An experimental device capable of measuring imaging quality of an optical system and laser damage threshold

Abstract

The application discloses an experimental device capable of measuring imaging quality and laser damage threshold of an optical system, and relates to the technical field of optical systems. In the device, first and second diaphragms are used for collimating a light path and limiting the size of a light spot entering an attenuation imaging-energy detection system; the first and second diaphragms are cooperated with a mirror group to realize adjustment of the light path; the second diaphragm limits the size of the light spot incident to the double detection system; and the attenuation imaging-energy detection system acquires the energy and imaging effect of the laser beam output by the second diaphragm. Through cooperation of the diaphragm assembly and the mirror assembly, the dimensions of the light path adjustment are effectively expanded, and the light path is more easily adjusted and collimated; through the attenuation sheet and the mirror assembly, the point spread function measurement of the optical system at different distances can be realized in a limited experimental site, and the test of the laser damage threshold of the optical system can be completed without changing the light path.

Description

Technical Field

[0001] This application relates to the field of optical system technology, and in particular to an experimental apparatus capable of measuring the imaging quality and laser damage threshold of an optical system. Background Technology

[0002] Optoelectronic imaging systems, with their advantages of high spatial resolution, real-time imaging capabilities, and simple and reliable structure, have been widely used in various fields such as scientific research, industry, daily life, and national security. To ensure image quality, traditional optoelectronic imaging systems typically place the image sensor near the optical focal plane. However, due to the extremely high optical gain in this region, the laser damage threshold of conventional optoelectronic imaging systems is relatively low, making them susceptible to laser damage.

[0003] In optical systems, the surface processing precision of optical elements and the size of the imaging aperture limit the imaging effect, leading to problems such as aberrations and high-frequency cutoff during the imaging process. Furthermore, factors such as the pixel size and spacing of the image detector, as well as the characteristics of the photosensitive material, significantly affect imaging resolution, signal sampling density, and image signal-to-noise ratio. To comprehensively characterize these influencing factors, the point spread function (PSF) has been introduced as a comprehensive tool for describing the imaging process. The PSF describes the response of a point light source at the target location on the imaging plane, reflecting the resolving power of the optical system for point light sources, and is a key indicator for evaluating the imaging performance of an optical system.

[0004] With the continuous development of high-energy, high-power laser source technology and its widespread application in numerous fields, optical systems face an increasing risk of laser damage. Against this backdrop, the laser damage threshold has become a crucial technical parameter for evaluating the damage resistance of optical systems. This invention aims to provide a device capable of simultaneously measuring the point spread function and laser damage threshold of an optical system, thereby comprehensively evaluating the imaging quality and damage resistance of the optical system. Summary of the Invention

[0005] The purpose of this application is to provide an experimental apparatus capable of measuring both the imaging quality and the laser damage threshold of an optical system.

[0006] To achieve the above objectives, this application provides the following solution:

[0007] This application provides an experimental apparatus capable of measuring the imaging quality and laser damage threshold of an optical system, comprising: a laser source, a first aperture, a mirror assembly, a second aperture, and an attenuation imaging-energy detection system arranged sequentially along the optical path;

[0008] The laser source is used to emit a laser beam as the light source for the experiment;

[0009] The first aperture is used to output the laser beam from the laser source to the reflector assembly;

[0010] The reflector assembly is used to reflect the laser beam output from the first aperture to the second aperture;

[0011] The second aperture is used to output the laser beam output by the mirror assembly to the attenuation imaging-energy detection system;

[0012] The first and second apertures are used to collimate the optical path and limit the size of the light spot entering the attenuation imaging-energy detection system; the first and second apertures work in conjunction with the mirror group to adjust the optical path; the second aperture is used to limit the size of the light spot incident on the dual detection system;

[0013] The attenuation imaging-energy detection system is used to obtain the energy and imaging effect of the laser beam output by the second aperture.

