Method for evaluating stray light of extreme ultraviolet band coronagraph

Abstract

The present application relates to the technical field of astronomical observation, and particularly relates to a stray light evaluation method for a far ultraviolet wave band coronagraph, which comprises the following steps: establishing a simulation model, simulating to obtain a first simulation value of stray light of the coronagraph in a visible light wave band, and simulating to obtain a second simulation value of stray light of the coronagraph in an ultraviolet wave band; experimentally measuring to obtain a first experimental value of stray light of the coronagraph in the visible light wave band, and experimentally measuring to obtain a second experimental value of stray light of the coronagraph in the ultraviolet wave band; correcting the simulation model, so that a difference between the first simulation value and the first experimental value is less than 10% of the first experimental value, and a difference between the second simulation value and the second experimental value is less than 10% of the second experimental value; and simulating to obtain a third simulation value of stray light of the coronagraph in a far ultraviolet wave band by using the corrected simulation model. The present application is at least beneficial to reduce the difficulty of stray light detection of the coronagraph in the far ultraviolet wave band.

Description

Technical Field

[0001] This invention belongs to the field of astronomical observation technology, and in particular relates to a method for evaluating stray light from a far-ultraviolet coronagraph. Background Technology

[0002] The corona is the outermost layer of the Sun's atmosphere, stretching thousands of kilometers outward from the Sun's surface and extending into interplanetary space. Coronavirus radiation has a wide wavelength range, from X-rays, far ultraviolet, and visible light to long-wavelength radio waves. Hydrogen, the most abundant element in the Sun, emits Lyman alpha (HI Lyman Alpha, or Ly-α) radiation at a wavelength of 121.6 nm in the far ultraviolet band, which is the strongest observable ultraviolet radiation from the corona. Lyman alpha radiation is an important component of chromospheric and coronavirus radiation. An enclosed coronagraph is an instrument used to image coronal radiation near the Sun's surface during non-total solar eclipses. Because these instruments need to capture extremely weak coronal radiation at the edge of strong solar radiation, they require very high stray light suppression capabilities. In the far ultraviolet Lyman alpha band, to image a distance of 2.5R from the Sun's center... ⊙ (R ⊙ The corona was observed at a distance of 2.5R from the sun's radius (the radius of the sun). The inner-occultation coronagraph observed a distance of 2.5R from the sun's center. ⊙ The stray light brightness contribution at the location should be reduced to 10. -6 B ⊙ (B ⊙ The ability to suppress stray light (the average brightness of the solar disk) will determine the success or failure of the development of the enclosed coronagraph.

[0003] The far-ultraviolet band exists only in a vacuum environment; the Earth's atmosphere absorbs this band of light. Therefore, to observe the solar corona in the far-ultraviolet band, a coronagraph must be launched outside the atmosphere. In China, the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences, in collaboration with Shandong University, has conducted research projects related to corona observation. Their ground-based coronagraph obtained radiation images of the solar E-corona at the 530.3 nm band in high-altitude regions, but it was unable to observe the far-ultraviolet corona in these areas with their thin atmospheres. Abroad, in 1995, the SOHO (Solar and Heliospheric Observatory) mission carried an externally masked coronagraph spectrometer, UVCS (UltraViolet Coronagraph Spectrometer). UVCS can acquire corona spectral information in the far-ultraviolet band, but it is not a corona imaging instrument. In 2022, Italy, in collaboration with several European research institutions, launched the Metis externally masked coronagraph. The Metis externally masked coronagraph is a coronagraph that can simultaneously image in the far-ultraviolet and visible light bands, and it is also the only coronagraph abroad capable of corona imaging in the far-ultraviolet band.

[0004] The ground-based coronagraph jointly developed by the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences and Shandong University adopts an externally shielded transmission imaging structure. Its operating wavelength is visible light, excluding the far-ultraviolet band. Therefore, it does not involve methods for detecting and evaluating stray light in the far-ultraviolet band. The Metis externally shielded coronagraph is the only coronagraph abroad with far-ultraviolet imaging capabilities. However, because the externally shielded coronagraph uses an externally shielded structure, it blocks the sun, the main source of stray light, from the coronagraph. Therefore, its stray light suppression capability is inherently superior to that of the internally shielded coronagraph. How to achieve stray light detection for the internally shielded coronagraph is a technical problem that urgently needs to be solved in the relevant technical field.

