entrance pupil by the following formula: :

[0008] Where: and are the photon number density at the image plane and the photon number density at the entrance pupil respectively; ; ; is the number of photons at the image plane; is the area of ​​the image plane; is the number of photons at the entrance pupil; is the area of ​​the entrance pupil; is the off-axis angle.

[0009] Furthermore, the collimating beam expansion module includes an off-axis parabolic mirror and a quadratic curved mirror; the off-axis parabolic mirror is arranged on the exit light path of the aperture, the quadratic curved mirror is arranged on the reflection light path of the off-axis parabolic mirror, and the entrance pupil of the spatial optical system to be measured is arranged on the exit light path of the quadratic curved mirror.

[0010] Furthermore, it also includes a reflector module; the reflector module includes a first reflector and a second reflector; the first reflector is arranged on the exit light path of the aperture, the second reflector is arranged on the reflection light path of the first reflector, and the off-axis parabolic mirror is arranged on the reflection light path of the second reflector.

[0011] Furthermore, the time-resolved detection module is an IsCMOS image intensification camera.

[0012] Furthermore, the output end of the photodetector is electrically connected to the external trigger end of the time-resolved detection module via a BNC cable.

[0013] At the same time, the present invention also provides a method for measuring stray light of a space optical system based on time channel screening, which adopts the aforementioned stray light measurement system of a space optical system based on time channel screening, and its special feature is that it includes the following steps: Step 1: When the spatial optical system to be tested is not installed, start the laser light source, divide the laser light beam emitted by it into reflected light and transmitted light through a beam splitter prism, guide the reflected light to the photodetector, and guide the transmitted light to the time-resolved detection module through an optical delay device, an aperture, and a collimating beam expansion module in sequence; Step 2: adjusting the incident light path of the time-resolved detection module and the outgoing light path of the collimation and beam expansion module to be parallel through the turntable module, and taking this state as the initial state; Step 3, photoelectrically detecting the reflected light through a photoelectric detector, obtaining an electrical signal, and sending the electrical signal to an external trigger terminal of the time-resolved detection module, thereby triggering the time-resolved detection module to start detection; Step 4, detecting the optical signal output by the collimating beam expansion module in the initial state through the time-resolved detection module, obtaining the number of photons in the initial state, and using it as the number of photons at the entrance pupil of the spatial optical system to be measured; Step 5, installing the spatial optical system to be tested on the turntable module, and making the entrance pupil of the spatial optical system to be tested be located on the output optical path of the collimating beam expansion module, and the image plane be located at the detection end of the time-resolved detection module; obtaining the number of photons in the initial state, that is, the number of photons under the 0th preset angle, in the same manner as steps 3 to 4, and taking it as the 0th photon number at the image plane of the spatial optical system to be tested; Step 6: adjust the axis of the entrance pupil of the spatial optical system to be measured and the output light path of the collimating beam expansion module to have a first preset angle through the turntable module; obtain the number of photons at the first preset angle in the same manner as steps 3 to 4, and use it as the first photon number at the image plane of the spatial optical system to be measured; The turntable module is used to adjust the axis of the entrance pupil of the spatial optical system to be measured and the output light path of the collimating beam expansion module to have a second preset angle; the number of photons at the second preset angle is obtained in the same manner as steps 3 to 4, and is used as the second number of photons at the image plane of the spatial optical system to be measured; Similarly, the turntable module is used to adjust the axis at the entrance pupil of the spatial optical system to be tested to have an Xth preset angle with the output light path of the collimating beam expansion module; the number of photons at the Xth preset angle is obtained in the same manner as steps 3 to 4, and is used as the Xth photon number at the image plane of the spatial optical system to be tested; X≥2; Step 7, pre-processing all the acquired photon numbers through the data acquisition and processing module, eliminating abnormal values ​​and noise, and then filtering the photon numbers according to the set time channel, and then obtaining the respective photon number densities according to the filtered photon number at the entrance pupil and the filtered photon number at the image plane under different preset angles, and finally obtaining the point source transmittance values ​​at 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; Step 8: Compare the point source transmittance values ​​at different off-axis angles with the corresponding standard values ​​to 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 spatial optical system.

[0014] Furthermore, before step 1, a step of calibrating the measurement system is also included, specifically: 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; calibrate the collimation and beam expansion module.

[0015] The beneficial effects of the present invention are: 1. High measurement accuracy The present invention adopts single-photon time-resolved technology, which can achieve picosecond-level time resolution and greatly improve the measurement accuracy. The time-resolved detection module can accurately capture and analyze weak light signals, thereby effectively detecting and distinguishing stray light signals from non-target signals, greatly improving the accuracy of stray light measurement in space optical systems.