[0014] According to the specific embodiments provided in this application, the following technical effects are disclosed:

[0015] This application provides an experimental apparatus capable of measuring the imaging quality and laser damage threshold of an optical system. Considering both the imaging quality and laser damage performance of the optical system, an experimental apparatus is designed to measure the point spread function and the laser damage threshold of the optical system. The effectiveness and reliability of the apparatus are verified through experiments. Using this apparatus, the measurement of the point spread function and the laser damage threshold can be switched by varying the attenuation level. By changing the distance of the reflector, the measurement of the point spread function and the laser damage threshold at different distances can be achieved within a limited experimental space without requiring significant modifications to the optical path. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram illustrating the process of calculating PSF using the inclined blade edge method in one embodiment of this application;

[0018] Figure 2 This is a schematic diagram of point spread function acquisition using the point pulse method in one embodiment of this application;

[0019] Figure 3This is a schematic diagram of the optical path of a laser-irradiated CMOS photodetector in one embodiment of this application;

[0020] Figure 4 This is a schematic diagram of an experimental apparatus capable of measuring the imaging quality and laser damage threshold of an optical system according to an embodiment of this application.

[0021] Figure 5 This is a schematic diagram of the point spread function of a conventional imaging system in one embodiment of this application;

[0022] Figure 6 This is a schematic diagram of the imaging effect and point spread function distribution of an experiment using a wavefront coding system in one embodiment of this application;

[0023] Figure 7 This is a schematic diagram of the damage morphology of an optical system in one embodiment of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] The inclined edge method: The PSF (Point Spread Function) is obtained using the ISO 12233 inclined edge method under ideal inclination angles. This technique selects the portion of the image with an inclined blade edge and uses fitting, interpolation, and differentiation techniques to determine the line spread function (LSF) of that portion, ultimately deriving the point spread function of the entire system. The process of calculating PSF using the edge method is as follows... Figure 1 As shown, the point spread function (PSF) estimation process is as follows: Obtain the edge spread function curve based on the blade edge; differentiate the edge spread function to obtain the line spread function; perform a Fourier transform on the line spread function to obtain the one-dimensional MTF, then perform vector operations to obtain the two-dimensional MTF; finally, perform an inverse Fourier transform to obtain the PSF. This method is based on a simplified assumption that the PSF follows a Gaussian distribution. In practical applications, the system's PSF is often much more complex than a Gaussian distribution, which limits the applicability and accuracy of this method. Furthermore, this method does not consider the influence of noise; when imaging noise is high, this method cannot accurately estimate the angle of the tilted blade edge, potentially leading to estimation failure.

[0027] Point Pulse Method: The point spread function is the response of an optical system to a point light source. In an ideal optical system, the light energy emitted from a point on the object plane is also concentrated at a single point on the image plane. However, in actual optical systems, the light emitted from a point on the object plane is always somewhat dispersed on the image plane. When the original image f(x,y) is a point pulse δ(x,y), the imaging model of the optical system can be written as: g(x,y)=δ(x,y)*h(x,y)+n(x,y)=h(x,y)+n(x,y); where h(x,y) represents the point spread function of the optical system, g(x,y) is the image intensity distribution on the imaging plane, δ(x,y) is a point pulse representing an ideal point light source, n(x,y) represents the noise distribution of the imaging detector, and * represents the convolution operation. Therefore, when the original image is a point light source, the resulting blurred image is a point spread function containing additive noise. By removing the additive noise, the point spread function of the system can be obtained. This is the principle of measuring the point spread function using the point pulse method. This method has a simple experimental principle and the apparatus is easy to set up. A schematic diagram of obtaining the point spread function using the point pulse method is shown below. Figure 2 As shown, the point pulse method is greatly affected by sensor noise. The presence of noise will interfere with the accurate acquisition of PSF, especially in cases of complex images or low signal-to-noise ratios, where the estimation accuracy of the point spread function will decrease significantly.

