Adjustment method of visible light space-based coronagraph

Abstract

The application discloses a visible light space-based coronagraph adjusting method, which comprises the following steps: 1, designing a space-based visible light coronagraph according to system design indexes; 2, using an interferometer and a standard plane mirror to finely adjust an off-axis parabolic primary mirror and determine an adjusting reference of the coronagraph; 3, using a scale to coarsely adjust a first spherical mirror and a plane reflective grating; 4, using two laser range finders to finely adjust the first spherical mirror and the plane reflective grating; and 5, using an interferometer to finely adjust the first spherical mirror and a second spherical mirror. The space-based coronagraph has the characteristics of simple element surface shape, compactness and light weight, so as to adapt to spaceborne requirements and obtain better imaging quality under a smaller volume. The adjusting method of the space-based coronagraph guarantees the imaging efficiency and use requirements of the coronagraph after adjustment.

Description

Technical Field

[0001] This invention belongs to the field of observational imaging, and in particular, it is a method for assembling and adjusting a visible light space-based coronagraph. Background Technology

[0002] The level of research and observation in solar physics directly impacts the ability to predict and forecast space weather, which in turn relates to a series of major national strategic needs, including aviation, aerospace satellite communication and navigation, and national security. As the sun is one of the key targets in deep space exploration plans, the construction of advanced space solar imaging observation equipment is of paramount importance for studying solar activity patterns, predicting changes in the space environment, achieving autonomous monitoring and early warning, and safeguarding national security.

[0003] The corona, as the outermost layer of the Sun's structure, generates a large amount of visible light radiation when the Sun experiences intense activities such as solar wind, flares, coronal mass ejections, and coronal holes. Changes in space weather directly stem from these activities. Because the Earth's atmosphere absorbs visible light, it is impossible to image and observe the corona from the ground. Therefore, imaging the corona in the visible light band from space is currently the primary method for observing solar activity phenomena internationally. This necessitates that the designed coronagraph be compact and lightweight to meet aerospace requirements. Traditional spectrometers cannot simultaneously meet the demands for a large field of view, high temporal resolution, high spatial resolution, and high spectral resolution in the visible light band. Therefore, this invention proposes a visible light coronaspectral imaging technology based on off-axis four-mirror systems. A single off-axis mirror achieves high spatial resolution imaging, while two spherical mirrors and a single planar reflection grating simultaneously achieve high spectral resolution spectroscopic imaging and aberration correction. This represents the ultimate simplification of the spectroscopic imager system to meet aerospace requirements. It can achieve simultaneous imaging with high spatial and spectral resolution under a large field of view. The use of multiple slits improves the temporal resolution, which is of great significance for observing rapidly changing solar activity phenomena. It also has important scientific research value for deepening the understanding of the triggering mechanism of solar eruptions and establishing space weather forecasting models. Summary of the Invention

[0004] The purpose of this invention is to provide a method for assembling and adjusting a visible light space-based coronagraph, so as to improve the imaging observation of the solar corona and reduce the difficulty of assembling and adjusting the coronagraph.

[0005] The technical solution of this invention is a method for assembling and adjusting a visible-light space-based coronagraph. It employs an external shielding structure to filter stray light from the solar surface; uses a multi-slit plate for scanning to achieve high temporal resolution imaging of the spectrometer system; and uses an off-axis four-mirror structure to achieve spectral dispersion and imaging of the visible light band of the solar corona. This structure includes an off-axis parabolic mirror for high spatial resolution imaging, a planar grating for high spectral resolution imaging, and two spherical mirrors for aberration correction. The specific steps are as follows:

[0006] Step 1: Design a space-based visible light coronagraph based on system design specifications.

[0007] Step 2: Use an interferometer and a standard plane mirror to fine-tune the off-axis parabolic primary mirror to determine the mounting reference for the coronagraph.

[0008] Step 3: Use a ruler to make coarse adjustments to the first spherical mirror and the plane reflection grating.

[0009] Step 4: Use two laser rangefinders to fine-tune the first spherical mirror and the plane reflection grating.

[0010] Step 5: Fine-tune the first and second spherical mirrors using an interferometer. Utilizing the principle of optical path reversibility, place the interferometer at the image plane and establish a sensitivity coefficient matrix for the six degrees of freedom of misalignment regarding the interferometer's wave aberrations. This matrix precisely guides the adjustment of the pitch and tilt of the second spherical mirror. When the wavefront measured by the interferometer matches the theoretical design value, it proves that the first and second spherical mirrors are now properly assembled and adjusted.