[0005] For stray light detection by coronagraphs in the ultraviolet band, it is difficult to perform because it can only be done in a vacuum environment and there is no high-brightness light source or high-sensitivity detector with a large dynamic range that can be used for stray light detection in this band. This makes the detection subject to multiple technical limitations in terms of detection environment, light source and detector. Therefore, stray light detection by coronagraphs in the far ultraviolet band is quite difficult. Summary of the Invention

[0006] In view of this, the present invention aims to provide a method for evaluating stray light in a coronagraph in the far-ultraviolet band, which at least helps to reduce the difficulty of detecting stray light in a coronagraph in the far-ultraviolet band.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0008] This invention provides a method for evaluating stray light from a coronagraph in the far-ultraviolet band, comprising: establishing a simulation model; using the simulation model to obtain a first simulated value of stray light from the coronagraph in the visible light band and a second simulated value of stray light from the coronagraph in the ultraviolet band; experimentally measuring a first experimental value of stray light from the coronagraph in the visible light band and a second experimental value of stray light from the coronagraph in the ultraviolet band; correcting the simulation model based on the difference between the first simulated value and the first experimental value, and further correcting the simulation model based on the difference between the second simulated value and the second experimental value, such that the difference between the first simulated value and the first experimental value is less than 10% of the first experimental value, and the difference between the second simulated value and the second experimental value is less than 10% of the second experimental value; and using the corrected simulation model to simulate a third simulated value of stray light from the coronagraph in the far-ultraviolet band.

[0009] Furthermore, the establishment of the simulation model includes: providing a coronagraph stray light detection device, which includes a light source and a coronagraph, the coronagraph being used to receive the light beam emitted by the light source to generate a radiation image; and establishing a simulation model based on the coronagraph stray light detection device.

[0010] Furthermore, the coronagraph includes: an entrance pupil, a primary mirror, a secondary mirror with a conical through-hole in the center, a light trap, a third mirror, a Leo diaphragm, a beam splitter, a fourth mirror, a first detector, and a second detector. Light emitted from the light source enters the primary mirror through the entrance pupil. The primary mirror images the light onto the secondary mirror. The light trap behind the secondary mirror absorbs the solar radiation from the light. The secondary mirror reflects the corona radiation from the light to the third mirror. After being reflected by the third mirror, the corona radiation passes through the Leo diaphragm and enters the beam splitter. The first detector receives the first beam split by the beam splitter. The second beam split by the beam splitter enters the fourth mirror and, after being reflected by the fourth mirror, reaches the second detector. The first detector is used to generate a radiation image including stray light.

[0011] Furthermore, the first detector includes a cooled CMOS deep space camera.

[0012] Furthermore, the experimental measurements obtained include: measuring the first experimental value of stray light at a preset position in the radiation image when the light source emits visible light using a coronagraph stray light detection device, and measuring the second experimental value of stray light at a preset position in the radiation image when the light source emits ultraviolet light.

[0013] Furthermore, obtaining the first and second simulation values ​​using the simulation model includes: performing simulation analysis using the simulation model to obtain the first simulation value of stray light at a preset position in the radiation image when the light source emits visible light, and obtaining the second simulation value of stray light at a preset position in the radiation image when the light source emits ultraviolet light; obtaining the third simulation value includes: performing simulation analysis using the corrected simulation model to obtain the third simulation value of stray light at a preset position in the radiation image when the light source emits far-ultraviolet light.

[0014] Furthermore, the simulation model established based on the coronagraph stray light detection device includes: establishing the Harvey-Shack ABg model based on the primary reflector, and establishing the detection model based on the coronagraph stray light detection device.

