A method for calculating internal stray radiation of all-optical surfaces in infrared optical systems

Abstract

The present invention belongs to the field of infrared optoelectronic imaging, and relates to a method for calculating the internal stray radiation of all optical machine surfaces of an infrared optical system. The method overcomes the technical problems of low calculation efficiency and inability to calculate the internal stray radiation energy of all optical machine surfaces in existing infrared optical system internal stray radiation analysis and testing methods. First, an optical machine model of the infrared optical system is established. Secondly, a reverse tracing light source is set at the detector position of the optical machine model to perform reverse tracing. Finally, the solid angle of all optical machine surfaces to the detector can be calculated by reverse tracing. According to the obtained solid angle calculation results, the internal spontaneous stray radiation of all optical machine surfaces of the infrared optical system at any temperature can be calculated. It provides real and reliable input for the design and implementation of infrared cold optics, and has strong engineering application value.

Description

Technical Field

[0001] The invention belongs to the field of infrared photoelectric imaging, and in particular relates to a method for calculating internal stray radiation on the surface of a full-optical machine of an infrared optical system. Background Art

[0002] In the infrared band, all objects with temperature will generate spontaneous radiation. Therefore, the infrared optical system itself will generate strong internal spontaneous stray radiation, which will be received by the detector and reduce the signal-to-noise ratio of the instrument. In severe cases, the target signal will be completely submerged by the internal stray radiation. Therefore, it is necessary to analyze and calculate the internal spontaneous stray radiation of the infrared optical system.

[0003] The existing infrared optical system internal stray radiation analysis and testing methods are mainly simulation forward tracing methods. This method simulates the infrared optical system and sets the optical surface to the optical surface gray body light source at different temperatures for forward tracing to obtain the internal stray radiation of the infrared optical system at that temperature. The advantage of this method is that the simulation results are more accurate, but one simulation analysis can only obtain the internal stray radiation energy at one temperature. If the internal stray radiation energy at different temperatures is to be analyzed, multiple simulations are required; and this method can only be analyzed based on a few specific optical surfaces set by humans, and it is impossible to calculate the internal stray radiation energy of all optical surfaces. Summary of the invention

[0004] The purpose of the present invention is to provide a method for calculating the internal stray radiation of all optical surfaces of an infrared optical system, so as to overcome the technical problems of low calculation efficiency and inability to calculate the internal stray radiation energy of all optical surfaces of the existing infrared optical system internal stray radiation analysis and testing methods. The present invention reasonably sets the radiation brightness of the reverse tracing light source, and can calculate the solid angle of all optical surfaces to the detector through reverse tracing, and can calculate the internal spontaneous stray radiation of all optical surfaces of the infrared optical system at any temperature.

[0005] The technical solution of the present invention is to provide a method for calculating the internal stray radiation of the surface of an infrared optical system, which is special in that it includes the following steps:

[0006] Step 1: Establish an optomechanical model of the infrared optical system and define the material and optomechanical surface properties of the optical components;

[0007] Step 2, setting a reverse tracing light source at the detector position of the optomechanical model;

[0008] Step 2.1, set a light source at the position of the image plane to be calculated on the detector, the area of ​​the light source is equal to the area of ​​the image plane to be calculated, and the radiation brightness L of the light source is the reciprocal of the light source area S1;

[0009] Step 2.2, set the light angle of the light source so that the light of the light source fills the entire solid angle hemisphere space, so that all the optical surfaces around the detector are illuminated by the light source;

[0010] Step 3: Perform reverse tracing;

[0011] Step 3.1: Perform reverse tracing. Combining the material of the optical element and the properties of the optomechanical surface defined in step 1, the radiation flux P received by any optomechanical surface i where the spontaneous stray radiation can directly reach the detector in the optomechanical model can be obtained. i ;

[0012] Step 3.2: Define P by the following formula: i :

[0013]

