Method capable of dynamically correcting off-axis aberration of liquid mirror telescope

Abstract

The invention discloses a method for dynamically correcting off-axis aberration of a liquid mirror telescope, which comprises the following steps of: S1, adjusting a secondary mirror body to perform dynamic full-angle circular motion around the center of a primary mirror by using a secondary mirror rotating system, so that the secondary mirror body acquires an incident beam from any direction; s2, acquiring attitude information of the secondary mirror body, and adjusting the secondary mirror body according to the dynamically changeable off-axis angle based on a preset secondary mirror pose adjustment sub-method to compensate for low-order aberration; s3, the light beams of the distorted wavefront compensated by the secondary mirror are adjusted to be emitted in a determined direction in parallel and enter an adjustable beam expanding and shrinking mirror through two groups of plane reflection systems; s4, the light beam with the light spot size adjusted through the adjustable beam expanding and shrinking mirror is reflected to the magnetic liquid deformable mirror through the reflecting mirror; and S5, the magnetic liquid deformable mirror receives the reflected light beam and performs residual aberration correction. According to the method, the observation view field of the liquid mirror telescope can be effectively improved, the imaging quality is improved, and an aberration correction system is endowed with excellent flexibility and wide adaptability.

Description

Technical Field

[0001] The invention relates to the technical field of off-axis aberration correction, and in particular to a method system capable of realizing dynamic correction of off-axis aberration of a liquid mirror telescope. Background Art

[0002] The rapid progress of space observation technology has led to a significant increase in the aperture and precision of optical telescopes, which has posed a severe challenge to the manufacturing process of traditional solid-state telescopes. Liquid mirror telescopes have become an ideal alternative to solid-state telescopes due to their simple structure, low manufacturing and maintenance costs. However, the structural characteristics of the main mirror of the liquid mirror telescope cannot be tilted, which limits the observation range to a small area near the zenith, and it shifts with the rotation of the earth, which significantly restricts its application scope and development potential.

[0003] At present, off-axis angle observation strategies are mostly used to improve the observation field of view of liquid mirror telescopes, but the resulting off-axis aberration problem will have a serious impact on the imaging quality. At present, the optical system based on the three-mirror reflection architecture can only correct the off-axis aberration at a specific angle, and cannot achieve dynamic correction. The three-mirror architecture proposed in the present invention combines a parabolic primary mirror, a secondary mirror and a magnetic fluid deformable mirror, wherein the primary mirror and the secondary mirror constitute an off-axis two-mirror system. The system reflects the light beam incident at an off-axis angle through the primary mirror to the secondary mirror to compensate for the optical path difference and correct some low-order static aberrations, and then the magnetic fluid deformable mirror further corrects the residual wavefront aberration.

[0004] In view of the variable orientation of the observation target, the secondary mirror needs to rotate around the center of the liquid mirror telescope to capture incident light beams from different directions. However, the position of the magnetic fluid deformable mirror is fixed, and the directions of light beams from different directions are different and non-constant after being reflected by the secondary mirror. At the same time, the magnetic fluid deformable mirror can correct the distorted wavefront within a certain range. Therefore, for the off-axis observation angle that varies within a certain range, the residual distorted wavefront can be controlled within the correction range of the magnetic fluid deformable mirror after adjusting the structural parameters and posture of the secondary mirror to the optimal value. Since the off-axis observation angle is not limited to a specific angle, the corresponding structure and posture parameters of the secondary mirror need to be determined according to different off-axis angles. However, the current research on optimizing the posture information of the secondary mirror corresponding to different off-axis observation angles is still scarce, and the existing structure that meets the posture adjustment of the secondary mirror has the disadvantages of high complexity, functional redundancy and cumbersome motion control, which is difficult to meet the actual correction needs of the off-axis aberration of the liquid mirror telescope.

[0005] In order to detect target objects at different orientations while keeping the position of the magnetic fluid deformable mirror fixed and to correct the off-axis aberrations caused by different observation angles, and to improve the observation field of the liquid mirror telescope, it is necessary to propose a method for dynamically correcting the off-axis aberration of the liquid mirror telescope. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for dynamically correcting the off-axis aberration of a liquid mirror telescope. The method not only has the function of flexibly capturing incident light beams from multiple directions through dynamic rotation, but also can adjust the working positions of the secondary mirror and two groups of plane mirrors accordingly according to the changes of the off-axis observation angle within a certain range, thereby ensuring that the light beam can be emitted in parallel in a certain direction and smoothly enter the magnetic liquid deformable mirror for effective correction of the distorted wavefront.

[0007] In order to achieve the above object, the present invention adopts a method for dynamically correcting the off-axis aberration of a liquid mirror telescope, comprising the following steps:

[0008] S1. Using the secondary mirror rotation system, the secondary mirror body is adjusted to perform dynamic full-angle circular motion around the center of the primary mirror, so that the secondary mirror body can obtain an incident light beam from any direction;

[0009] S2, simultaneously acquiring the posture information of the secondary mirror body, and adjusting the secondary mirror body according to the dynamically changeable off-axis angle based on a preset secondary mirror posture adjustment sub-method to compensate for part of the low-order aberrations;

[0010] The secondary mirror posture adjustment sub-method in S2 comprises the following sub-steps:

[0011] S201. Initial structural design of coaxial dual-mirror system based on Seidel aberration theory;

[0012] S202, using a particle swarm optimization algorithm to optimize the three parameters of the secondary mirror body, namely, the vertical height, horizontal offset and deflection angle. The target optimization function of the particle swarm optimization algorithm uses a combination of wavefront error and Zernike polynomial coefficients as the target function to achieve a combination of global search and fine optimization to avoid falling into a local optimal solution.

