A method for dynamically correcting off-axis aberrations in liquid mirror telescopes

Abstract

This invention discloses a method for dynamically correcting off-axis aberrations in liquid mirror telescopes, comprising the following steps: S1, using a secondary mirror rotation system to adjust the secondary mirror body to perform dynamic full-angle circular motion around the center of the primary mirror, enabling the secondary mirror body to acquire incident beams from any direction; S2, simultaneously acquiring the attitude information of the secondary mirror body, and adjusting the secondary mirror body according to a preset secondary mirror pose adjustment sub-method based on the dynamically changing off-axis angle to compensate for low-order aberrations; S3, adjusting the beam of light that has passed through the secondary mirror to compensate for distortion and then projecting it parallel to a defined direction through two sets of planar reflection systems, and then into an adjustable beam expander / contractor; S4, the beam of light, after its spot size has been adjusted by the adjustable beam expander / contractor, is reflected by a reflector to a magnetofluid deformable mirror; S5, the magnetofluid deformable mirror receives the reflected beam and performs residual aberration correction. This method can effectively improve the observation field of view of liquid mirror telescopes, improve imaging quality, and endow the aberration correction system with excellent flexibility and wide adaptability.

Description

Technical Field

[0001] This invention relates to the technical field of off-axis aberration correction, and specifically to a method and system for dynamically correcting off-axis aberration in liquid mirror telescopes. Background Technology

[0002] The rapid advancements in space observation technology have led to a significant increase in the aperture and precision requirements of optical telescopes, posing a severe challenge to the manufacturing processes of traditional solid-state telescopes. Liquid mirror telescopes, with their advantages of simple structure and low manufacturing and maintenance costs, have become an ideal alternative to solid-state telescopes. However, the structural characteristic of liquid mirror telescopes—that their primary mirrors cannot be tilted—limits their observation range to a small area near the zenith, and this range shifts with the Earth's rotation, significantly restricting their application scope and development potential.

[0003] Currently, off-axis angle observation strategies are commonly used to improve the field of view of liquid mirror telescopes. However, the resulting off-axis aberrations severely impact image quality. Currently, optical systems based on a three-mirror reflection architecture can only correct off-axis aberrations at specific angles and cannot achieve dynamic correction. This invention proposes a three-mirror architecture that combines a parabolic primary mirror, a secondary mirror, and a magnetofluid deformable mirror, with the primary and secondary mirrors forming an off-axis two-mirror system. This system compensates for optical path differences and corrects some low-order static aberrations by reflecting a beam incident at an off-axis angle through the primary mirror to the secondary mirror. The magnetofluid deformable mirror then further corrects residual wavefront aberrations.

[0004] Given the variable orientation of the observed target, the secondary mirror needs to rotate around the center of the liquid mirror telescope to capture incident beams from different directions. However, the magnetofluid deformable mirror (MFD) has a fixed position, and beams from different directions, after being reflected by the secondary mirror, exhibit varying and non-constant horizontal directions. Simultaneously, the MFD can correct for a certain range of distorted wavefronts. Therefore, for varying off-axis observation angles within a certain interval, even after optimizing the secondary mirror's structural parameters and pose, the residual distorted wavefront can still be controlled within the MFD's correction range. Since the off-axis observation angle is not limited to a specific angle, the corresponding structural and pose parameters of the secondary mirror need to be determined based on the varying off-axis angles. However, current research on optimizing the secondary mirror's pose information for different off-axis observation angles is still scarce, and existing structures that satisfy the secondary mirror's pose adjustment suffer from high complexity, functional redundancy, and cumbersome motion control, making it difficult to meet the actual off-axis aberration correction requirements of liquid mirror telescopes.

[0005] In order to detect targets in different orientations while keeping the position of the magnetofluid deformable mirror fixed, and to correct off-axis aberrations caused by different observation angles, thereby improving the field of view of the liquid mirror telescope, it is necessary to propose a method that can dynamically correct off-axis aberrations of the liquid mirror telescope. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for dynamically correcting off-axis aberrations in a liquid mirror telescope. This method not only allows for flexible capture of incident beams from multiple directions through dynamic rotation, but also adjusts the working posture of the secondary mirror and two sets of plane mirrors according to the variation of the off-axis observation angle within a certain range. This ensures that the beam can maintain a certain direction of parallel emission and smoothly enter the magnetofluid deformable mirror for effective correction of the distortion wavefront.

