Wavefront detection system and method for large-aperture reflection type low-temperature optical system

Abstract

The invention discloses a wavefront detection system and method for a large-aperture reflective low-temperature optical system, and belongs to the field of optical system detection, and the wavefront detection system comprises an interferometer, a low-temperature vacuum tank, a to-be-detected optical system, a standard plane mirror, an optical window, a six-dimensional adjustment device, a liquid nitrogen pipeline, a detection compensation mirror group, a flexible cold chain, a heat insulation sliding platform and a low-temperature cold platform. According to the wavefront detection system and method for the large-aperture reflection type low-temperature optical system, the low-temperature working environment of the to-be-detected optical system is realized by utilizing the low-temperature vacuum tank and the liquid nitrogen pipeline, and the wavefront change of the optical system after the optical system is reduced to the designed temperature is detected through the interferometer outside the low-temperature vacuum tank; and the adaptability and low-temperature performance parameters of the optical-mechanical structure of the optical system to the low-temperature environment are inspected.

Description

Technical Field

[0001] The present invention relates to an optical detection system and method, and particularly to a wavefront detection system and method for a large-aperture reflective cryogenic optical system. Background Art

[0002] With the development of infrared detection technology, high-sensitivity infrared detection has become one of the main research directions and has broad application prospects in fields such as thermal infrared remote sensing imaging, long-distance detection of dim targets, and deep-space infrared astronomical observations. For the long-distance detection of dim targets near room temperature, a large-aperture reflective optical system is required to collect target signals. However, the peak infrared radiation signal of the target overlaps with the infrared signal emitted by the optical system also at room temperature, and the target infrared signal is submerged in the self-radiation signal of the optical system, making it difficult to achieve long-distance detection of the target. By reducing the temperature of the large-aperture reflective optical system itself, the infrared radiation of the optical system itself can be effectively suppressed, which is a necessary means to achieve high-sensitivity infrared detection.

[0003] The large-aperture reflective optical system operates in a low-temperature environment. The system design first meets the requirements of system indicators under low-temperature conditions. The processing and detection of the mirror are carried out at room temperature. When the working environment temperature changes, the radius of curvature of the large-aperture mirror, the aspheric coefficient, the stress generated by the thermal expansion and contraction of the support structure, etc. will all change. However, it is still very difficult to process and align the large-aperture reflective optical system in a low-temperature environment. Therefore, a method is needed to detect the large-aperture reflective optical system after processing and alignment at room temperature, so that the system indicator parameters can meet the design requirements after entering the low temperature.

[0004] The existing detection of the surface shape of optical components is all carried out at room temperature. To achieve low temperature for the large-aperture reflective optical system, a vacuum environment is required to avoid condensation and contamination of water vapor, etc. Affected by factors such as material uniformity, low-temperature support method, and cold chain fixation, the large-aperture reflective optical system is prone to low-temperature deformation at low temperature, resulting in stress on the large-aperture reflective optical system and affecting the performance of the optical system, which cannot be directly evaluated at room temperature. Therefore, it is necessary to use low-temperature detection of the parameters of the large-aperture reflective optical system to evaluate the adaptability of the opto-mechanical structure of the large-aperture reflective optical system to the low-temperature environment and the low-temperature performance parameters. Summary of the Invention

[0005] To solve the problems existing in the above-mentioned prior art, the present invention provides a wavefront detection system and method for a large-aperture reflective cryogenic optical system, including an interferometer, a cryogenic vacuum chamber, a to-be-detected optical system, a standard flat mirror, an optical window, a six-dimensional adjustment device, a liquid nitrogen pipeline, a flexible cold chain, a cryogenic cold platform, and a detection compensation mirror group arranged on an insulating sliding platform;

[0006] The optical system to be measured is composed of a primary mirror, a secondary mirror and a large-aperture mirror support structure, with a minimum temperature of 80K. The primary mirror is arranged on the large-aperture mirror support structure, and the primary mirror and the large-aperture mirror support structure are symmetrically arranged on both sides of the secondary mirror.

