Evaluation method for stray light of far ultraviolet band coronagraph

Abstract

The invention relates to the technical field of astronomical observation, in particular to a far ultraviolet band coronagraph stray light evaluation method, which comprises the following steps: establishing a simulation model, simulating to obtain a first simulation value of stray light of a coronagraph in a visible light band, and simulating to obtain a second simulation value of stray light of the coronagraph in an ultraviolet band; performing experimental measurement to obtain a first experimental value of stray light of the coronagraph in a visible light band, and performing experimental measurement to obtain a second experimental value of stray light of the coronagraph in an ultraviolet band; the simulation model is corrected, so that the difference value between the first simulation value and the first experiment value is smaller than 10% of the first experiment value, and the difference value between the second simulation value and the second experiment value is smaller than 10% of the second experiment value; and performing simulation by using the corrected simulation model to obtain a third simulation value of stray light of the coronagraph in the far ultraviolet band. According to the invention, at least the difficulty of stray light detection of the coronagraph in the far ultraviolet band can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of astronomical observation, and in particular relates to a far ultraviolet band coronagraph stray light evaluation method. Background Art

[0002] The corona is the outermost layer of the sun's atmosphere, stretching thousands of kilometers from the sun's surface to the interplanetary space. The wavelength range of coronal radiation is very wide, from X-rays, far ultraviolet, visible light to very long wavelength radio waves. Hydrogen, the element with the highest content in the sun, emits Lyman Alpha (HI Lyman Alpha, referred to as Ly-α) radiation with a wavelength of 121.6nm in the far ultraviolet band. It is the strongest ultraviolet radiation that can be observed in the coronal radiation. Lyman Alpha radiation is an important component of chromospheric radiation and coronal radiation. An endocrystal coronagraph is an instrument that images the coronal radiation near the solar disk in non-total solar eclipse conditions. Since this type of instrument needs to obtain extremely weak coronal radiation at the edge of very strong solar disk radiation, the stray light suppression capability of the endocrystal coronagraph is very high. In the far ultraviolet Lyman Alpha band, if you want to image the solar disk 2.5R from the center of the sun, ⊙ (R ⊙ The inner-occulting coronagraph observes the corona at a distance of 2.5R from the sun center. ⊙ The stray light brightness contribution of the position should be reduced to 10 -6 B ⊙ (B ⊙ is the average brightness of the solar disk), the ability to suppress stray light will determine the success or failure of the development of the endocrystal coronagraph.

[0003] The far ultraviolet band only exists in a vacuum environment, and the ground atmosphere will absorb the light in this band. If you want to observe the corona in the far ultraviolet band, you have to launch the coronagraph outside the atmosphere. In China, the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences and Shandong University have carried out scientific research projects related to corona observations. The ground-based coronagraph they developed obtained radiation images of the solar E corona in the 530.3nm band at high altitudes, but the far ultraviolet corona cannot be observed in high altitudes with thin atmosphere. Abroad, in 1995, the SOHO (Solar and Heliospheric Observatory) mission carried an exo-occulted reflective coronagraph UVCS (UltraViolet Coronagraph Spectrometer). UVCS can obtain coronal spectral information in the far ultraviolet band, but UVCS is not a coronagraph imaging observer. In 2022, Italy jointly launched the Metis exo-occulted coronagraph with several European scientific research institutions. The Metis exo-occulted coronagraph is a coronagraph that can simultaneously image in the far ultraviolet and visible light bands. It is also the only coronagraph abroad that can perform coronagraph 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 external occultation transmission imaging structure. Its working band is visible light, which does not include the far ultraviolet band. Therefore, it does not involve stray light detection and evaluation methods in the far ultraviolet band. The Metis external occultation coronagraph is the only coronagraph abroad with far ultraviolet band imaging function. However, since the external occultation coronagraph adopts an external occultation structure, the most important stray light source, the sun, will be blocked outside the coronagraph. Therefore, its stray light suppression ability is inherently better than that of the internal occultation coronagraph. How to realize stray light detection of the internal occultation coronagraph is a technical problem that needs to be urgently solved in the relevant technical field.