[0007] To achieve the above objectives, the present invention employs a method for dynamically correcting off-axis aberrations in liquid mirror telescopes, comprising the following steps:

[0008] S1. The secondary mirror body is dynamically rotated around the center of the primary mirror using the secondary mirror rotation system to achieve full-angle circular motion, so that the secondary mirror body can acquire incident light beams from any direction.

[0009] S2. Simultaneously acquire the attitude information of the secondary mirror body, and adjust the secondary mirror body based on the preset secondary mirror pose adjustment sub-method according to the dynamically changing off-axis angle to compensate for some low-order aberrations.

[0010] The secondary mirror pose adjustment sub-method described in S2 includes the following sub-steps:

[0011] S201. Initial structural design of a coaxial two-reflection system based on Seidel aberration theory;

[0012] S202. A particle swarm optimization algorithm is used to optimize three parameters of the secondary mirror body: vertical height, horizontal offset, and deflection angle. The objective function of the particle swarm optimization algorithm uses a combination of wavefront error and Zernike polynomial coefficients as the objective function, achieving a combination of global search and fine optimization, and avoiding getting trapped in local optima.

[0013] The objective function in step S02 is shown below:

[0014] Where: N is the number of sampling measurement points, is the wavefront error of the i-th measurement point, is the ideal expected wavefront, T is the total number of Zernike polynomials, is the j-th Zernike polynomial, is the weighting weight to balance the influence of wavefront error and Zernike coefficients, and p is the norm of the Zernike coefficients (usually taken as 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. Determine the optimal structural parameters of the secondary mirror body, and adjust the three-free pose of the secondary mirror body based on the optimized parameters of vertical height, horizontal offset and deflection angle.

[0016] S2054. Adjust the structural parameters and pose of the secondary mirror body according to different off-axis observation angles. If the change in off-axis angle is small (less than the preset value), only the three-degree-of-freedom pose of the secondary mirror body needs to be adjusted. If the change in off-axis angle is significant (greater than the preset value), the structural parameters need to be re-optimized and the pose adjusted.

[0017] S3. The beam with off-axis distortion compensated by the secondary mirror is adjusted to a certain direction and emitted parallel to the beam through two sets of planar reflection systems and enters the adjustable beam expander and shrinker.

[0018] S4. The beam, after its spot size is adjusted by the adjustable beam expander and reducer, is reflected by the reflector to the magnetofluid deformable mirror.

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

[0020] A system structure for dynamically correcting off-axis aberrations in liquid mirror telescopes, wherein the correction system structure applies a method for dynamically correcting off-axis aberrations in liquid mirror telescopes as described in any of the above-mentioned technical solutions, and the system structure includes the following components:

[0021] The main mirror is the body of a liquid mirror telescope. Liquid metal is placed inside the main mirror, and the liquid metal generates a parabolic shape through rotation.

[0022] A support structure is installed on the outer circumference of the primary mirror;

[0023] Secondary camera pose adjustment system, which is installed on the aforementioned support structure;

[0024] The secondary mirror body is mounted on the secondary mirror pose adjustment system and receives light beams from the primary mirror.

[0025] A beam path adjustment system having two sets of planar reflection systems that receive the output beam from the secondary mirror body, and the beam path adjustment system providing pose adjustment for the two sets of planar reflection systems;

[0026] A reflector is positioned on the beam output path of two sets of planar reflection systems and reflects the output beams of the two sets of planar reflection systems to the magnetofluid deformable mirror; wherein:

[0027] The support structure includes support columns connected around the primary mirror and connecting components. The connecting components are installed at the confluence of the cantilevered ends of several support columns, and the aforementioned secondary mirror pose adjustment system is installed on the connecting components.

[0028] The secondary mirror pose adjustment system includes at least 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 rotation shaft. The drive motor is connected to the adjustment seat through the rotation shaft and drives the adjustment seat to rotate dynamically. 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 includes a secondary mirror hoisting frame, a secondary mirror mounting frame, and a high-precision servo motor. The secondary mirror hoisting frame is installed on the aforementioned secondary mirror horizontal offset adjustment system and has two mounting posts extending downward along the secondary mirror horizontal offset adjustment system. The two mounting posts are arranged opposite to each other. The secondary mirror mounting frame is arranged between the two mounting posts, and the secondary mirror body is installed on the aforementioned secondary mirror mounting frame. The high-precision servo motor is installed on the mounting posts, and the output end of the high-precision servo motor is connected to the secondary mirror mounting frame.

