Infrared optical system with large area array and long rear working distance

Abstract

The invention relates to the technical field of infrared optics, in particular to a large-area-array long-rear-working-distance infrared optical system which comprises a head cover, a first lens, a second lens, a third lens, a fourth lens and a detector, the head cover serves as an optical window, the specific surface curvature radius and thickness design of the head cover optimizes the light incidence and preliminary convergence effect, and the light intensity is improved. The structure of the four lenses is reasonably distributed according to positive and negative focal powers to form a stable optical structure, and the diffraction surface design of the first lens can effectively correct chromatic aberration and improve the imaging quality. Meanwhile, the second emergent surface, the third incident surface, the fourth emergent surface and the fifth incident surface all adopt aspheric surface design, aberration is further reduced, and high-resolution imaging of the large-area-array detector is guaranteed. In addition, through reasonable spacing arrangement between the elements, the long rear working distance of the system is realized, and the requirements of adapting to detectors of different models are met. In conclusion, the system successfully realizes an imaging target with a large area array and a long rear working distance.

Description

Technical Field

[0001] The present invention relates to the field of infrared optical technology, and in particular to a large area array long back working distance infrared optical system. Background Art

[0002] With the development of infrared technology, higher and higher requirements are placed on the imaging quality of infrared optical systems. Especially missile-borne and airborne infrared systems often require operation within a wide temperature range. Under different temperature conditions, due to the thermal effects of optical materials and mechanical materials, some parameters of the optical system change accordingly, which in turn causes the optimal image plane of the system to deviate, reduces the imaging quality, makes the image blurred, the contrast decreases, and ultimately affects the performance of the seeker.

[0003] Uncooled infrared focal plane detectors are developing towards large area arrays, multi-bands, and digitization. Compared with 640×512 pixel area array detectors, the number of pixels of large area array 1280×1024 pixel detectors has increased significantly, improving the system's resolution ability for scenes and enabling more scene details to be seen.

[0004] The three-dimensional dimensions, shutter positions, and shutter sizes of large area array 1280×1204 pixel detectors from different manufacturers are not the same. To ensure that the lens can be applicable to different models of large area array detectors, a longer back working distance of the lens is required.

[0005] Therefore, while adapting to different models of detectors, how to achieve a large area array and a long back working distance is an urgent problem to be solved in the current infrared optical field. Summary of the Invention

[0006] The purpose of the present invention is to provide a large area array long back working distance infrared optical system, which effectively overcomes the dilemma of poor imaging quality of missile-borne and airborne infrared systems in complex temperature environments, and at the same time solves the problem that it is difficult to have both a large area array and a long back working distance when adapting to different models of large area array detectors.

[0007] To achieve the above object, the present invention provides a large area array long back working distance infrared optical system. The large area array long back working distance infrared optical system includes a radome, a first lens, a second lens, a third lens, a fourth lens, and a detector. The radome, the first lens, the second lens, the third lens, the fourth lens, and the detector are sequentially arranged on the optical path of the infrared optical system. The radome is the optical window of the infrared optical system. A first incident surface is provided on a surface of the radome away from the first lens, and a first exit surface is provided on a surface of the radome close to the first lens. In the infrared long wave band, the surface curvature radius of the first incident surface of the radome is 60 mm, the surface curvature radii of the first exit surface of the radome are 56 mm, and the thickness of the radome is 4 mm;

[0008] The first lens has a positive optical power. A second incident surface is provided on one side of the first lens close to the hood, and a second exit surface is provided on the other side of the first lens away from the hood. The second incident surface is a convex surface, and the second exit surface is a concave surface;

[0009] The second lens has a negative optical power. A third incident surface is provided on one side of the second lens close to the first lens, and a third exit surface is provided on the other side of the second lens away from the first lens. The third incident surface is a convex surface, and the third exit surface is a concave surface;

[0010] The third lens has a negative optical power. A fourth incident surface is provided on one side of the third lens close to the second lens, and a fourth exit surface is provided on the other side of the third lens away from the second lens. The fourth incident surface is a concave surface, and the fourth exit surface is a convex surface;

[0011] The fourth lens has a positive optical power. A fifth incident surface is provided on one side of the fourth lens close to the third lens, and a fifth exit surface is provided on the other side of the fourth lens away from the third lens. The fifth incident surface is a concave surface, and the fifth exit surface is a convex surface;

[0012] The second exit surface is a diffractive surface, and the second exit surface, the third incident surface, the fourth exit surface, and the fifth incident surface are all aspherical surfaces.

