Long-wave infrared area scan optical system

Abstract

The application discloses a long-wave infrared area array scanning optical system, which comprises a telescope group, a scanning galvanometer, a first imaging group and an image plane which are sequentially arranged from an object direction to an image direction; the telescope group comprises a primary mirror, a secondary mirror, a first collimating mirror group, a first turning mirror group and a second collimating mirror group which are sequentially arranged from the object direction to the image direction; the scanning galvanometer has a fixed state and a return scanning state which moves towards or away from the second collimating mirror group; light is folded through the primary mirror, the secondary mirror, the first turning mirror group and the scanning galvanometer; the working wave band of the long-wave infrared area array scanning optical system is 7.7-10.5 microns, the focal length is 600 mm, and the F number ranges from 2 to 5.5. The light is folded for multiple times in the transmission process, the design is flexible, and it is beneficial to large field of view and compact design.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical systems, in particular to a long-wave infrared area array scanning optical system. BACKGROUND

[0002] In the existing long-wave infrared scanning optical system for a search and tracking system, one is to use a long-wave linear array 288*4 refrigeration type detector, although it can realize all-around scanning imaging, but the integration time is limited by the scanning rate, and the time spent on each pixel is usually in the order of tens of microseconds, so the output signal strength is low, and the signal-to-noise ratio is limited. In practical application, the detection capability of the target, especially the detection capability of the remote target, has great limitations.

[0003] Another is to use a staring type area array focal plane detector, and the integration time is much longer, which is in the order of milliseconds, so the detection capability is greatly improved. Under normal circumstances, the field of view of the staring type area array detector is limited. In order to improve the action distance, the focal length of the general staring type infrared imaging system is as long as possible to obtain a smaller instantaneous field of view. This results in that the field of view cannot cover the required airspace. If the multi-area array detector is used to divide the field of view and stare, the volume, mass and cost of the system will be greatly increased. Therefore, the continuous scanning type area array imaging system has application value. However, the scanning of the continuous scanning type area array imaging system in the integration time will cause the relative motion between the focal plane and the scene, resulting in tailing and making the image blurred.

[0004] Therefore, how to optimize the long-wave infrared scanning optical system is still the content that the person skilled in the art needs to continuously study. SUMMARY

[0005] The main purpose of the present application is to provide a long-wave infrared area array scanning optical system, which has the design characteristics of large aperture and long focal length, and the light is folded several times in the transmission process. The scanning galvanometer is introduced in the parallel light path, and the scanning galvanometer swings in the opposite direction at a certain rate within the integration time of the area array detector, so as to compensate for the change of the azimuth field of view.

[0006] In order to achieve the above purpose, the present application provides a long-wave infrared area array scanning optical system, which comprises a telescope group, a scanning galvanometer, a first imaging group and an image plane arranged in sequence from the object direction to the image direction. The telescope group comprises a primary mirror, a secondary mirror, a first collimating mirror group, a first folding mirror group and a second collimating mirror group arranged in sequence from the object direction to the image direction. The scanning galvanometer has a fixed state and a return sweep state which moves towards or away from the second collimating mirror group. The light is folded through the primary mirror, the secondary mirror, the first folding mirror group and the scanning galvanometer.

[0007] The working wave band of the long-wave infrared area array scanning optical system is 7.7-10.5 microns, the focal length is 600 mm, and the F number is in the range of 2F5.5.

[0008] Optionally, the primary mirror is a negative focal length meniscus mirror, and the secondary mirror is a negative focal length meniscus mirror.

[0009] Optionally, the first collimating lens group comprises a first collimating lens, a second collimating lens and a third collimating lens arranged in order from the object side to the image side.

[0010] The first collimating lens is a negative focal length meniscus aspheric chalcogenide lens curved toward the image side, the second collimating lens is a negative focal length meniscus aspheric germanium lens curved toward the object side, and the third collimating lens is a positive focal length meniscus aspheric germanium lens curved toward the object side.

[0011] Optionally, the first turning mirror group comprises a first mirror, a fourth collimating lens and a second mirror arranged in order from the object side to the image side, the second mirror and the first mirror are arranged at an angle with the optical axis for turning the optical path, and the first mirror and the first collimating lens group are arranged along the same straight line.

