CN103234734A - large-caliber stray light testing device and testing method - Google Patents

Abstract

The invention relates to a large-diameter stray light test device and a test method. The large-diameter stray light test device includes a target simulator, a spherical collimator, a detection system, and a data acquisition and processing system; the target simulator is arranged on the spherical collimator. The optical system to be tested is set on the outgoing light path of the spherical collimator; the detection system is set at the image plane of the optical system to be tested; the detection system is connected with the data acquisition and processing system. The invention provides a large-aperture stray light testing device and a testing method capable of effectively evaluating the stray light suppression ability of an optical system structure.

Description

Large aperture stray light test device and test method

technical field

The invention belongs to the field of optical detection, and relates to a large-aperture stray light testing device and a testing method, in particular to a large-aperture stray light coefficient mainly used in the assessment of optical system performance of various optical cameras before optical-mechanical docking test equipment and test methods.

Background technique

In recent years, with the development of high-sensitivity, low-detection-threshold detectors, higher requirements have been placed on the suppression of stray light in optical systems, which requires higher precision in stray light measurement systems.

When the optical system is imaging, in addition to imaging (or non-imaging) according to the normal optical path on the image plane, there are still some non-imaging rays falling on the image plane. These harmful lights that do not participate in imaging are called stray light. Stray light has a great impact on the image quality of the optical system. Due to the reflection and scattering of light by optical elements and mechanical components in the system, non-imaging light rays diffuse on the image surface, resulting in poor imaging clarity and reduced contrast. . The modulation transfer function of the optical system will decrease with the increase of the stray light coefficient in the whole spatial frequency range. Therefore, the stray light coefficient is an important index reflecting the imaging quality of the optical system, and stray light detection is one of the important aspects of the image quality detection of the optical system.

Most spaceborne space cameras work in the case of detecting extremely weak target signals, while the target source and ambient light are diffracted by the aperture of the optical system, as well as scattered and reflected by the structure and the surface of the optical element to reach the image plane detector to form stray light. The reasons for it are intricate, not only related to the manufacturing process and materials of the optical system, but also related to aberration characteristics, diffraction phenomena, and target characteristics. If it is bad, it may even form stray light spots, and in severe cases, the target signal will be completely submerged by stray light radiation noise.

The large-aperture and long-focal-length stray light test method currently being researched is mainly aimed at the stray light test of the large-aperture optical system. It is based on the aerospace on-orbit high-image-quality detection camera as the background, and the calibration technology of the stray light suppression ability of the aerospace camera on the ground is carried out. for research.

The traditional optical system stray light measurement generally uses the black spot method of testing with an integrating sphere after the overall coating. This test method can verify the stray light radiation generated by the target source after passing through the optical system. Traditional measuring devices can only evaluate the impact of stray light radiation generated by on-axis target light sources on detection capabilities, and lack the ability to measure off-axis stray light; however, for aerospace high-sensitivity detection cameras, they will be affected by stray light generated by other off-axis radiation sources Therefore, the research on the off-axis stray light test device is particularly important for evaluating the suppression level of off-axis stray light in the optical system.

At present, in the development of various large-aperture and long-focus aerospace cameras, the common stray light measurement device (black spot method measurement system) can only test the stray light of small-aperture optical systems, such as optical systems with an aperture of less than or equal to Φ300mm , however, the full-aperture test cannot be performed for the stray light coefficient of the optical system with an aperture exceeding Φ300mm. This is mainly due to the fact that the large aperture and long focal length optical system has too large aperture and too long focal length, and the measurement device cannot use large aperture transmission optical glass to make achromatic collimation objective lens due to the reason of optical materials; at the same time, for long focal length optical system For stray light measurement, if the collimating objective lens is not used, the target radiation at infinity cannot be simulated, so it cannot truly reflect the stray light suppression level of the optical system. Therefore, the previous stray light coefficient measurement device needs to be further improved to meet the needs of current optical system stray light measurement.

In addition, the target simulators of previous stray light measurement devices all use "horn plugs" as the extinction system to provide high-contrast black spot targets, and their extinction efficiency is 1000:1; for the measurement of high-precision stray light coefficient, 1000 If the target contrast ratio is :1, the extinction ability is too poor, which will affect the final stray light measurement accuracy (often, the stray light measurement result is too large due to the reason that the black spot is not black).

In summary, considering that the research on this subject is the key technology for stray light testing of large-aperture and long-focus optical systems, the successful research of this technology will herald the large-aperture and long-focus stray light ground calibration technology in China. Enter a new level. Therefore, carrying out research on large-aperture, long-focus, and high-precision stray light measurement technology will play a role in promoting the development of my country's optical system stray light measurement field.