[0014] In the formula, θ i1 is the angle between the light source and the normal line of the optical machine surface and the transmission path, θ i2 is the angle between the normal of any optical machine surface i and the transmission path, r i is the distance of the transmission path from the light source to any optical machine surface i, τ i is the transmittance of the transmission path from the light source to any optical machine surface i, S i is the area of ​​any optomechanical surface i, Ω i is the solid angle of any optomechanical surface i to the light source;

[0015] Step 4, determine the stray radiation of all optical and mechanical surfaces of the infrared optical system;

[0016] Step 4.1: The spontaneous stray radiation generated by any optical machine surface i is transmitted, and the radiation illuminance E received by the detector is i for:

[0017]

[0018] In the formula, Φ i is the radiation flux received by the detector on any optomechanical surface i, ε i is the emissivity of any optomechanical surface i, L(T) is the blackbody radiation brightness at temperature T;

[0019] Step 4.2: In the infrared optical system, the spontaneous stray radiation generated by all optical surfaces that can directly reach the detector is transmitted, and the radiation illuminance received by the detector is:

[0020]

[0021] Where n is the number of all optomechanical surfaces in the infrared optical system from which spontaneous stray radiation can directly reach the detector.

[0022] Furthermore, the image plane to be calculated in step 2 is a certain pixel on the detector or the entire image plane of the detector.

[0023] Furthermore, the light source in step 2 is a Lambertian light source.

[0024] Furthermore, the optical-mechanical surface characteristics in step 1 include reflectivity, transmittance, emissivity and scattering characteristics of the optical-mechanical surface.

[0025] The beneficial effects of the present invention are:

[0026] The method of the present invention reasonably sets the radiation brightness of the reverse tracing light source, and can calculate the solid angle of all optomechanical surfaces to the detector through reverse tracing. According to the obtained solid angle calculation results, all key surfaces of the infrared optical system can be determined, that is, all optomechanical surfaces whose spontaneous radiation can be directly received by the detector, and the internal spontaneous stray radiation of all optomechanical surfaces of the infrared optical system at any temperature can be calculated, providing real and reliable input for the design and implementation of infrared cold optics, and has strong engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of a method for calculating internal stray radiation of a full optical machine surface of an infrared optical system of the present invention;

[0028] Figure 2 Schematic diagram of a long-wave infrared spectrometer of an implementation example, wherein a is a light path diagram and b is an optical-mechanical structure diagram;

[0029] The accompanying drawings in the figure are marked as follows:

[0030] 01-detector, 02-reflector, 03-slit, 04-mirror one, 05-mirror two, 06-mirror three, 07-mirror four, 08-grating; 1-first lens barrel, 2-second lens barrel, 3-third lens barrel, 4-fourth lens barrel, 5-fifth lens barrel, 6-sixth lens barrel, 7-seventh lens barrel, 8-eighth lens barrel;

[0031] Figure 3 It is a model diagram of the long-wave infrared spectrometer of the implementation example in the tracepro simulation software; DETAILED DESCRIPTION

[0032] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0033] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0034] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present invention. The term "in other embodiments" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0035] According to the radiation transmission theory, the radiation flux P radiated by a light source with a radiation brightness of L1 to the surface of any receiving light machine can be given by the following formula:

[0036]

[0037] Wherein, r is the distance between the light source and the transmission path of the receiving optical machine surface, s1 is the area of ​​the microelement of the light source optical machine surface, s2 is the area of ​​the microelement of the receiving optical machine surface, τ is the optical transmittance of the transmission path from the light source to the receiving optical machine surface, θ1 is the angle between the normal line of the light source optical machine surface and the transmission path, θ2 is the angle between the normal line of the receiving optical machine surface and the transmission path; L1(T) is the radiation brightness of the light source at temperature T;

[0038] Simplifying this formula, we can get:

[0039]

[0040] Among them, S1 is the area of ​​the light source's optomechanical surface, and S2 is the area of ​​the receiving optomechanical surface. According to this formula, by reasonably setting the radiation brightness of the reverse tracing light source, the solid angle of all optomechanical surfaces to the detector can be calculated through reverse tracing. According to the obtained solid angle calculation results, the main internal radiation source of the infrared optical system can be known, and the internal spontaneous stray radiation of all optomechanical surfaces of the infrared optical system at any temperature can be calculated. The specific steps are as follows:

[0041] (1) Establish an optomechanical model of the infrared optical system in the simulation software and define the material and optomechanical surface properties of the optical components.