[0030] The secondary mirror horizontal offset adjustment system includes a second lead screw guide rail, a horizontal lead screw, a gear transmission system, a first servo motor, and a horizontal motion slider. The second lead screw guide rail is mounted on the vertical height adjustment system. The horizontal lead screw is connected to the vertical height adjustment system at one end via a bearing, and to the second lead screw guide rail at the other end. The gear transmission system has a housing connected to the second lead screw guide rail via fasteners. A driving wheel and a driven wheel that mesh with each other are mounted 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 via a thread. The two airfoil-shaped extension ends of the horizontal motion slider contact the second lead screw guide rail so that the second lead screw guide rail guides the horizontal motion slider.

[0031] The vertical height adjustment system includes a first lead screw guide rail with a limit block, a vertical lead screw, a second servo motor, and a vertical motion slider. The first lead screw guide rail is mounted on the adjustment seat by fasteners. The vertical lead screw is connected to the adjustment seat at one end by a bearing and to the first lead screw guide rail at the other end. The second servo motor is fixed to one end of the first lead screw guide rail by fasteners and provides power to the vertical lead screw. The vertical motion slider is connected to the vertical lead screw by threads. The two airfoil-shaped protruding ends of the vertical motion slider contact the first lead screw guide rail so that the first lead screw guide rail guides the vertical motion slider.

[0032] The beam path adjustment system also includes a follower-type planar reflection pose adjustment system and a fixed planar reflection pose adjustment system that rotate synchronously with the secondary mirror pose adjustment system. The follower-type planar reflection pose adjustment system is fixed to the housing of the gear transmission system by an extension hanger, and the fixed planar reflector position adjustment system is fixed to the first lead screw guide rail by a hoisting rod.

[0033] An adjustable beam expander / contractor is provided between the reflector and the secondary mirror pose adjustment system. The adjustable beam expander / contractor consists of three sets of lenses with adjustable relative positions, and the three sets of lenses are installed in the mechanical assembly with an air gap 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, and the micro coil is fixedly installed below the thin-walled container.

[0035] The present invention provides a method for dynamically correcting off-axis aberrations in liquid mirror telescopes, which has the following beneficial effects:

[0036] 1. This invention provides a method for dynamically correcting off-axis aberrations in liquid mirror telescopes. Through the dynamic rotation function of the secondary mirror orientation adjustment system, the secondary mirror body is precisely controlled to capture incident light beams from multiple directions, endowing the aberration correction system with excellent flexibility and wide adaptability. The direction of the aberration correction system can be flexibly adjusted according to actual observation needs, ensuring accurate reception of incident light beams from different directions, significantly improving the telescope's observation efficiency, effectively expanding its observation range, and thus providing strong technical support for scientific research fields such as astronomical observation and space exploration.

[0037] 2. The present invention provides a method for dynamically correcting off-axis aberration of a liquid mirror telescope. The method adjusts the working posture of the secondary mirror body and the two sets of plane mirrors according to the off-axis observation angle that varies within a certain range, so as to ensure that the beam can be emitted in parallel in a certain direction and enter the magnetic fluid deformation mirror for distortion wavefront correction. This effectively improves the stability and beam quality of the system, and also effectively reduces 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 off-axis aberrations of liquid mirror telescopes. Based on a precision servo drive motor and a high-precision servo motor, it achieves high-accuracy pose positioning of the secondary mirror and two sets of plane mirrors, ensuring the accuracy and stability of the system. This provides strong support for long-term continuous observation and high-precision measurement of the telescope, and further enhances the application value of aberration correction systems in astronomical observation and space science.

[0039] Specific embodiments of the present invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the present invention can be adopted. It should be understood that the embodiments of the present invention are not limited in scope as a result, and the embodiments of the present invention include many changes, modifications and equivalents. Attached Figure Description

[0040] Figure 1This is a schematic diagram of a method for dynamically correcting off-axis aberrations in a liquid mirror telescope.

[0041] Figure 2 This is a schematic diagram of the primary mirror structure in this invention;

[0042] Figure 3 In this invention Figure 2 Enlarged structural diagram at point A;

[0043] Figure 4 This is a schematic diagram of the structure of the secondary mirror body in this invention;

[0044] Figure 5 In this invention Figure 4 Enlarged structural diagram at point B;

[0045] Figure 6 This is a schematic diagram of the supporting structure in this invention;

[0046] Figure 7 In this invention Figure 6 Enlarged structural diagram at point C;

[0047] Figure 8 This is a schematic diagram of the planar reflection system in this invention;

[0048] Figure 9 In this invention Figure 8 Enlarged structural diagram at point D;

[0049] Figure 10 This is a schematic diagram of the secondary mirror pose adjustment system in this invention;

[0050] Figure 11 In this invention Figure 10 Enlarged structural diagram at point E;

[0051] Figure 12 This is a schematic diagram of the adjustable beam expander / contractor in this invention.