[0013] Among them, the surface curvature radius of the second incident surface of the first lens is 31.45 mm, and the surface curvature radii of the second exit surface of the first lens are 52.979 mm. The aperture stop is located on the second incident surface of the first lens.

[0014] Among them, the surface curvature radius of the third incident surface of the second lens is 24.474 mm, and the surface curvature radii of the third exit surface of the second lens are 16.84 mm.

[0015] Among them, the surface curvature radius of the fourth incident surface of the third lens is -25.39 mm, and the surface curvature radii of the fourth exit surface of the third lens are -33.377 mm.

[0016] Among them, the surface curvature radius of the fifth incident surface of the fourth lens is -136.018 mm, and the surface curvature radii of the fifth exit surface of the fourth lens are -34.45 mm.

[0017] Among them, the distance between the hood and the first lens is 2.5 mm, the distance between the first lens and the second lens is 1 mm, the distance between the second lens and the third lens is 8.5 mm, the distance between the third lens and the fourth lens is 4.82 mm, and the distance between the fourth lens and the detector is 15.42 mm.

[0018] Among them, the aspheric surface satisfies the following formula:

[0019]

[0020] Among them, Z is the height of any point on the aspheric surface relative to the reference plane, c is the curvature of the aspheric vertex, r is the radial distance from the aspheric vertex to this point, k is the conic coefficient, and A, B, C, D, and E are high-order aspheric coefficients;

[0021] The calculation formula of c is:

[0022]

[0023] Among them, c is the curvature of the aspheric vertex, and R is the radius of curvature.

[0024] Among them, the diffractive surface satisfies the following formula:

[0025] Φ = A1ρ2 + A2ρ4

[0026] Among them, Φ is the phase of the diffractive surface;

[0027] ρ = r n ,r n is the planned radius of the diffractive surface;

[0028] A1 and A2 are the phase coefficients of the diffractive surface.

[0029] Among them, the preparation material of the hood is zinc sulfide, the first lens, the second lens, and the fourth lens are all made of chalcogenide glass, and the preparation material of the third lens is zinc selenide.

[0030] Among them, the parameters of the detector are 1280×1024@12μm, the working band of the detector is 8μm - 12μm, and the field of view of the detector ≥ 24.75°×19.9°.

[0031] A large-area array long back working distance infrared optical system of the present invention includes a head cover, a first lens, a second lens, a third lens, a fourth lens and a detector. The head cover serves as an optical window, and its specific surface curvature radius and thickness are designed to optimize the light incidence and preliminary convergence effects. The structure of the four lenses is reasonably allocated according to positive and negative optical powers to form a stable optical structure. Among them, the diffraction surface design of the first lens can effectively correct chromatic aberration and improve imaging quality. At the same time, the second exit surface, the third entrance surface, the fourth exit surface and the fifth entrance surface all adopt aspherical designs to further reduce aberrations and ensure high-resolution imaging of the large-area array detector. In addition, through reasonable spacing settings between components, the system realizes a long back working distance and meets the requirements of adapting to different types of detectors. In summary, through the specific layout and surface type design of optical elements, the system successfully achieves the imaging goals of a large-area array and a long back working distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 FIG. is a schematic structural diagram of the large-area array long back working distance infrared optical system provided by the present invention.

[0034] Figure 2 FIG. is the 20°C MTF diagram of the large-area array long back working distance infrared optical system provided by the present invention.

[0035] Figure 3 FIG. is the energy distribution curve diagram of the large-area array long back working distance infrared optical system provided by the present invention.

[0036] Figure 4 FIG. is the distortion and field curvature diagram of the large-area array long back working distance infrared optical system provided by the present invention.

[0037] Figure 5 FIG. is the -40°C MTF diagram of the large-area array long back working distance infrared optical system provided by the present invention.

[0038] Figure 6 FIG. is the +70°C MTF diagram of the large-area array long back working distance infrared optical system provided by the present invention.