[0042] (2) A Lambertian light source is set at the detector of the optomechanical model. The light source area is the area of ​​a single pixel of the detector. The light source position is the position of the pixel to be calculated on the detector. Its radiation brightness is the inverse of the light source area, that is, L = 1 / S1. The light angle of the light source is set so that the light of the detector light source fills the entire hemispherical space, so that all optomechanical surfaces around the detector are illuminated by the light source. In other embodiments, the light source area can also be the area of ​​the entire image plane of the detector, and the light source is located on the entire image plane of the detector.

[0043] (3) Perform reverse tracing and combine the material of the optical element and the properties of the optomechanical surface defined in step 1 to obtain the radiation flux P received by any optomechanical surface i in the optomechanical model where the spontaneous stray radiation can directly reach the detector: i ;

[0044] Since the radiation brightness of the light source is 1 / S1, according to formula (2), the radiation flux received by any optomechanical surface i in the optomechanical model can be expressed as:

[0045]

[0046] In the formula, S i is the area of ​​any optomechanical surface i, τ i is the transmittance of the transmission path from the light source to any optical machine surface i, θ i1 is the angle between the normal line of the light source optical machine surface and the transmission path, θ i2 is the angle between the normal of any optical machine surface i and the transmission path, Ω i is the solid angle of any optomechanical surface i to the light source.

[0047] Therefore, the radiation flux P received by any optomechanical surface i in the optomechanical model is i It is numerically equal to the product of the solid angle of the optical machine surface to the light source and the optical transmittance of the transmission path from the light source to any optical machine surface i.

[0048] (4) According to formulas (2) and (3), the spontaneous stray radiation generated by any optical surface i in the infrared optical system is transmitted and the radiation illuminance received by the detector is:

[0049]

[0050] In the infrared optical system, spontaneous stray radiation can directly reach the detector. The spontaneous stray radiation generated by all optical surfaces is transmitted, and the radiation illuminance received by the detector is:

[0051]

[0052] In the formula, E iis the radiation intensity received by the detector after the spontaneous stray radiation generated by any optomechanical surface i is transmitted, Φ i is the radiation flux received by the detector on any optomechanical surface i, ε i is the emissivity of any optomechanical surface i, L(T) is the blackbody radiation brightness at temperature T, and n is the number of all optomechanical surfaces in the infrared optical system whose spontaneous stray radiation can directly reach the detector.

[0053] Therefore, the spontaneous stray radiation generated by all optomechanical surfaces is transmitted, and the radiation illumination received by the detector can be calculated based on the emissivity of the optomechanical surface, the radiation brightness of the black body at any temperature, and the radiation flux value received by the optomechanical surface in the reverse tracing.

[0054] The following is an example of calculating a Litrow-type long-wave infrared grating spectrometer. The working band of the spectrometer is 8-12 μm. The optical path diagram and optomechanical structure diagram of the long-wave infrared grating spectrometer are as follows: Figure 2 As shown, the light emitted from the slit 03 is reflected by the off-axis reflector 02 and then incident on the coaxial lens group, which includes mirror 1 04, mirror 2 05, mirror 3 06, mirror 4 07 and grating 08. The light is diffracted after being incident on the grating 08. After being diffracted by the grating 08, the diffracted light of different wavelengths is reflected from the grating optical machine surface, passes through the coaxial lens group in the opposite direction again, and finally incident on the photosensitive surface of the detector 01. The detector 01 receives the spectral information of different wavelengths of the target of the slit 03. The following is a specific implementation method according to the calculation method of the internal stray radiation of the full optical machine surface of the infrared optical system described in the present invention.

[0055] (1) Establish an optomechanical model of the infrared optical system in the simulation software, such as Figure 3 As shown, the materials and optomechanical surface characteristics of the optical elements are defined. The optomechanical surface characteristics are shown in the following table.