[0052] Figure 13 This is a schematic diagram of the structure of the magnetofluid deformable mirror in this invention;

[0053] Figure 14 This is a schematic diagram of the optical path during the implementation of a method for dynamically correcting off-axis aberrations in liquid mirror telescopes.

[0054] In the diagram: 1. Primary mirror; 11. Liquid metal; 2. Support structure; 21. Support column; 22. Connecting component; 3. Secondary mirror pose adjustment system; 31. Secondary mirror rotation system; 311. Drive motor; 32. Rotation shaft; 33. Adjustment seat; 34. Secondary mirror vertical height adjustment system; 341. First lead screw guide rail; 342. Vertical lead screw; 343. Second servo motor; 344. Vertical motion slider; 35. Secondary mirror horizontal offset adjustment system; 351. Second lead screw guide rail; 352. Horizontal lead screw; 353. Gear transmission system; 354. First servo motor; 355. Horizontal motion slider. 356. Moving slider; 357. Housing; 358. Driving wheel; 36. Driven wheel; 37. Secondary mirror angle deflection adjustment system; 38. Secondary mirror hoisting frame; 39. Secondary mirror mounting frame; 30. High-precision servo motor; 31. Mounting post; 4. Secondary mirror body; 52. Beam path adjustment system; 53. Plane reflection system; 54. Follow-type plane reflection posture adjustment system; 555. Fixed plane reflection posture adjustment system; 6. Reflector; 7. Magnetofluid deformable mirror; 756. Uniform magnetic field; 777. Magnetic fluid; 78. Thin-walled container; 79. Miniature coil; 80. Adjustable beam expander / contractor; 81. Lens. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

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

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in the specification herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

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

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

[0060] The support structure 2 includes support columns 21 and connecting components 22. Preferably, in this embodiment, the support columns 21 are cylindrical structures. One end of the four support columns 21 is fixedly installed around the rotating container, and the other end is joined to the connecting components 22 by threaded fasteners, providing installation conditions for the secondary mirror pose adjustment device 3.

[0061] The secondary mirror pose 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 that can realize dynamic correction of off-axis aberration of liquid mirror telescope, the secondary mirror rotation system 31 includes a drive motor 311 and a rotation shaft 32. The drive motor 311 is fixed to the connecting component 22 by threaded fasteners, and its extended end is connected to the rotation shaft 32 by a coupling and drives it to rotate. The rotation shaft 32 is installed inside the connecting component 22 by multiple sets of bearings.

[0063] Furthermore, the drive motor 311 is connected to the adjustment seat 33 via the rotating shaft 32 and drives the adjustment seat 33 to rotate dynamically. 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 lead screw guide rail 341 with a limit block, a vertical lead screw 342, a second servo motor 343, and a vertical motion slider 344. The first lead screw guide rail 341 is mounted on the adjustment seat 33 by fasteners. One end of the vertical lead screw 342 is connected to the adjustment seat 33 by a bearing, and the other end is connected to the limit block of the first lead screw guide rail 341. The second servo motor 343 is fixedly set at the lower end of the limit block by fasteners and provides rotational power for the vertical lead screw 342. The vertical motion slider 344 is connected to the vertical lead screw 342 by threads, and its two wing-shaped protruding ends contact the first lead screw guide rail 341 to receive guidance. The secondary mirror body 4 can move up and down under the rotation of the vertical lead screw 342 and the guidance of the first lead screw guide rail 341.

[0065] The secondary mirror horizontal offset adjustment system 35 includes 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 both sides of the vertical motion slider 344 by fasteners. One end of the horizontal lead screw 352 is connected to the vertical motion slider 344 via a bearing, and the other end is connected to the limiting block of the second lead screw guide rail 351. The gear transmission system 353 consists of a housing 356 and a... The secondary mirror body 4 is composed of intermeshing gears. The housing 356 is connected to the limit block by fasteners. 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 threads. Its two wing-shaped protruding ends contact the second lead screw guide rail 351 to receive the guiding action. The secondary mirror body 4 can move horizontally left and right under the rotation of the horizontal lead screw 352 and the guiding action of the second lead screw guide rail 351.

[0066] The secondary mirror angle deflection adjustment system 36 includes a secondary mirror hoisting frame 361, a secondary mirror mounting frame 362, and a high-precision servo motor 363. The secondary mirror hoisting frame 361 is fixedly mounted on the lower end of the horizontal motion slider 355 by a threaded component. The secondary mirror hoisting frame 361 has two mounting posts 364 extending downward along the secondary mirror horizontal offset adjustment system 35. The two mounting posts 364 are arranged opposite to each other. The secondary mirror mounting frame 362 is arranged between the two mounting posts 364. The high-precision servo motor 363 is fixed on the secondary mirror hoisting 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 aberrations and make the residual distortion wavefront meet the correction capability of the magnetofluid deformable mirror 7.