[0005] For the stray light detection of coronagraphs in the ultraviolet band, it can only be carried out in a vacuum environment. There is no high-brightness light source and high-sensitivity and large dynamic range detector that can be used for stray light detection in this band. Therefore, this detection is subject to technical limitations in many aspects such as the detection environment, light source and detector. Therefore, it is difficult to detect stray light of coronagraphs in the far ultraviolet band. Summary of the invention

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

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

[0008] The invention provides a method for evaluating stray light of a coronagraph in a far ultraviolet band, comprising: establishing a simulation model, using the simulation model to simulate and obtain a first simulation value of the stray light of the coronagraph in the visible light band, and simulating and obtaining a second simulation value of the stray light of the coronagraph in the ultraviolet band; experimentally measuring and obtaining a first experimental value of the stray light of the coronagraph in the visible light band, and experimentally measuring and obtaining a second experimental value of the stray light of the coronagraph in the ultraviolet band; correcting the simulation model according to the difference between the first simulation value and the first experimental value, and correcting the simulation model according to 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; and using the corrected simulation model to simulate and obtain a third simulation value of the stray light of the coronagraph in the far ultraviolet band.

[0009] Furthermore, establishing a simulation model includes: providing a coronagraph stray light detection device, the coronagraph stray light detection device includes a light source and a coronagraph, the coronagraph is used to receive a 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 main reflector, a secondary reflector with a conical through hole in the center, a light trap, a third reflector, a Leo aperture, a beam splitter, a fourth reflector, a first detector and a second detector. The light emitted by the light source is incident on the main reflector from the entrance pupil, the main reflector images the light on the secondary reflector, the light trap behind the secondary reflector absorbs the solar disk light in the light, the secondary reflector reflects the coronal light in the light to the third reflector, the coronal light is reflected by the third reflector and then enters the beam splitter through the Leo aperture, the first detector receives the first light beam split by the beam splitter, the second light beam split by the beam splitter is incident on the fourth reflector, and reaches the second detector after being reflected by the fourth reflector, and 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 first experimental value and the second experimental value obtained by experimental measurement include: using a coronagraph stray light detection device to measure a first experimental value of stray light at a preset position in a radiation image when the light source emits visible light, and measuring a second experimental value of stray light at a preset position in a radiation image when the light source emits ultraviolet light.

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

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

[0015] Further, the simulation model is used to perform simulation analysis to obtain the first simulation value and the second simulation value, including: bringing the surface roughness σ of the primary reflector into the Harvey-Shack ABg model to obtain a BSDF function, and the expression of 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 main reflector, 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 brought into the detection model for simulation analysis to obtain the first simulation value and the second simulation value; when obtaining the first simulation value, the value of λ is the wavelength of the visible light emitted by the light source; when obtaining the second simulation value, the value of λ is the wavelength of the ultraviolet light emitted by the light source.

[0018] Furthermore, correcting the simulation model includes: correcting g and l of the BSDF function.

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

[0020] Compared with the prior art, the invention can achieve the following beneficial effects: based on the correlation characteristics between stray light brightness contribution and wavelength, the invention proposes a method of combining experimental detection results of stray light in different bands with simulation results, the experimental detection results are the stray light brightness contribution in the visible light band and the stray light brightness contribution in the ultraviolet band directly detected by a coronagraph stray light detection device in the atmosphere, on this basis, combined with the simulation value of the coronagraph stray light brightness contribution in the visible light band and the simulation value 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, and the stray light brightness contribution of the coronagraph in the far ultraviolet band is derived according to the correlation characteristics between the coronagraph stray light brightness contribution and the working wavelength. In this way, although it is impossible to directly detect stray light in the far ultraviolet band, the correlation characteristics of stray light and wavelength can be verified through stray light analysis and detection in different bands. This is conducive to reducing the difficulty of stray light detection for coronagraphs in the far ultraviolet band and ensuring the accuracy of stray light evaluation results in the far ultraviolet band, which is conducive to promoting the development of astronomical target observation technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0022] Figure 1 A schematic diagram of the optical structure of the coronagraph according to an embodiment of the present invention;

[0023] Figure 2 An experimental radiation image of the stray light diffracted by the edge of the entrance pupil in the visible light band with an operating wavelength of 700nm provided by the embodiment of the invention;

[0024] Figure 3 A stray light simulation radiation image in the visible light band provided by the present invention;

[0025] Figure 4 A stray light simulation radiation image in the ultraviolet band provided by the present invention;

[0026] Figure 5 A stray light simulation radiation image in the far ultraviolet band is provided for an embodiment of the present invention.