[0011] The space-based visible coronagraph includes a front outer shield, a rear outer shield, an off-axis parabolic primary mirror, a multi-slit device, a first spherical reflector, a plane reflection grating, a second spherical reflector, and a CMOS detector. Sunlight entering the spectrometer system passes sequentially along the optical axis through the front outer shield, the rear outer shield, the off-axis parabolic primary mirror, the multi-slit device, the first spherical reflector, the plane reflection grating, and the second spherical reflector before finally being imaged onto the CMOS detector. The front and rear outer shields together constitute the outer shielding structure of the spectrometer system. The rear outer shield coincides with the system's pupil. The outer shielding structure can reflect light from the solar surface out of the system and block stray light outside the field of view before it enters the spectrometer's optical system, improving the system's imaging efficiency. The movement of the multi-slit device, controlled by a micro-displacement motor, allows the system to quickly scan and image the entire field of view of the corona, improving the system's imaging temporal resolution.

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] (1) The coronagraph system takes into account the characteristics of simple component surface, compact component layout and lightweight to meet the needs of spaceborne applications.

[0014] (2) A design method and assembly steps for a visible light coronagraph were proposed. The sensitivity matrix of the system was solved to accurately guide the assembly and adjustment of the system, improve the timeliness of the assembly and adjustment, and ensure the imaging performance of the spectrometer. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the visible light space-based coronagraph of the present invention.

[0016] Figure 2 This is a schematic diagram of the outer shielding structure composed of the front outer shield and the rear outer shield of the present invention.

[0017] Figure 3 This is a schematic diagram of the fine-tuning off-axis parabolic primary mirror of the present invention.

[0018] Figure 4 This is a schematic diagram of the fine-tuning of the first spherical reflector and the planar reflective grating of the present invention.

[0019] Figure 5 This is a schematic diagram of the fine-tuning of the first and second spherical reflectors according to the present invention.

[0020] Figure 6 This is a flowchart illustrating the design and assembly method of the visible light space-based coronagraph of the present invention. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings.

[0022] Combination Figure 1 and Figure 6 This invention relates to a method for assembling and adjusting a visible light space-based coronagraph, comprising: Step 1, designing a space-based visible light coronagraph according to system design specifications; Step 2, fine-tuning an off-axis parabolic primary mirror 3 using an interferometer and a standard plane mirror to determine the assembly and adjustment reference of the coronagraph; Step 3, coarsely adjusting a first spherical mirror 5 and a plane reflection grating 6 using a ruler; Step 4, fine-tuning a first spherical mirror 5 and a plane reflection grating 6 using two laser rangefinders; and Step 5, fine-tuning a first spherical mirror 5 and a second spherical mirror 7 using an interferometer.

[0023] Combination Figure 1The visible light celestial-based coronagraph designed in this invention includes a front outer shield 1, a rear outer shield 2, an off-axis parabolic primary mirror 3, a multi-slit plate 4, a first spherical reflector 5, a plane reflection grating 6, a second spherical reflector 7, and a CMOS detector 8. Sunlight entering the spectrometer passes sequentially along the optical axis through the front outer shield 1, the rear outer shield 2, the off-axis parabolic primary mirror 3, the multi-slit plate 4, the first spherical mirror 5, the plane reflection grating 6, and the second spherical mirror 7 before finally being imaged on the CMOS detector 8. Controlling the movement of the multi-slit plate 4 enables the system to quickly scan and image the full field of view of the corona, improving the system's imaging temporal resolution.

[0024] Combination Figure 1 and Figure 2 The external shielding structure includes a front outer shield 1 and a rear outer shield 2. Solar surface and coronal rays outside the system's field of view will be blocked outside the coronagraph by the front outer shield 1. The rear outer shield 2 is a spherical reflector with a central opening and an inclined angle. Its inclined angle is related to the pointing angle of the satellite. The size of its central opening is the entrance pupil size designed for the system. The distance between the front outer shield 1 and the rear outer shield 2 is related to the vignetting of the system. The edge field of view vignetting is 50%, and the distance between the two needs to be designed to be 1500mm. Solar surface rays within the system's field of view will be focused by the rear outer shield 2 onto the annular light-transmitting surface of the front outer shield 1, thereby reflecting them out of the system.