[0067] In the secondary mirror angle deflection adjustment system 36, the secondary mirror body 4 is embedded in the secondary mirror mounting bracket 362.

[0068] The beam path adjustment system 5 consists of two sets of adjustable planar reflection systems 51, and a follow-type planar reflection posture adjustment system 52 and a fixed planar reflection posture adjustment system 53 that rotate synchronously with the secondary mirror posture adjustment system 3 provide posture adjustment actions for the two sets of planar reflection systems 51.

[0069] The function of the following planar reflection posture adjustment system 52 is to receive the parallel light emitted after secondary mirror compensation and reflect it onto the fixed planar reflector 6. Its overall structure is fixed on the housing 356 of the gear transmission system 353 by an extension bracket. Its working principle is the same as that of the secondary mirror vertical height adjustment system. The difference is that two sets of high-precision servo motors 363 are added to drive the planar mirror to rotate along the axial and radial directions respectively.

[0070] The function of the fixed planar reflection posture adjustment system 53 is to adjust the received beam of light to be emitted in a certain direction in parallel. It is fixed on the first lead screw guide rail 341 by a hoisting rod, and drives the plane mirror to rotate along the axial and radial directions by a set of servo motors and high-precision servo motors 363.

[0071] When the off-axis angle changes or the orientation of the observed target changes, causing the secondary mirror system to rotate as a whole, the following 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 onto 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 sets of plane mirrors 51, the light beam that has passed through the secondary mirror to compensate for off-axis distortion can be adjusted to be emitted in a determined direction and smoothly enter the magnetofluid deformable mirror 7 for residual aberration correction.

[0072] An adjustable beam expander / contractor 8 is provided, consisting of three sets of lenses 81 with adjustable relative positions. These three sets of lenses 81 are mounted in a mechanical assembly with air gaps between them. The relative displacement of the first and second sets of lenses changes the magnification of the beam expander, while the relative displacement of the second and third sets of lenses changes the divergence angle. Specifically, the focal lengths of the three sets of lenses are f1, f2, and f3, respectively. The combined focal length f of two sets of lenses is obtained by adjusting the relative displacement d1 between lens groups f1 and f2. 12 =f1+f2-d1·f1·f2, then by adjusting the relative displacement d2 between the first two lens groups and the third lens group, f 12The beam is confocal with f3 to produce a corresponding magnification of beam expansion output, thereby adjusting the spot size. Since the beam spot size 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 miniature coils 74, it 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, thereby adjusting different spot sizes to a fixed size to fit the effective correction range of the magnetic fluid deformable mirror 7.

[0073] The magnetic fluid deformation mirror 7 includes a uniform magnetic field 71, a magnetic fluid 72, a thin-walled container 73, and a micro coil 74. In this embodiment, in order to linearly control the magnetic fluid deformation mirror 7, a large uniform magnetic field 71 is generated based on Maxwell coils or Helmholtz coils. The magnetic fluid 72 is a stable colloidal liquid, which is composed of magnetic solid particles with a diameter of less than 10 nm, a base liquid, and a surfactant. The thin-walled container 73 can be square or circular. The magnetic fluid 72 is spread 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 made of electromagnetic wire and generates magnetic induction intensity when current is passed through it. It is fixedly set directly below the container of magnetic fluid 72. Under the action of the large uniform magnetic field 71, the current input to the micro coil 74 is linearly related to the deformation of the magnetic fluid 72.

[0074] The miniature coil 74 can be arranged in a single-layer or double-layer layout, uniformly arranged in a regular hexagonal or square pattern.

[0075] Preferably, as an embodiment of the above-mentioned system structure for dynamically correcting off-axis aberrations of a liquid mirror telescope, a double-layer drive coil is arranged in a regular hexagonal configuration. The lower coil has a large size and low density to compensate for low-order aberrations with large amplitude and low spatial resolution, while the upper coil has a small size and high density to correct high-order aberrations with small amplitude and high spatial resolution, thus adapting 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 not only meets the response requirements for a large stroke but also satisfies the linear superposition of the deformations 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-coils 74 can be adjusted in real time through a control algorithm to linearly drive the magnetic fluid 72 to produce corresponding deformation, thereby generating the desired waveform to compensate for residual aberrations.