[0012] Optionally, the angle between the first mirror and the second mirror and the optical axis is 45°; and / or,

[0013] The fourth collimating lens is a positive focal length meniscus chalcogenide lens curved toward the image side.

[0014] Optionally, the second collimating lens group comprises a fifth collimating lens and a sixth collimating lens arranged in order from the object side to the image side, the fifth collimating lens is a negative focal length meniscus aspheric germanium lens curved toward the object side, and the sixth collimating lens is a positive focal length meniscus aspheric chalcogenide lens curved toward the object side.

[0015] Optionally, the first imaging group comprises a first lens, a second lens, a third mirror, a third lens and a fourth lens arranged in order from the object side to the image side.

[0016] The first lens is a positive focal length meniscus aspheric germanium lens curved toward the image side, the second lens is a positive focal length meniscus aspheric germanium lens curved toward the object side, the angle between the third mirror and the optical axis is 45° for turning the optical path, the third lens is a positive focal length meniscus aspheric germanium lens curved toward the image side, and the fourth lens is a positive focal length double-convex spherical germanium lens.

[0017] Optionally, the primary mirror is located between the first collimating lens and the first turning mirror group.

[0018] Optionally, the direction in which light enters the telescope assembly is opposite to the direction in which light enters the image plane.

[0019] Optionally, the scanning galvanometer is at an angle of 45° to the optical axis.

[0020] In the technical solution of this invention, the imaging beam from the object side is refracted by the primary mirror and secondary mirror, then passes through the first collimating mirror group and enters the first folding mirror group where it is refracted again. After passing through the second collimating mirror group, it is refracted by the scanning galvanometer and enters the first imaging group, finally forming an image on the image plane. The scanning galvanometer is designed to achieve optical image stabilization through a catadioptric structure. Introduced in the parallel optical path, the scanning galvanometer swings in opposite directions at a specific rate during the integration time of the area array detector to compensate for changes in the azimuth field of view. Specifically, the scanning galvanometer is located in the parallel optical path and has two working states. In the fixed state, it mainly performs optical path reversal, and the optical system is in a long-wavelength staring tracking mode. In the retrace state, the image plane imaging is in focus and can be applied to long-wavelength area array peripheral scan search modes. This structure features a large aperture and long focal length design. The multiple refractings during light transmission help reduce the overall volume and compress the spatial dimensions, resulting in a flexible overall design. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 A schematic diagram of an embodiment of the long-wavelength infrared external array scanning optical system provided by the present invention;

[0023] Figure 2 for Figure 1 MTF curve of a medium- and long-wave infrared external array scanning optical system at +20℃;

[0024] Figure 3 for Figure 1 MTF curve of a medium- and long-wave infrared external array scanning optical system at -55℃;

[0025] Figure 4 for Figure 1 MTF curve of a medium- and long-wave infrared external array scanning optical system at +70℃.

[0026] Explanation of icon numbers:

[0027]

[0028]

[0029] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments in combination with the accompanying drawings. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0031] It should be noted that if the directionality indication is involved in the embodiments of the present application, the directionality indication is only used to explain the relative position relationship, movement condition and the like between components in a certain specific posture, and if the specific posture changes, the directionality indication also changes accordingly.

[0032] In addition, if the description of "first", "second" and the like is involved in the embodiments of the present application, the description of "first", "second" and the like is only for the description purpose, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one feature. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person of ordinary skill in the art can realize it, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is also not within the protection scope required by the present application.

[0033] Since the airborne infrared search and tracking system is mainly used for air combat, it mainly detects and tracks the lateral or head-on enemy aircraft. In the front or side front of the aircraft, most of the short-wave radiation of the aircraft engine is blocked by the aircraft body, and the sun's short-wave infrared reflected by the aircraft body is very weak. At the same time, considering the day and night detection requirements, the airborne infrared search and tracking system cannot use the short-wave infrared band. Similarly, for the front or side front of the enemy aircraft, most of the exhaust flow of the engine nozzle is also blocked, and the use of the medium-wave infrared band for detection will also be greatly affected. As forward detection, the skin radiation is mainly long-wave radiation, and the best solution is to use the long-wave infrared band. Therefore, the airborne infrared search and tracking system selects long-wave infrared as the working band of the system.