Contents of the invention

In order to solve the above-mentioned technical problems in the background technology, the present invention provides a large-aperture stray light testing device and a testing method that can effectively assess the stray light suppression ability of the optical system structure.

The technical solution of the present invention is: the present invention provides a large-diameter stray light test device, which is special in that: the large-diameter stray light test device includes a target simulator, a spherical collimator, a detection system and a data acquisition system. and processing system; the target simulator is arranged on the incident optical path of the spherical collimator; the optical system to be measured is arranged on the outgoing optical path of the spherical collimator; the detection system is arranged on the image plane of the optical system to be measured; The detection system is connected with the data acquisition and processing system.

The above-mentioned spherical collimator includes an integrating sphere, a collimating objective lens arranged on the wall of the integrating sphere and a light source arranged inside the integrating sphere; the integrating sphere includes a light inlet and a light outlet; the target simulator is arranged on the integrating sphere The optical system to be tested is set at the light outlet of the integrating sphere; the light emitted by the light source illuminates the target simulator and then collimates to the optical system to be tested through the collimating objective lens.

The above-mentioned target simulator is arranged at the light entrance of the integrating sphere and at the focal point of the collimating objective lens.

The collimating objective described above is an off-axis parabolic mirror.

The upper target simulator is the black target source as well as the white target source.

The target contrast ratio of the above black target source to white target source is at least 10000:1.

The above-mentioned large-aperture stray light testing device also includes an iris diaphragm arranged between the optical system to be tested and the detection system.

The above-mentioned large-aperture stray light testing device also includes a turntable; the optical system to be tested and the detection system are both arranged on the turntable.

A test method based on the above-mentioned large-aperture stray light test device, which is special in that: the test method includes the following steps:

1) Set the optical system to be tested on the outgoing optical path of the integrating sphere, and make the optical system to be tested and the off-axis parabolic mirror on the same optical axis;

2) Select the white target source as the target simulator and pass through the spherical collimator and the optical system to be tested, and obtain the image of the white target source on the detection surface of the detection system;

3) Collect and read the image of the white target source formed in step 2) through the data acquisition and processing system to obtain the illuminance value of the image of the white target source;

4) Replace the white target source with a black target source, and after passing through the spherical collimator and the optical system to be tested, the image of the black target source obtained on the detection surface of the detection system;

5) Collect and read the image of the black target source formed in step 4) through the data acquisition and processing system to obtain the illuminance value of the image of the black target source;

6) Calculate the stray light coefficient of the optical system under test according to the illuminance value of the image of the white target source obtained in step 3) and the illuminance value of the image of the black target source obtained in step 5).

The stray light coefficient of the optical system to be tested in the above step 6) is the ratio between the illuminance value of the image of the white target source and the illuminance value of the image of the black target source.

Advantage of the present invention is:

In order to solve the problems caused by the measurement of stray light in the full-field of view of the large-aperture and long-focus optical system, the present invention combines the traditional stray light test principle of the black spot method to propose a stray light in the full-field of view of the large-aperture and long-focus optical system. The high-precision measurement method can effectively assess the stray light suppression ability of the optical system structure, estimate the signal-to-noise ratio of the whole camera, and propose a structural modification design scheme to ensure that the optical system can image clearly. The invention has The advantages are as follows:

1) This invention uses the classic black spot method measurement principle to propose a full-field stray light test method for high-precision, large-aperture, and long-focus optical systems. 1% increased to 0.5%;

2) The present invention is aimed at the design of the large-aperture achromatic collimating objective lens, which solves the problem that the stray light coefficient of the large-aperture and long-focus optical system cannot be measured in the past, and can measure the stray light coefficient of the optical system with an aperture of Φ300mm or more;

3) The present invention uses an off-axis parabolic mirror as the collimating objective lens, which can effectively reduce the impact of the stray light introduced by the transmissive collimating objective lens and the low measurement accuracy of the system;

4) For the first time, the invention cooperates with the turntable to realize the measurement of the stray light coefficient of the full field of view of the optical system;

5) The target simulator used in the present invention adopts a special multi-sided absorption cavity design form, which can increase the target contrast ratio of white spots and dark spots from 1000:1 to 10000:1, effectively reducing the noise caused by the target simulator. Stray light causes measurement errors.

Description of drawings

Fig. 1 is the schematic diagram of the principle of the large aperture stray light testing device provided by the present invention;

in:

1-target simulator; 2-light source; 3-integrating sphere; 4-off-axis parabolic mirror; 5-turntable; 6-detection system; 7-optical system to be tested; 8-data acquisition and processing system.