[0076] Based on the above embodiment of a system structure capable of dynamically correcting off-axis aberrations in a liquid mirror telescope, the present invention also proposes a method for dynamically correcting off-axis aberrations in a liquid mirror telescope, as detailed below:

[0077] S1: The primary mirror 1 is the main body of the liquid mirror telescope. The secondary mirror body 4 is dynamically rotated around the center of the primary mirror 1 using the secondary mirror rotation system 31. This allows the secondary mirror body 4 to capture incident light beams from different directions, enabling all-round tracking of the target.

[0078] S2: After the beam is reflected by the primary mirror 1, there is a large off-axis aberration. It is necessary to compensate for some low-order aberrations through the secondary mirror. At the same time, the attitude information of the secondary mirror body 4 is obtained, and the secondary mirror body 4 is adjusted according to the preset secondary mirror pose adjustment sub-method based on the dynamically changing off-axis angle.

[0079] The secondary mirror pose adjustment method is as follows: Based on Seidel aberration theory, a coaxial two-mirror system is designed, focusing on the correction of three primary aberrations: spherical aberration, astigmatism, and coma, to determine the radius of curvature and initial installation position of the secondary mirror body 4. A particle swarm optimization algorithm is used to optimize three parameters of the secondary mirror body: vertical height, horizontal offset, and deflection angle. The objective function of the particle swarm optimization algorithm uses a combination of wavefront error and Zernike polynomial coefficients as the objective function, achieving a combination of global search and fine optimization to avoid getting trapped in local optima. This determines the optimal structural parameters and pose of the secondary mirror body 4, enabling it to receive the incident beam and ensuring that the residual distortion wavefront meets the correction capability of the magnetohydraulic deformable mirror. Once the parameters are determined, the three-free pose (i.e., vertical height, horizontal offset, and deflection angle) of the secondary mirror body 4 is adjusted through the secondary mirror pose adjustment system 3. Since the magnetofluid 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 fluctuate within a certain range. In this case, the structural parameters and pose information of the secondary mirror body 4 need to be adjusted according to different off-axis observation angles. If the off-axis angle change is not significant, the structural parameters of the secondary mirror do not need to change; only the three-degree-of-freedom pose needs to be adjusted to ensure that the residual distorted wavefront meets the correction capability of the magnetofluid deformable mirror 7. The secondary mirror pose adjustment system 3 can dynamically adjust the parameters and pose of the secondary mirror body 4 according to changes in the off-axis angle, thereby enabling the observation and tracking of different targets and improving the observation field of view of the liquid mirror telescope.

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

[0081] In calculating the initial structure of the coaxial two-reflector system, a profile parameter is introduced to characterize the interrelationships of the various optical components. Considering the profile parameter occlusion ratio φ and magnification γ, the following definitions are made:

[0082] Secondary mirror's blocking ratio to primary mirror: Secondary mirror magnification:

[0083] To better correct off-axis aberrations, the initial structural design of coaxial systems focuses on balancing the correction of the three primary aberrations: spherical aberration, astigmatism, and coma. Based on Gaussian optics theory, the expressions for the coefficients of primary spherical aberration, coma, and astigmatism can be derived as follows:

[0084] Ball difference: Like scattered:

[0085] Coma:

[0086] By setting spherical aberration, coma, and astigmatism coefficients to zero (i.e., S1 = S2 = S3 = 0), φ and γ can be determined. Since the primary mirror is obtained by rotating liquid metal, its radius of curvature is known, thus 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 objective optimization function:

[0088] The objective optimization function is shown below:

[0089]

[0090] Where: N is the number of sampling measurement points, WE i WE is the wavefront error at the i-th measurement point. iexp It is the wavefront of the ideal expectation, T is the total number of Zernike polynomials, and Z is the wavefront of the ideal expectation. j ω is the j-th Zernike polynomial, ω is the weighting 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.

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

[0092] S4: The effective correction area of ​​the magnetofluid deformable mirror 7 is related to the arrangement, density and number of the micro coils 74. It is generally a fixed size. An adjustable beam expander and shrinker 8 is set between the beam path adjustment system 5 and the magnetofluid deformable mirror 7. This allows the different spot sizes after correction by the secondary mirror body 4 to be continuously adjusted to a fixed size to fit the effective correction range of the magnetofluid deformable mirror 7, thereby maximizing the performance of the magnetofluid deformable mirror 7.

[0093] S5: The beam adjusted by the adjustable beam expander and reducer 8 is reflected by the plane mirror 6 to the magnetic fluid deformation 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 by the control algorithm to linearly drive the magnetic fluid 72 to produce corresponding deformation, thereby generating the desired waveform to compensate for residual aberration.