[0028] Damage threshold testing system: The optical path system of the laser irradiation CMOS photodetector experimental device, such as... Figure 3 As shown, the system mainly consists of a light source module, a beam splitting and monitoring module, an irradiation control module, and a detection and analysis module. The experimental system uses a 1064nm fiber laser source as the light source. The output laser is split into two paths by a beam splitter: one path passes through a neutral density filter for energy attenuation, and then a focusing lens precisely focuses the light spot onto the surface of the CMOS photodetector; the other path is directly fed into the energy meter probe to achieve real-time monitoring of the incident laser energy. To precisely control the irradiation conditions, the system is equipped with a three-dimensional translation stage for adjusting the spatial position of the detector. Combined with the rotation function of the bottom angle stage, the incident angle can be continuously adjusted. In terms of the control system, the computer is connected to the CMOS detection unit and the laser source through dual channels, which can both acquire the device damage status in real time and dynamically adjust key parameters such as laser energy and repetition frequency. In addition, an electric baffle device is set at the front end of the beam splitter, which, through linkage with a high-precision timer, can control the irradiation time. Since this scheme only conducts damage testing on pure CMOS photodetectors, the lenses in the optical path are only used to precisely focus the light spot onto the surface of the CMOS photodetector and do not have actual imaging capabilities. This results in severe aberrations in the measurement of the point spread function of the optical system, and the scheme cannot meet the requirements for measuring the laser damage threshold under different distance conditions.

[0029] To address the limitation of existing experimental setups in simultaneously considering the imaging quality of the measurement optical system and the laser damage threshold—two distinct dimensions—this application, in an exemplary embodiment, such as... Figure 4 As shown, an experimental apparatus for measuring the imaging quality and laser damage threshold of an optical system is provided, comprising: a laser source, a first aperture, a mirror assembly, a second aperture, and an attenuation imaging-energy detection system arranged sequentially along the optical path; the laser source is used to emit a laser beam as the light source for the experiment; the first aperture is used to output the laser beam output from the laser source to the mirror assembly; the mirror assembly is used to reflect the laser beam output from the first aperture to the second aperture; the second aperture is used to output the laser beam output from the mirror assembly to the attenuation imaging-energy detection system. A detection system is included. The first and second apertures are used to collimate the optical path and limit the size of the light spot entering the attenuation imaging-energy detection system. The first and second apertures work in conjunction with the mirror assembly to adjust the optical path. The second aperture limits the size of the light spot incident on the dual detection system. Through the coordinated configuration of the first and second apertures with the mirror assembly, optical path collimation can be achieved using the apertures during optical path adjustment. The direction of the optical path can be changed by adjusting the pitch angle of the mirrors, making it easier for the light to be incident perpendicularly onto the imaging lens, thus improving the convenience of optical path adjustment. The attenuation imaging-energy detection system is used to acquire the energy and imaging effect of the laser beam output from the second aperture. The mirror assembly includes multiple mirrors arranged along the optical path. The mirror assembly includes a first mirror and a second mirror. The first mirror reflects the laser beam output from the first aperture to the second mirror; the second mirror reflects the laser beam output from the first mirror to the second aperture. The laser source emits a laser beam parallel to the ground. The angle between the first reflector and the laser beam emitted from the laser source is 45 degrees; the angle between the second reflector and the laser beam output from the first reflector is 45 degrees.

[0030] The attenuation imaging-energy detection system includes: a beam splitter, an imaging optical path assembly, and an energy acquisition assembly. The beam splitter splits the laser beam output from the second aperture into a transmitted beam and a reflected beam. The imaging optical path assembly receives the transmitted beam and obtains a damage threshold or imaging effect on the detector surface. The energy acquisition assembly acquires the energy of the reflected beam. The imaging optical path assembly includes: an attenuator, an imaging lens, and a CMOS sensor arranged along the optical path. The attenuator attenuates the energy of the laser beam and outputs the attenuated laser beam to the imaging lens and CMOS sensor. The energy acquisition assembly includes: a lens and an energy meter arranged along the optical path.

[0031] This application effectively expands the optical path adjustment dimension through the configuration of the aperture assembly and the reflector assembly, making it easier to adjust and collimate the optical path; by adjusting the position of multiple reflectors in the reflector assembly, it is possible to measure the imaging performance and laser damage capability of different optical systems at different distances within a limited experimental space; by changing the number of attenuators, the point spread function measurement and laser damage performance testing of the optical system can be switched.