[0027] Explanation of the reference numerals: 1. entrance pupil; 2. primary reflector; 3. secondary reflector; 4. third reflector; 5. Rio aperture; 6. beam splitter; 7. fourth reflector; 8. first detector; 9. second detector; 10. light trap. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0029] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0030] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0031] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

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

[0033] The invention provides a method for evaluating stray light of a coronagraph in a far ultraviolet band, comprising: establishing a simulation model, using the simulation model to simulate and obtain a first simulation value of the stray light of the coronagraph in the visible light band, and simulating and obtaining a second simulation value of the stray light of the coronagraph in the ultraviolet band; experimentally measuring and obtaining a first experimental value of the stray light of the coronagraph in the visible light band, and experimentally measuring and obtaining a second experimental value of the stray light of the coronagraph in the ultraviolet band; correcting the simulation model according to the difference between the first simulation value and the first experimental value, and correcting the simulation model according to 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; and using the corrected simulation model to simulate and obtain a third simulation value of the stray light of the coronagraph in the far ultraviolet band.

[0034] It should be noted that the coronagraph provided in the embodiment of the present invention is an internally masked reflection coronagraph. The third simulation value is the inferred stray light brightness contribution of the coronagraph in the far ultraviolet band. After correcting the simulation model, under the condition that the various optomechanical parameters of each instrument in the simulation model remain unchanged, only the working wavelength is changed to the wavelength of the far ultraviolet band, and the third simulation value is obtained by simulation analysis. Among them, the various optomechanical parameters include the surface roughness, surface defects, contamination, and obstruction of the optical structure of the optical element.

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

[0036] In an embodiment of the present invention, the difference between the first simulation value and the first experimental value may also be: the minimum value that the difference between the first simulation value and the first experimental value can reach, and the difference between the second simulation value and the second experimental value may also be: the minimum value that the difference between the second simulation value and the second experimental value can reach. Ideally, the difference between the first simulation value and the first experimental value is zero or approximately zero, and the difference between the second simulation value and the second experimental value is zero or approximately zero.

[0037] In view of the problem that the prior art is limited by the propagation environment of far-ultraviolet band light and the technical level of detectors and cannot directly detect the stray light of the coronagraph in the far-ultraviolet band, an embodiment of the present invention proposes a method based on combining stray light detection results in different bands with simulation results to evaluate the stray light of the coronagraph in the far-ultraviolet band. Specifically, under atmospheric conditions, the stray light brightness contribution of the coronagraph in the visible light band and the stray light brightness contribution of the ultraviolet band are obtained, and the correlation characteristics of the coronagraph stray light and the working wavelength are obtained. The correlation characteristics of the coronagraph stray light and the working wavelength are reflected in the corrected simulation model, and then the stray light brightness contribution of the coronagraph in the far-ultraviolet band is inferred based on the corrected simulation model, and then the stray light suppression capability of the far-ultraviolet band coronagraph is obtained. That is to say, the embodiment of the present invention utilizes the correlation between the brightness contribution of the coronagraph stray light and the working wavelength, and proposes a far-ultraviolet band stray light evaluation method based on the combination of visible light band and ultraviolet band stray light experimental detection results and simulation results, which solves the problem that the coronagraph stray light cannot be directly detected in the far-ultraviolet band, and is suitable for the stray light evaluation of coronagraphs of all different bands.

[0038] Furthermore, establishing the simulation model includes: providing a coronagraph stray light detection device, the coronagraph stray light detection device includes a light source and a coronagraph, the coronagraph is used to receive a light beam emitted by the light source to generate a radiation image; and establishing the simulation model according to the coronagraph stray light detection device. Specifically, it is necessary to establish the simulation model according to 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 having a 32' solar disk angle, and the solar radiation simulation device may include an LED light source.