[0013] The target optimization function in step S02 is as follows:

[0014] Where: N is the number of sampled measurement points, is the wavefront error of the ith measurement point, is the ideal desired wavefront, T is the total number of Zernike polynomials, is the jth Zernike polynomial, is the weighted weight to balance the influence of wavefront error and Zernike coefficients, and p is the norm of the Zernike coefficients (usually 1 or 2). The goal of this optimization function is to minimize the wavefront error while controlling the Zernike polynomial coefficients, ultimately improving the imaging quality of the optical system.

[0015] S203, determining the optimal structural parameters of the secondary mirror body, and adjusting the three-freedom posture of the secondary mirror body based on the optimized parameters of the vertical height, horizontal offset and deflection angle;

[0016] S2054, adjusting the structural parameters and the posture of the secondary mirror body according to different off-axis observation angles. If the off-axis angle changes slightly (less than a preset value), only the three-degree-of-freedom posture of the secondary mirror body needs to be adjusted. If the off-axis angle changes significantly (greater than the preset value), the structural parameters need to be re-optimized and the posture needs to be adjusted.

[0017] S3, adjusting the light beam that has been compensated for the off-axis distortion wavefront through the secondary mirror to emit in parallel in a determined direction through two sets of plane reflection systems and entering the adjustable beam expander and reducer;

[0018] S4, the light beam after the spot size is adjusted by the adjustable beam expander and reducer is reflected by the reflector to the magnetic fluid deformable mirror;

[0019] S5. The magnetic fluid deformable mirror receives the light beam adjusted by the adjustable beam expander and reducer and performs residual aberration compensation.

[0020] A system structure capable of dynamically correcting off-axis aberration of a liquid mirror telescope, the correction system structure applies a method capable of dynamically correcting off-axis aberration of a liquid mirror telescope as described in any of the above technical solutions, and the system structure comprises the following components:

[0021] A primary mirror, which is a liquid mirror telescope body, in which liquid metal is laid and the liquid metal generates a parabolic shape through a rotating action;

[0022] a support structure mounted at an outer circumference of the primary mirror;

[0023] A secondary mirror position adjustment system, which is installed on the above-mentioned supporting structure;

[0024] A secondary mirror body, which is mounted on the secondary mirror posture adjustment system and receives the light beam from the primary mirror;

[0025] A beam path adjustment system, the beam path adjustment system having two sets of planar reflection systems receiving output beams from the secondary mirror body, and the beam path adjustment system providing posture adjustment actions for the two sets of planar reflection systems;

[0026] A reflector, the reflector is located on the light beam output path of the two sets of plane reflection systems and reflects the output light beams of the two sets of plane reflection systems to the magnetic fluid deformable mirror; wherein:

[0027] The support structure includes support columns connected around the primary mirror and a connecting component. The connecting component is installed at the junction of the overhanging ends of several support columns and the secondary mirror posture adjustment system is installed on the connecting component.

[0028] The secondary mirror position adjustment system at least includes a secondary mirror rotation system for adjusting the position of the secondary mirror body, the secondary mirror rotation system includes a drive motor and a rotating shaft, the drive motor is connected to the adjustment seat through the rotating shaft and drives the adjustment seat to dynamically rotate through the rotating shaft, and the adjustment seat is equipped with a secondary mirror vertical height adjustment system, a secondary mirror horizontal offset adjustment system and a secondary mirror angle deflection adjustment system.

[0029] The secondary mirror angle deflection adjustment system comprises a secondary mirror hanging frame, a secondary mirror mounting frame and a high-precision servo, wherein the secondary mirror hanging frame is mounted on the secondary mirror horizontal offset adjustment system and has two mounting columns extending downward along the secondary mirror horizontal offset adjustment system, the two mounting columns are arranged opposite to each other, the secondary mirror mounting frame is arranged between the two mounting columns and the secondary mirror body is mounted on the secondary mirror mounting frame, the high-precision servo is mounted on the mounting columns and the output end of the high-precision servo is connected to the secondary mirror mounting frame.

[0030] The secondary mirror horizontal offset adjustment system includes a second lead screw guide, a horizontal lead screw, a gear transmission system, a first servo motor and a horizontal motion slider. The second lead screw guide is installed on the vertical height adjustment system. The horizontal lead screw is connected to the vertical height adjustment system at one end through a bearing and is connected to the second lead screw guide at the other end. The gear transmission system has a housing connected to the second lead screw guide through a fastener. A driving wheel and a driven wheel meshing with each other are installed inside the housing. The driving wheel is connected to the output end of the first servo motor, and the driven wheel is connected to the horizontal lead screw. The horizontal motion slider is connected to the horizontal lead screw through a thread. The wing-shaped protruding ends on both sides of the horizontal motion slider are in contact with the second lead screw guide to guide the above-mentioned second lead screw guide to the above-mentioned horizontal motion slider.

[0031] The vertical height adjustment system includes a first lead screw guide with a limit block, a vertical lead screw, a second servo motor and a vertical motion slider. The first lead screw guide is installed on the adjustment seat through fasteners. The vertical lead screw is connected to the adjustment seat at one end through a bearing and is connected to the first lead screw guide at the other end. The second servo motor is fixed at one end of the first lead screw guide through fasteners and provides power for the vertical lead screw. The vertical motion slider is connected to the vertical lead screw through threads. The wing-shaped protruding ends on both sides of the vertical motion slider are in contact with the first lead screw guide so that the first lead screw guide guides the vertical motion slider.