[0039] Figure 7 FIG. is the defocus curve diagram of the large-area array long back working distance infrared optical system provided by the present invention.

[0040] Figure 8It is the relative illuminance diagram of the large area array long back working distance infrared optical system provided by the present invention.

[0041] G1 - Hood, G2 - First lens, G3 - Second lens, G4 - Third lens, G5 - Fourth lens, G6 - Detector protection window, S1 - First incident surface, S2 - First exit surface, S3 - Second incident surface, S4 - Second exit surface, S5 - Third incident surface, S6 - Third exit surface, S7 - Fourth incident surface, S8 - Fourth exit surface, S9 - Fifth incident surface, S10 - Fifth exit surface. Detailed implementation manners

[0042] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, in which the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described by referring to the drawings below are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0043] Please refer to Figures 1 to 8 , the present invention provides a large area array long back working distance infrared optical system. The large area array long back working distance infrared optical system includes a hood G1, a first lens G2, a second lens G3, a third lens G4, a fourth lens G5 and a detector. The hood G1, the first lens G2, the second lens G3, the third lens G4, the fourth lens G5 and the detector (the detector is represented by the detector protection window G6 in the figure) are sequentially arranged on the optical path of the infrared optical system. The hood G1 is the optical window of the infrared optical system. A first incident surface S1 is provided on the surface of the hood G1 away from the first lens G2, and a first exit surface S2 is provided on the surface of the hood G1 close to the first lens G2. In the infrared long wave band (i.e., when the wavelength is 8μm - 12μm), the surface curvature radius of the first incident surface S1 of the hood G1 is 60mm, the surface curvature radius of the first exit surface S2 of the hood G1 is 56mm respectively, and the thickness of the hood G1 is 4mm;

[0044] The first lens G2 has a positive optical power. A second incident surface S3 is provided on the surface of the first lens G2 close to the hood G1, and a second exit surface S4 is provided on the surface of the first lens G2 away from the hood G1. The second incident surface S3 is a convex surface, and the second exit surface S4 is a concave surface;

[0045] The second lens G3 has a negative optical power. A third incident surface S5 is provided on the surface of the second lens G3 close to the first lens G2, and a third exit surface S6 is provided on the surface of the second lens G3 away from the first lens G2. The third incident surface S5 is a convex surface, and the third exit surface S6 is a concave surface;

[0046] The third lens G4 has a negative optical power. A fourth incident surface S7 is provided on a surface of the third lens G4 close to the second lens G3, and a fourth exit surface S8 is provided on a surface of the third lens G4 away from the second lens G3. The fourth incident surface S7 is a concave surface, and the fourth exit surface S8 is a convex surface;

[0047] The fourth lens G5 has a positive optical power. A fifth incident surface S9 is provided on a surface of the fourth lens G5 close to the third lens G4, and a fifth exit surface S10 is provided on a surface of the fourth lens G5 away from the third lens G4. The fifth incident surface S9 is a concave surface, and the fifth exit surface S10 is a convex surface;

[0048] The second exit surface S4 is a diffractive surface, and the second exit surface S4, the third incident surface S5, the fourth exit surface S8, and the fifth incident surface S9 are all aspherical surfaces.

[0049] In this embodiment, the hood G1 serves as an optical window. With its specific surface curvature radius and thickness designed, the incident and preliminary convergence effects of light are optimized. The structure of the four lenses is reasonably allocated according to positive and negative optical powers to form a stable optical structure. Among them, the diffractive surface design of the first lens G2 can effectively correct chromatic aberration and improve the imaging quality. At the same time, the second exit surface S4, the third incident surface S5, the fourth exit surface S8, and the fifth incident surface S9 all adopt aspherical designs, further reducing aberrations and ensuring high-resolution imaging of the large-area array detector. In addition, through reasonable spacing settings between components, the system achieves a long back working distance and meets the requirements of adapting to different types of detectors. To sum up, through the specific layout and surface type design of the optical elements, the system successfully achieves the imaging goal of a large-area array and a long back working distance.