[0007] The interferometer, the secondary mirror, the optical window, the detection compensator group, the secondary mirror and the reference flat mirror are coaxially arranged in sequence from left to right. The detection compensator is fixed on the six-degree-of-freedom adjustment device, and the six-degree-of-freedom adjustment device is arranged between the cryogenic cold platform and the optical window. The detection compensator and the six-degree-of-freedom adjustment device have the function of active heating temperature control. The reference flat mirror, the six-degree-of-freedom adjustment device and the optical system to be measured are installed on the same reference plane, and the working temperature is 20°C ± 3°C.

[0008] The cryogenic cold platform is symmetrically arranged on both sides of the detection compensator group. One end of the cryogenic cold platform is connected to the cryogenic vacuum tank through the liquid nitrogen pipeline, and the other end is connected to the large-aperture mirror support structure through the flexible cold chain.

[0009] The cryogenic cold platform is a universal platform, on which a non-contact radiation cooling plate is provided, and the working temperature range is 100K - 293K.

[0010] Further, the reference flat mirror has a two-dimensional adjustment function and an active heating temperature control function, and the working temperature is 20°C ± 3°C.

[0011] Further, the material of the optical window is sapphire, and the surface shape is better than 0.03λ (λ = 0.632μm).

[0012] Further, the load capacity of the heat-insulating sliding platform is greater than 1T.

[0013] A method for wavefront detection of a large-aperture reflective cryogenic optical system includes the steps of:

[0014] S1: The spherical standard lens of the interferometer f# ≤ R / D; the fixing method of the product to be measured is a stress-free support method.

[0015] S2: Build the optical path. The product to be measured is fixed on the vacuum platform through the test tooling, the compensator is controlled by the vacuum adjustment mechanism, and the interferometer is placed outside the vacuum tank.

[0016] S3: Close the vacuum tank and let the vacuum tank window enter the detection optical path.

[0017] S4: Positioning. For the positioning of the plane mirror angle, use a theodolite to measure the included angle between the optical reference mirror of the product under test and the standard plane mirror, and adjust the angle of the standard plane mirror to the theoretical value; for interferometer positioning, use an optical alignment tooling to determine the image plane position of the main optical system, and use the interferometer equipped with a standard lens to determine the position of the interferometer by the interference method; for compensator positioning, use the interference method to determine the position of the compensator.

[0018] S5: Set the parameters of the laser interferometer, and set the parameters of the laser interferometer according to the measurement plan.

[0019] S6: Fine adjustment. Adjust the translation and angular positions of the six-axis adjustment frame according to the interference pattern until the RMS of the product under test is better than 0.1λ (λ = 0.632μm).

[0020] S7: Start pumping the vacuum in the vacuum chamber. When the vacuum degree reaches 10 -3 Pa; then repeat S6, and record the surface shape in the vacuum and normal temperature state; compare with the data collected in S6 to eliminate the error of the vacuum chamber window.

[0021] S8: Start cooling by passing liquid nitrogen into the heat sink of the vacuum chamber. When the cooling rate of the mirror under test is 0.3 degrees / min and the measured point temperature reaches the target temperature, maintain it for 6 hours, and start measurement after stabilization;

[0022] Repeat step S6, record the surface shape in the vacuum and low temperature state, and compare with the data collected in S6 to eliminate the error of the change of the vacuum chamber window after pumping the vacuum.

[0023] S9: Detect the validity of the data and complete the interpretation.

[0024] S10: Cut off the power of the test equipment and let the test system return to room temperature.

[0025] In summary, the present invention has the following beneficial effects compared with the prior art:

[0026] The present invention provides a wavefront detection system and method for a large-aperture reflective cryogenic optical system. By detecting the wavefront parameters of the large-aperture reflective optical system at low temperature, it evaluates the adaptability of the opto-mechanical structure of the large-aperture reflective optical system to the low-temperature environment and the low-temperature performance parameters. It solves the problem that the large-aperture reflective optical system is easily deformed at low temperature due to factors such as material uniformity, low-temperature support method, and cold chain fixation, resulting in stress on optical components and affecting the performance of the optical system, and it cannot be directly evaluated at normal temperature. Description of the Drawings

[0027] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0028] Schematic diagram of the composition of a wavefront detection system and method for a large-aperture reflective cryogenic optical system.