[0016] 2. Strong anti-interference ability By using a single-photon detector and a time-resolved detection method, the present invention effectively reduces the influence of ambient light and other interference factors. In a high background noise environment, the present invention can still accurately detect the target signal, significantly improve the anti-interference ability of the system, and ensure the stability and reliability of the measurement.

[0017] 3. Wide range of applications and high cost-effectiveness The present invention is applicable to stray light measurement of various space optical systems, including space telescopes, star sensors, imaging systems, etc. The measurement system of the present invention can work stably and efficiently in both ground laboratory environments and space environments. At the same time, the system and method of the present invention do not require high construction costs and harsh working environments, have high cost performance, and significantly reduce system construction and operation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of an embodiment of a stray light measurement system of a spatial optical system based on time channel screening of the present invention; Figure 2 It is a flow chart of an embodiment of a method for measuring stray light of a spatial optical system based on time channel screening of the present invention.

[0019] In the figure: 01- Space optical system; 1-laser light source, 2-beam splitter, 3-optical delay device, 4-aperture, 5-reflector module, 51-first reflector, 52-second reflector, 6-collimation and beam expansion module, 61-off-axis parabolic mirror, 62-quadratic curved mirror, 7-turntable module, 8-time-resolved detection module, 9-photodetector, 10-BNC cable. DETAILED DESCRIPTION

[0020] In order to make the purpose, advantages and features of the present invention clearer, the following is a further detailed description of a spatial optical system stray light measurement system and method based on time channel screening proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will be clearer according to the following specific implementation methods.

[0021] like Figure 1 As shown, the present embodiment is a stray light measurement system of a spatial optical system based on time channel screening, which mainly includes a laser light source 1, a beam splitter prism 2, an optical delay device 3, an aperture 4, a reflector module 5, 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.

[0022] The laser light source 1 is a solid pulse laser capable of emitting pulsed laser.

[0023] The reflector module 5 includes a first reflector 51 and a second reflector 52 , which can realize the turning of the laser light path.

[0024] The collimation and beam expansion module 6 includes an off-axis parabolic mirror 61 and a quadratic curved mirror 62, which can realize the beam expansion and collimation of the pulsed laser.

[0025] The time-resolved detection module 8 uses an IsCMOS image intensification camera, including a photocathode, a microchannel plate (MCP) and a CMOS image sensor, and achieves high-sensitivity and high-time-resolution detection through photon counting and precise time gating technology. Single photons are converted into electronic signals through the photocathode, multiplied by the microchannel plate, and finally achieve high-time-resolution photon counting on the CMOS image sensor. Precise time gating technology uses high-speed time gating circuits to selectively capture light signals at specific time points within a very short time window.

[0026] Specifically, the beam splitter prism 2 is disposed on the outgoing light path of the laser light source 1 and can split the pulse laser emitted by the laser light source 1 into two paths, one being a reflected light path and the other being a transmitted light path.

[0027] The optical delay device 3 is arranged on the transmission light path, and the optical path delay can be realized by the optical delay device 3, so as to ensure that the pulse laser arrives when the IsCMOS image intensification camera is synchronously triggered.

[0028] The photodetector 9 is arranged on the reflected light path, and the received pulse laser is converted into an electrical signal by the photodetector 9. The output end of the photodetector 9 is electrically connected to the external trigger end of the IsCMOS image intensification camera through a BNC cable 10, so that the IsCMOS image intensification camera is synchronously triggered by the electrical signal output by the output end of the photodetector 9, thereby realizing external trigger synchronization.

[0029] The aperture 4 is arranged on the outgoing light path of the optical delay device 3 to control the size of the laser beam.

[0030] The first reflecting mirror 51 is disposed on the outgoing light path of the aperture 4 , and the second reflecting mirror 52 is disposed on the reflected light path of the first reflecting mirror 51 .

[0031] The off-axis parabolic mirror 61 is disposed on the reflected light path of the second reflector 52 , and the quadratic curved mirror 62 is disposed on the reflected light path of the off-axis parabolic mirror 61 .

[0032] The entrance pupil of the spatial optical system 01 to be measured is arranged on the output light path of the quadratic curved mirror 62, and the detection end of the IsCMOS image intensified camera is arranged at the image plane of the spatial optical system 01 to be measured, and the optical signal detection of the laser output by the spatial optical system 01 to be measured is performed, and the time-resolved detection module 8 and the spatial optical system 01 to be measured are respectively arranged on the turntable module 7, and the relative angle between the entrance pupil of the spatial optical system 01 to be measured and the output light path of the collimation and expansion module 6 is adjusted by the turntable module 7 to realize the measurement of different off-axis angles.