[0050] Specifically, the surfaces of the first lens G2 are a convex surface and a concave surface in sequence, the surfaces of the second lens G3 are a convex surface and a concave surface in sequence, the surfaces of the third lens G4 are a concave surface and a convex surface in sequence, and the surfaces of the fourth lens G5 are a concave surface and a convex surface in sequence. The structures of the first lens G2, the second lens G3 and the third lens G4, the fourth lens G5 are symmetrical. During the assembly process of the infrared optical system, the second lens G3 and the third lens G4 can be assembled first, and then the first lens G2 and the fourth lens G5 can be assembled, achieving the advantages of easy operation and convenient disassembly during the assembly process.

[0051] Specifically, the reasonable distribution of positive and negative optical powers among the four lenses means that: the first lens G2, as the front group of the optical system, has a positive optical power, and the light transmission mode is convergent; the combination of the second lens G3 and the third lens G4 has a negative optical power, and the light transmission mode is divergent; the fourth lens G5, as the front group of the optical system, has a positive optical power, and the light transmission mode is convergent; the four-piece structure of the infrared optical system adopts a positive-negative-positive combination form, which can independently control the total optical power and aberration balance of the system, ensuring the imaging quality and transmittance of the infrared optical system, reducing the overall length of the optical system, and increasing the back working distance.

[0052] Specifically, the statement that "a diffractive surface and multiple aspherical surfaces are provided in the overall structure of the four lenses, which can effectively correct aberrations and improve imaging quality" means that: the second exit surface S4 is set as a diffractive surface, which can effectively correct chromatic aberration in the infrared optical system, thereby improving the imaging quality of the optical system, and can eliminate the influence of high and low temperatures on the infrared optical system, enabling the infrared optical system to have unaffected imaging within a wide temperature range of -40°C to +70°C, achieving athermalization. The second exit surface S4, the third entrance surface S5, the fourth exit surface S8, and the fifth entrance surface S9 are all aspherical surfaces, which can effectively improve the imaging performance of the infrared optical system and ensure the system size during the design of the large area array back working distance infrared optical system.

[0053] Furthermore, the surface curvature radius of the second entrance surface S3 of the first lens G2 is 31.45 mm, the surface curvature radius of the second exit surface S4 of the first lens G2 is 52.979 mm, the aperture stop is located on the second entrance surface S3 of the first lens G2, the surface curvature radius of the third entrance surface S5 of the second lens G3 is 24.474 mm, the surface curvature radius of the third exit surface S6 of the second lens G3 is 16.84 mm, the surface curvature radius of the fourth entrance surface S7 of the third lens G4 is -25.39 mm, the surface curvature radius of the fourth exit surface S8 of the third lens G4 is -33.377 mm, the surface curvature radius of the fifth entrance surface S9 of the fourth lens G5 is -136.018 mm, the surface curvature radius of the fifth exit surface S10 of the fourth lens G5 is -34.45 mm, the distance between the head cover G1 and the first lens G2 is 2.5 mm, the distance between the first lens G2 and the second lens G3 is 1 mm, the distance between the second lens G3 and the third lens G4 is 8.5 mm, the distance between the third lens G4 and the fourth lens G5 is 4.82 mm, and the distance between the fourth lens G5 and the detector is 15.42 mm.

[0054] Further, the parameters of the detector are 1280×1024@12μm, the working wavelength range of the detector is 8μm - 12μm, and the field of view of the detector is ≥24.75°×19.9°.

[0055] Further, as Figure 1 shown, the aspheric surface satisfies the following formula:

[0056]

[0057] where Z is the height of any point on the aspheric surface relative to the reference plane, c is the curvature of the aspheric surface vertex, r is the radial distance from the aspheric surface vertex to this point, k is the conic coefficient, and A, B, C, D, E, F are the high-order aspheric coefficients;

[0058] The calculation formula of c is:

[0059]

[0060] where c is the curvature of the aspheric surface vertex and R is the radius of curvature.

[0061] Further, the aspheric coefficients of the second exit surface S4, the third entrance surface S5, the fourth exit surface S8, and the fifth entrance surface S9 are shown in Table 1:

[0062] Table 1. Aspheric coefficients

[0063] Surface 4 6 8 10 S4 -2.1825e-006 5.8049e-008 -1.8138e-010 3.0201e-012 S5 -6.296e-006 2.5006e-007 -1.7896e-009 6.145e-012 S8 1.777e-005 -1.8652e-007 4.4673e-009 -4.9619e-011 S9 2.239e-006 4.0169e-008 -2.8144e-010 1.4585e-012

[0064] Further, the diffractive surface satisfies the following formula:

[0065] Φ = A1ρ2 + A2ρ4

[0066] where Φ is the phase of the diffractive surface;

[0067] ρ = r n , r n is the planned radius of the diffractive surface;

[0068] A1 and A2 are the phase coefficients of the diffractive surface.