[0029] Among them, the above-mentioned drawings include the following reference numerals:

[0030] 1. Interferometer; 2. Cryogenic vacuum chamber; 3. Optical system to be measured; 3-1. Primary mirror; 3-2. Secondary mirror; 3-3. Large-aperture mirror support structure; 4. Standard flat mirror; 5. Optical window; 6. Six-axis adjustment device; 7. Liquid nitrogen pipeline; 8. Detection compensation mirror group; 9. Flexible cold chain; 10. Heat-insulating sliding platform; 11. Cryogenic cold platform. Detailed implementation manners

[0031] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0032] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless otherwise clearly specified in the context, the singular form can also include the plural form. In addition, it should be understood that when the terms "include" and / or "comprise" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] Unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that, for the sake of convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but should be regarded as part of the authorization specification when appropriate. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that: similar reference numerals and letters indicate similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0034] See Figure 1As shown in the figure, the present invention provides a wavefront detection system and method for a large-aperture reflective cryogenic optical system. The present invention uses a cryogenic vacuum chamber 2 and a liquid nitrogen pipeline 7 to realize the cryogenic working environment of the optical system to be measured. The interferometer 1 outside the cryogenic vacuum chamber 2 is used to detect the wavefront change of the optical system after it is reduced to the designed temperature, and to test the adaptability of the opto-mechanical structure of the optical system to the cryogenic environment and the cryogenic performance parameters. Its main components include an interferometer 1, a cryogenic vacuum chamber 2, an optical system to be measured 3, a standard flat mirror 4, an optical window 5, a six-degree-of-freedom adjustment device 6, a liquid nitrogen pipeline 7, a detection compensation mirror group 8, a flexible cold chain 9, a heat-insulating sliding platform 10, and a cryogenic cold platform 11. Among them, the optical system to be measured 3 includes a primary mirror 3-1, a secondary mirror 3-2, and a large-aperture mirror support structure 3-3. The optical system to be measured 3 completes optical alignment and fixation at room temperature, completes thermal implementation according to the designed state, is installed on the heat-insulating sliding platform 10 through a tooling, and uses the flexible cold chain 9 to connect the cold chain installation interface on the back of the primary mirror 3-1 and the cryogenic cold platform 11. According to the method of self-collimation test optical system, the detection optical path is built. After the detection is completed at room temperature, the cryogenic vacuum chamber 2 is closed. After pumping to vacuum, the temperature of the optical system to be measured 3 is reduced to the designed temperature by using the cryogenic cold platform 11 through the flexible cold chain 9. The interferometer 1 emits a spherical wave, which forms an aspherical wave after passing through the vacuum chamber window and the detection compensator, makes the light incident perpendicularly on the measured system, is reflected by the secondary mirror 3-2 and the primary mirror 3-1 to form parallel light, and after being reflected on the surface of the standard flat mirror 4, returns to the interferometer 1 along the original optical path to form an interference image, completing the wavefront detection of the cryogenic system of the optical system.

[0035] The cryogenic cold platform 11 has a liquid nitrogen pipeline 7 connected to the cryogenic vacuum chamber 2, and the lowest temperature is 80K;

[0036] The detection compensator is fixed on the six-degree-of-freedom adjustment device 6. The six-degree-of-freedom adjustment device 6 meets the use conditions of the vacuum chamber. The detection compensator and the six-degree-of-freedom adjustment device 6 have an active heating and temperature control function, and the working temperature is 20°C ± 3°C;

[0037] The cryogenic cold platform 11 is a general platform, has a flexible cold chain 9 interface connected to the system to be measured, and at the same time has a non-contact radiation cooling plate, which meets the requirements of different test systems and meets the measurement temperature range of 100K to 293K of the optical system to be measured 3;

[0038] As a preference, the standard flat mirror 4 has a two-dimensional adjustment function, is installed in a heat-insulating manner, has an active heating and temperature control function, and the working temperature is 20°C ± 3°C;

[0039] As a preference, the material of the optical window 5 is sapphire, and the surface shape is better than 0.03λ (λ = 0.632μm);

[0040] As a preference, the load capacity of the heat-insulating sliding platform 10 is greater than 1T.