[0034] In the prior art, in 2012, the Xi'an Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences designed a large field of view and large relative aperture long-wave infrared scanning optical system, the focal length of the system is 21.5 mm, F / 1.67, and a long-wave linear array 288x4 refrigeration type detector is matched (Fan Zheyuan, Yang Hongtao, etc. Large field of view and large relative aperture long-wave infrared scanning optical system design, Infrared and Laser Engineering, 2012 41(10): 2740-2744).

[0035] In 2013, the Luoyang Institute of Electro-Optics of China Aviation Industry Group designed a long-wave infrared double-view scanning optical system, the focal length of the system is 165 / 66 mm, F / 1.67, and a long-wave linear array 288x4 refrigeration type detector is matched (Qiao Mingxia, Zeng Wei, etc. Long-wave infrared double-view scanning optical system, Electro-Optics and Control, 2013 20(3): 77-80).

[0036] It can be seen that the long-wave infrared scanning optical systems for search and tracking systems reported at present all adopt long-wave linear array 288x4 refrigeration type detectors, although all-around scanning imaging can be realized, but the integration time is limited by the scanning rate, and the time spent on each pixel is usually in the order of tens of microseconds, so the output signal strength is low, and the signal-to-noise ratio is limited. Therefore, in actual application, the detection capability of the target, especially the detection capability of the remote target, has great limitations. The integration time of the staring type area array focal plane detector is much longer, in the order of milliseconds, so the detection capability is greatly improved. Under normal circumstances, the field of view of the staring type area array detector is limited. In order to improve the action distance, the focal length of the general staring type infrared imaging system is as long as possible to obtain a smaller instantaneous field of view. This results in that the field of view cannot cover the required airspace. If the multi-area array detector is used to divide the field of view and stare, the volume and mass of the system will be greatly increased, and the cost is expensive. Therefore, the continuous scanning type area array detector imaging system has application value. However, the scanning of the continuous scanning type area array imaging system in the integration time will cause relative motion between the focal plane and the scene, causing tailing and making the image blurred. This is the biggest obstacle for the application of the area array detector in the scanning system.

[0037] In view of this, the present application provides a long-wave infrared area array scanning optical system, Figures 1 to 4 The present application provides an embodiment of the long-wave infrared area array scanning optical system.

[0038] Please refer to Figure 1The long-wave infrared area array scanning optical system 100 comprises, sequentially arranged from the object direction to the image direction, a telescope group, a scanning galvanometer 2, a first imaging group 3, and an image plane, the telescope group comprises, sequentially arranged from the object direction to the image direction, a primary mirror 11, a secondary mirror 12, a first collimating mirror group, a first turning mirror group, and a second collimating mirror group, the scanning galvanometer 2 has a fixed state and a backswing state of moving towards the direction close to or away from the second collimating mirror group, and light rays are folded through the primary mirror 11, the secondary mirror 12, the first turning mirror group, and the scanning galvanometer 2; wherein the working waveband of the long-wave infrared area array scanning optical system 100 is long-wave 7.7-10.5 μm, the focal length is 600 mm, and the F number ranges from 2 to 5.5.

[0039] In the technical scheme of the present application, the imaging light beams from the object direction are folded through the primary mirror 11 and the secondary mirror 12, then enter the first turning mirror group after passing through the first collimating mirror group, are folded again, pass through the second collimating mirror group, are turned through the scanning galvanometer 2 to enter the first imaging group 3, and are finally imaged on the image plane. The scanning galvanometer 2 is designed to realize optical image stabilization through the catadioptric structure, the scanning galvanometer 2 is introduced into the parallel light path, and the scanning galvanometer 2 swings at a specific rate in the opposite direction within the integration time of the area array detector to compensate for the change of the azimuth field of view. Specifically, the scanning galvanometer 2 is located in the parallel light path and has two working states, in the fixed state, the light path is mainly turned, and the optical system is in the long-wave staring tracking mode, and in the backswing state, the image plane is imaged without defocus, and the optical system can be applied to the long-wave area array circumferential scanning search mode. The structure has the design characteristics of large aperture and long focal length, and the light rays are folded multiple times in the transmission process, which is beneficial to reducing the overall volume, compressing the spatial size, and improving the flexibility of the overall design.