Detailed ways

Referring to Fig. 1, the present invention provides a large-diameter stray light test device, which includes a target simulator 1, a spherical collimator, a detection system 6 and a data acquisition and processing system 8; the target simulator 1 It is arranged on the incident optical path of the spherical collimator; the optical system 7 to be measured is arranged on the outgoing optical path of the spherical collimator; the detection system 6 is arranged at the image plane of the optical system 7 to be measured; the detection system 6 is connected with data acquisition and processing System 8 is connected.

The spherical collimator includes an integrating sphere 3, a collimating objective lens arranged on the wall of the integrating sphere 3 and a light source 2 arranged inside the integrating sphere 3; the integrating sphere 3 includes a light inlet and a light outlet; the target simulator 1 is arranged on the integrating The light entrance of the sphere 3; the optical system 7 to be tested is set at the light exit of the integrating sphere 3; the light emitted by the light source 2 illuminates the target simulator 1 and then collimates to the optical system 7 to be tested through the collimating objective lens.

The target simulator 1 is set at the light entrance of the integrating sphere 3 and at the focus of the collimating objective lens.

The collimating objective is an off-axis parabolic mirror 4 . The upper target simulator 1 is the black target source and the white target source. The target contrast ratio of black target source to white target source is at least 10000:1. The large-aperture stray light testing device also includes an iris diaphragm arranged between the optical system 7 to be tested and the detection system 6 . The large-aperture stray light testing device also includes a turntable 5 ; the optical system 7 to be tested and the detection system 6 are both arranged on the turntable 5 .

A test method based on the above large-aperture stray light test device, which is special in that the test method includes the following steps:

1) Set the optical system 7 to be tested on the outgoing optical path of the integrating sphere 3, and make the optical system 7 to be tested and the off-axis parabolic mirror 4 be on the same optical axis;

2) Selecting the white target source as the target simulator 1 and passing through the spherical collimator and the optical system 7 to be tested, the image of the white target source obtained on the detection surface of the detection system 6;

3) Collect and read the image of the white target source formed in step 2) through the data acquisition and processing system 8 to obtain the illuminance value of the image of the white target source;

4) Replace the white target source with a black target source, and after passing through the spherical collimator and the optical system 7 to be tested, the image of the black target source obtained on the detection surface of the detection system 6;

5) Collect and read the image of the black target source formed in step 4) through the data acquisition and processing system 8 to obtain the illuminance value of the image of the black target source;

6) Calculate the stray light coefficient of the optical system 7 to be tested according to the illuminance value of the image of the white target source obtained in step 3) and the illuminance value of the image of the black target source obtained in step 5).

The stray light coefficient of the optical system 7 under test in step 6) is the ratio between the illuminance value of the image of the white target source and the illuminance value of the image of the black target source.

The working principle of the present invention is: select target simulator 1 as black and white target source, be arranged on the side wall of integrating sphere 3, be positioned at the focal point of off-axis parabolic mirror 4, light the light source that the integrating sphere 3 inner wall goes out, from The exit of the integrating sphere 3 looks like light and dark target radiation from infinity. At the same time, the exit of the integrating sphere 3 can form light energy radiation with a solid angle of 2π to form a spherical collimator.

Before the measurement, first set the optical system 7 to be tested at the exit of the spherical collimator (integrating sphere), and make its optical axis consistent with the optical axis of the objective lens (on-axis stray light test). The spherical collimator target simulator 1 is equipped with a black plug, and the image of the black plug hole of the spherical collimator can be seen on the focal plane of the optical system 7 to be tested. Adjust the black spot to the center of the field of view. Usually, the diameter of the black spot seen in the field of view of the optical system to be tested is less than 1/5 of the diameter of the reticle to select the diameter of the black plug. The detection system 6 is arranged on the top, and the variable diaphragm is arranged in front of the window of the detection system 6, and its diameter should be adjusted to be smaller than the diameter of the collimator black plug hole image.

When measuring, first replace the black plug of the spherical collimator with a white plug without a hole. At this time, after passing through the objective lens of the collimator and the optical system to be measured, what is obtained at the incident hole of the detection system 6 is the white plug. Image, the illuminance at the incident hole is the sum of the illuminance of the imaging beam and the stray illuminance. At this time, a reading m ₁ can be obtained from the data acquisition and processing system 8 . Remove the white plug and replace it with a black plug, and you can get a black spot image at the incident hole of the detection system. If the system has no stray light, the illuminance of the black spot image is zero. Due to the existence of stray light, there is a certain illuminance in the black spot image. When a reading m ₀ can be obtained on the data acquisition and processing system, then the stray light coefficient of the optical system to be tested is:

$\mathrm{<span\; class="notranslate">\; \&eta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: θ is the point source target with different viewing angles of the optical system, η (θ) is the stray light coefficient of the optical system to be tested, m ₀ (θ) is the black plug in the target simulator generated by the optical system at the image plane illuminance, m ₁ (θ) is the illuminance produced by the Behceton in the target simulator at the image plane through the optical system. During the test, with the turntable, the measurement of the stray light coefficient of the entire field of view of the optical system can be realized. The specific measurement method is the same as the measurement method of the on-axis stray light coefficient.