[0015] Furthermore, simulation analysis is performed using a simulation model to obtain the first and second simulation values. This includes substituting the surface roughness σ of the primary reflector into the Harvey-Shack ABg model to obtain the BSDF function. The expression for the BSDF function is as follows:

[0016]

[0017] in, g is the slope of the BSDF function curve, Δn is the change in refractive index, σ is the surface roughness of the primary mirror, λ is the working wavelength, l is the autocorrelation length determined by the surface scattering characteristics, and θ is the angle between the scattering direction and the ideal mirror reflection direction. The BSDF function is substituted into the detection model for simulation analysis to obtain the first and second simulation values. When obtaining the first simulation value, λ is the wavelength of visible light emitted by the light source. When obtaining the second simulation value, λ is the wavelength of ultraviolet light emitted by the light source.

[0018] Furthermore, modifications to the simulation model include correcting the g and l functions of the BSDF function.

[0019] Furthermore, when obtaining the third simulation value, λ is taken as the wavelength of the far-ultraviolet light emitted by the light source.

[0020] Compared with existing technologies, this invention achieves the following beneficial effects: Based on the correlation characteristics between stray light brightness contribution and wavelength, this invention proposes a method that combines experimental detection results and simulation results of stray light in different wavelength bands. The experimental detection results are the stray light brightness contributions in the visible light band and the ultraviolet light band directly detected by a coronagraph stray light detection device under atmospheric conditions. On this basis, by combining the simulated values ​​of the coronagraph stray light brightness contribution in the visible light band and the simulated values ​​of the coronagraph stray light brightness contribution in the ultraviolet band, the correlation characteristics between the coronagraph stray light brightness contribution and the working wavelength are obtained. Based on the correlation characteristics between the coronagraph stray light brightness contribution and the working wavelength, the stray light brightness contribution of the coronagraph in the far ultraviolet band is derived. Thus, although stray light in the far-ultraviolet band cannot be directly detected, the correlation characteristics between stray light and wavelength can be verified through stray light analysis and detection in different bands. This helps to reduce the difficulty of detecting stray light in the far-ultraviolet band of coronagraphs and ensures the accuracy of stray light evaluation results in the far-ultraviolet band, which is conducive to promoting the development of astronomical target observation technology. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 A schematic diagram of the optical structure of the coronagraph described in the embodiments of the present invention;

[0023] Figure 2 An experimental radiation image of the entrance pupil edge diffraction stray light in the visible light band at a working wavelength of 700 nm is provided as an embodiment of the present invention.

[0024] Figure 3 A stray light simulation radiation image in the visible light band is provided as an embodiment of the present invention;

[0025] Figure 4 A stray light simulation radiation image in the ultraviolet band is provided as an embodiment of the present invention;

[0026] Figure 5 This invention provides a simulated image of stray light radiation in the far-ultraviolet band, which is an embodiment of the invention.

[0027] Explanation of reference numerals in the attached diagram: 1. Entrance pupil; 2. Primary reflector; 3. Secondary reflector; 4. Third reflector; 5. Leo stop; 6. Beam splitter; 7. Fourth reflector; 8. First detector; 9. Second detector; 10. Light trap. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0030] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] This invention provides a method for evaluating stray light from a coronagraph in the far-ultraviolet band, comprising: establishing a simulation model; using the simulation model to obtain a first simulated value of stray light from the coronagraph in the visible light band and a second simulated value of stray light from the coronagraph in the ultraviolet band; experimentally measuring a first experimental value of stray light from the coronagraph in the visible light band and a second experimental value of stray light from the coronagraph in the ultraviolet band; correcting the simulation model based on the difference between the first simulated value and the first experimental value, and further correcting the simulation model based on the difference between the second simulated value and the second experimental value, such that the difference between the first simulated value and the first experimental value is less than 10% of the first experimental value, and the difference between the second simulated value and the second experimental value is less than 10% of the second experimental value; and using the corrected simulation model to simulate a third simulated value of stray light from the coronagraph in the far-ultraviolet band.