[0032] The beam path adjustment system also includes a follow-up plane reflection posture adjustment system and a fixed plane reflection posture adjustment system, which respectively rotate synchronously with the secondary mirror posture adjustment system. The follow-up plane reflection posture adjustment system is fixed to the box of the gear transmission system through an extension hanger, and the fixed plane reflector position adjustment system is fixed to the first screw guide rail through a lifting rod.

[0033] An adjustable beam expander and reducer is arranged between the reflector and the secondary mirror posture adjustment system. The adjustable beam expander and reducer consists of three groups of lenses with adjustable relative positions. The three groups of lenses are installed in the mechanical component with air gaps between them.

[0034] The magnetic fluid deformable mirror includes a uniform magnetic field, a magnetic fluid, a thin-walled container and a micro coil. The thin-walled container is installed in the uniform magnetic field. The magnetic fluid is spread on the upper surface of the thin-walled container and placed at the center of the uniform magnetic field. The micro coil is fixedly arranged below the thin-walled container.

[0035] A method for dynamically correcting off-axis aberration of a liquid mirror telescope according to the present invention has the following beneficial effects:

[0036] 1. The present invention provides a method for dynamically correcting off-axis aberrations of a liquid mirror telescope. Through the dynamic rotation function of the secondary mirror posture adjustment system, the secondary mirror body is precisely controlled to capture incident light beams from multiple directions, giving the aberration correction system excellent flexibility and wide adaptability. According to actual observation needs, the direction of the aberration correction system is flexibly adjusted to ensure accurate reception of incident light beams from different directions, significantly improving the observation efficiency of the telescope and effectively expanding its observation range, thereby providing strong technical support for scientific research fields such as astronomical observation and space exploration;

[0037] 2. A method for dynamically correcting off-axis aberrations of a liquid mirror telescope according to the present invention adjusts the working positions of the secondary mirror body and two sets of plane mirrors according to the off-axis observation angles that vary within a certain range, so as to ensure that the light beam can be emitted in parallel in a certain direction and enter the magnetic liquid deformable mirror for distortion wavefront correction, effectively improving the stability of the system and the quality of the light beam, and also effectively reducing the energy loss in the optical path, further improving the imaging quality and observation accuracy of the telescope;

[0038] 3. The present invention provides a method for dynamically correcting the off-axis aberration of a liquid mirror telescope, which realizes high-accuracy posture positioning of the secondary mirror and two groups of plane mirrors based on a precision servo drive motor and a high-precision servo gear, thereby ensuring the accuracy and stability of the system, providing a strong guarantee for long-term continuous observation and high-precision measurement of the telescope, and further enhancing the application value of the aberration correction system in the fields of astronomical observation and space science.

[0039] With reference to the following description and drawings, a specific embodiment of the present invention is disclosed in detail, indicating the manner in which the principle of the present invention can be adopted. It should be understood that the scope of the embodiment of the present invention is not limited thereby, and the embodiment of the present invention includes many changes, modifications and equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1A schematic diagram of a method for dynamically correcting off-axis aberrations of a liquid mirror telescope is provided;

[0041] Figure 2 Schematic diagram of the structure of the primary mirror in the present invention;

[0042] Figure 3 For the present invention Figure 2 A schematic diagram of the enlarged structure at A in the middle;

[0043] Figure 4 is a schematic structural diagram of the secondary mirror body in the present invention;

[0044] Figure 5 For the present invention Figure 4 A schematic diagram of the enlarged structure at B in the middle;

[0045] Figure 6 It is a structural schematic diagram of the support structure in the present invention;

[0046] Figure 7 For the present invention Figure 6 Schematic diagram of the enlarged structure at C in the middle;

[0047] Figure 8 It is a schematic diagram of the structure of the plane reflection system in the present invention;

[0048] Fig. 9 For the present invention Figure 8 Schematic diagram of the enlarged structure at D in the middle;

[0049] Fig.10 Schematic diagram of the structure of the secondary mirror posture adjustment system in the present invention;

[0050] Fig.11 For the present invention Fig.10 Schematic diagram of the enlarged structure at E in the middle;

[0051] Fig.12 It is a schematic diagram of the structure of the adjustable beam expander and reducer in the present invention;

[0052] Fig.13 It is a structural schematic diagram of the magnetic liquid deformable mirror in the present invention;

[0053] Fig.14 The present invention is a schematic diagram of the corresponding optical path during the implementation of a method for dynamically correcting the off-axis aberration of a liquid mirror telescope.

[0054] In the figure: 1, primary mirror; 11, liquid metal; 2, supporting structure; 21, supporting column; 22, connecting parts; 3, secondary mirror posture adjustment system; 31, secondary mirror rotation system; 311, driving motor; 32, rotating shaft; 33, adjusting seat; 34, secondary mirror vertical height adjustment system; 341, first lead screw guide; 342, vertical lead screw; 343, second servo motor; 344, vertical motion slider; 35, secondary mirror horizontal offset adjustment system; 351, second lead screw guide; 352, horizontal lead screw; 353, gear transmission system; 354, first servo motor; 355, horizontal motion Movable slider; 356, box; 357, driving wheel; 358, driven wheel; 36, secondary mirror angle deflection adjustment system; 361, secondary mirror lifting frame; 362, secondary mirror mounting frame; 363, high-precision servo; 364, mounting column; 4, secondary mirror body; 5, beam path adjustment system; 51, plane reflection system; 52, follow-up plane reflection posture adjustment system; 53, fixed plane reflection posture adjustment system; 6, reflector; 7, magnetic fluid deformable mirror; 71, uniform magnetic field; 72, magnetic fluid; 73, thin-walled container; 74, micro coil; 8, adjustable beam expander and reducer; 81, lens. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below through the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0056] It should be noted that when an element is referred to as being "disposed on, provided with" another element, it may be directly on the other element or there may also be a central element. When an element is considered to be "connected, connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. "Fixed connection" means a fixed connection. There are many ways of fixed connection, which are not within the scope of protection of this article. The terms "vertical", "horizontal", "left", "right" and similar expressions used in this article are for illustrative purposes only and do not represent the only implementation method.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0058] Please refer to the instruction manual Figure 1-13The present invention provides an embodiment of a method for dynamically correcting off-axis aberrations of a liquid mirror telescope. The system structure for dynamically correcting off-axis aberrations of a liquid mirror telescope described in this embodiment includes a primary mirror 1, a support structure 2, a secondary mirror posture adjustment system 3, a beam path adjustment system 5, an adjustable beam expander and reducer 8, and a magnetic liquid deformable mirror 7, wherein:

[0059] The primary mirror 1 is a liquid mirror telescope body. Liquid metal 11 placed in the container of the primary mirror 1 produces a perfect parabola shape through rotational motion under the combined action of gravity and centrifugal force.

[0060] The support structure 2 includes a support column 21 and a connecting component 22. Preferably, in the present embodiment, the support column 21 is a cylindrical structure. One end of the four support columns 21 is fixedly installed around the rotating container, and one end is joined to the connecting component 22 through threaded fasteners, and provides installation conditions for the secondary mirror posture adjustment device 3.

[0061] The secondary mirror position adjustment system 3 includes a secondary mirror rotation system 31 , a secondary mirror vertical height adjustment system 34 , a secondary mirror horizontal offset adjustment system 35 and a secondary mirror angle deflection adjustment system 36 .

[0062] Preferably, as an embodiment of the above-mentioned system structure capable of realizing dynamic correction of off-axis aberration of a liquid mirror telescope, the secondary mirror rotation system 31 comprises a driving motor 311 and a rotating shaft 32, the driving motor 311 is fixed to the connecting component 22 by means of threaded fasteners, the extended end of the driving motor 311 is connected to the rotating shaft 32 by means of a coupling and drives the rotating shaft 32 to rotate, and the rotating shaft 32 is installed inside the connecting component 22 by means of a plurality of bearings;

[0063] Furthermore, the driving motor 311 is connected to the adjustment seat 33 through the rotating shaft 32 and drives the adjustment seat 33 to dynamically rotate through the rotating shaft 32. The adjustment seat 33 is equipped with a secondary mirror vertical height adjustment system 34, a secondary mirror horizontal offset adjustment system 35 and a secondary mirror angle deflection adjustment system 36.

[0064] In this embodiment, the secondary mirror vertical height adjustment system 34 includes a first screw guide 341 with a limit block, a vertical screw 342, a second servo motor 343 and a vertical motion slider 344. The first screw guide 341 is installed on the adjustment seat 33 through fasteners, the vertical screw 342 is connected to the adjustment seat 33 through one end of a bearing, and the other end is connected to the limit block of the first screw guide 341. The second servo motor 343 is fixed to the lower end of the limit block through fasteners and provides rotational power for the vertical screw 342. The vertical motion slider 344 is connected to the vertical screw 342 through threads, and the wing-shaped protruding ends on both sides are in contact with the first screw guide 341 to receive the guiding action. The secondary mirror body 4 can make up and down translational movements under the rotation of the vertical screw 342 and the guiding action of the first screw guide 341.

[0065] The secondary mirror horizontal offset adjustment system 35 includes a second lead screw guide 351, a horizontal lead screw 352, a gear transmission system 353, a first servo motor 354 and a horizontal motion slider 355. The second lead screw guide 351 is installed on both sides of the vertical motion slider 344 through fasteners. One end of the horizontal lead screw 352 is connected to the vertical motion slider 344 through a bearing, and the other end is connected to the limit block of the second lead screw guide 351. The gear transmission system 353 consists of a box 356 and a The housing 356 is connected to the limit block by a fastener, the driving wheel 357 is connected to the output end of the first servo motor 354, the driven wheel 358 is connected to the horizontal lead screw 352, the horizontal motion slider 355 is connected to the horizontal lead screw 352 by a thread, and the wing-shaped protruding ends on both sides of the slider contact with the second lead screw guide rail 351 to receive the guiding effect, and the secondary mirror body 4 can move horizontally left and right under the rotation of the horizontal lead screw 352 and the guiding effect of the second lead screw guide rail 351;

[0066] The secondary mirror angle deflection adjustment system 36 includes a secondary mirror hanging frame 361, a secondary mirror mounting frame 362 and a high-precision servo 363. The secondary mirror hanging frame 361 is fixedly arranged at the lower end of the horizontal moving slider 355 by a screw member. The secondary mirror hanging frame 361 has two mounting columns 364 extending downward along the secondary mirror horizontal offset adjustment system 35. The two mounting columns 364 are arranged opposite to each other. The secondary mirror mounting frame 362 is arranged between the two mounting columns 364. The high-precision servo 363 is fixed on the secondary mirror hanging frame 361, and its output end is connected to the secondary mirror mounting frame 362, thereby driving the secondary mirror deflection angle adjustment to compensate for the aberration and make the residual distortion wavefront meet the correction capability of the magnetic fluid deformable mirror 7.

[0067] The secondary mirror body 4 in the secondary mirror angle deflection adjustment system 36 is embedded in the secondary mirror mounting frame 362 .