[0041] A method for wavefront detection of a large-aperture reflective cryogenic optical system, comprising the steps:

[0042] S1: The spherical standard lens of the interferometer 1 has f# ≤ R / D (R is the focal length of the product under test, D is the aperture of the product under test); the fixing method of the product under test. Select a stress-free support method to avoid the influence of mechanical stress on the surface shape of the product;

[0043] S2: Build the optical path. The product under test is fixed on the vacuum platform through the test fixture. The standard flat mirror 4 has two-dimensional adjustable functions for the interference auto-collimation of the product under test. The compensator is controlled by the vacuum adjustment mechanism, and the interferometer 1 is placed outside the vacuum chamber;

[0044] S3: Close the vacuum chamber and let the window of the vacuum chamber enter the detection optical path;

[0045] S4: Positioning. Position the flat mirror, measure the angle between the optical reference mirror of the product under test and the standard flat mirror 4 with a theodolite, and adjust the standard flat mirror 4 to the theoretical angle; Position the interferometer 1, determine the image plane position of the main optical system using the optical alignment fixture, and determine the position of the interferometer 1 using the interferometer method with the standard lens; Position the compensator, and determine the position of the compensator using the interferometer method;

[0046] S5: Set the parameters of the laser interferometer 1. Set the parameters of the laser interferometer 1 according to the measurement scheme, such as the effective aperture, interference factor, etc.;

[0047] S6: Fine adjustment. Adjust the translation and angular positions of the six-axis adjustment frame according to the interference pattern until the RMS of the product under test is better than 0.1λ (λ = 0.632μm);

[0048] S7: Start pumping the vacuum chamber, and the vacuum degree reaches 10 -3 Pa; then repeat S6, record the surface shape under vacuum and normal temperature conditions; compare with the data collected in S6 to eliminate the error of the vacuum chamber window;

[0049] S8: Inject liquid nitrogen into the heat sink of the vacuum chamber to start cooling. When the cooling rate of the mirror under test is 0.3 degrees / min and the measured point temperature reaches the target temperature, keep it for 6 hours, and start measuring after stabilization;

[0050] Repeat step S6, record the surface shape under vacuum and low temperature conditions, compare with the data collected in S6, and eliminate the error of the change of the vacuum chamber window after pumping the vacuum;

[0051] S9: Check the validity of the detection data and complete the interpretation;

[0052] S10: Cut off the power of the test equipment and let the test system return to room temperature.

[0053] During actual use, the implementation manner of the present invention is as follows: the optical system 3 to be measured is fixed by optical alignment at normal temperature, and the thermal implementation is completed according to the designed state. It is installed on the heat-insulating sliding platform 10 through a tooling, and the cold chain installation interface on the back of the primary mirror 3-1 is connected to the low-temperature cold platform 11 by using the flexible cold chain 9; according to the method of the autocollimation test optical system, the detection optical path is built. After the detection is completed at normal temperature, the low-temperature vacuum chamber 2 is closed and evacuated, and then the temperature of the optical system 3 to be measured is reduced to the designed temperature by using the low-temperature cold platform 11 through the flexible cold chain 9. The spherical wave is emitted by the interferometer 1, and after passing through the vacuum chamber window and the detection compensator, an aspherical wave is formed, so that the light is normally incident on the measured system. After being reflected by the secondary mirror 3-2 and the primary mirror 3-1, a parallel light is formed. After being reflected on the surface of the standard flat mirror 4, it returns to the interferometer 1 along the original optical path to form an interference image, so as to complete the wavefront detection of the low-temperature optical system.

