A catadioptric low-temperature long-wave infrared optical system

Abstract

The present invention discloses a catadioptric low-temperature long-wave infrared optical system, which relates to the technical field of long-wave infrared optical systems. The key points of its technical solution are as follows: The optical system adopts a secondary imaging structure with an intermediate image plane and is composed of a coaxial RC main optical system, a field lens, an optical path after secondary imaging, a Dewar window, and a filter. The advantages of this optical system are strong suppression capabilities for external stray light and internal thermal radiation stray light, high sensitivity for long-wave infrared detection, and a compact structure, small volume, light weight, and less resource requirements for satellite platforms.

Description

Technical Field

[0001] The present invention relates to the technical field of long-wave infrared optical systems, and more specifically, it relates to a catadioptric cryogenic long-wave infrared optical system. Background Art

[0002] With the wide application of long-wave infrared optical remote sensing technology in the fields of agricultural and forestry monitoring, disaster prevention and mitigation, astronomical observation, and space military target detection, the detection sensitivity requirements for long-wave infrared optical payloads are getting higher and higher. Especially in the field of detecting dim targets in the near space, the detection sensitivity of traditional long-wave infrared optical systems with a normal working temperature is low, and their own thermal radiation stray light will obscure the target signal light, resulting in inability to detect. In view of this, the present invention proposes a catadioptric cryogenic long-wave infrared optical system. Summary of the Invention

[0003] The purpose of the present invention is to provide a catadioptric cryogenic long-wave infrared optical system to effectively suppress the self-thermal radiation of the long-wave optical system.

[0004] The above technical purpose of the present invention is achieved through the following technical solutions: A catadioptric cryogenic long-wave infrared optical system, the optical system adopts a secondary imaging structure, and the optical system is sequentially provided with an RC main optical system, a field lens, a post-secondary imaging optical path, a Dewar window, and a filter from the object plane to the image plane.

[0005] The present invention is further provided as: The RC main optical system is a hyperbolic mirror combination system, which consists of a primary mirror, a secondary mirror, and their support structures. The primary mirror, the secondary mirror, and their support structures are all made of SIC material.

[0006] The present invention is further provided as: The field lens is a meniscus lens with a positive optical power.

[0007] The present invention is further provided as: The post-secondary imaging optical path consists of four long-wave infrared lenses, and a first infrared lens, a second infrared lens, a third infrared lens, and a fourth infrared lens are sequentially arranged from the object plane to the image plane direction.

[0008] The present invention is further provided as: The post-secondary imaging optical path consists of four long-wave infrared lenses, and a first infrared lens, a second infrared lens, a third infrared lens, and a fourth infrared lens are sequentially arranged from the object plane to the image plane direction.

[0009] The present invention is further provided as: A field stop is arranged at the primary image plane of the optical system to suppress the out-of-field stray light of the optical system, and a Lyot stop is arranged at the exit pupil position of the optical system to suppress the self-radiation stray light inside the optical system.

[0010] The present invention is further configured such that the operating temperature of the optical system is room temperature of 300K and low temperature of 180K - 120K, and good imaging quality can be obtained at both room temperature and low temperature.

[0011] In summary, the present invention has the following beneficial effects: A catadioptric low-temperature long-wave infrared optical system of the present invention has strong suppression ability for off-field stray light and self-thermal radiation stray light, and high detection sensitivity; the optical system adopts a coaxial symmetric form and has an optical-mechanical material matching design, which is beneficial to eliminating low-temperature deformation; the optical system has a compact structure and convenient thermal control implementation; the main optical system and the optical path after secondary imaging are modularly designed, which is beneficial to the installation, adjustment, testing and maintenance of the low-temperature optical system. This optical system has the advantages of a compact structure, small size, light weight, high detection sensitivity and good low-temperature imaging quality. Description of the Drawings

[0012] Figure 1 is the optical path diagram of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention;

[0013] Figure 2 is the wavefront diagram of the main optical system of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention;

[0014] Figure 3 is the wavefront diagram of the optical path system after secondary imaging of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention;

[0015] Figure 4 is the spot diagram of the imaging spots of different fields of view of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention;

[0016] Figure 5 is the MTF curve graph of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention;

[0017] Figure 6 is the energy concentration curve of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention;

[0018] Figure 7 is the distortion diagram of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention.