[0040] Specifically, the primary mirror 11 is a negative focal power meniscus mirror, and the secondary mirror 12 is a negative focal power meniscus mirror.

[0041] Since the focal length of the optical system is long, the primary mirror 11 and the secondary mirror 12 bear the main optical power, and the corresponding collimating mirror group bears the auxiliary optical power. The primary mirror 11 and the secondary mirror 12 are preferably made of low-expansion microcrystalline glass. Considering the athermalization design of the system, the best support material between the primary mirror 11 and the secondary mirror 12 is indium steel with small thermal expansion coefficient, and the best mirror barrel material, spacer ring material, and support mirror barrel material in the transmission assembly are all aluminum, so that good athermalization effect can be achieved.

[0042] In order to ensure the collimation effect of the light after the light is folded, the first collimating lens group comprises, in order from the object side to the image side, a first collimating lens 13, a second collimating lens 14 and a third collimating lens 15; wherein the first collimating lens 13 is a negative focal length meniscus aspherical chalcogenide lens curved toward the image side, the second collimating lens 14 is a negative focal length meniscus aspherical germanium lens curved toward the object side, and the third collimating lens 15 is a positive focal length meniscus aspherical germanium lens curved toward the object side.

[0043] In order to further reduce the overall volume, the first folding mirror group comprises, in order from the object side to the image side, a first reflecting mirror 16, a fourth collimating lens 17 and a second reflecting mirror 18, the second reflecting mirror 18 and the first reflecting mirror 16 are arranged at an angle with the optical axis, for folding the light path, the first reflecting mirror 16 and the first collimating lens group are arranged along the same straight line. That is, the secondary mirror 12, the first collimating lens group and the first reflecting mirror 16 are arranged along the same straight line, the fourth collimating lens 17 is arranged to ensure the cooperation effect of the two reflecting mirrors, and the light is folded again through the second reflecting mirror 18, at this time the transmission direction of the light is consistent with the initial incident direction.

[0044] It can be understood that, according to the actual spatial size design requirement, the number of reflecting mirrors can be more or less, so as to realize the miniaturization of the volume through light folding.

[0045] Preferably, the angle between the first reflecting mirror 16 and the second reflecting mirror 18 and the optical axis is 45°, so as to fold the light path by 90° in turn, at this time the two are arranged along the same straight line, which is beneficial to reduce the system length. In other embodiments, the angles of the two can also be set to be different, and the corresponding angles can be 30°, 60°, etc., and the present application does not limit this.

[0046] Further, the fourth collimating lens 17 is a positive focal length meniscus chalcogenide lens curved toward the image side.

[0047] In order to ensure the angle of the light entering the scanning galvanometer 2, the second collimating lens group comprises, in order from the object side to the image side, a fifth collimating lens 19a and a sixth collimating lens 19b, wherein the fifth collimating lens 19a is a negative focal length meniscus aspherical germanium lens curved toward the object side, and the sixth collimating lens 19b is a positive focal length meniscus aspherical chalcogenide lens curved toward the object side.

[0048] In order to ensure clear imaging, in the embodiment, the first imaging group 3 comprises a first lens 31, a second lens 32, a third mirror 33, a third lens 34 and a fourth lens 35 arranged in the order of object direction and image direction; wherein the first lens 31 is a positive focal length meniscus aspheric germanium lens bending to the image direction, the second lens 32 is a positive focal length meniscus aspheric germanium lens bending to the object direction, the third mirror 33 is arranged at an angle of 45° with the optical axis, used for folding the light path, the third lens 34 is a positive focal length meniscus aspheric germanium lens bending to the image direction, and the fourth lens 35 is a positive focal length double-convex spherical germanium lens. It can be understood that in other embodiments, the number of lenses described above can be more or less, and the spacing can be reasonably designed according to the actual lens selection.