[0068] The beam path adjustment system 5 is composed of two sets of plane reflection systems 51 with adjustable postures, and a following plane reflection posture adjustment system 52 that keeps synchronous rotation with the secondary mirror posture adjustment system 3 and a fixed plane reflection posture adjustment system 53 provide posture adjustment actions for the two sets of plane reflection systems 51.

[0069] The function of the follower plane reflection posture adjustment system 52 is to receive the parallel light emitted after the secondary mirror compensation and reflect it onto the fixed plane reflector 6. Its overall structure is fixed to the box 356 of the gear transmission system 353 through an extension hanger. The working principle is the same as that of the secondary mirror vertical height adjustment system. The difference is that two sets of high-precision servos 363 are added to drive the plane mirror to rotate in the axial and radial directions respectively.

[0070] The function of the fixed plane reflection posture adjustment system 53 is to adjust the received light beam to emit in parallel in a certain direction. It is fixed on the first screw guide rail 341 through a lifting rod, and drives the plane mirror to rotate axially and radially through a set of servo motors and a high-precision steering gear 363.

[0071] When the off-axis angle changes or the azimuth of the observed target drives the secondary mirror system to rotate as a whole, the follower plane mirror 6 can receive the light beam reflected by the secondary mirror body 4 through vertical displacement and axial radial rotation and reflect it to the fixed plane mirror 6. The fixed plane mirror 6 can adjust the light beam to be emitted in a fixed direction through axial radial rotation. Through the combined action of the two groups of plane mirrors 51, the light beam that passes through the secondary mirror to compensate for the off-axis distortion wavefront can be adjusted to be emitted in parallel in a determined direction and smoothly enter the magnetic fluid deformable mirror 7 for residual aberration correction.

[0072] The adjustable beam expander and reducer 8 is composed of three groups of lenses 81 with adjustable relative positions. The three groups of lenses 81 are installed in the mechanical assembly in an air gap manner, wherein the relative displacement of the first group and the second group of lenses will change the magnification of the beam expander, and the relative displacement of the second group and the third group of lenses will change the divergence angle of the beam expander. Specific process: The focal lengths of the three groups of lenses are f1, f2 and f3 respectively, and the combined focal length f of the two groups of lenses is obtained by adjusting the relative displacement d1 between the lens groups f1 and f2. 12 =f1+f2-d1·f1·f2, and then adjust the relative displacement d2 between the first two lens groups and the third lens group to make f 12Confocal with f3 to produce a corresponding multiple of beam expansion output to adjust the spot size. Since the spot size of the light beam compensated by the secondary mirror body 4 and passed through the path adjustment system is not fixed, but the effective correction area of ​​the magnetic fluid deformable mirror 7 is related to the arrangement, density and number of micro coils 74, which is generally a fixed size, an adjustable beam expander and reducer 8 is installed between the beam path adjustment system 5 and the magnetic fluid deformable mirror 7, so as to adjust different spot sizes to a fixed size to fit the effective correction range of the magnetic fluid deformable mirror 7.

[0073] The magnetic fluid deformable mirror 7 includes a uniform magnetic field 71, a magnetic fluid 72, a thin-walled container 73 and a micro coil 74. In the present embodiment, in order to be able to linearly control the magnetic fluid deformable mirror 7, a large uniform magnetic field 71 is generated based on a Maxwell coil or a Helmholtz coil. The magnetic fluid 72 is a stable colloidal liquid, which is a mixture of magnetic solid particles with a diameter less than 10 nm, a base carrier liquid and a surfactant. The thin-walled container 73 can be square or circular. The magnetic liquid 72 is laid on the upper surface of the thin-walled container 73 and placed at the center of the uniform magnetic field 71. The micro coil 74 is wound by electromagnetic wire, and a current is passed through it to generate a magnetic induction intensity. The micro coil 74 is fixedly arranged directly below the magnetic fluid 72 container. Under the action of the large uniform magnetic field 71, the current input by the micro coil 74 is linearly related to the deformation of the magnetic fluid 72.

[0074] The micro coils 74 can be arranged in a single-layer or double-layer layout in a regular hexagonal or square pattern.

[0075] Preferably, as an embodiment of the above-mentioned system structure that can realize dynamic correction of off-axis aberrations of liquid mirror telescopes, a double-layer drive coil is arranged in a regular hexagonal shape, wherein the lower coil is a large-size low-density structure to compensate for low-order aberrations with large amplitude and low spatial resolution, and the upper coil is a small-size high-density structure to correct high-order aberrations with small amplitude and high spatial resolution, which can adapt to various application scenarios. By utilizing the superposition effect of the magnetic field generated by the double-layer electromagnetic coil 74 and the large uniform constant magnetic field 71, the double-layer magnetic fluid deformable mirror 7 can not only meet the response requirements of a large stroke, but also meet the linear superposition of the deformation of the upper and lower micro coils 74 in the environment of the large uniform magnetic field 71. Under the action of the large uniform magnetic field 71, the magnetic field of the micro coil 74 can be adjusted in real time through the control algorithm to linearly drive the magnetic liquid 72 to produce corresponding deformation, thereby generating the desired waveform to compensate for the residual aberration.