[0032] This application provides an experimental apparatus capable of measuring the imaging quality and laser damage threshold of an optical system, comprising a laser source, an attenuator, a mirror, an aperture, a beam splitter, a focusing lens, an energy meter, and an imaging system. The experimental system is composed as follows: Figure 4 As shown. During optical path adjustment, optical path collimation can be achieved through the synergistic action of the aperture assembly and the mirror assembly: the aperture calibrates the beam path, and the optical path direction is changed by precisely adjusting the pitch angle of the mirror, allowing the beam to be incident perpendicularly onto the imaging lens, thus improving the efficiency and accuracy of optical path adjustment. Point spread function and laser damage threshold testing can be achieved by dynamically adjusting the attenuation of the attenuator: keeping the incident laser energy constant, increasing the attenuation of the attenuator allows for the measurement of the point spread function of the optical system, while decreasing the attenuation of the incident energy allows for the measurement of the laser damage threshold of different optical systems. When it is desired to measure the point spread function under different distance conditions and investigate the effect of distance on the laser damage capability of the optical system, it is only necessary to adjust the distance between the two mirrors and the laser source and the optical imaging system.

[0033] The optical path setup for the experimental setup mainly includes three processes: laser collimation, mirror adjustment, and camera alignment. Laser collimation: Using a double-aperture positioning method, the two apertures are first adjusted to the same height as the laser source's output port. The first aperture is placed approximately 5 cm from the front of the laser source, and the second aperture is arranged parallel to it at a 20-meter interval. By finely adjusting the pitch angle and horizontal direction of the laser source, the emitted beam is simultaneously and accurately penetrated through the central apertures of both apertures, at which point the laser beam axis is perfectly parallel to the ground. Mirror adjustment: First, based on... Figure 4The optical path design involves roughly placing the reflectors in the designated positions. Then, the reflectors are adjusted sequentially according to their numbers. Taking reflector 1 as an example, it's necessary to ensure the laser beam illuminates the center area of ​​the reflector. Adjust its angle with the beam to approximately 45 degrees, causing the laser to reflect near reflector 2, and then fix reflector 1 in place. Next, place a movable aperture on the reflected light path, adjust the pitch angle of reflector 1 to make the reflected beam parallel to the ground, and use the fine-tuning function of the frame to precisely align the laser with the center of reflector 2. Adjust subsequent reflectors in the same way until the laser accurately returns to the vicinity of the camera, completing the optical path calibration. After optical path calibration, place the second aperture in front of the beam splitter to limit the size of the light spot entering the dual-detection system. Camera alignment: Mount the imaging lens on the camera, use a lens cap to shield the camera (to prevent damage), and adjust the camera's height and horizontal displacement to center the incident laser on the imaging lens. This completes the optical path setup process.

[0034] The experimental setup can measure the point spread function of both conventional imaging systems and wavefront-coded imaging systems. The measurement method is as follows:

[0035] The laser beam is reflected by a mirror, then passes through a beam splitter to reach the detector surface. As the transmission distance increases to a certain extent, the laser beam received by the detector becomes equivalent to a parallel incident beam, and the response at the detector surface is expressed as a point spread function. The point spread function measurement method for conventional imaging systems is as follows:

[0036] After adjusting the optical path, an attenuator needs to be added in front of the imaging lens to regulate the light intensity, thereby protecting the detector from damage caused by excessively strong laser light. Simultaneously, the driver program should be activated to monitor the histogram display of the image in real time. The energy of the incident laser is precisely controlled by increasing or decreasing the number of attenuators to ensure that pixels in the image do not become oversaturated. To reduce stray light interference with the measurement results, the illumination source should be turned off to create a dark environment. The point spread function should then be captured and saved. The point spread function of a conventional imaging system is shown below. Figure 5 As shown, the modulation transfer function obtained by Fourier transform can effectively depict the contrast transfer characteristics of the system at different spatial frequencies, highlighting its ability to resolve fine spatial details, and thus intuitively reflecting the imaging quality of the optical system.