[0034] It should be noted that the coronagraph provided in this embodiment of the invention is an internally masked reflector type coronagraph. The third simulation value is the predicted stray light brightness contribution of the coronagraph in the far-ultraviolet band. After correcting the simulation model, while ensuring that the various optomechanical parameters of each instrument in the simulation model remain unchanged, only the operating wavelength is changed to the wavelength in the far-ultraviolet band, and the simulation analysis yields the third simulation value. Among them, the various optomechanical parameters include the surface roughness of optical elements, surface defects, contamination, and obstruction of optical structures.

[0035] The first, second, and third simulated values ​​involved in this embodiment of the invention are the brightness contributions of stray light obtained through simulation, while the first and second experimental values ​​are the brightness contributions of stray light obtained through actual experiments. The brightness contribution is the ratio of stray light brightness to the average brightness of the solar surface.

[0036] In this embodiment of the invention, the difference between the first simulated value and the first experimental value can also be the minimum value that the difference between the first simulated value and the first experimental value can reach. Similarly, the difference between the second simulated value and the second experimental value can also be the minimum value that the difference between the second simulated value and the second experimental value can reach. Ideally, the difference between the first simulated value and the first experimental value is zero or approximately zero, and the difference between the second simulated value and the second experimental value is zero or approximately zero.

[0037] To address the limitation of existing technologies on the propagation environment of far-ultraviolet light and the level of detector technology, which prevent direct detection of stray light from coronagraphs in the far-ultraviolet band, this invention proposes a method for evaluating stray light from coronagraphs in the far-ultraviolet band by combining stray light detection results from different bands with simulation results. Specifically, under atmospheric conditions, the stray light brightness contributions of the coronagraph in the visible light band and the stray light brightness contribution in the ultraviolet band are obtained, and the correlation characteristics between the stray light of the coronagraph and the operating wavelength are obtained. These correlation characteristics are reflected in the modified simulation model, and the stray light brightness contribution of the coronagraph in the far-ultraviolet band is inferred based on the modified simulation model, thereby obtaining the stray light suppression capability of the coronagraph in the far-ultraviolet band. In other words, this invention proposes a stray light evaluation method for the far-ultraviolet band by utilizing the correlation characteristics between the stray light contribution of a coronagraph and its operating wavelength. This method combines experimental detection results and simulation results of stray light in the visible and ultraviolet bands, solving the problem of not being able to directly detect stray light from a coronagraph in the far-ultraviolet band. It is applicable to the evaluation of stray light from coronagraphs in all different bands.

[0038] Furthermore, establishing the simulation model includes: providing a coronagraph stray light detection device, which includes a light source and a coronagraph. The coronagraph is used to receive the light beam emitted by the light source to generate a radiation image; and establishing a simulation model based on the coronagraph stray light detection device. Specifically, a simulation model needs to be established based on the light source and the coronagraph in the coronagraph stray light detection device.

[0039] In some embodiments of the present invention, the light source may be a solar radiation simulation device with a solar plane angle of 32′, and the solar radiation simulation device may include an LED light source.

[0040] In some embodiments of the present invention, when acquiring stray light in the visible light band, the solar radiation simulation device may include a visible light LED light source; when acquiring stray light in the ultraviolet band, the solar radiation simulation device may include a deuterium lamp, a mercury lamp, or an ultraviolet LED light source.

[0041] Further reference Figure 1The coronagraph includes: entrance pupil 1, primary mirror 2, secondary mirror 3 with a conical through-hole in the center, light trap 10, third mirror 4, Leo aperture 5, beam splitter 6, fourth mirror 7, first detector 8, and second detector 9. Light emitted from the light source enters the primary mirror 2 through the entrance pupil 1. The primary mirror 2 images the light onto the secondary mirror 3. The light trap 10 behind the secondary mirror 3 absorbs the solar surface light in the light. After entering the light trap 10, the solar surface light cannot enter the subsequent light path. The secondary mirror 3 reflects the corona light in the light to the third mirror 4. After being reflected by the third mirror 4, the corona light passes through the Leo aperture 5 and enters the beam splitter 6. The first detector 8 receives the first beam split by the beam splitter 6. The second beam split by the beam splitter 6 enters the fourth mirror 7. After being reflected by the fourth mirror 7, it reaches the second detector 9. The first detector 8 is used to generate a radiation image of stray light.

