Refraction-reflection type low-temperature long-wave infrared optical system

Abstract

The invention discloses a catadioptric low-temperature long-wave infrared optical system, which relates to the technical field of long-wave infrared optical systems, and is characterized in that the optical system adopts a secondary imaging structure with an intermediate image plane, and consists of a coaxial RC main optical system, a field lens, a secondary imaging rear optical path, a Dewar window and an optical filter. The optical system has the advantages of high external stray light and internal heat radiation stray light suppression capability, high long-wave infrared detection sensitivity, compact structure, small size, light weight and low resource requirements on a satellite platform.

Description

Technical Field

[0001] The invention relates to the technical field of long-wave infrared optical systems, and more specifically, to a refraction-type low-temperature long-wave infrared optical system. Background Art

[0002] With the widespread 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 near-space dim target detection, the detection sensitivity of traditional long-wave infrared optical systems with room temperature working temperature is low, and its own thermal radiation stray light will annihilate the target signal light, resulting in failure to detect. In view of this, the present invention proposes a refraction-type low-temperature long-wave infrared optical system. Summary of the invention

[0003] The purpose of the present invention is to provide a refraction-type low-temperature long-wave infrared optical system to effectively suppress the thermal radiation of the long-wave optical system itself.

[0004] The above technical objectives of the present invention are achieved through the following technical solutions: a refractive index low-temperature long-wave infrared optical system, which adopts a secondary imaging structure, and the optical system is provided with an RC main optical system, a field lens, a secondary imaging rear optical path, a Dewar window and a filter in sequence from the object plane to the image plane.

[0005] The present invention is further configured as follows: the RC primary optical system is a hyperbolic reflector combination system, which is composed of a primary reflector, a secondary reflector and a supporting structure thereof, and the primary reflector, the secondary reflector and the supporting structure thereof are all made of SIC material.

[0006] The present invention is further configured such that: the field lens is a meniscus lens with positive optical power.

[0007] The present invention is further configured as follows: the secondary imaging rear optical path is composed 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.

[0008] The present invention is further configured as follows: the secondary imaging rear optical path is composed 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.

[0009] The present invention is further configured as follows: a field stop is provided at the primary image plane of the optical system to suppress stray light emitted from the field of view of the optical system, and a Rio stop is provided at the exit pupil position of the optical system to suppress self-radiated stray light inside the optical system.

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

[0011] In summary, the present invention has the following beneficial effects: the refractive low-temperature long-wave infrared optical system of the present invention has strong suppression capability for stray light outside the field of view and self-thermal radiation stray light, and high detection sensitivity; the optical system adopts a coaxial symmetric form and performs an optical-mechanical material matching design, which is conducive to eliminating low-temperature deformation; the optical system has a compact structure and convenient thermal control implementation; the main optical system and the secondary imaging rear optical path are modularly designed, which is conducive to the installation, testing and maintenance of the low-temperature optical system. The optical system has the advantages of compact structure, small size, light weight, high detection sensitivity and good low-temperature imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a light path diagram of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention; Figure 2 It is a wavefront diagram of a main optical system of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention; Figure 3 It is a wavefront diagram of an optical path system after secondary imaging of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention; Figure 4 It is a point diagram of imaging spots of different fields of view of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention; Figure 5 This is an MTF graph of a refraction-type low-temperature long-wave infrared optical system in an embodiment of the present invention; Figure 6 This is an energy concentration curve of a refractive-type low-temperature long-wave infrared optical system in an embodiment of the present invention; Figure 7 It is a distortion diagram of a catadioptric low-temperature long-wave infrared optical system in an embodiment of the present invention.

[0013] In the figure: 1. primary reflector; 2. secondary reflector; 3. field mirror; 4. first infrared lens; 5. second infrared lens; 6. third infrared lens; 7. fourth infrared lens; 8. Dewar window; 9. filter. DETAILED DESCRIPTION

[0014] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] Example

[0016] A catadioptric low temperature long wave infrared optical system, such as Figure 1 As shown, it includes a main reflector 1, a secondary reflector 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 imaged at the primary image plane after being converged by the main reflector 1 and the secondary reflector 2. The field lens 3 is placed on the left side of the primary image plane to compress the light beam to reduce the size of the infrared lens in the optical path after the secondary imaging; the light emitted from the primary image plane is converged into the long-wave infrared dewar after being acted upon by the first infrared lens 4, the second infrared lens 5, the third infrared lens 6 and the fourth infrared lens 7, and reaches the long-wave infrared photosensitive surface after being transmitted through the dewar window 8 and the filter 9.

[0017] The folding-reflecting cryogenic long-wave optical system was modularly designed. During the optical design process, the wavefront of the main optical system and the optical path after secondary imaging were constrained. The main optical system and the optical path after secondary imaging can be used as separate modules to improve imaging, which is beneficial to the integration, testing and maintenance of the cryogenic optical system.