[0040] In some embodiments of the present invention, when obtaining stray light in the visible light band, the solar radiation simulation device may include a visible light LED light source; when obtaining 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] For further reference, Figure 1The coronagraph includes: an entrance pupil 1, a main reflector 2, a secondary reflector 3 with a tapered through hole in the center, a light trap 10, a third reflector 4, a Rio aperture 5, a beam splitter 6, a fourth reflector 7, a first detector 8 and a second detector 9. The light emitted by the light source is incident on the main reflector 2 from the entrance pupil 1, and the main reflector 2 images the light on the secondary reflector 3. The light trap 10 behind the secondary reflector 3 absorbs the solar disk light in the light. After the solar disk light enters the light trap 10, it cannot enter the subsequent light path. The secondary reflector 3 reflects the coronal light in the light to the third reflector 4. After the coronal light is reflected by the third reflector 4, it passes through the Rio aperture 5 and enters the beam splitter 6. The first detector 8 receives the first light beam split by the beam splitter 6. The second light beam split by the beam splitter 6 is incident on the fourth reflector 7, and reaches the second detector 9 after being reflected by the fourth reflector 7. The first detector 8 is used to generate a radiation image of the stray light.

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

[0043] The stray light of the internally occulted reflection coronagraph mainly includes the scattered stray light from the surface of the main reflector 2, the direct stray light from the solar disk and the diffraction stray light at the edge of the entrance pupil. When the surface defects and surface contamination of the main reflector 2 are low, the source of the scattered stray light from the surface of the main reflector 2 is mainly the scattered stray light caused by the surface roughness. Therefore, the scattered stray light caused by the surface roughness of the main reflector 2 is mainly analyzed.

[0044] For the diffraction stray light at the edge of the entrance pupil of the coronagraph, strong sunlight directly hits the edge of the entrance pupil 1, and a strong diffraction phenomenon will occur. Similarly, using a solar radiation simulation device to directly illuminate the entrance pupil 1, a bright diffraction bright ring will be formed at the conjugate position of the object and image of the entrance pupil 1, such as Figure 2 As shown, it should be noted that due to the limitation of the detector target surface size, Figure 2 Only part of the diffraction bright ring is collected. It should be noted that the protrusions in some areas of the bright ring are caused by burrs during the processing of the entrance pupil 1. By installing a Leo aperture 5 of appropriate size, the diffraction stray light at the edge of the entrance pupil can be effectively blocked to prevent it from reaching the imaging target surface of the first detector 8.

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

[0046] That is to say, the stray light diffracted by the edge of the entrance pupil, the direct stray light from the solar disk, and the stray light scattered on the surface of the main reflector 2 caused by surface defects and surface contamination of the main reflector 2 can all be solved by optimizing the performance of the optical-mechanical structure. Therefore, the embodiment of the present invention mainly analyzes the stray light scattered on the surface of the main reflector 2 caused by the surface roughness of the main reflector 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 first experimental value and the second experimental value obtained by experimental measurement include: using a coronagraph stray light detection device to measure a first experimental value of stray light at a preset position in a radiation image when the light source emits visible light, and measuring a second experimental value of stray light at a preset position in a radiation image when the light source emits ultraviolet light.

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

[0050] Further, using the simulation model to simulate and obtain the first simulation value and the second simulation value includes: using the simulation model to perform simulation analysis 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; simulating and obtaining the third simulation value includes: using the modified simulation model to perform simulation analysis 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. Wherein, the light source involved in the simulation is a light source simulation model established according to an actual light source.

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

[0052] Further, the simulation model is used to perform simulation analysis to obtain the first simulation value and the second simulation value, including: bringing the surface roughness σ of the primary reflector 2 into the Harvey-Shack ABg model to obtain a BSDF function (Bidirectional Scattering Distribution Function), and the expression of the BSDF function is as follows:

[0053]

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

[0055] Furthermore, correcting the simulation model includes: correcting g and l of the BSDF function.

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

[0057] A specific embodiment provided by the embodiment of the present invention is described in detail below, which is as follows:

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

[0059] For the scattered stray light caused by the surface roughness of the main reflector 2, the surface roughness σ of the main reflector 2 is substituted into the Harvey-Shack ABg model to obtain the BSDF function, and the stray light generated by the surface roughness of the main reflector 2 under visible light of 700nm wavelength is analyzed. Specifically, for Among them, g is 2, Δn is 2, λ is 700nm, σ is 0.3nm, l is 100μm, and A is calculated to be 1.15×10 -6 , B=1.24×10 -6 , the BSDF function is obtained according to the expression of the BSDF function; the other optical elements except the main reflector 2 in the detection model are set to ideal conditions, that is, no surface roughness, and the light source is located at infinity, the light source angle is 32', and the detection model established by the stray light analysis software is simulated to obtain the stray light radiation image of the coronagraph when the working wavelength is 700nm, as shown in Figure 3 As shown, the stray light analysis software obtains the stray light generated by the surface roughness of the main reflector 2 at 2.5R according to the stray light radiation image. ⊙ The brightness contribution is about 10 -8 B ⊙Among them, the simulation using the detection model established by the stray light analysis software includes: substituting the BSDF function into the detection model established by the stray light analysis software, and the ray tracing results show that the stray light generated by the surface roughness of the primary mirror at the imaging target surface of the coronagraph is 2.5R ⊙ (The outer edge position of the simulation image provided by the present invention is 2.5R ⊙ The brightness contribution of -8 B ⊙ .