[0033] The data acquisition and processing module is electrically connected to the time-resolved detection module 8 to receive the number of photons at the image plane and the number of photons at the entrance pupil of the spatial optical system 01 to be measured output by the time-resolved detection module 8, and pre-process them, and then filter the number of photons according to the set time window, and then calculate the respective photon number densities according to the filtered number of photons at the image plane and the number of photons at the entrance pupil, and finally obtain the point source transmittance value according to the photon number density at the image plane and the photon number density at the entrance pupil.

[0034] See also Figure 2 , the measurement process of the point source transmittance stray light measurement system based on time channel screening is as follows: 1) System calibration Calibrate the output power and pulse frequency of the laser light source 1 to ensure its stability. Calibrate the sensitivity and response time of the photodetector 9 to ensure the accuracy of signal reception. Calibrate the time resolution and photon counting accuracy of the IsCMOS image intensification camera to ensure high time resolution and high sensitivity of detection. Calibrate the off-axis parabolic mirror 61 and the quadratic curved mirror 62 to ensure the collimation and parallelism of the laser beam.

[0035] 2) Laser beam modulation When the spatial optical system 01 to be measured is not installed, the laser light source 1 is started, and the laser light beam emitted by the laser light source 1 is divided into two paths, namely, reflected light and transmitted light, by the beam splitter prism 2. The reflected light is received by the photodetector 9, and the transmitted light is delayed by the optical delay device 3. The delayed laser light beam passes through the aperture 4 and reaches the first reflector 51. After the optical path of the laser light beam is turned by the first reflector 51 and the second reflector 52 in turn, the laser light beam is collimated and expanded by the off-axis parabolic mirror 61 and the quadratic curved mirror 62 to ensure the parallelism of the laser light beam.

[0036] 3) The incident light path of the time-resolved detection module 8 and the outgoing light path of the collimating beam expansion module 6 are adjusted to be parallel through the turntable module 7, and this state is taken as the initial state.

[0037] 4) The optical signal of the reflected light path is photoelectrically detected by the photodetector 9 to obtain an electrical signal, which is then sent to the external trigger terminal of the IsCMOS image intensification camera through the BNC cable 10 to trigger the IsCMOS image intensification camera to start detection.

[0038] 5) The laser beam emitted from the quadratic curved mirror 62 in the initial state is detected by the IsCMOS image intensification camera to obtain the number of photons in the initial state, which is used as the number of photons at the entrance pupil of the spatial optical system 01 to be measured.

[0039] 6) Off-axis angle adjustment and signal acquisition The spatial optical system to be tested 01 is mounted on the turntable module 7, and the entrance pupil of the spatial optical system to be tested 01 is located on the output light path of the collimating beam expansion module 6, and the detection end of the IsCMOS image intensification camera is located at the image plane of the spatial optical system to be tested 01; the number of photons in the initial state, that is, the number of photons at the 0th preset angle, is obtained in the same manner as steps 4 to 5, and is used as the 0th photon number at the image plane of the spatial optical system to be tested 01.

[0040] 7) The turntable module 7 is used to adjust the axis at the entrance pupil of the spatial optical system 01 to be measured and the output light path of the collimating and expanding module 6 to have a first preset angle. In this embodiment, the first preset angle of 10° is taken as an example. In other embodiments of the present invention, other angles can be set according to actual needs. The number of photons at the first preset angle is obtained in the same manner as steps 4 to 5, and is used as the first photon number at the image plane of the spatial optical system 01 to be measured.

[0041] The turntable module 7 is used to adjust the axis of the entrance pupil of the spatial optical system 01 to be tested and the output light path of the collimating and expanding module 6 to have a second preset angle. In this embodiment, the second preset angle of 20° is taken as an example. The number of photons at the second preset angle is obtained in the same manner as steps 4 to 5, and is used as the second photon number at the image plane of the spatial optical system 01 to be tested.

[0042] The turntable module 7 is used to adjust the axis at the entrance pupil of the spatial optical system 01 to be tested and the output light path of the collimating and expanding module 6 to have a third preset angle. In this embodiment, the third preset angle of 30° is taken as an example. In the same manner as steps 4 to 5, the number of photons at the third preset angle is obtained and used as the third photon number at the image plane of the spatial optical system 01 to be tested.

[0043] In this embodiment, the number of photons at the image plane under four different preset angles is obtained as an example. In other embodiments of the present invention, those skilled in the art can obtain the number of photons under more preset angles according to actual needs. The more times of measurement, the more accurate the measurement result, but more time is required and the amount of calculation is greater.