[0069] Further, the diffractive surface coefficients of the second exit surface S4 are shown in Table 2:

[0070] Table 2. Diffractive surface coefficients

[0071] S4 -0.2053 2.5825e-005

[0072] Further, the preparation material of the hood G1 is zinc sulfide, the first lens G2, the second lens G3, and the fourth lens G5 are all made of chalcogenide glass, and the preparation material of the third lens G4 is zinc selenide.

[0073] In this embodiment, the preparation material of the hood G1 is selected as multi-spectral zinc sulfide, and the first incident surface S1 of the hood G1 is coated with an HD film to improve the infrared transmittance, the friction resistance of the product, and the strong environmental adaptability. The first lens G2, the second lens G3, and the fourth lens G5 are all made of chalcogenide glass, and the material of the third lens G4 is zinc selenide. By mainly selecting chalcogenide glass for the materials of each lens and not selecting germanium single crystal, after the optical power is reasonably distributed, both the material cost is reduced, and the transmittance and response speed of the infrared optical system are improved.

[0074] Further, Figure 2 This is the MTF graph of the infrared optical system provided in this embodiment at room temperature (20 °C). Figure 5 This is the MTF graph of the infrared optical system provided in this embodiment at low temperature (-40 °C). Figure 6 This is the MTF graph of the infrared optical system provided in this embodiment at high temperature (+70 °C). The spatial frequency of the lens reaches 42 lp / mm, and it is still greater than 0.3 within the full field of view, ensuring the imaging quality and significantly improving the overall imaging resolution of the scheme.

[0075] Figure 3 This is the energy distribution curve graph of the infrared optical system provided in this embodiment at room temperature (20 °C), which reflects the energy concentration. It can be seen from the graph that more than 80% of the energy is concentrated within the range of 15 μm, which can meet the high-resolution imaging requirements of the optical system.

[0076] Figure 4 This is the distortion and field curvature graph of the infrared optical system provided in this embodiment at room temperature (20 °C). The left side represents the field curvature astigmatism, and the right side represents the distortion. From Figure 4 it can be seen that the field curvature is less than 0.2, the full field of view distortion is less than 3%, and the number of pixels occupied by the edge and the center is close, ensuring that the image does not deform.

[0077] Figure 7 This is the defocus curve graph of the infrared optical system provided in this embodiment at room temperature (20 °C), which symbolizes the change of MTF when the image plane deviates from the design value. The abscissa represents the distance of the image plane deviating forward and backward, and the ordinate represents the MTF value. It can be seen from the graph that the infrared optical system has good defocus performance and meets the design requirements.

[0078] Figure 8The relative illuminance diagram of the infrared optical system provided in this embodiment at room temperature (20 °C) shows the illuminance values corresponding to different fields of view. The relative illuminance within the entire field of view is greater than 77%, and the illuminance of the entire target surface image is uniform.

[0079] Furthermore, the performance indicators achieved by this technical solution specifically include:

[0080] 1. Focal length: 35 mm

[0081] 2. F-number: 1.1

[0082] 3. Working wavelength range: 8 - 12 μm

[0083] 4. Resolution: Matches uncooled detectors with 12 μm pixels and 1280 × 1024 pixels; matches uncooled detectors with 25 μm pixels and 640 × 512 pixels

[0084] 5. Operating temperature: -40 °C to +70 °C

[0085] 6. Optical transmittance ≥ 80%

[0086] 7. Maximum distortion of the full field of view < 3%

[0087] The specific design parameters of this optical system are as shown in Table III below:

[0088] Table III. Specific Design Parameter Table of the Optical System

[0089]

[0090]