[0042] In some embodiments of the present invention, the primary reflector 2 can be an off-axis parabolic reflector, the secondary reflector 3 can be an annular convex spherical reflector, the third reflector 4 can be an off-axis parabolic reflector, the beam splitter 6 can be a far-ultraviolet / visible light plane beam splitter 6, and the fourth reflector 7 can be a plane reflector.

[0043] The stray light of the internally masked coronagraph mainly includes stray light scattered from the surface of the primary mirror 2, direct sunlight stray light, and stray light diffracted at the edge of the entrance pupil. When the surface defects and contamination of the primary mirror 2 are low, the source of stray light scattered from the surface of the primary mirror 2 is mainly the stray light scattered by the surface roughness. Therefore, the stray light scattered by the surface roughness of the primary mirror 2 is mainly analyzed.

[0044] For stray light diffracted at the edge of the entrance pupil of a coronagraph, strong sunlight directly hitting the edge of entrance pupil 1 will cause strong diffraction. Similarly, when a solar radiation simulation device directly illuminates entrance pupil 1, a bright diffraction ring will form at the conjugate position of the object and image in entrance pupil 1, such as... Figure 2 As shown, it should be noted that due to the limitations of the detector target surface size, Figure 2 Only a portion of the bright diffraction rings were collected. It should be noted that the protrusions in some areas of the bright rings are caused by burrs during the processing of the entrance pupil 1. By installing a Leo aperture 5 of appropriate size, stray diffraction light at the edge of the entrance pupil can be effectively blocked, preventing it from reaching the imaging target surface of the first detector 8.

[0045] For the direct sunlight stray light from the coronagraph, a conical through-hole is opened in the center of the secondary mirror 3. The direct sunlight stray light falls into the light trap 10 behind the secondary mirror along with the sunlight and is completely absorbed, so that it cannot return to the normal imaging light path and becomes stray light.

[0046] In other words, the stray light diffracted at the entrance pupil edge, the stray light directly incident on the solar surface, and the stray light scattered from the surface of the primary mirror 2 caused by surface defects and contamination can all be resolved by optimizing the performance of the optomechanical structure. Therefore, this embodiment of the invention mainly analyzes the stray light scattered from the surface of the primary mirror 2 caused by the surface roughness of the primary mirror 2.

[0047] Furthermore, the first detector 8 may include a cooled CMOS deep space camera or a high-sensitivity photon counting detector.

[0048] Furthermore, the experimental measurements obtained include: measuring the first experimental value of stray light at a preset position in the radiation image when the light source emits visible light using a coronagraph stray light detection device, and measuring the second experimental value of stray light at a preset position in the radiation image when the light source emits ultraviolet light.

[0049] In some embodiments of the present invention, the preset position is a distance of 2.5R from the center of the field of view, where R is the radius of the light source. In some examples, stray light at the preset position can be used to simulate a distance of 2.5R from the center of the chromosphere. ⊙ Stray light at location.

[0050] Furthermore, obtaining the first and second simulation values ​​using the simulation model includes: performing simulation analysis using the simulation model to obtain the first simulation value of stray light at a preset position in the radiation image when the light source emits visible light, and obtaining the second simulation value of stray light at a preset position in the radiation image when the light source emits ultraviolet light; obtaining the third simulation value includes: performing simulation analysis using the corrected simulation model to obtain the third simulation value of stray light at a preset position in the radiation image when the light source emits far-ultraviolet light. The light source involved in the simulation is a simulation model of the actual light source.

[0051] Furthermore, the simulation model established based on the coronagraph stray light detection device includes: establishing the Harvey-Shack ABg model based on the primary reflector 2, and establishing the detection model based on the coronagraph stray light detection device.