[0044] 8) Data processing All the acquired photon numbers are preprocessed through the data acquisition and processing module to eliminate outliers and noise, and then the photon numbers are screened according to the set time channel. The respective photon number densities are obtained based on the photon number at the entrance pupil after screening and the photon number at the image plane at different preset angles after screening. Finally, the point source transmittance values ​​at different off-axis angles are obtained based on the photon number density at the entrance pupil and the photon number density at the image plane at different preset angles.

[0045] Define point source transmittance value PSTThe irradiance of the image plane is the off-axis angle of the point source target radiation outside the field of view. and entrance pupil irradiance The ratio is expressed as:

[0046] Photon Energy The formula is ,in is Planck's constant, is the frequency of light. Assume that the radiation source emits photons, and the energy of each photon is , then the radiation flux It can be expressed as , then the irradiance can be expressed as:

[0047] in, Is the irradiated area. represents the photon number density per unit area, then the point source transmittance value is PST It can be converted into the ratio of the photon number density at the image plane to the photon number density at the entrance pupil, expressed as:

[0048] Where: and are the photon number density at the image plane and the photon number density at the entrance pupil respectively; ; ; is the number of photons at the image plane; is the area of ​​the image plane; is the number of photons at the entrance pupil; is the entrance pupil area.

[0049] 9) Results comparison Compare the point source transmittance values ​​at different off-axis angles 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 space optical system.

Claims

1. A stray light measurement system for a spatial optical system based on time channel screening, characterized in that: It comprises a laser light source (1), a beam splitter (2), an optical delay device (3), an aperture (4), a collimation and beam expansion module (6), a turntable module (7), a time-resolved detection module (8), a photoelectric detector (9) and a data acquisition and processing module; The beam splitter prism (2) is arranged on the outgoing light path of the laser light source (1); The optical delay device (3) and the aperture (4) are sequentially arranged on the transmission light path of the beam splitter prism (2); The collimating and beam expanding module (6) is used to collimate and beam expand the delayed laser light, and its light inlet is arranged on the exit light path of the aperture (4); The entrance pupil of the spatial optical system to be measured (01) is arranged on the exit light path of the collimating beam expansion module (6), and the detection end of the time-resolving detection module (8) is arranged at the image plane of the spatial optical system to be measured (01), and is used to measure the number of photons at the image plane and the number of photons at the entrance pupil of the spatial optical system to be measured (01); The time-resolved detection module (8) and the spatial optical system to be measured (01) are respectively arranged on a turntable module (7), and the turntable module (7) is used to adjust the relative angle between the entrance pupil of the spatial optical system to be measured (01) and the exit light path of the collimating beam expansion module (6), so as to achieve measurement of different off-axis angles; The photodetector (9) is arranged on the reflection light path of the beam splitter prism (2), and the output end of the photodetector (9) is electrically connected to the external trigger end of the time-resolved detection module (8) to realize the external triggering of the time-resolved detection module (8); The data acquisition and processing module is electrically connected to the time-resolved detection module (8) and is used to receive the number of photons at the image plane and the number of photons at the entrance pupil of the spatial optical system (01) to be measured output by the time-resolved detection module (8), perform preprocessing on the number of photons, filter the number of photons according to a set time window, calculate the respective photon number densities according to the filtered number of photons at the image plane and the number of photons at the entrance pupil, and finally obtain the point source transmittance value according to the photon number density at the image plane and the photon number density at the entrance pupil.

2. The spatial optical system stray light measurement system based on time channel screening according to claim 1, characterized in that: The data acquisition and processing module calculates the point source transmittance value according to the photon number density at the image plane and the photon number density at the entrance pupil by the following formula: : ； Where: and are the photon number density at the image plane and the photon number density at the entrance pupil respectively; ; ; is the number of photons at the image plane; is the area of ​​the image plane; is the number of photons at the entrance pupil; is the area of ​​the entrance pupil; is the off-axis angle.

3. The stray light measurement system of a spatial optical system based on time channel screening according to claim 1 or 2, characterized in that: The collimating beam expanding module (6) comprises an off-axis parabolic mirror (61) and a quadratic curved mirror (62); The off-axis parabolic mirror (61) is arranged on the outgoing light path of the aperture (4), the quadratic curved mirror (62) is arranged on the reflected light path of the off-axis parabolic mirror (61), and the entrance pupil of the spatial optical system (01) to be measured is arranged on the outgoing light path of the quadratic curved mirror (62).