[0025] Combination Figure 1 and Figure 3 The fine-tuning scheme for the off-axis parabolic primary mirror includes a standard plane mirror 9, an off-axis parabolic primary mirror 3, and an interferometer 10. First, the interferometer 10 is aligned with the standard plane mirror 9, and the position and angle of the standard plane mirror 9 are adjusted until the surface shape measured by the interferometer 10 matches the processed surface shape of the standard plane mirror 9. At this point, the standard plane mirror 9 is properly installed and adjusted. Using it as a reference, the off-axis parabolic primary mirror 3 is placed, and the interferometer 10 is positioned in front of the aberration-free point of the off-axis parabolic primary mirror 3, so that the interference... When the focal point of the standard spherical wave emitted from instrument 10 coincides with the aberration-free point of the off-axis parabolic primary mirror 3, the spherical wave emitted by interferometer 3 forms parallel light after passing through the off-axis parabolic primary mirror 3. The parallel light returns after contacting the standard plane mirror 9 and is collimated. After passing through the off-axis parabolic primary mirror 3 again, it enters the interferometer and interferes with the reference beam. When the position and orientation of the off-axis parabolic primary mirror are adjusted so that the surface shape measured by the interferometer matches the theoretical surface shape of the off-axis parabolic primary mirror, it proves that the off-axis parabolic primary mirror has been properly installed and adjusted.

[0026] Combination Figure 1 , Figure 3 and Figure 4The fine-tuning of the first spherical mirror 5 and the plane reflection grating 6 includes two laser rangefinders 11 and two parallel guide rails 12. After the off-axis parabolic primary mirror 3 is installed and adjusted, the position coordinates of the first spherical mirror 5 and the plane reflection grating 6 relative to the off-axis parabolic primary mirror 3 are determined by single-ray tracing. The first spherical mirror 5 and the plane reflection grating 6 are then coarsely adjusted to their corresponding positions using a ruler. Then, one parallel guide rail 12 is horizontally installed above the off-axis parabolic primary mirror 3, and the other parallel guide rail 12 is vertically installed to the side of the off-axis parabolic primary mirror. The two laser rangefinders 11 are respectively installed on the two parallel guide rails 12. First, two laser rangefinders 11 are aligned with the off-axis parabolic primary mirror 3 to obtain two sets of data corresponding to the off-axis parabolic primary mirror 3. Then, the two laser rangefinders 11 are moved along the guide rail 12 and aligned with the first spherical reflector 5 to obtain two sets of data corresponding to the first spherical reflector 5. Finally, the two laser rangefinders 11, moved along the parallel guide rail 12, are aligned with the plane reflection grating 6 to obtain two sets of data corresponding to the plane reflection grating 6. By subtracting the two sets of data corresponding to the off-axis parabolic primary mirror 3 from the two sets of data corresponding to the first spherical reflector 5 and the plane reflection grating 6, the actual position coordinates of the first spherical mirror 5 and the plane reflection grating 6 relative to the off-axis parabolic primary mirror 3 can be obtained. When the measured actual position coordinates of the first spherical mirror 5 and the plane reflection grating 6 are adjusted to match the relative theoretical position coordinates of single-ray tracing, it indicates that the first spherical mirror 5 and the plane reflection grating 6 have been properly installed and adjusted. Since the planar reflective grating 6 does not introduce aberrations and only serves to fold the optical path during assembly and adjustment, its accuracy is already sufficient after adjustment with a laser rangefinder. However, the first spherical reflector 5 and the second spherical reflector 7 need to be finely adjusted again to eliminate the final aberrations of the coronagraph system.

[0027] Combination Figure 1 , Figure 3 , Figure 4 and Figure 5 Fine-tuning the first spherical mirror 5 and the second spherical mirror 7 includes firstly using two laser rangefinders 11 to precisely adjust the horizontal and vertical positions of the second spherical mirror 7. At this point, the first spherical mirror 5 and the second spherical mirror 7 still have three degrees of freedom—pitch, tilt, and height—that need precise adjustment. First, the pitch and tilt of the first spherical mirror 5 and the second spherical mirror 7 are coarsely adjusted to the theoretical angle using a theodolite. Then, using the principle of optical path reversibility, the interferometer is placed at the image plane, and a sensitivity coefficient matrix is ​​established for the pitch, tilt, and height of the first spherical mirror 5 and the second spherical mirror 7 with respect to the interferometer wave aberration. This matrix precisely guides the adjustment of the pitch and tilt of the first spherical mirror 5 and the second spherical mirror 7. When the wavefront measured by the interferometer matches the theoretical design value of the coronagraph system, it proves that the first spherical mirror 5 and the second spherical mirror 7 have been properly installed and adjusted, meaning that the coronagraph system has been fully installed and adjusted.