[0018] The main optical system adopts the RC structure, which consists of a main reflector 1, a secondary reflector 2 and their supporting structure. The main reflector 1, the secondary reflector 2 and their supporting structure are all designed with SIC materials for athermalization and low-temperature deformation elimination. The main reflector 1 and the secondary reflector 2 are both hyperbolic reflectors. The specific parameters are listed in Table 1. The curvature radius and interval units in the table are mm. The focal length of the main system is 2500 mm, and the imaging quality reaches the diffraction limit. Figure 2 It is the wavefront diagram of the main optical system. The RMS of the main system wavefront is 0.0007l (l=10μm).

[0019] Table 1 Specific parameters of primary reflector and secondary reflector Optical component name Radius of curvature interval Cone coefficient Primary reflector 1076.2 400 -1.018 Secondary reflector 352.09 640.7 -2.546 The field lens 3 is a meniscus lens with positive focal length bent toward the object. It is made of germanium and its main function is to compress the light beam size. It is supported by a titanium alloy flexible structure to eliminate low-temperature deformation.

[0020] The optical path after secondary imaging 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 focal meniscus lens made of zinc selenide material, and is bent toward the object side. The second infrared lens 5 is a positive focal meniscus lens made of germanium material, and is bent toward the image side. The third infrared lens 6 is a positive focal meniscus lens made of zinc selenide material, and the fourth infrared lens 7 is a positive focal meniscus lens made of germanium material. The third infrared lens 6 and the fourth infrared lens 7 are both bent toward the object side. The above lenses are all supported by a titanium alloy flexible structure to eliminate low-temperature deformation.

[0021] After secondary imaging, the imaging quality of the optical path reaches the diffraction limit. Figure 3 It is the wavefront diagram of the optical path after secondary imaging. The system wavefront RMS is 0.0357l (l=10μm).

[0022] In the optical path after secondary imaging, the second infrared lens 5 and the third infrared lens 6 are even-high-order aspheric lenses, and the expression of the aspheric surface is:

[0023] Wherein, Z is the optical mirror sag along the optical axis; c is the curvature of the optical mirror surface; r is the mirror aperture perpendicular to the optical axis; is the cone coefficient; a 4 、a 6 、a 8 、a 10 is the high-order non-curved surface coefficient; The specific parameters of each lens in the optical path after secondary imaging of the embodiment of the present invention are listed in Table 2. The units of the curvature radius and thickness in the table are mm.

[0024] Table 2 Specific parameters of each lens in the optical path after secondary imaging

[0025] After the light is converged by the primary reflector 1 and the secondary reflector 2, it is focused by the field lens to form a primary image plane. A field stop is set at the primary image plane to suppress stray light outside the field of view. After secondary imaging, the optical path 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.

[0026] The Dewar window 8 and the filter 9 are both flat glass with no optical power.

[0027] In this embodiment, the optical element is cooled to a low temperature of 180K-120K by a large-capacity Stirling refrigerator and a high-thermal-conductivity flexible graphene cold chain to suppress the thermal radiation stray light of the long-wave infrared optical system and achieve high-sensitivity long-wave infrared detection.

[0028] Figure 4 This is the spot diagram of the optical system of this embodiment. The RMS diameter of the imaging spot in each field of view is less than 13 μm, the spot is within the diffraction Airy disk, and the imaging quality reaches the diffraction limit level; Figure 5 This is the MTF curve of the optical system of this embodiment. At the Nyquist frequency of 20lp / mm, the MTF of each field of view is greater than 0.43; Figure 6is an energy concentration curve of the optical system of this embodiment. In a pixel with a size of 25 μm, 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 of this embodiment. The maximum distortion of the optical system is 1.5%.

[0029] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A catadioptric low-temperature long-wave infrared optical system, characterized by: The optical system adopts a secondary imaging structure, and the optical system is provided with an RC main optical system, a field lens, a secondary imaging rear optical path, a Dewar window and a filter in sequence from the object plane to the image plane.

2. The catadioptric low-temperature long-wave infrared optical system according to claim 1, characterized in that: The RC main optical system is a hyperbolic reflector combination system, which is composed of a main reflector, a secondary reflector and a supporting structure thereof. The main reflector, the secondary reflector and the supporting structure thereof are all made of SIC material.

3. The catadioptric low-temperature long-wave infrared optical system according to claim 1, characterized in that: The field lens is a meniscus lens with positive optical power.

4. The catadioptric low-temperature long-wave infrared optical system according to claim 1, characterized in that: The secondary imaging rear optical path is composed 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 arranged in sequence from the object plane to the image plane.

5. The catadioptric low-temperature long-wave infrared optical system according to claim 4, characterized in that: The first infrared lens, the second infrared lens, the third infrared lens and the fourth infrared lens all adopt a titanium alloy flexible support structure.

6. The catadioptric low-temperature long-wave infrared optical system according to claim 1, characterized in that: A field stop is arranged at the primary image plane of the optical system to suppress stray light emitted from the field of view of the optical system, and a Rio stop is arranged at the exit pupil position of the optical system to suppress self-radiated stray light inside the optical system.

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

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