[0052] Furthermore, simulation analysis was performed using a simulation model to obtain the first and second simulation values. This included substituting the surface roughness σ of the primary reflector 2 into the Harvey-Shack ABg model to obtain the BSDF function (Bidirectional Scattering Distribution Function). The expression for the BSDF function is as follows:

[0053]

[0054] in, g is the slope of the BSDF function curve, Δn is the change in refractive index before and after the reflecting surface of the primary mirror, σ is the surface roughness of the primary mirror 2, λ is the working wavelength, l is the autocorrelation length determined by the surface scattering characteristics of the primary mirror, and θ is the angle between the scattering direction and the ideal mirror reflection direction. The BSDF function is substituted into the detection model for simulation analysis to obtain the first simulation value and the second simulation value. When obtaining the first simulation value, λ is the wavelength of visible light emitted by the light source. When obtaining the second simulation value, λ is the wavelength of ultraviolet light emitted by the light source.

[0055] Furthermore, modifications to the simulation model include correcting the g and l functions of the BSDF function.

[0056] Furthermore, when obtaining the third simulation value, λ is taken as the wavelength of the far-ultraviolet light emitted by the light source.

[0057] The following is a detailed description of a specific embodiment provided by the present invention:

[0058] First, the stray light of the coronagraph in the visible light band is simulated and analyzed. The following analysis takes visible light with a wavelength of 700nm as an example. Based on the structural characteristics of the coronagraph, the stray light scattered by the primary reflector 2 is mainly analyzed. When the surface defects and surface contamination of the primary reflector 2 are suppressed to a low level, the source of the stray light scattered by the primary reflector 2 is mainly the stray light scattered by the surface roughness.

[0059] For stray light scattered by the surface roughness of primary mirror 2, the surface roughness σ of primary mirror 2 is substituted into the Harvey-Shack ABg model to obtain the BSDF function. The stray light generated by the surface roughness of primary mirror 2 under visible light at a wavelength of 700 nm is analyzed. Specifically, for... Where g is 2, Δn is 2, λ is 700 nm, σ is 0.3 nm, and l is 100 μm, A is calculated to be 1.15 × 10⁻⁶. -6 B = 1.24 × 10 -6 The BSDF function is obtained based on its expression. All optical elements in the detection model, except for the primary reflector 2, are set to ideal conditions: no surface roughness, the light source is located at infinity, and the light source's angular displacement is 32′. The stray light radiation image of the coronagraph at a working wavelength of 700 nm is obtained using the detection model established with stray light analysis software. Figure 3 As shown, the stray light analysis software obtains the stray light generated by the surface roughness of the primary reflector 2 at 2.5R based on the stray light radiation image. ⊙ The brightness contribution is approximately 10 -8 B ⊙The simulation using the stray light analysis software included: substituting the BSDF function into the stray light analysis software; ray tracing results showed that the stray light generated by the surface roughness of the primary mirror at the imaging target surface of the coronagraph was at 2.5R. ⊙ The outer edge of the simulation image provided in this invention is 2.5R. ⊙ The brightness contribution of (location) is 10. -8 B ⊙ .

[0060] Then, the stray light of the coronagraph in the ultraviolet band is simulated and analyzed. The following analysis uses 360nm ultraviolet light as an example. Specifically, the surface roughness σ of the primary mirror 2 is substituted into the Harvey-Shack ABg model to obtain the BSDF function, where the working wavelength λ is taken as 360nm, and other parameters remain unchanged. The simulation shows that the stray light in the ultraviolet band is within 2.5R... ⊙ The brightness contribution is 10 - 7 B ⊙ Stray light radiation images such as Figure 4 As shown.

[0061] Secondly, the coronagraph was illuminated with a solar radiation simulation device with a 32′ angle. The light sources were selected as 700nm visible light LEDs and 360nm ultraviolet light LEDs, respectively. The first detector 8 of the coronagraph could be a cooled CMOS deep-space camera. Cooled CMOS deep-space cameras have high sensitivity and very low readout noise in the visible and ultraviolet bands, and can collect very weak stray light. The stray light brightness contribution in the visible band and the stray light brightness contribution in the ultraviolet band were experimentally measured. For the specific detection process, please refer to the invention patent application "A High-Sensitivity Coronagraph Stray Light Detection Device" with application publication number CN111060289A and application publication date of April 24, 2020. It will not be described in detail here.