[0054] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A wavefront detection system for a large-aperture reflective cryogenic optical system, characterized in that, It includes an interferometer (1), a cryogenic vacuum chamber (2), an optical system under test (3), a standard flat mirror (4), an optical window (5), a six-axis adjustment device (6), a liquid nitrogen pipeline (7), a flexible cold chain (9), a cryogenic cold platform (11), and a detection compensation mirror group (8) arranged on a heat-insulating sliding platform (10); The optical system under test (3) is composed of a primary mirror (3-1), a secondary mirror (3-2), and a large-aperture mirror support structure (3-3), with a minimum temperature of 80K; the primary mirror (3-1) is arranged on the large-aperture mirror support structure (3-3), and the primary mirror (3-1) and the large-aperture mirror support structure (3-3) are symmetrically arranged on both sides of the secondary mirror (3-2); The interferometer (1), the secondary mirror (3-2), the optical window (5), the detection compensation mirror group (8), the secondary mirror (3-2), and the standard flat mirror (4) are coaxially arranged in sequence from left to right; the detection compensator is fixed on the six-axis adjustment device (6), and the six-axis adjustment device (6) is arranged between the cryogenic cold platform (11) and the optical window (5); the detection compensator and the six-axis adjustment device (6) have an active heating temperature control function, and the standard flat mirror (4), the six-axis adjustment device (6), and the optical system under test (3) are installed on the same reference plane, with an operating temperature of 20°C ± 3°C; The cryogenic cold platform (11) is symmetrically arranged on both sides of the detection compensation mirror group (8), and one end of the cryogenic cold platform (11) is connected to the cryogenic vacuum chamber (2) through the liquid nitrogen pipeline (7), and the other end is connected to the large-aperture mirror support structure (3-3) through the flexible cold chain (9); The cryogenic cold platform (11) is a universal platform, on which a non-contact radiation cooling plate is provided, and the operating temperature range is 100K - 293K.

2. The wavefront detection system for a large-aperture reflective cryogenic optical system according to claim 1, characterized in that, The standard flat mirror (4) has a two-dimensional adjustment function and an active heating temperature control function, and the operating temperature is 20°C ± 3°C.

3. The wavefront detection system of the large-aperture reflective cryogenic optical system according to claim 1, characterized in that, The material of the optical window (5) is sapphire, and the surface shape is better than 0.03λ (λ = 0.632μm).

4. The wavefront detection system for a large-aperture reflective cryogenic optical system according to claim 1, characterized in that, The load capacity of the heat-insulating sliding platform (10) is greater than 1T.

5. A method for wavefront detection of a large-aperture reflective cryogenic optical system, which is realized by the large-aperture reflective cryogenic optical system wavefront detection system described in any one of claims 1 to 5, characterized in that, It includes the steps: S1: For the spherical standard lens of the interferometer (1), f# ≤ R / D; the fixing method of the tested product is a stress-free support method; S2: Build the optical path. The tested product is fixed on the vacuum platform through a test fixture, the compensator is controlled by a vacuum adjustment mechanism, and the interferometer (1) is placed outside the vacuum chamber; S3: Close the vacuum chamber and let the vacuum chamber window enter the detection optical path; S4: Positioning. For the flat mirror angle positioning, use a theodolite to measure the angle between the optical reference mirror of the tested product and the standard flat mirror (4), and adjust the angle of the standard flat mirror (4) to the theoretical value; for the interferometer (1) positioning, use an optical alignment fixture to determine the image plane position of the main optical system, and use the interferometer (1) with a standard lens to determine the position of the interferometer (1) by the interference method; for the compensator positioning, use the interference method to determine the position of the compensator; S5: Set the parameters of the laser interferometer (1), and set the parameters of the laser interferometer (1) according to the measurement scheme; S6: Fine-tuning. Adjust the translation and angular positions of the six-dimensional adjustment frame according to the interference pattern until the RMS of the product under test is better than 0.1λ (λ = 0.632μm); S7: Start evacuating the vacuum tank until the vacuum degree reaches 10 -3 Pa; then repeat S6 to record the surface shape at normal temperature under vacuum; compare with the data collected in S6 to eliminate the error of the vacuum tank window; S8: Start cooling by introducing liquid nitrogen into the vacuum chamber heat sink. When the cooling rate of the mirror under test is 0.3 degrees / min and the temperature at the measurement point reaches the specified temperature, maintain for 6 hours and start measurement after stabilization; Repeat step S6, record the surface shape in the vacuum and low-temperature state, compare with the data collected in S6, and eliminate the error caused by the change of the vacuum chamber window after evacuation; S9: Detect the validity of the data and complete the interpretation; S10: Power off the test equipment and let the test system return to room temperature.

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