The functions of each part are as follows:

The target simulator 1 is mainly to provide a high-contrast target simulation source; through the design of the multi-faceted absorption cavity, the target contrast ratio of the black plug and the white plug can reach 10000:1, thereby eliminating the measurement error caused by the target simulation stray light . The light source is mainly for providing illumination of the integrating sphere 3 and simulating the radiation source of the optical system to be tested. The integrating sphere 3 constitutes one of the main components of the spherical collimator, which can provide simulated uniform exit radiant light and form a light energy distribution of 2π solid angle. The function of the off-axis parabolic mirror 4 is to provide a target source simulating infinity; since the traditional transmissive collimation objective lens cannot meet the purpose of large-aperture achromatism, here we break through the previous transmissive design method and use an off-axis parabolic mirror to achieve Design of large aperture, long focal length, achromatic spherical collimator device. The turntable 5 mainly provides simulation of different viewing angles of the optical system to be tested. The detection system 6 is mainly used to receive light energy from the image plane of the optical system to be measured, and the iris diaphragm is set in front of the detector window to effectively suppress the impact of ambient stray light on the measurement accuracy. The optical system 7 to be tested is a test piece of the test method, and is used to verify the feasibility of the test method. The data acquisition and processing system 8 mainly completes the light energy collection of the optical system to be tested at different viewing angles, and at the same time completes the data processing and curve drawing of the stray light test.

Claims (10)

1. A large-caliber stray light test device, characterized in that: the large-caliber stray light test device comprises a target simulator, a spherical collimator, a detection system and a data acquisition and processing system; the target simulator is arranged on a spherical The incident optical path of the collimator; the optical system to be measured is arranged on the outgoing optical path of the spherical collimator; the detection system is arranged at the image plane of the optical system to be measured; the detection system is connected with the data acquisition and processing system. 2. The large-aperture stray light testing device according to claim 1, wherein the spherical collimator comprises an integrating sphere, a collimating objective lens arranged on the wall of the integrating sphere, and a light source arranged inside the integrating sphere; The integrating sphere includes a light entrance and a light exit; the target simulator is arranged at the light entrance of the integrating sphere; the optical system to be measured is arranged at the light exit of the integrating sphere; the light emitted by the light source illuminates the target simulation After the detector, it is collimated to the optical system to be tested through the collimating objective lens. 3. The large-aperture stray light testing device according to claim 2, characterized in that: the target simulator is set at the light entrance of the integrating sphere and at the focal point of the collimating objective lens. 4. The large-aperture stray light testing device according to claim 3, wherein the collimating objective lens is an off-axis parabolic mirror. 5. The large-aperture stray light testing device according to any one of claims 1-4, wherein the target simulator is a black target source and a white target source. 6 . The large-aperture stray light testing device according to claim 5 , wherein the target contrast ratio between the black target source and the white target source is at least 10000:1. 7. The large-aperture stray light test device according to claim 6, characterized in that: the large-aperture stray light test device further comprises an iris diaphragm arranged between the optical system to be tested and the detection system. 8. The large-aperture stray light testing device according to claim 7, characterized in that: the large-aperture stray light testing device further comprises a turntable; the optical system to be tested and the detection system are both arranged on the turntable. 9. A test method based on the large-aperture stray light test device according to any one of claims 5-8, characterized in that: the test method comprises the following steps: 1) Set the optical system to be tested on the outgoing optical path of the integrating sphere, and make the optical system to be tested and the off-axis parabolic mirror on the same optical axis; 2) Select the white target source as the target simulator and pass through the spherical collimator and the optical system to be tested, and obtain the image of the white target source on the detection surface of the detection system; 3) Collect and read the image of the white target source formed in step 2) through the data acquisition and processing system to obtain the illuminance value of the image of the white target source; 4) Replace the white target source with a black target source, and after passing through the spherical collimator and the optical system to be tested, the image of the black target source obtained on the detection surface of the detection system; 5) Collect and read the image of the black target source formed in step 4) through the data acquisition and processing system to obtain the illuminance value of the image of the black target source; 6) Calculate the stray light coefficient of the optical system under test according to the illuminance value of the image of the white target source obtained in step 3) and the illuminance value of the image of the black target source obtained in step 5). 10. The test method according to claim 9, wherein the stray light coefficient of the optical system to be tested in step 6) is the difference between the illuminance value of the image of the white target source and the illuminance value of the image of the black target source ratio between.

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