[0062] Finally, by comparing the simulation results and experimental measurements of stray light at 700nm and 360nm, the parameters g and l of the simulation model were corrected. By comparing the simulation results and experimental results at 700nm and 360nm, the parameters g and l were repeatedly modified until the simulation results were basically consistent with the experimental results. The simulation results are basically consistent with the experimental results when the difference between the simulation results and the experimental results is less than 10% of the experimental results. Thus, the final corrected simulation model was obtained.

[0063] The modified simulation model was used to analyze the brightness contribution of the surface roughness of the primary reflector 2 to the stray light from the coronagraph in the far-ultraviolet band. In some cases, when λ is 121.6 nm and σ is 0.3 nm, A = 3.82 × 10⁻⁶.-5 B = 4.13 × 10 -8 With the corrected values ​​of g = 2.2 and l ≈ 0.095 mm, the simulated stray light radiation image at the target surface of the coronagraph is as follows: Figure 5 As shown, for Figure 5 In the far-ultraviolet band, the surface roughness of primary mirror 2 is 2.5R. ⊙ The stray light brightness contribution at the location is 10. -6 B ⊙ .

[0064] The generation mechanism of entrance pupil edge diffraction stray light in the far ultraviolet band is the same as that in the visible light band, and the optical system is also completely identical. Therefore, the distribution of entrance pupil edge diffraction stray light is also the same as that in the visible light band. However, as the wavelength becomes shorter, the diffraction effect becomes less and less obvious, and the intensity of entrance pupil edge diffraction stray light becomes weaker. But in all cases, the Leo stop 5 can be used to effectively block entrance pupil edge diffraction stray light in different radiation bands.

[0065] For direct sunlight stray light in the far ultraviolet band, which is independent of wavelength, a secondary reflector 3 with a centrally conical through-hole and an optical trap 10 can completely absorb it, preventing it from returning to the normal imaging optical path and becoming stray light.

[0066] The above embodiments first model and simulate the stray light of the coronagraph in the visible and ultraviolet bands. Then, a solar simulation device with a 32′ solar disk angle is used to detect the stray light of the coronagraph in the visible and ultraviolet bands. In other embodiments of the present invention, different bands of visible light (e.g., 700nm and 550nm) and different bands of ultraviolet light (e.g., 360nm and 254nm) can be selected to detect the stray light of the coronagraph respectively. Then, the parameters of the simulation model are corrected by combining the stray light detection results. Finally, under the condition that the various optomechanical parameters in the simulation model remain unchanged, that is, under the condition that the surface roughness, surface defects, contamination, structural obstruction, etc. remain unchanged, only the working wavelength is changed to the far ultraviolet wavelength, and the stray light of the coronagraph in the far ultraviolet band is simulated and analyzed.

[0067] This invention, based on the correlation between the brightness contribution of coronagraph stray light and its operating wavelength, proposes a method combining stray light detection results from different wavelength bands with simulation results. This method directly detects coronagraph stray light in the visible and ultraviolet bands under atmospheric conditions. By combining the simulation analysis results of coronagraph stray light in the visible and ultraviolet bands, the parameters of the simulation model are corrected. The corrected simulation model is then used to analyze the stray light of the coronagraph in the far-ultraviolet band, solving the problem of directly detecting coronagraph stray light in the far-ultraviolet band. Given the limitations of light source and detector technology, this invention verifies the correlation characteristics between stray light and wavelength by analyzing and detecting stray light in different wavelength bands under atmospheric conditions, ensuring the accuracy of the stray light evaluation results in the far-ultraviolet band.