[0094] Preferably, as an embodiment of the method for dynamically correcting off-axis aberrations of a liquid mirror telescope according to the present invention, the following will be combined with... Figure 14 A specific example is provided to compare and illustrate the parameters of the off-axis two-mirror optimization design. In this embodiment, the liquid mirror telescope has a diameter of 3 meters and a focal ratio of 2. The maximum deformation of the magnetofluid deformable mirror 7 is 4 mm, which can correct wavefront aberrations with a maximum amplitude of 8 mm. Referring to the table below, this example uses 5°, 15°, 22°, and 25° as the base angles for secondary mirror structure parameter design within the observation angle ranges of 0–9°, 10°–18°, 19°–23°, and 24°–26°, respectively. For the above observation angle ranges, only the pose parameters such as the vertical height, horizontal offset, and deflection angle of the corresponding secondary mirror need to be adjusted to achieve partial low-order aberration compensation.

[0095]

[0096] In this embodiment, to further verify the practicality of the above system, the secondary mirror structure parameters designed with a 15° off-axis observation angle are adjusted by adjusting the pose parameters such as vertical height, horizontal offset, and deflection angle to correct the off-axis aberration caused by the varying off-axis angle within a certain range, as shown in the table below. When the secondary mirror parameters are determined, if the off-axis angle varies within the range of -5° to +3°, only the pose parameters of the secondary mirror need to be changed to compensate for the aberration, thereby enabling it to meet the correction capability of the magnetohydraulic deformable mirror.

[0097]

[0098] Without changing the secondary mirror parameters, the range of variation of the off-axis angle is related to the maximum correction capability of the magnetofluid 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 modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for dynamically correcting off-axis aberrations in a liquid mirror telescope, characterized in that: The steps include: S1. Using the secondary mirror rotation system (31), 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 incident beams from any direction. S2. Simultaneously acquire the attitude information of the secondary mirror body (4), and adjust the secondary mirror body (4) based on the preset secondary mirror pose adjustment sub-method according to the dynamically changing off-axis observation angle to compensate for some low-order aberrations. The secondary mirror pose adjustment sub-method described in S2 includes the following sub-steps: S201. Initial structural design of a coaxial two-reflection system based on Seidel aberration theory; S202. 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 objective function of the particle swarm optimization algorithm is a combination of wavefront error and Zernike polynomial coefficients. The objective optimization function in step S202 is as follows: ， in: N It is the number of measurement points sampled. It is the first i Wavefront error at each measurement point It is the wavefront of ideal expectations. T It is the total number of Zernike polynomials. It is the first j A Zernike polynomial, The weighting is used to balance the effects of wavefront error and Zernike coefficient. p It is the norm of the Zernike coefficient; S203. Determine the optimal structural parameters of the secondary mirror body (4), and adjust the three-free pose of the secondary mirror body (4) based on the optimized parameters of vertical height, horizontal offset and deflection angle. S204. Adjust the structural parameters and pose of the secondary mirror body (4) according to different off-axis observation angles. If the off-axis observation angle is less than the preset value, only the three-degree-of-freedom pose 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 pose adjusted. S3. The beam of light with off-axis distortion compensated by the secondary mirror is adjusted to a certain direction and emitted parallel to the secondary mirror through two sets of planar reflection systems (51) and enters the adjustable beam expander and shrinker (8). S4. The beam, after its spot size is adjusted by the adjustable beam expander and reducer (8), is reflected by the reflector (6) to the magnetofluid deformable mirror (7). S5, the magnetic fluid deformation mirror (7) receives the beam adjusted by the adjustable beam expander and shrinker mirror (8) and performs residual aberration compensation.

2. A system structure for dynamically correcting off-axis aberrations in a liquid mirror telescope, characterized in that, This system applies the method for dynamically correcting off-axis aberrations in liquid mirror telescopes as described in claim 1. The system structure includes the following components: The main mirror (1) is the main body of the liquid mirror telescope. Liquid metal (11) is laid in the main mirror (1) and the liquid metal (11) generates a parabolic shape through rotation. Support structure (2), which is installed on the outer circumference of the main mirror (1); Secondary camera pose adjustment system (3), which is installed on the above-mentioned support structure (2); Secondary mirror body (4), which is mounted on secondary mirror pose adjustment system (3) and receives light beams from primary mirror (1); The beam path adjustment system (5) has two sets of planar reflection systems (51) that receive the output beam from the secondary mirror body (4), and the beam path adjustment system (5) provides pose adjustment action for the two sets of planar reflection systems (51); A reflector (6) is located on the beam output path of the two sets of planar reflection systems (51) and reflects the output beams of the two sets of planar reflection systems (51) to the magnetic fluid deformation mirror (7); wherein: The secondary mirror pose adjustment system (3) includes at least a secondary mirror rotation system (31) for adjusting the position of the secondary mirror body (4). The secondary mirror rotation system (31) includes a drive motor (311) and a rotation shaft (32). The drive motor (311) is connected to the adjustment seat (33) through the rotation shaft (32) and drives the adjustment seat (33) to rotate dynamically through the rotation 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).