[0049] It should be noted that the primary mirror 11 is located between the first collimating lens 13 and the first folding mirror group. In addition to the reasonable arrangement of different lens assemblies to ensure the incidence and folding of light, the structure is compact and the space utilization is higher.

[0050] In the embodiment, the direction of the light entering the telescope group is opposite to the direction of the light entering the image plane. In this way, the orientation of the image plane is limited, and the straight-line distance between the primary mirror 11 and the image plane is further reduced.

[0051] The present application does not limit the angle between the mirror 14 and the optical axis. In the embodiment, the angle between the mirror 14 and the optical axis is 45°, that is, the light path is folded by 90°, which is beneficial to reduce the system length. In other embodiments, the angle between the mirror 14 and the optical axis can also be 30°, 60°, etc., and the present application does not limit this.

[0052] Specifically, in the embodiment Figures 2 to 4 The corresponding MTF curves at different temperatures can reflect the characteristics of the optical system of the embodiment.

[0053] In order to quickly and effectively design a better optical structure, the present application proposes a method of joint design using parameter setting and optical design software, and the specific design steps are as follows:

[0054] Step 1: According to the rotation speed of the turntable, the minimum field of view increase of the telescope group that satisfies the back-scan compensation without vignetting or light blocking is determined as

[0055] ΔωFOV = ωt

[0056] Wherein, ω is the rotation speed of the turntable, and t is the integration time of the optical system face array detector;

[0057] The total field of view of the telescope system is obtained as

[0058] ωFOV = ωmax + ΔωFOV

[0059] Wherein, omega max is the maximum value of the field of view required in the optical system;

[0060] Step 2: according to the telescope group entrance pupil diameter and the structure size limit, the exit pupil diameter in the telescope group is determined, that is, the size of the corresponding scanning galvanometer 2 is determined;

[0061] Step 3: according to the telescope group magnification M=f0' / fe', the objective lens group focal length f0' and the eyepiece group focal length fe' are determined in combination with the F number of the system;

[0062] Step 4: the exit pupil position of the telescope group is strictly matched with the entrance pupil position of the first imaging group 3, and the scanning galvanometer 2 is placed at the entrance pupil position of the first imaging group 3;

[0063] Step 5: the telescope group and the first imaging group 3 are matched and optimized to obtain a long-wave composite area array scanning optical system;

[0064] Step 6: considering the thermal expansion coefficient of the optical lens, the barrel structure and the displacement amount of the long-wave infrared detector at high and low temperatures, the long-wave composite area array scanning optical system is designed to be athermal, thereby meeting the temperature range of-55℃ to +70℃.

[0065] In the technical scheme of the present application, the following advantages are achieved compared with the prior art:

[0066] The telescope group adopts a structure type of combining a reflecting mirror and a lens for one-time imaging, and the beam is folded multiple times in order to reduce the volume, thereby compressing the spatial size. Since the focal length of the optical system is relatively long, the primary mirror 11 and the secondary mirror 12 bear the main optical power, and the collimating mirror group bears the auxiliary optical power. The primary mirror 11 and the secondary mirror 12 are made of low-expansion microcrystalline glass, and the collimating mirror group is made of germanium and chalcogenide optical materials.

[0067] Considering the athermal design of the system, the best support material between the primary mirror 11 and the secondary mirror 12 is indium steel with a small thermal expansion coefficient, and the best barrel material, spacer material and support barrel material in the transmission assembly are all aluminum, so that good athermal effect can be achieved.

[0068] Considering the thermal expansion coefficient of the optical lens, the barrel structure and the displacement amount of the long-wave infrared detector at high and low temperatures, the long-wave area array scanning optical system is designed to be athermal, thereby meeting the temperature range of-55℃ to +70℃.

[0069] In order to effectively reduce the aperture of the primary mirror 11 and the aperture of the lens group, and to meet the lightweight design requirement of the system, the telescope group adopts a one-time imaging structure, and the entrance pupil position of the optical system is located near the primary mirror 11 of the telescope system; the first imaging group 3 adopts a one-time imaging structure, the exit pupil of the first imaging group 3 is coincided with the cold light stop of the detector, and the cold light stop efficiency reaches 100%, that is, the entire long-wave surface array scanning system is a three-time imaging structure.