[0068] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0069] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for evaluating stray light from a far-ultraviolet coronagraph, characterized in that, include: A simulation model is established, and the model is used to simulate and obtain a first simulated value of stray light from the coronagraph in the visible light band and a second simulated value of stray light from the coronagraph in the ultraviolet band. Establishing the simulation model includes: providing a coronagraph stray light detection device, which includes a light source and a coronagraph. The coronagraph is used to receive the light beam emitted by the light source to generate a radiation image. The simulation model is established based on the coronagraph stray light detection device, which includes a primary reflector. Establishing the simulation model based on the coronagraph stray light detection device includes: establishing a Harvey-Shack ABg model based on the primary reflector and establishing a detection model based on the coronagraph stray light detection device. Obtaining the first and second simulation values ​​using the simulation model includes: performing simulation analysis using the simulation model to obtain the first simulation value of stray light at a preset position in the radiation image when the light source emits visible light, and obtaining the second simulation value of stray light at the preset position in the radiation image when the light source emits ultraviolet light; obtaining the first and second simulation values ​​using the simulation model includes: substituting the surface roughness σ of the primary reflector into the Harvey-Shack ABg model to obtain the BSDF function, the expression of which is as follows: ;in, , , g Let be the slope of the BSDF function curve as it descends. Δn The change in refractive index σ The surface roughness of the main reflector. λ For the operating wavelength, l The autocorrelation length is determined by the surface scattering properties. θ The angle between the scattering direction and the ideal specular reflection direction is used; the BSDF function is substituted into the detection model for simulation analysis to obtain the first simulation value and the second simulation value; The experiment measured the first experimental value of stray light in the visible light band of the coronagraph, and the experiment measured the second experimental value of stray light in the ultraviolet band of the coronagraph. The simulation model is corrected based on the difference between the first simulation value and the first experimental value, and the simulation model is also corrected based on the difference between the second simulation value and the second experimental value, so that the difference between the first simulation value and the first experimental value is less than 10% of the first experimental value, and the difference between the second simulation value and the second experimental value is less than 10% of the second experimental value. The modification of the simulation model includes: modifying the BSDF function. g and l Make corrections; The third simulated value of stray light in the far-ultraviolet band of the coronagraph was obtained by using the modified simulation model.

2. The method for evaluating stray light from a far-ultraviolet coronagraph according to claim 1, characterized in that, The coronagraph includes: an entrance pupil, a secondary mirror with a conical through-hole in the center, a light trap, a third mirror, a Leo diaphragm, a beam splitter, a fourth mirror, a first detector, and a second detector. Light emitted from the light source enters the primary mirror through the entrance pupil. The primary mirror images the light onto the secondary mirror. The light trap behind the secondary mirror absorbs solar rays from the light. The secondary mirror reflects corona rays from the light to the third mirror. After reflection by the third mirror, the corona rays pass through the Leo diaphragm and enter the beam splitter. The first detector receives the first beam split by the beam splitter. The second beam split by the beam splitter enters the fourth mirror, is reflected by the fourth mirror, and reaches the second detector. The first detector generates the radiation image including stray light.

3. The method for evaluating stray light from a far-ultraviolet coronagraph according to claim 2, characterized in that, The first detector includes a cooled CMOS deep space camera.

4. The method for evaluating stray light from a far-ultraviolet coronagraph according to claim 2, characterized in that, The experimental measurements obtained for the first and second experimental values ​​include: Using the coronagraph stray light detection device, the first experimental value of stray light at a preset position in the radiation image is measured when the light source emits visible light, and the second experimental value of stray light at the preset position in the radiation image is measured when the light source emits ultraviolet light.

5. The method for evaluating stray light from a far-ultraviolet coronagraph according to claim 2, characterized in that, The simulation to obtain the third simulation value includes: using the corrected simulation model to perform simulation analysis and obtain the third simulation value of stray light at a preset position in the radiation image when the light source emits far-ultraviolet light.

6. The method for evaluating stray light from a far-ultraviolet coronagraph according to claim 5, characterized in that, When obtaining the first simulation value, λ The value of is the wavelength of the visible light emitted by the light source; When obtaining the second simulation value, λ The value is taken as the wavelength of the ultraviolet light emitted by the light source.

7. The method for evaluating stray light from a far-ultraviolet coronagraph according to claim 6, characterized in that, When obtaining the third simulation value, λ The value is the wavelength of the far-ultraviolet light emitted by the light source.

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