[0076] Based on the above embodiment of a system structure capable of dynamically correcting the off-axis aberration of a liquid mirror telescope, the present invention further proposes an implementation method capable of dynamically correcting the off-axis aberration of a liquid mirror telescope, the specific situation is as follows:

[0077] S1: The primary mirror 1 is the main body of the liquid mirror telescope, and the secondary mirror rotation system 31 is used to adjust the secondary mirror body 4 to perform dynamic full-angle circular motion around the center of the primary mirror 1, so that the secondary mirror body 4 captures incident light beams in different directions to achieve all-round tracking of the target object;

[0078] S2: After the light beam is reflected by the primary mirror 1, due to the presence of large off-axis aberrations, some low-order aberrations need to be compensated by the secondary mirror, and the posture information of the secondary mirror body 4 is obtained at the same time, and the secondary mirror body 4 is adjusted based on the preset secondary mirror posture adjustment sub-method according to the dynamically changeable off-axis angle;

[0079] Sub-method for adjusting the secondary mirror posture: Based on the Seidel aberration theory, the coaxial two-mirror system is designed, focusing on the correction of the three primary aberrations of spherical aberration, astigmatism and coma to determine the curvature radius and initial installation position of the secondary mirror body 4, and the particle swarm optimization algorithm is used to optimize the three parameters of the secondary mirror body: vertical height, horizontal offset and deflection angle. The target optimization function of the particle swarm optimization algorithm uses the wavefront error and the combination of Zernike polynomial coefficients as the target function to achieve the combination of global search and fine optimization to avoid falling into the local optimal solution. In this way, the optimal structural parameters and posture of the secondary mirror body 4 are determined, so that the secondary mirror body 4 can receive the incident light beam and make the residual distortion wavefront meet the correction capability of the magnetic fluid deformable mirror. When the parameters are determined, the three free postures (i.e., vertical height, horizontal offset and deflection angle) of the secondary mirror body 4 are adjusted through the secondary mirror posture adjustment system 3. Since the magnetic fluid deformable mirror 7 can correct the distorted wavefront within a certain range, the off-axis observation angle is not limited to a specific angle, but can float within a certain range. At this time, the structural parameters and posture information of the secondary mirror body 4 need to be adjusted according to different off-axis observation angles. If the off-axis angle does not change very much, the structural parameters of the secondary mirror may not change, and it is only necessary to adjust the three-degree-of-freedom posture so that the residual distorted wavefront meets the correction capability of the magnetic fluid deformable mirror 7. The secondary mirror posture adjustment system 3 can dynamically adjust the parameters and posture of the secondary mirror body 4 according to the off-axis angle change, thereby realizing the observation and tracking of different targets and improving the observation field of the liquid mirror telescope.

[0080] Preferably, in this embodiment, the off-axis two-mirror system consists of a parabolic primary mirror and a spherical secondary mirror.

[0081] Among them, when calculating the initial structure of the coaxial two-mirror system, the profile parameters are introduced as the representation of the mutual relationship between the optical components. Considering the profile parameters of the obstruction ratio φ and the magnification γ, the definitions are as follows:

[0082] The ratio of secondary mirror to primary mirror: Secondary mirror magnification:

[0083] In order to better correct off-axis aberrations, the initial structural design of the coaxial system focuses on balancing the correction of three types of primary aberrations: spherical aberration, astigmatism and coma. According to Gaussian optical theory, the expressions of primary spherical aberration, coma and astigmatism coefficients can be derived:

[0084] Spherical aberration: Astigmatism:

[0085] Coma:

[0086] By setting the spherical aberration, coma and astigmatism coefficient equal to zero, that is, S1 = S2 = S3 = 0, φ and γ can be determined. Since the primary mirror is obtained by rotating liquid metal and the radius of curvature is known, the initial structure and position parameters R and d of the secondary mirror can be determined.

[0087] Preferably, a combination of wavefront error and Zernike polynomial coefficients is used as the target optimization function:

[0088] Among them, the target optimization function is as follows:

[0089]

[0090] Where: N is the number of sampled measurement points, WE i is the wavefront error of the ith measurement point, WE iexp is the ideal expected wavefront, T is the total number of Zernike polynomials, Z j is the jth Zernike polynomial, ω is the weighted weight to balance the influence of wavefront error and Zernike coefficient, p is the norm of Zernike coefficient (usually 1 or 2), and the goal of this optimization function is to minimize the wavefront error while controlling the Zernike polynomial coefficients, ultimately improving the imaging quality of the optical system.

[0091] S3: Since the magnetic fluid deformable mirror 7 is placed in a fixed position, when the off-axis angle changes or the azimuth of the observed target changes, the follower plane mirror 6 in the beam path adjustment system 5 can receive the light beam reflected by the secondary mirror and reflect it to the fixed plane mirror 6 through three-degree-of-freedom posture adjustment (i.e. vertical displacement, axial and radial rotation). The fixed plane mirror 6 can adjust the light beam to be emitted in a fixed direction through two-degree-of-freedom posture adjustment (i.e. axial and radial rotation). Through the combined action of the two groups of plane mirrors 51, the light beam that compensates for the off-axis distortion wavefront through the secondary mirror can be adjusted to be emitted in parallel in a determined direction and smoothly enter the magnetic fluid deformable mirror 7 for residual aberration correction.

[0092] S4: The effective correction area of ​​the magnetic fluid deformable mirror 7 is related to the arrangement, density and number of the micro coils 74, and is generally of a fixed size. An adjustable beam expander and reducer 8 is arranged between the beam path adjustment system 5 and the magnetic fluid deformable mirror 7, so that different spot sizes corrected by the secondary mirror body 4 can be continuously adjusted to a fixed size to fit the effective correction range of the magnetic fluid deformable mirror 7, thereby maximizing the performance of the magnetic fluid deformable mirror 7.