[0060] Then, the stray light of the coronagraph in the ultraviolet band is simulated and analyzed. The following analysis is taken as an example of 360nm ultraviolet light. Specifically, the surface roughness σ of the main reflector 2 is brought 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 results show that the stray light in the ultraviolet band is 2.5R ⊙ The brightness contribution is 10 - 7 B ⊙ , stray light radiation image as Figure 4 shown.

[0061] Secondly, a solar radiation simulation device with a 32′ aperture angle is used to illuminate the coronagraph. The light sources are 700nm visible light LED and 360nm ultraviolet light LED respectively. The first detector 8 of the coronagraph can select a cooled CMOS deep space camera. The cooled CMOS deep space camera has high sensitivity and very low readout noise in the visible light band and the ultraviolet band, and can collect very weak stray light. The stray light brightness contribution in the visible light band and the stray light brightness contribution in the ultraviolet band are measured experimentally. The specific detection process can be referred to the invention patent application “A High-Sensitivity Coronagraph Stray Light Detection Device” with application publication number CN111060289A and application publication date April 24, 2020, which will not be repeated here.

[0062] Finally, the simulation results of stray light at 700nm are compared with the experimental measurement results, and the simulation results of stray light at 360nm are compared with the experimental measurement results, and the parameters g and l of the simulation model are corrected. By comparing the simulation results and experimental results at 700nm and 360nm, the parameters g and l are repeatedly modified to make the simulation results 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, thereby obtaining the final corrected simulation model.

[0063] The modified simulation model is used to simulate and analyze the brightness contribution of the main reflector 2's surface roughness to the coronagraph stray light in the far ultraviolet band. In some examples, when λ is 121.6nm and σ is 0.3nm, A=3.82×10-5 , B = 4.13 × 10 -8 , after correction, g = 2.2, l ≈ 0.095 mm, the simulated stray light radiation image at the imaging target position of the coronagraph is as follows Figure 5 As shown, for Figure 5 In the far ultraviolet band, the surface roughness of the main reflector 2 is 2.5R ⊙ The stray light brightness contribution at position is 10 -6 B ⊙ .

[0064] The generation mechanism of the diffraction stray light at the edge of the entrance pupil in the far ultraviolet band is the same as that of the diffraction stray light at the edge of the entrance pupil in the visible light band, and the optical system is also completely consistent. Therefore, the distribution of the diffraction stray light at the edge of the entrance pupil 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 the diffraction stray light at the edge of the entrance pupil becomes weaker. However, the Rio aperture 5 can be used to effectively block the diffraction stray light at the edge of the entrance pupil in different radiation bands.

[0065] The direct solar stray light in the far ultraviolet band has nothing to do with the wavelength. The secondary reflector 3 with a tapered through hole in the center and the light trap 10 can completely absorb it, so that it cannot return to the normal imaging light path and become stray light.