[0091] The above-disclosed is only a preferred embodiment of the present invention. Of course, the scope of rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A large area array long back working distance infrared optical system, characterized in that it includes a radome, a first lens, a second lens, a third lens, a fourth lens and a detector. The radome, the first lens, the second lens, the third lens, the fourth lens and the detector are sequentially arranged on the optical path of the infrared optical system. The radome is the optical window of the infrared optical system. A first incident surface is provided on the surface of the radome away from the first lens, and a first exit surface is provided on the surface of the radome close to the first lens. In the long-wave infrared band, the surface curvature radius of the first incident surface of the radome is 60 mm, and the surface curvature radius of the first exit surface of the radome is 56 mm respectively. The thickness of the radome is 4 mm; The first lens has a positive optical power. A second incident surface is provided on the surface of the first lens close to the radome, and a second exit surface is provided on the surface of the first lens away from the radome. The second incident surface is a convex surface, and the second exit surface is a concave surface; The second lens has a negative optical power. A third incident surface is provided on the surface of the second lens close to the first lens, and a third exit surface is provided on the surface of the second lens away from the first lens. The third incident surface is a convex surface, and the third exit surface is a concave surface; The third lens has a negative optical power. A fourth incident surface is provided on the surface of the third lens close to the second lens, and a fourth exit surface is provided on the surface of the third lens away from the second lens. The fourth incident surface is a concave surface, and the fourth exit surface is a convex surface; The fourth lens has a positive optical power. A fifth incident surface is provided on the surface of the fourth lens close to the third lens, and a fifth exit surface is provided on the surface of the fourth lens away from the third lens. The fifth incident surface is a concave surface, and the fifth exit surface is a convex surface; The second exit surface is a diffractive surface, and the second exit surface, the third incident surface, the fourth exit surface and the fifth incident surface are all aspherical surfaces.

2. The large area array long back working distance infrared optical system according to claim 1, characterized in that the surface curvature radius of the second incident surface of the first lens is 31.45 mm, and the surface curvature radius of the second exit surface of the first lens is 52.979 mm respectively. The aperture stop is located on the second incident surface of the first lens.

3. The large area array long back working distance infrared optical system according to claim 2, characterized in that the surface curvature radius of the third incident surface of the second lens is 24.474 mm, and the surface curvature radius of the third exit surface of the second lens is 16.84 mm respectively.

4. The large area array long back working distance infrared optical system according to claim 3, characterized in that the surface curvature radius of the fourth incident surface of the third lens is -25.39 mm, and the surface curvature radius of the fourth exit surface of the third lens is -33.377 mm respectively.

5. The large area array long back working distance infrared optical system according to claim 4, characterized in that The surface curvature radius of the fifth incident surface of the fourth lens is -136.018 mm, and the surface curvature radii of the fifth exit surface of the fourth lens are -34.45 mm respectively.

6. The large area array long back working distance infrared optical system according to claim 5, characterized in that The distance between the head cover and the first lens is 2.5 mm, the distance between the first lens and the second lens is 1 mm, the distance between the second lens and the third lens is 8.5 mm, the distance between the third lens and the fourth lens is 4.82 mm, and the distance between the fourth lens and the detector is 15.42 mm.

7. The large area array long back working distance infrared optical system according to claim 1, characterized in that The aspherical surface satisfies the following formula: Where Z is the height of any point on the aspherical surface relative to the reference plane, c is the curvature of the aspherical vertex, r is the radial distance from the aspherical vertex to this point, k is the conic coefficient, and A, B, C, D, E, F are high-order aspherical coefficients; The calculation formula of c is: Where c is the curvature of the aspherical vertex and R is the curvature radius.

8. The large area array long back working distance infrared optical system according to claim 7, characterized in that The diffractive surface satisfies the following formula: Φ = A1ρ2 + A2ρ4 Where Φ is the phase of the diffractive surface; ρ = r n , r n is the planned radius of the diffraction surface; A1 and A2 are the phase coefficients of the diffractive surface.

9. The large area array long back working distance infrared optical system according to claim 1, characterized in that The preparation material of the head cover is zinc sulfide, the first lens, the second lens and the fourth lens are all made of chalcogenide glass, and the preparation material of the third lens is zinc selenide.

10. The large area array long back working distance infrared optical system according to claim 1, characterized in that The parameters of the detector are 1280×1024@12μm, the working band of the detector is 8μm - 12μm, and the field of view of the detector ≥ 24.75°×19.9°.

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