[0093] S5: The light beam adjusted by the adjustable beam expander and reducer 8 is reflected by the plane mirror 6 to the magnetic fluid deformable mirror 7 for residual aberration compensation. Under the action of the large uniform magnetic field 71, the magnetic induction intensity of the micro coil 74 is adjusted in real time through the control algorithm to linearly drive the magnetic fluid 72 to produce corresponding deformation, thereby generating the desired waveform to compensate for the residual aberration.

[0094] Preferably, as an embodiment of the present invention, a method for dynamically correcting the off-axis aberration of a liquid mirror telescope is described below in combination with Fig.14 The specific example of the off-axis two-mirror optimization design parameters is compared and explained. In this embodiment, the diameter of the liquid mirror telescope is 3 meters, the focal ratio is 2, and the maximum deformation of the magnetic liquid deformable mirror 7 is 4mm, which can correct the wavefront aberration with a maximum amplitude of 8mm. Referring to the table below, this example takes 5°, 15°, 22° and 25° as the basis angles for the secondary mirror structure parameter design in the observation angle ranges of 0-9°, 10°-18°, 19°-23°, and 24°-26°. For the above-mentioned observation angle range, it is only necessary to adjust the posture parameters such as the vertical height, horizontal offset and deflection angle of the corresponding secondary mirror to achieve partial low-order aberration compensation.

[0095]

[0096] In this embodiment, in order to further verify the practicality of the above system, the secondary mirror structure parameters designed with an off-axis observation angle of 15° are used to correct the off-axis aberration caused by the off-axis angle varying within a certain range by adjusting the posture parameters such as vertical height, horizontal offset and deflection angle, as shown in the following table. When the secondary mirror parameters are determined, if the off-axis angle varies within the range of -5° to +3°, it is only necessary to change the secondary mirror posture parameters to compensate for the aberration so that it meets the correction capability of the magnetic fluid deformable mirror.

[0097]

[0098] Under the premise of not changing the secondary mirror parameters, the variation range of the off-axis angle is related to the maximum correction capability of the magnetic fluid deformable mirror 7 .

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or 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 dynamically correcting off-axis aberration of a liquid mirror telescope, characterized in that: The steps include: S1, using the secondary mirror rotation system (31) to adjust the secondary mirror body (4) to perform dynamic full-angle circular motion around the center of the primary mirror (1), so that the secondary mirror body (4) can obtain an incident light beam from any direction; S2, simultaneously acquiring the posture information of the secondary mirror body (4), and adjusting the secondary mirror body (4) based on a preset secondary mirror posture adjustment sub-method according to the dynamically changeable off-axis observation angle to compensate for part of the low-order aberrations; S3, adjusting the light beam that has been compensated for the off-axis distortion wavefront through the secondary mirror to emit in parallel in a determined direction through two sets of plane reflection systems (51) and entering the adjustable beam expander and reducer (8); S4, the light beam after the spot size is adjusted by the adjustable beam expander and reducer (8) is reflected by the reflector (6) to the magnetic fluid deformable mirror (7); S5. The magnetic fluid deformable mirror (7) receives the light beam adjusted by the adjustable beam expander and reducer (8) and performs residual aberration compensation.

2. A method for dynamically correcting off-axis aberration of a liquid mirror telescope according to claim 1, characterized in that: The secondary mirror posture adjustment sub-method in S2 comprises the following sub-steps: S201. Initial structural design of coaxial dual-mirror system based on Seidel aberration theory; S202, using a particle swarm optimization algorithm to optimize the three parameters of the secondary mirror body, namely, the vertical height, the horizontal offset, and the deflection angle, wherein the target optimization function of the particle swarm optimization algorithm uses a combination of wavefront error and Zernike polynomial coefficients as the target function; S203, determining the optimal structural parameters of the secondary mirror body (4), and adjusting the three-freedom posture of the secondary mirror body (4) based on the optimized parameters of the vertical height, the horizontal offset and the deflection angle; S204, adjusting the structural parameters and posture of the secondary mirror body (4) according to different off-axis observation angles. If the off-axis observation angle is less than a preset value, only the three-degree-of-freedom posture of the secondary mirror body (4) needs to be adjusted. If the off-axis observation angle is greater than the preset value, the structural parameters need to be re-optimized and the posture adjusted.

3. A method for dynamically correcting off-axis aberration of a liquid mirror telescope according to claim 2, characterized in that: The target optimization function in step S202 is as follows: Where: N is the number of sampled measurement points, WE i is the wavefront error of the ith measurement point, WE iexp is the ideal expected wavefront, T is the total number of Zernike polynomials, Z j is the jth Zernike polynomial, ω is the weight to balance the influence of wavefront error and Zernike coefficient, and p is the norm of the Zernike coefficient.

4. A system structure capable of dynamically correcting off-axis aberration of a liquid mirror telescope, characterized in that: The system applies a method for dynamically correcting off-axis aberration of a liquid mirror telescope as described in any one of claims 1 to 3. The system structure includes the following components: A primary mirror (1), the primary mirror (1) being a liquid mirror telescope body, the primary mirror (1) being provided with liquid metal (11) and the liquid metal (11) generating a parabolic shape through a rotating action; A support structure (2), the support structure (2) being mounted on the outer circumference of the primary mirror (1); A secondary mirror position adjustment system (3), wherein the secondary mirror position adjustment system (3) is installed on the supporting structure (2); A secondary mirror body (4), the secondary mirror body (4) being mounted on the secondary mirror position adjustment system (3) and the secondary mirror body (4) receiving a light beam from the primary mirror (1); A beam path adjustment system (5), the beam path adjustment system (5) having two sets of plane reflection systems (51) receiving output beams from the secondary mirror body (4), and the beam path adjustment system (5) providing position adjustment actions for the two sets of plane reflection systems (51); A reflector (6), the reflector (6) being located on the light beam output path of the two sets of plane reflection systems (51) and the reflector (6) reflecting the output light beams of the two sets of plane reflection systems (51) to the magnetic fluid deformation mirror (7); wherein: The secondary mirror position adjustment system (3) at least comprises a secondary mirror rotation system (31) for adjusting the position of the secondary mirror body (4); the secondary mirror rotation system (31) comprises a driving motor (311) and a rotating shaft (32); the driving motor (311) is connected to an adjustment seat (33) via the rotating shaft (32) and drives the adjustment seat (33) to rotate dynamically via the rotating shaft (32); and a secondary mirror vertical height adjustment system (34), a secondary mirror horizontal offset adjustment system (35) and a secondary mirror angle deflection adjustment system (36) are mounted on the adjustment seat (33).