[0028] Combination Figure 1 , Figure 3 , Figure 4 , Figure 5 and Figure 6 The entire process of assembling and adjusting the coronagraph is as follows:

[0029] Step 1: Design a visible light space-based coronagraph using the PW method based on the coronagraph design specifications.

[0030] Step 2: Use an interferometer and a standard plane mirror to fine-tune the off-axis parabolic primary mirror 3 to determine the mounting reference of the coronagraph.

[0031] Step 3: Use a ruler to make coarse adjustments to the first spherical mirror 5 and the planar reflective grating 6.

[0032] Step 4: Use two laser rangefinders to fine-tune the first spherical mirror 5 and the planar reflective grating 6.

[0033] Step 5: Solve for the sensitivity matrix of the coronagraph. Based on the sensitivity matrix, use the interferometer to fine-tune the first spherical mirror 5 and the second spherical mirror 7. The sensitivity coefficient matrix of the six misalignment degrees of freedom of the first spherical mirror 5 and the second spherical mirror 7 with respect to the interferometer wave aberration is solved as follows:

[0034] CΔA=ΔB

[0035]

[0036] C is the sensitivity matrix, ΔA is a first-order matrix composed of the variables a that need to be adjusted, and ΔB is a first-order matrix composed of the difference b between the measured value of the Zernike object Z and the design value of the optical system.

[0037]

[0038] The sensitivity matrix C obtained from the simulation design parameters of the space-based coronagraph is:

[0039]

[0040] In this system, Z5, Z6, Z7, Z8, and Z9 represent the fifth to ninth coefficients of the Zernike coefficients, D1y and D2y represent the height degrees of freedom of the first spherical mirror 5 and the second spherical mirror 7, R1x and R2x represent the tilt degrees of freedom of the first spherical mirror 5 and the second spherical mirror 7, and R1y and R2y represent the pitch degrees of freedom of the first spherical mirror 5 and the second spherical mirror 7. During the assembly and adjustment process, the Zernike coefficient values ​​corresponding to each degree of freedom can be measured in real time. The required correction value for each degree of freedom corresponding to the Zernike coefficient can be calculated using the sensitivity matrix C. Finally, through iterative adjustments, the system's design specifications are met.