[0066] The above-mentioned embodiment firstly models and simulates to obtain the stray light of the coronagraph in the visible light band and the ultraviolet band, and then uses a solar simulation device with a 32' solar disk angle to detect the stray light of the coronagraph in the visible light band and the ultraviolet band. In other embodiments of the present invention, visible light of different bands (for example: 700nm and 550nm) and ultraviolet light of different bands (for example: 360nm and 254nm) can be selected to respectively detect the stray light of the coronagraph, and then the parameters of the simulation model are corrected in combination with the stray light detection results. Finally, it is ensured that the various optical and mechanical parameters in the simulation model remain unchanged, that is, under the condition that the surface roughness, surface defects, pollution, 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] Based on the correlation between the brightness contribution of the coronagraph stray light and the working wavelength, the embodiment of the present invention proposes a method of combining the detection results of stray light in different bands with the simulation results, directly detecting the coronagraph stray light in the visible light band and the ultraviolet band in the atmosphere, combining the simulation analysis results of the coronagraph stray light in the visible light band and the ultraviolet band, correcting the parameters of the simulation model, and using the corrected simulation model to analyze the stray light of the coronagraph in the far ultraviolet band, thereby solving the problem of being unable to directly detect the coronagraph stray light in the far ultraviolet band. Under the premise that there are technical limitations on light sources and detectors, the correlation between stray light and wavelength is verified by analyzing and detecting stray light in different bands in the atmosphere, thereby ensuring the accuracy of the evaluation results of stray light 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 the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0069] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating stray light of a coronagraph in the far ultraviolet band, characterized in that: include: Establishing a simulation model, using the simulation model to simulate and obtain a first simulation value of stray light of the coronagraph in the visible light band, and simulating and obtaining a second simulation value of stray light of the coronagraph in the ultraviolet band; Experimentally measuring and obtaining a first experimental value of stray light of the coronagraph in the visible light band, and experimentally measuring and obtaining a second experimental value of stray light of the coronagraph in the ultraviolet band; Correcting the simulation model according to the difference between the first simulation value and the first experimental value, and correcting the simulation model according to 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 corrected simulation model is used to simulate and obtain a third simulation value of the stray light of the coronagraph in the far ultraviolet band.

2. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 1, characterized in that: Establishing the simulation model includes: providing a coronagraph stray light detection device, the coronagraph stray light detection device includes a light source and a coronagraph, the coronagraph is used to receive a light beam emitted by the light source to generate a radiation image; The simulation model is established according to the coronagraph stray light detection device.

3. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 2, characterized in that: The coronagraph includes: an entrance pupil, a primary reflector, a secondary reflector with a conical through hole at the center, a light trap, a third reflector, a Riorge aperture, a beam splitter, a fourth reflector, a first detector and a second detector. The light emitted by the light source is incident on the primary reflector from the entrance pupil, the primary reflector images the light on the secondary reflector, the light trap behind the secondary reflector absorbs the solar disk light in the light, the secondary reflector reflects the coronal light in the light to the third reflector, the coronal light is reflected by the third reflector and then enters the beam splitter through the Riorge aperture, the first detector receives the first light beam split by the beam splitter, the second light beam split by the beam splitter is incident on the fourth reflector, and reaches the second detector after being reflected by the fourth reflector, and the radiation image including stray light is generated by the first detector.

4. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 3, characterized in that: The first detector includes a cooled CMOS deep space camera.

5. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 3, characterized in that: The first experimental value and the second experimental value obtained by experimental measurement include: The coronagraph stray light detection device is used to measure the first experimental value of the stray light at a preset position in the radiation image when the light source emits visible light, and the second experimental value of the stray light at the preset position in the radiation image when the light source emits ultraviolet light.

6. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 3, characterized in that: Using the simulation model to simulate and obtain the first simulation value and the second simulation value 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; The simulation to obtain 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.

7. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 6, characterized in that: Establishing the simulation model according to the coronagraph stray light detection device includes: establishing a Harvey-Shack ABg model according to the primary reflector, and establishing a detection model according to the coronagraph stray light detection device.

8. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 7, characterized in that: Performing simulation analysis using the simulation model to obtain the first simulation value and the second simulation value includes: The surface roughness σ of the primary reflector is brought into the Harvey-Shack ABg model to obtain the BSDF function, and the expression of the BSDF function is as follows: in, g is the slope of the BSDF function curve, Δn is the change in refractive index, σ is the surface roughness of the main reflector, 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; Bringing the BSDF function into the detection model for simulation analysis to obtain the first simulation value and the second simulation value; When obtaining the first simulation value, the value of λ is the wavelength of the visible light emitted by the light source; When acquiring the second simulation value, the value of λ is the wavelength of the ultraviolet light emitted by the light source.

9. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 8, characterized in that: The modifying of the simulation model includes: modifying g and l of the BSDF function.

10. The method for evaluating stray light of a coronagraph in the far ultraviolet band according to claim 9, characterized in that: When acquiring the third simulation value, the value of λ is the wavelength of the far ultraviolet light emitted by the light source.

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