[0056] Table 1 Definition of the optical-mechanical surface characteristics of the simulation model

[0057] Surface type Transmittance Absorption rate Mirror reflectivity Scattering rate Optically Transmissive Surfaces 0.979 0.01 0.01 0.001 Optical reflective surface 0 0.03 0.969 0.001 Blackened mechanical surface 0 0.85 0.08 0.07

[0058] (2) A Lambertian light source is set at the detector of the optomechanical model. The area of ​​the light source is the area of ​​a single pixel of the detector. The position of the light source is the center of the detector (i.e., the position of the central pixel). Its radiation brightness is the inverse of the light source area, i.e., L = 1 / S1. The light of the light source fills the entire hemispherical space, so that all optomechanical surfaces around the detector are illuminated by the light source.

[0059] (3) By performing reverse tracing, the radiation flux received by all optomechanical surfaces in the optomechanical model can be obtained. According to formula (3), the radiation flux received by each optomechanical surface is numerically equal to the product of the solid angle of the optomechanical surface to the light source and the optical transmittance.

[0060] In order to compare with the calculation results of the simulation analysis method, the following are listed here Figure 2 The product of the solid angle and transmittance of the middle lens tubes 1 to 8 is calculated as shown in Table 2.

[0061] (4) According to formula (4), the radiation intensity received by the detector after the spontaneous stray radiation generated by any optical machine surface i is calculated. The spontaneous stray radiation of the lens tubes 1 to 8 in the long-wave band (8 to 12 μm) at 300K and 100K is calculated. In order to compare with the calculation results of the simulation analysis method, the following are listed here: Figure 2 The calculation results of the internal spontaneous stray radiation of the middle tubes 1 to 8 are shown in Table 2.

[0062] Table 2 Calculation results of optical-mechanical surface solid angle and internal stray radiation

[0063]

[0064] In order to verify the accuracy of the calculation method described in the present invention, the simulation forward analysis method is used to simulate and analyze the internal stray radiation of the long-wave infrared spectrometer in the example. The optical-mechanical model of the infrared optical system is established in the tracepro simulation software, and the optical-mechanical material and optical-mechanical surface characteristics are defined. The lens barrels 1 to 8 are set to a gray body light source with an emissivity of 0.85 and forward ray tracing is performed. The internal spontaneous stray radiation illumination of the lens barrels 1 to 8 at 300K and 100K is simulated and compared with the calculation results of the present invention, as shown in Table 3.

[0065] Table 3 Comparison of calculated results and simulation results of internal stray radiation illumination

[0066] Optical surface 300K calculation results 300K simulation results 100K calculation results 100K simulation results First lens barrel 1 8.7469 10.6158 8.5854E-04 1.0570E-03 Second lens barrel 2 2.8528 2.6601 2.8001E-04 2.6531E-04 Third lens barrel 3 4.4482 3.4762 4.3661E-04 5.7338E-04 Fourth lens barrel 4 13.5374 12.7870 1.3288E-03 1.6617E-03 Fifth lens barrel 5 5.3233 5.6351 5.2250E-04 8.3273E-04 Sixth lens barrel 6 6.8274 8.0388 6.7013E-04 9.6109E-05 Seventh lens tube 7 0.6690 1.6399 6.5663E-05 7.0580E-05 Eighth lens tube 8 3.0664 2.9913 3.0098E-04 2.9897E-04 sum 45.4713 47.8442 4.4632E-03 4.8558E-03

[0067] By comparing the calculation results of the present invention with the calculation results of the simulation analysis method, it can be seen that the calculation results of the present invention are basically consistent with the simulation results. Therefore, the calculation results of the calculation method of the present invention are accurate.

[0068] Since the method for calculating the internal stray radiation of the entire optical machine surface of the infrared optical system described in the present invention can realize the calculation of the internal spontaneous stray radiation of all optical machine surfaces at any temperature, the product of the solid angle and the transmittance of all optical machine surfaces calculated in step (3) is calculated, and some optical machine surfaces with a solid angle of 0 are removed. The spontaneous stray radiation generated by a total of 224 optical machine surfaces can be received by the detector. The spontaneous stray radiation of all optical machine surfaces of the long-wave infrared spectrometer is calculated as shown in Table 4.