Claims

1. A method for assembling and adjusting a visible light space-based coronagraph, characterized in that, The steps are as follows: Step 1: Design a visible light-based coronagraph: The visible light space-based coronagraph includes a front outer shield (1), a rear outer shield (2), an off-axis parabolic primary mirror (3), a multi-slit plate (4), a first spherical reflector (5), a plane reflection grating (6), a second spherical reflector (7), and a CMOS detector (8) arranged sequentially along the optical path. The sunlight entering the spectrometer passes sequentially along the optical axis through the front outer shield (1), the rear outer shield (2), the off-axis parabolic primary mirror (3), the multi-slit plate (4), the first spherical reflector (5), the plane reflection grating (6), and the second spherical reflector (7) before finally being imaged onto the CMOS detector (8). The front outer shield (1) and the rear outer shield (2) together constitute the outer shielding structure of the spectrometer, and the rear outer shield (2) coincides with the pupil of the spectrometer. Step 2: Use an interferometer and a standard plane mirror to fine-tune the off-axis parabolic primary mirror (3) to determine the mounting reference of the coronagraph; First, align the interferometer with the standard plane mirror. When the wavefront mass measured by the interferometer matches the theoretical mass of the standard plane mirror, fix the standard plane mirror and use it as the assembly reference for the coronagraph. Based on the principle of reversibility of light, the interferometer is aligned with the off-axis parabolic primary mirror (3), and the position and attitude of the interferometer and the off-axis parabolic primary mirror (3) are adjusted so that the surface shape of the off-axis parabolic primary mirror (3) detected by the interferometer matches the theoretical value. This indicates that the off-axis parabolic primary mirror (3) has been properly installed and adjusted. Step 3: Use a ruler to make coarse adjustments to the first spherical mirror (5) and the planar reflection grating (6); The position coordinates of the first spherical mirror (5), the plane reflection grating (6), and the second spherical mirror (7) relative to the off-axis parabolic primary mirror (3) are determined by single-ray tracing. Then, the first spherical mirror (5), the plane reflection grating (6), and the second spherical mirror (7) are coarsely adjusted to their theoretical positions using a ruler. Since the first spherical mirror (5) and the plane reflection grating (6) are both placed vertically, only their position and height on the horizontal plane need to be finely adjusted. Step 4: Use two laser rangefinders to fine-tune the first spherical mirror (5) and the plane reflection grating (6); Two laser rangefinders were used to fine-tune the first spherical mirror (5) and the plane reflection grating (6), as follows: Two laser rangefinders were placed on the horizontal and vertical guide rails respectively to facilitate the precise adjustment of the coordinate positions of the first spherical mirror (5) and the plane reflection grating (6) on the horizontal plane relative to the off-axis parabolic primary mirror (3). Since the plane reflection grating (6) does not introduce aberrations, it only plays the role of folding the optical path during assembly and adjustment. Therefore, its accuracy has met the requirements after adjustment with laser rangefinders. Step 5: Fine-tune the first spherical mirror (5) and the second spherical mirror (7) using an interferometer: The first spherical mirror (5) and the second spherical mirror (7) are finely adjusted using an interferometer, as follows: First, the position of the second spherical mirror (7) on the horizontal plane is precisely adjusted using two laser rangefinders. At this time, the first spherical mirror (5) and the second spherical mirror (7) still have three degrees of freedom: pitch, tilt, and height, which need to be precisely adjusted. Then, the pitch and tilt of the first spherical mirror (5) and the second spherical mirror (7) are coarsely adjusted to the theoretical angle using a theodolite. Using the principle of optical path reversibility, the interferometer is placed at the image plane, and a sensitivity coefficient matrix of six misaligned degrees of freedom with respect to the wave aberration of the interferometer is established to precisely guide the adjustment of the pitch and tilt of the first spherical mirror (5) and the second spherical mirror (7). When the wavefront measured by the interferometer matches the design theoretical value, it proves that the first spherical mirror (5) and the second spherical mirror (7) have been properly installed and adjusted. At this time, the coronagraph system has been fully installed and adjusted.

2. The assembly and adjustment method of the visible light space-based coronagraph according to claim 1, characterized in that: The front outer shield (1) is a ring-shaped light-transmitting structure, and the rear outer shield (2) is an inclined spherical mirror with an opening in the middle, which also serves as the pupil of the spectrometer system; the off-axis parabolic primary mirror (3) has an off-axis angle of 15 degrees, the multi-slit plate (4) is opaque and coated with light-absorbing material, and eight transparent light-transmitting slits are etched on it, with equal spacing between the slits of 1.4 mm and a width of 50 μm for each slit; the first spherical mirror (5) and the second spherical mirror (7) have the same focal length; the first spherical mirror (5) and the planar reflective grating (6) are placed vertically, i.e., without tilt or pitch; the total length of the outer shielding structure is 1500 mm, and the total length of the spectrometer optical system is 650 mm.

3. The assembly and adjustment method for a visible light space-based coronagraph according to claim 1, characterized in that, The sensitivity coefficient matrix of the six misaligned degrees of freedom with respect to the interferometer wave aberration is as follows: C = ， ， ， Where C is the sensitivity matrix. For the variables that need to be adjusted The first-order matrix formed The first-order matrix formed to correct the difference b between the measured value and the design value of the Zernike coefficient Z; ， The obtained sensitivity matrix C is: ， in, , , , These correspond to the fifth to ninth coefficients of the Zernike coefficients, respectively. D1y is the height degree of freedom of the first spherical mirror (5), D2y is the height degree of freedom of the second spherical mirror (7), R1x is the tilt degree of freedom of the first spherical mirror (5), R2x is the tilt degree of freedom of the second spherical mirror (7), R1y is the pitch degree of freedom of the first spherical mirror (5), and R2y is the pitch degree of freedom of the second spherical mirror (7).

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