3. The system structure for dynamically correcting off-axis aberrations of a liquid mirror telescope according to claim 2, characterized in that: The support structure (2) includes support columns (21) connected around the main mirror (1) and connecting components (22), which are installed at the junction of the cantilever ends of several support columns (21) and the secondary mirror pose adjustment system (3) is installed on the connecting components (22).

4. The system structure for dynamically correcting off-axis aberrations of a liquid mirror telescope according to claim 3, characterized in that: The secondary mirror angle deflection adjustment system (36) includes a secondary mirror hoisting frame (361), a secondary mirror mounting frame (362), and a high-precision servo motor (363). The secondary mirror hoisting frame (361) is mounted on the secondary mirror horizontal offset adjustment system (35) and has two mounting posts (364) extending downward along the secondary mirror horizontal offset adjustment system (35). The two mounting posts (364) are arranged opposite to each other. The secondary mirror mounting frame (362) is arranged between the two mounting posts (364) and the secondary mirror body (4) is mounted on the secondary mirror mounting frame (362). The high-precision servo motor (363) is mounted on the mounting post (364) and the output end of the high-precision servo motor (363) is connected to the secondary mirror mounting frame (362).

5. The system structure for dynamically correcting off-axis aberrations of a liquid mirror telescope according to claim 4, characterized in that: The secondary mirror horizontal offset adjustment system (35) includes 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). The horizontal lead screw (352) is connected to the vertical height adjustment system (34) at one end via a bearing and to the second lead screw guide rail (351) at the other end. The gear transmission system (353) is connected to the second lead screw guide rail (351) via fasteners. The housing (356) is connected to the drive wheel (357) and driven wheel (358) which mesh with each other. The drive wheel (357) is connected to the output end of the first servo motor (354), and 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. The two wing-shaped protruding ends of the horizontal motion slider (355) contact the second lead screw guide rail (351) so that the second lead screw guide rail (351) guides the horizontal motion slider (355). The vertical height adjustment system (31) includes a first lead screw guide rail (341) with a limit block, a vertical lead screw (342), a second servo motor (343), and a vertical motion slider (344). The first lead screw guide rail (341) is mounted on the adjustment seat (33) by fasteners. The vertical lead screw (342) is connected to the adjustment seat (33) at one end by a bearing and to the first lead screw guide rail (341) at the other end. The second servo motor (343) is fixedly mounted on one end of the first lead screw guide rail (341) by fasteners and provides power to the vertical lead screw (342). The vertical motion slider (344) is connected to the vertical lead screw (342) by threads. The two wing-shaped protruding ends of the vertical motion slider (344) contact the first lead screw guide rail (341) so that the first lead screw guide rail (341) guides the vertical motion slider (344).

6. The system structure for dynamically correcting off-axis aberration of a liquid mirror telescope according to claim 5, characterized in that: The beam path adjustment system (5) further includes a follow-type planar reflection pose adjustment system (52) and a fixed planar reflection pose adjustment system (53) that rotate synchronously with the secondary mirror pose adjustment system (3). The follow-type planar reflection pose adjustment system (52) is fixed on the housing (356) of the gear transmission system (353) by an extension hanger, and the fixed planar reflection mirror pose adjustment system (53) is fixed on the first lead screw guide rail (341) by a hoisting rod.

7. The system structure for dynamically correcting off-axis aberrations of a liquid mirror telescope according to claim 2, characterized in that: An adjustable beam expander / contractor (8) is provided between the reflector (6) and the secondary mirror pose adjustment system (3). The adjustable beam expander / contractor (8) consists of three sets of lenses (81) with adjustable relative positions. The three sets of lenses are installed in the mechanical assembly with an air gap between them.

8. The system structure for dynamically correcting off-axis aberrations of a liquid mirror telescope according to claim 2, characterized in that: 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). The thin-walled container (73) is installed in the uniform magnetic field (71). The magnetic fluid (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 fixedly installed below the thin-walled container (73).

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