[0069] Table 4 Internal spontaneous stray radiance of all optomechanical surfaces

[0070]

[0071]

[0072] It can be seen from the calculation results that the internal spontaneous stray radiation of 300K and 100K is greater than the simulation results of the simulation analysis method that only simulates specific optomechanical surfaces. This is because in the long-wave infrared spectrometer, there are a large number of optomechanical surfaces with small areas and small angles to the detector. If the traditional simulation analysis method is used for calculation, in order to simplify the model and save simulation time, these optomechanical surfaces will not be set as light sources for simulation. However, it can be seen from the calculation results in Table 4 that these seemingly unimportant optomechanical surfaces together contribute a large amount of internal stray radiation, and it is necessary to use the calculation method of the present invention for calculation.

[0073] In summary, the present invention realizes the accurate calculation of the internal spontaneous stray radiation of all optical and mechanical surfaces of the infrared optical system. The calculation results can provide real and reliable input for the design and implementation of infrared cold optics, and have strong engineering application value.

[0074] The above is only a description of the preferred implementation mode of the present invention, and the technical solution of the present invention is not limited thereto. Any known deformation made by those skilled in the art on the basis of the main technical concept of the present invention belongs to the technical scope to be protected by the present invention.

Claims

1. A method for calculating internal stray radiation of a full optical machine surface of an infrared optical system, characterized in that: The following steps are involved: Step 1: Establish an optomechanical model of the infrared optical system and define the material and optomechanical surface properties of the optical components; Step 2, setting a reverse tracing light source at the detector position of the optomechanical model; Step 2.1, a light source is set at the position of the image plane to be calculated on the detector, the area of ​​the light source is equal to the area of ​​the image plane to be calculated, and the radiation brightness L of the light source is the reciprocal of the light source area S1; the light source is a Lambertian light source; Step 2.2, set the light angle of the light source so that the light of the Lambertian light source fills the entire solid angle hemisphere space, so that all the optical and mechanical surfaces around the detector are illuminated by the light source; Step 3: Perform reverse tracing; Step 3.1: Perform reverse tracing. Combining the material of the optical element and the properties of the optomechanical surface defined in step 1, the radiation flux P received by any optomechanical surface i where the spontaneous stray radiation can directly reach the detector in the optomechanical model can be obtained. i ; Step 3.2: Define P by the following formula: i : In the formula, θ i1 is the angle between the light source and the normal line of the optical machine surface and the transmission path, θ i2 is the angle between the normal of any optical machine surface i and the transmission path, r i is the distance of the transmission path from the light source to any optical machine surface i, τ i is the transmittance of the transmission path from the light source to any optical machine surface i, S i is the area of ​​any optomechanical surface i, Ω i is the solid angle of any optomechanical surface i to the light source; Step 4, determine the stray radiation of all optical and mechanical surfaces of the infrared optical system; Step 4.1: The spontaneous stray radiation generated by any optical machine surface i is transmitted, and the radiation illuminance E received by the detector is i for: In the formula, Φ i is the radiation flux received by the detector on any optomechanical surface i, ε i is the emissivity of any optomechanical surface i, L(T) is the blackbody radiation brightness at temperature T; Step 4.2: In the infrared optical system, the spontaneous stray radiation generated by all optical surfaces that can directly reach the detector is transmitted, and the radiation illuminance received by the detector is: Where n is the number of all optomechanical surfaces in the infrared optical system from which spontaneous stray radiation can directly reach the detector.

2. The method for calculating internal stray radiation of the surface of the infrared optical system plenoptical machine according to claim 1, characterized in that: The image plane to be calculated in step 2 is a certain pixel on the detector or the entire image plane of the detector.

3. The method for calculating internal stray radiation of a full optical machine surface of an infrared optical system according to claim 1, characterized in that: The optical-mechanical surface characteristics in step 1 include reflectivity, transmittance, emissivity and scattering characteristics of the optical-mechanical surface.

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