[0037] For point spread function measurement methods in wavefront-coded imaging systems:

[0038] After adjusting the optical path, an attenuator was added in front of the imaging lens to increase attenuation and prevent damage to the detector. Simultaneously, the driver was activated to display the image histogram. The incident laser energy was controlled by adjusting the number of attenuators to prevent pixel saturation in the image. A low-light environment was created by turning off the lights to avoid the influence of stray light on the point spread function measurement. The point spread function was then photographed and saved. A phase plate was added in front of the conventional imaging system to form a wavefront-coded imaging system. The point spread function was measured according to the conventional imaging system's point spread function measurement method. The imaging effect and point spread function distribution of the wavefront-coded system experiment are shown below. Figure 6 As shown. The intermediate encoded object is photographed and saved. A clear image is captured without a phase plate as a reference image. The decoded image is obtained by using a Wiener filter with a point spread function, and its PSNR compared to the clear image is 21.3977 dB. The reference image and the [other image] are obtained using the experimental apparatus provided in this application, which can measure the imaging quality and laser damage threshold of an optical system. Figure 6 Before encoding the image, the attenuator in the imaging optical path assembly needs to be removed.

[0039] The distribution shape of the point spread function (PSF) corresponds to the beam modulation shape of the cubic phase plate, exhibiting an "L" shape. Using the PSF obtained from the experiment, Wiener filtering was employed to decode the intermediate encoded image. The decoded image was clearer than the intermediate encoded image, with significantly reduced blur, better preservation of detail and edge information, higher signal-to-noise ratio, and better restoration results. This fully demonstrates that this system can be used to obtain the PSF of different optical systems.

[0040] Experimental setup for measuring laser damage threshold in imaging systems:

[0041] The laser damage threshold of an imaging system refers to the maximum laser energy density or power density at which optical components (such as lenses, detectors, filters, etc.) in the imaging system do not suffer irreversible physical damage (such as melting, cracking, or permanent degradation of optical performance) under laser irradiation.

[0042] For conventional imaging systems, laser damage threshold measurement methods are as follows:

[0043] First, the conventional imaging system focuses on the target to ensure the optical system is in focus. After the laser is activated, the beam is transmitted to the beam splitter via the optical path. The reflected light is monitored in real time by the energy meter, while the transmitted light passes through an adjustable attenuator and the imaging lens to reach the CMOS sensor. The laser source is set to operate stably at a fixed pulse frequency, employing a stepped energy loading strategy—starting with high attenuation and decreasing the value by 0.1 OD each time until the pulse energy stabilizes. Then, the obstruction in front of the camera is removed, and the detector is observed for any damage. If damage occurs, the experimental data is recorded; if no damage occurs, the attenuation is continued to decrease until the detector is damaged.

[0044] For laser damage threshold measurement methods in wavefront-coded imaging systems:

[0045] A wavefront-coded imaging system was constructed by adding a phase plate in front of a conventional imaging system. After the laser was turned on, the beam was transmitted to the beam splitter via the optical path. The reflected light was monitored in real time by an energy meter, while the transmitted light passed through an adjustable attenuator and an imaging lens to reach the CMOS sensor. The laser source was set to operate stably at a fixed pulse frequency, and a stepped energy loading strategy was adopted—starting from high attenuation, the energy was reduced by 0.1 OD value each time until the pulse energy stabilized. Then, the obstruction in front of the camera was removed, and the detector was observed for any damage. If damage occurred, the experimental data was recorded; if no damage occurred, the attenuation was reduced further until the detector was damaged.