5. A system structure capable of dynamically correcting off-axis aberration of a liquid mirror telescope according to claim 4, characterized in that: The support structure (2) comprises support columns (21) connected around the primary mirror (1) and a connecting component (22); the connecting component (22) is installed at the junction of the overhanging ends of several support columns (21), and the secondary mirror position adjustment system (3) is installed on the connecting component (22).

6. The system structure capable of realizing dynamic correction of off-axis aberration of a liquid mirror telescope according to claim 5, characterized in that: The secondary mirror angle deflection adjustment system (36) comprises a secondary mirror hanging frame (361), a secondary mirror mounting frame (362) and a high-precision steering gear (363); the secondary mirror hanging frame (361) is mounted on the secondary mirror horizontal offset adjustment system (35) and the secondary mirror hanging frame (361) has two mounting columns (364) extending downward along the secondary mirror horizontal offset adjustment system (35); the two mounting columns (364) are arranged opposite to each other; the secondary mirror mounting frame (362) is arranged between the two mounting columns (364) and the secondary mirror body (4) is mounted on the secondary mirror mounting frame (362); the high-precision steering gear (363) is mounted on the mounting columns (364) and an output end of the high-precision steering gear (363) is connected to the secondary mirror mounting frame (362).

7. The system structure capable of realizing dynamic correction of off-axis aberration of a liquid mirror telescope according to claim 6, characterized in that: The secondary mirror horizontal offset adjustment system (35) comprises a second lead screw guide rail (351), a horizontal lead screw (352), a gear transmission system (353), a first servo motor (354) and a horizontal motion slider (355); the second lead screw guide rail (351) is mounted on the vertical height adjustment system (34); one end of the horizontal lead screw (352) is connected to the vertical height adjustment system (34) via a bearing and the other end is connected to the second lead screw guide rail (351); the gear transmission system (353) is connected to the second lead screw guide rail (351) via a fastener. A box body (356) is connected to the horizontal guide screw (352), a driving wheel (357) and a driven wheel (358) that mesh with each other are installed inside the box body (356), the driving wheel (357) is connected to the output end of the first servo motor (354), the driven wheel (358) is connected to the horizontal guide screw (352), the horizontal motion slider (355) is connected to the horizontal guide screw (352) through a thread, and the wing-shaped protruding ends on both sides of the horizontal motion slider (355) are in contact with the second guide screw rail (351) so that the second guide screw rail (351) guides the horizontal motion slider (355). The vertical height adjustment system (31) comprises a first screw guide rail (341) with a limit block, a vertical screw (342), a second servo motor (343) and a vertical motion slider (344); the first screw guide rail (341) is mounted on the adjustment seat (33) through a fastener; one end of the vertical screw (342) is connected to the adjustment seat (33) through a bearing and the other end is connected to the first screw guide rail (341); the second servo motor (343) is fixedly arranged at one end of the first screw guide rail (341) through a fastener and provides power for the vertical screw (342); the vertical motion slider (344) is connected to the vertical screw (342) through a thread; the wing-shaped protruding ends on both sides of the vertical motion slider (344) are in contact with the first screw guide rail (341) so that the first screw guide rail (341) guides the vertical motion slider (344).

8. The system structure capable of dynamically correcting off-axis aberration of a liquid mirror telescope according to claim 4, characterized in that: The beam path adjustment system (5) also includes a follow-up plane reflection posture adjustment system (52) and a fixed plane reflection posture adjustment system (53) which respectively rotate synchronously with the secondary mirror posture adjustment system (3); the follow-up plane reflection posture adjustment system (52) is fixed to the box (356) of the gear transmission system (353) via an extension hanger, and the fixed plane reflection mirror posture adjustment system (53) is fixed to the first screw guide rail (341) via a hanging rod.

9. The system structure capable of dynamically correcting off-axis aberration of a liquid mirror telescope according to claim 4, characterized in that: An adjustable beam expander and reducer (8) is arranged between the reflector (6) and the secondary mirror position adjustment system (3); the adjustable beam expander and reducer (8) is composed of three groups of lenses (81) whose relative positions are adjustable; the three groups of lenses are installed in the mechanical assembly in an air gap spacing manner.

10. The system structure capable of realizing dynamic correction of off-axis aberration of a liquid mirror telescope according to claim 4, characterized in that: The magnetic liquid deformable mirror (7) comprises a uniform magnetic field (71), a magnetic liquid (72), a thin-walled container (73) and a micro coil (74); the thin-walled container (73) is installed in the uniform magnetic field (71); the magnetic liquid (72) is spread on the upper surface of the thin-walled container (73) and is placed at the center of the uniform magnetic field (71); and the micro coil (74) is fixedly arranged below the thin-walled container (73).

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