4. The stray light measurement system of a spatial optical system based on time channel screening according to claim 3, characterized in that: Also includes a reflector module (5); The reflector module (5) comprises a first reflector (51) and a second reflector (52); The first reflector (51) is arranged on the outgoing light path of the aperture (4), the second reflector (52) is arranged on the reflected light path of the first reflector (51), and the off-axis parabolic mirror (61) is arranged on the reflected light path of the second reflector (52).

5. The spatial optical system stray light measurement system based on time channel screening according to claim 4, characterized in that: The time-resolved detection module (8) is an IsCMOS image intensification camera.

6. The spatial optical system stray light measurement system based on time channel screening according to claim 5, characterized in that: The output end of the photoelectric detector (9) is electrically connected to the external trigger end of the time-resolved detection module (8) via a BNC cable (10).

7. A method for measuring stray light of a space optical system based on time channel screening, using the stray light measurement system of a space optical system based on time channel screening according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: When the spatial optical system to be measured (01) is not installed, the laser light source (1) is started, and the laser light beam emitted by the laser light source (1) is divided into reflected light and transmitted light by a beam splitter (2), and the reflected light is guided to a photodetector (9), and the transmitted light is guided to a time-resolved detection module (8) in sequence through an optical delay device (3), an aperture (4) and a collimating beam expansion module (6); Step 2: adjusting the incident light path of the time-resolved detection module (8) and the outgoing light path of the collimating beam expansion module (6) to be parallel through the turntable module (7), and taking this state as the initial state; Step 3, photoelectrically detecting the reflected light through a photoelectric detector (9), obtaining an electrical signal, and sending the electrical signal to an external trigger terminal of the time-resolved detection module (8), thereby triggering the time-resolved detection module (8) to start detection; Step 4, detecting the optical signal output by the collimating beam expansion module (6) in the initial state through the time-resolved detection module (8), obtaining the number of photons in the initial state, and using it as the number of photons at the entrance pupil of the spatial optical system (01) to be measured; Step 5, installing the spatial optical system to be tested (01) on the turntable module (7), and making the entrance pupil of the spatial optical system to be tested (01) located on the output light path of the collimating beam expansion module (6), and the image plane located at the detection end of the time-resolved detection module (8); obtaining the number of photons in the initial state, that is, the number of photons at the 0th preset angle, in the same manner as steps 3 to 4, and taking it as the 0th photon number at the image plane of the spatial optical system to be tested (01); Step 6: adjusting the axis of the entrance pupil of the spatial optical system (01) to be tested and the exit light path of the collimating beam expansion module (6) to have a first preset angle through the turntable module (7); obtaining the number of photons at the first preset angle in the same manner as steps 3 to 4, and using it as the first number of photons at the image plane of the spatial optical system (01) to be tested; The axial direction at the entrance pupil of the spatial optical system to be measured (01) and the exit light path of the collimating beam expansion module (6) are adjusted by a turntable module (7) so that a second preset angle exists between the angle; the number of photons at the second preset angle is obtained in the same manner as steps 3 to 4, and is used as the second number of photons at the image plane of the spatial optical system to be measured (01); Similarly, the turntable module (7) is used to adjust the axis at the entrance pupil of the spatial optical system (01) to be tested and the output light path of the collimating beam expansion module (6) to have an Xth preset angle; the number of photons at the Xth preset angle is obtained in the same manner as steps 3 to 4, and is used as the Xth photon number at the image plane of the spatial optical system (01) to be tested; X≥2; Step 7, pre-processing all the acquired photon numbers through the data acquisition and processing module, eliminating abnormal values ​​and noise, and then filtering the photon numbers according to the set time channel, and then obtaining the respective photon number densities according to the filtered photon number at the entrance pupil and the filtered photon number at the image plane under different preset angles, and finally obtaining the point source transmittance values ​​at 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; Step 8: Compare the point source transmittance values ​​at different off-axis angles with the corresponding standard values ​​to 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 spatial optical system.

8. The method for measuring stray light of a spatial optical system based on time channel screening according to claim 7, characterized in that: In step 7, the data acquisition and processing module calculates the point source transmittance value according to the photon number density at the image plane and the photon number density at the entrance pupil by the following formula: : ； Where: and are the photon number density at the image plane and the photon number density at the entrance pupil respectively; ; ; is the number of photons at the image plane; is the area of ​​the image plane; is the number of photons at the entrance pupil; is the area of ​​the entrance pupil; is the off-axis angle.

9. The method for measuring stray light of a spatial optical system based on time channel screening according to claim 7 or 8, characterized in that: Before step 1, the step of calibrating the measurement system is also included, specifically: The output power and pulse frequency of the laser light 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 resolution detection module (8) are calibrated; and the collimation and beam expansion module (6) is calibrated.

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