[0019] In the figure: 1, main reflector; 2, secondary reflector; 3, field lens; 4, first infrared lens; 5, second infrared lens; 6, third infrared lens; 7, fourth infrared lens; 8, Dewar window; 9, filter. Detailed Embodiments

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] Embodiment

[0022] A catadioptric low-temperature long-wave infrared optical system, as Figure 1 shown, includes a primary mirror 1, a secondary mirror 2, a field lens 3, a first infrared lens 4, a second infrared lens 5, a third infrared lens 6, a fourth infrared lens 7, a Dewar window 8, and a filter 9. The target light is converged by the primary mirror 1 and the secondary mirror 2 and imaged at the primary image plane. A field lens 3 is placed on the left side of the primary image plane to compress the light beam, so as to reduce the size of the infrared lens in the optical path after the secondary imaging; the light emitted from the primary image plane passes through the first infrared lens 4, the second infrared lens 5, the third infrared lens 6, and the fourth infrared lens 7 and is converged into the long-wave infrared Dewar, and reaches the long-wave infrared photosensitive surface after passing through the Dewar window 8 and the filter 9.

[0023] The catadioptric low-temperature long-wave optical system is modularly designed. During the optical design process, the wavefronts of the main optical system and the optical path after the secondary imaging are constrained. The main optical system and the optical path after the secondary imaging can be used as separate modules to improve imaging, which is beneficial to the integration, testing, and maintenance of the low-temperature optical system.

[0024] The main optical system adopts the RC structure form and is composed of the primary mirror 1, the secondary mirror 2, and their support structures. The primary mirror 1, the secondary mirror 2, and their support structures are all designed for athermalization and low-temperature deformation elimination using SIC materials. The primary mirror 1 and the secondary mirror 2 are both hyperbolic mirrors. The specific parameters are listed in Table 1. The unit of the radius of curvature and the interval in the table is mm. The focal length of the main system is 2500 mm, and the imaging quality reaches the diffraction limit. Figure 2 is the wavefront diagram of the main optical system, and the RMS of the wavefront of the main system is 0.0007l (l = 10 μm).

[0025] Table 1 Specific parameters of the primary mirror and the secondary mirror

[0026] Optical element name Radius of curvature Spacing Conic coefficient Primary mirror 1076.2 400 -1.018 Secondary mirror 352.09 640.7 -2.546

[0027] The field lens 3 is a meniscus lens with a positive optical power bent towards the object side. The material is germanium. Its main function is to compress the light beam size and is supported by a titanium alloy flexible structure to eliminate low-temperature deformation.

[0028] After secondary imaging, the optical path is composed of the first infrared lens 4, the second infrared lens 5, the third infrared lens 6, and the fourth infrared lens 7, and its magnification is 0.48. The first infrared lens 4 is a negative meniscus lens made of zinc selenide material and bent towards the object side. The second infrared lens 5 is a positive meniscus lens made of germanium material and bent towards the image side. The third infrared lens 6 is a positive meniscus lens made of zinc selenide material, and the fourth infrared lens 7 is a positive meniscus lens made of germanium material. Both the third infrared lens 6 and the fourth infrared lens 7 are bent towards the object side. The above lenses are all supported by a titanium alloy flexible structure to eliminate low-temperature deformation.

[0029] The imaging quality of the optical path after secondary imaging reaches the diffraction limit. Figure 3 is the wavefront diagram of the optical path after secondary imaging, and the system wavefront RMS is 0.0357l (l = 10μm).