[0070] The exit pupil position of the telescope group is strictly matched with the entrance pupil position of the first imaging group 3, and the scanning galvanometer 2 is placed at the entrance pupil position of the first imaging group 3;

[0071] In order to reduce the size of the galvanometer, the exit pupil position of the telescope group is located near the scanning galvanometer 2. When the scanning galvanometer 2 is in the system circumferential scanning working state, the working frequency reaches 50-100 Hz, so the size of the galvanometer is required to be small and the weight is required to be light.

[0072] The distortion value caused by the control of the scanning galvanometer 2 is less than 0.5%, the image accurate registration in the full field of view range during the scanning process is ensured, and the clear and stable imaging is ensured.

[0073] The above only describes the preferred embodiments of the present application, and does not limit the patent range of the present application, and any equivalent structural transformation made under the inventive concept of the present application, and directly / indirectly applied in other related technical fields are included in the patent protection range of the present application.

Claims

1. A long-wave infrared area scan optical system, characterized by, The long-wave infrared surface array scanning optical system comprises a telescope group, a scanning galvanometer, a first imaging group and an image plane arranged in sequence from an object to an image, the telescope group comprises a primary mirror, a secondary mirror, a first collimating lens group, a first folding mirror group and a second collimating lens group arranged in sequence from the object to the image, the scanning galvanometer has a fixed state and a return sweep state moving towards or away from the second collimating lens group, and light is folded through the primary mirror, the secondary mirror, the first folding mirror group and the scanning galvanometer; The working wave band of the long-wave infrared surface array scanning optical system is 7.7-10.5 μm, the focal length is 600 mm, and the F number is in the range of 2≤F≤5.

5. The primary mirror is located between the first collimating lens group and the first folding mirror group. The direction of light entering the telescope group is opposite to the direction of light entering the image plane.

2. The long-wave infrared area scan optical system of claim 1, wherein, The primary mirror is a negative focal length meniscus mirror, and the secondary mirror is a negative focal length meniscus mirror.

3. The long-wave infrared area scan optical system of claim 1, wherein, The first collimating lens group comprises a first collimating lens, a second collimating lens and a third collimating lens arranged in sequence from the object to the image. The first collimating lens is a negative focal length meniscus aspheric chalcogenide lens curved towards the image, the second collimating lens is a negative focal length meniscus aspheric germanium lens curved towards the object, and the third collimating lens is a positive focal length meniscus aspheric germanium lens curved towards the object.

4. The long-wave infrared area scan optical system of claim 1, wherein, The first folding mirror group comprises a first mirror, a fourth collimating lens and a second mirror arranged in sequence from the object to the image, the second mirror and the first mirror are arranged at an angle with the optical axis for folding the light path, and the first mirror and the first collimating lens group are arranged along the same line.

5. The long-wave infrared area scan optical system of claim 4, wherein, The angle between the first mirror, the second mirror and the optical axis is 45°; and / or The fourth collimating lens is a positive focal length meniscus chalcogenide lens curved towards the image.

6. The long-wave infrared area scan optical system of claim 1, wherein, The second collimating lens group comprises a fifth collimating lens and a sixth collimating lens arranged in sequence from the object to the image, the fifth collimating lens is a negative focal length meniscus aspheric germanium lens curved towards the object, and the sixth collimating lens is a positive focal length meniscus aspheric sulfur lens curved towards the object.

7. The long-wave infrared area scan optical system of claim 1, wherein, The first imaging group comprises a first lens, a second lens, a third mirror, a third lens and a fourth lens arranged in sequence from the object to the image. The first lens is a positive focal length meniscus aspheric germanium lens curved towards the image, the second lens is a positive focal length meniscus aspheric germanium lens curved towards the object, the angle between the third mirror and the optical axis is 45° for folding the light path, the third lens is a positive focal length meniscus aspheric germanium lens curved towards the image, and the fourth lens is a positive focal length double-convex spherical germanium lens.

8. The long-wave infrared area scan optical system of claim 1, wherein, The angle between the scanning galvanometer and the optical axis is 45°.

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