[0046] The morphology of damage to the optical system is as follows Figure 7 As shown, the image within the red box is an enlarged view. Figure 7 In the diagram, number 1 represents the point damage morphology of a conventional imaging system, and number 2 represents the point damage morphology of a wavefront-coded imaging system. If the energy meter reading is E, the beam splitting ratio of the beam splitter's reflection to transmission is R:T, the attenuation value of the attenuator is OD, and the spot size is r, the laser energy density E reaching the lens surface can be calculated. d for: When testing a conventional imaging system, the energy meter reading was 35.12 μJ, the OD value was 2.8, the beam splitter ratio was 45%:55%, the spot diameter was 22 mm, and the damage threshold of the conventional imaging system was measured to be 0.0179 μJ / cm². 2 When testing the wavefront-coded imaging system, the energy meter reading was 36.4 μJ, the OD value was 1.8, the beam splitter ratio was 45%:55%, and the spot diameter was 22 mm. The damage threshold of the conventional imaging system was measured to be 0.1856 μJ / cm². 2 This verifies that the system can perform laser damage performance testing on optical systems.

[0047] In this application, camera parameters can be changed, such as the main lens size and focal length. Since the liquid crystal spatial light modulator has the characteristic of flexibly generating different phase modulation functions, the phase plate can also be replaced by the liquid crystal spatial light modulator, and its principle is the same as that of the embodiment. The wavefront coding image reconstruction algorithm in this application is not limited to the Wiener filtering described in the embodiment, but also includes algorithms such as inverse filtering, improved Wiener filtering, Lucy-Richardson filtering, wavelet analysis, and other deep learning-related deblurring algorithms.

[0048] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An experimental apparatus capable of measuring the imaging quality and laser damage threshold of an optical system, characterized in that, include: A laser source, a first aperture, a mirror assembly, a second aperture, and an attenuation imaging-energy detection system are arranged sequentially along the optical path; The laser source is used to emit a laser beam as the light source for the experiment; The first aperture is used to output the laser beam from the laser source to the reflector assembly; The reflector assembly is used to reflect the laser beam output from the first aperture to the second aperture; The reflector assembly includes: a first reflector and a second reflector; The first reflector is used to reflect the laser beam output from the first aperture to the second reflector; The second reflector is used to reflect the laser beam output from the first reflector to the second aperture. The second aperture is used to output the laser beam output by the mirror assembly to the attenuation imaging-energy detection system; The first and second apertures are used to collimate the optical path and limit the size of the light spot entering the attenuation imaging-energy detection system; the first and second apertures work in conjunction with the mirror group to adjust the optical path; the second aperture is used to limit the size of the light spot incident on the dual detection system; The attenuation imaging-energy detection system is used to obtain the energy and imaging effect of the laser beam output by the second aperture; The attenuation imaging-energy detection system includes: a beam splitter, an imaging optical path assembly, and an energy harvesting assembly; The beam splitter is used to split the laser beam output from the second aperture into a transmitted beam and a reflected beam; The imaging optical path assembly is used to receive the transmitted light beam and obtain the damage threshold or imaging effect on the detector surface. The energy acquisition component is used to acquire the energy of the reflected beam; The imaging optical path assembly includes: an attenuator, an imaging lens, and a CMOS sensor arranged along the optical path; The attenuator is used to attenuate the energy of the laser beam and output the attenuated laser beam to the imaging lens and CMOS sensor. The energy harvesting component includes: a lens and an energy meter arranged along the optical path; The experimental apparatus capable of measuring the imaging quality and laser damage threshold of an optical system can, by adjusting the positions of multiple mirrors in the mirror assembly, measure the imaging performance and laser damage capability of different optical systems at different distances within a limited experimental space. The experimental apparatus capable of measuring the imaging quality and laser damage threshold of an optical system switches between measuring the point spread function and testing the laser damage performance of the optical system by changing the number of attenuators: keeping the incident laser energy constant, increasing the attenuation of the attenuator allows for the measurement of the point spread function of the optical system, while decreasing the attenuation of the incident energy allows for the measurement of the laser damage threshold of different optical systems.

2. The experimental apparatus for measuring the imaging quality and laser damage threshold of an optical system according to claim 1, characterized in that, The laser source emits a laser beam parallel to the ground.

3. The experimental apparatus for measuring the imaging quality and laser damage threshold of an optical system according to claim 1, characterized in that, The angle between the first reflector and the laser beam emitted from the laser source is 45 degrees. The angle between the laser beam output from the second reflector and the first reflector is 45 degrees.

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