[0030] In the optical path after secondary imaging, the second infrared lens 5 and the third infrared lens 6 are even high-order aspherical lenses, and the expression of the aspherical surface is:

[0031]

[0032] Among them, Z is the sagittal height of the optical mirror surface along the optical axis direction;

[0033] c is the curvature of the optical mirror surface;

[0034] r is the mirror aperture perpendicular to the optical axis direction;

[0035] is the conic coefficient;

[0036] a4, a6, a8, a 10 are the high-order aspheric coefficients;

[0037] The specific parameters of each lens in the optical path after secondary imaging in the embodiment of the present invention are listed in Table 2. The unit of the radius of curvature and the thickness in the table is mm.

[0038] Table 2 Specific parameters of each lens in the optical path after secondary imaging

[0039]

[0040] The light rays are converged by the primary mirror 1 and the secondary mirror 2 and then focused by the field lens to form a primary image plane. A field stop is set at the primary image plane to suppress off-axis stray light. The optical path after secondary imaging images the primary image plane onto the photosensitive surface of the detector in the dewar and images the exit pupil of the main optical system to the position of the dewar cold stop. The cold stop matching efficiency is 100%, which can effectively suppress the thermal radiation and scattered stray light of the mechanical support structure.

[0041] Both the dewar window 8 and the filter 9 are plano-glass with no optical power.

[0042] In this embodiment, a large-cooling-capacity Stirling refrigerator and a high-thermal-conductivity flexible graphene cold chain are used to cool the optical element to a low temperature of 180K - 120K, so as to suppress the thermal radiation stray light of the long-wave infrared optical system and achieve high-sensitivity long-wave infrared detection.

[0043] Figure 4 This is the spot diagram of the optical system in this embodiment. The RMS diameter of the imaging spot in each field of view is less than 13μm, the spot is within the diffraction Airy disk, and the imaging quality reaches the diffraction limit level. Figure 5 This is the MTF curve graph of the optical system in this embodiment. At the Nyquist frequency of 20 lp / mm, the MTF of each field of view is greater than 0.43. Figure 6 This is the energy concentration curve graph of the optical system in this embodiment. Within a pixel with a size of 25μm, the energy concentration of each field of view is greater than 0.61. Figure 7 This is the full-field distortion diagram of the optical system in this embodiment. The maximum distortion of this optical system is 1.5%.

[0044] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. 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 catadioptric low-temperature long-wave infrared optical system, characterized in that: The optical system adopts a secondary imaging structure. From the object plane to the image plane, the optical system is successively provided with an RC main optical system, a field lens, an optical path after secondary imaging, a Dewar window, and a filter. The RC main optical system is a hyperbolic mirror combination system, which consists of a primary mirror, a secondary mirror, and their support structures. The primary mirror, the secondary mirror, and their support structures are all made of SIC material. The field lens is a meniscus lens with positive optical power. The optical path after secondary imaging consists of four long-wave infrared lenses. From the object plane to the image plane direction, a first infrared lens, a second infrared lens, a third infrared lens, and a fourth infrared lens are successively provided. The first infrared lens is a meniscus lens with negative optical power made of zinc selenide material and bent towards the object side. The second infrared lens is a meniscus lens with positive optical power made of germanium material and bent towards the image side. The third infrared lens is a meniscus lens with positive optical power made of zinc selenide material. The fourth infrared lens is a meniscus lens with positive optical power made of germanium material. Both the third infrared lens and the fourth infrared lens are bent towards the object side. The target light rays are converged by the primary mirror and the secondary mirror and imaged at the primary image plane. A field lens is placed on the left side of the primary image plane to compress the light beam. A field stop is arranged at the primary image plane of the optical system to suppress the stray light outside the field of view of the optical system. A Lyot stop is arranged at the exit pupil position of the optical system to suppress the self-radiation stray light inside the optical system.

2. The catadioptric low temperature long wave infrared optical system according to claim 1, characterized in that: The infrared lens adopts a titanium alloy flexible support structure.

3. The catadioptric low-temperature long-wave infrared optical system according to claim 1, characterized in that: The operating temperature of the optical system is room temperature 300K and low temperature 180K - 120K.

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