Compact, large-caliber and variable-focal-length collimator system

Abstract

The invention discloses a compact, large-aperture and variable-focal-length collimator system, which comprises a Cassegrain reflector group, a correction lens group and a thermal compensation piece, the Cassegrain reflector group and the correction lens group are in optical conjugate design; the thermal compensation part is arranged in the Cassegrain reflector group so as to compensate the thermal expansion effect of the Cassegrain reflector group; the correction lens group is located on one side, close to the focal plane, of the Cassegrain reflector group, and the correction lens group is detachably connected with the Cassegrain reflector group; the Cassegrain reflector group comprises a primary mirror and a secondary mirror which are coaxially arranged; the correction lens group is used for collimating the short-focal-length parallel light beams output by the Cassegrain reflector group into long-focal-length parallel light beams; the correction lens group comprises one or more optical lenses, and the correction lens group is configured to be assembled with optical lenses with different focal powers and different numbers so as to realize focal length switching of the collimator system. Therefore, not only is the light beam collimation precision ensured, but also the collimator system is compact in structure and can quickly change the focal length.

Description

Technical Field

[0001] This invention relates to the field of optical testing, and more specifically to a compact, large-aperture, variable-focal-length collimator system. Background Technology

[0002] High-precision collimator systems, as core equipment in optical testing systems, are primarily used to simulate targets at infinity, playing a crucial role in the assembly, testing, and calibration of optical systems. Their focal length directly affects the parallelism and divergence angle accuracy of the emitted beam, thus determining the reliability of the optical system's measurement, calibration, and other performance indicators.

[0003] Traditional refractive collimator systems often employ cemented doublet lens groups, but due to the dispersive properties of the glass material, they suffer from significant second-order spectral aberrations. Their long focal length design relies on long-axis-distance lens groups, and the lens weight causes stress deformation on the cemented surface, typically limiting the aperture to below 100mm and the focal length to within 2m. Therefore, long-focal-length collimator systems usually employ reflective systems.

[0004] In reflective collimator systems, the commonly used Newtonian optical path employs a combination of a single concave primary mirror and a plane mirror. Although there is no chromatic aberration, the total length of the optical path is approximately equal to the focal length, resulting in a large system size, difficult transportation and installation. Furthermore, the plane mirror has high angular tolerance sensitivity, leading to significant assembly and adjustment challenges. In addition, most existing reflective solutions are designed with a fixed focal length. Adjusting the distance between the primary and secondary mirrors or replacing lenses to achieve focusing can worsen aberrations, making it difficult to meet the requirements of precision testing.

[0005] Cassegrain collimator systems use a combination of primary and secondary mirrors to compress the overall axial length of the optical path, significantly improving system compactness. However, existing designs all use fixed focal lengths. Adjusting the distance between the primary and secondary mirrors or changing mirror assemblies to alter the focal length, relying on high-precision motorized stages or similar devices, can lead to increased system aberrations and decreased accuracy. Furthermore, the focusing process requires high-precision displacement mechanisms and complex calibration procedures, failing to meet the demands of rapid focal length switching in practical testing. Compared to Newtonian systems, Cassegrain systems are more sensitive to the distance tolerance between the primary and secondary mirrors, with their focal length and backstop varying significantly with the gap. While component manufacturing tolerances can be compensated for through system assembly and adjustment, changes in ambient temperature after assembly and adjustment cause variations in the distance between the primary and secondary mirrors due to thermal expansion and contraction of the truss structure, resulting in a decrease in the parallelism of the emitted light rays. Summary of the Invention

[0006] To address the problems of large size, low focal length adjustment efficiency, and image quality degradation caused by focusing in existing long focal length collimator systems, this invention proposes a compact, large-aperture, variable focal length collimator system. Through the optical conjugate design of the Cassegrain mirror group and the switchable negative optical power correction mirror group, the collimator system achieves a compact structure and the ability to quickly change the focal length while ensuring beam collimation accuracy.

[0007] According to one aspect of this invention, a compact, large-aperture, variable-focal-length collimator system is provided. The collimator system includes a Cassegrain mirror assembly, a corrector mirror assembly, and a thermal compensation component. The Cassegrain mirror assembly and the corrector mirror assembly are optically conjugate. The thermal compensation component is disposed inside the Cassegrain mirror assembly to compensate for the thermal expansion effect of the Cassegrain mirror assembly. The corrector mirror assembly is located on the side of the Cassegrain mirror assembly closest to the focal plane and is detachably connected to the Cassegrain mirror assembly. The Cassegrain mirror assembly includes a primary mirror and a secondary mirror arranged coaxially. The corrector mirror assembly is used to collimate a short-focal-length parallel beam output from the Cassegrain mirror assembly into a long-focal-length parallel beam. The corrector mirror assembly includes one or more optical lenses, configured to equip different powers and different numbers of optical lenses to achieve focal length switching of the collimator system.

[0008] Furthermore, the Cassegrain mirror assembly also includes a primary mirror support, a secondary mirror support, and a truss structure. The truss structure is disposed between the primary mirror support and the secondary mirror support. The thermal compensation component is disposed on the side of the secondary mirror support away from the primary mirror support. The thermal compensation component is used to compensate for the thermal expansion effect of the primary mirror support, the secondary mirror support, and the truss structure.

[0009] Furthermore, the thermal compensation component satisfies the thermal compensation condition formula: ;in, and These are the coefficient of thermal expansion and the axial length of the truss structure, respectively. and These are the coefficient of thermal expansion and the axial length of the thermal compensation structure, respectively. and These are the coefficient of thermal expansion and the axial length of the secondary mirror support, respectively. and These are the coefficient of thermal expansion and the axial length of the primary mirror support, respectively.

[0010] Furthermore, the optical power of the Cassegrain reflector group is positive, and the optical power of the correction mirror group is negative.

[0011] Furthermore, the optical power matching formula for the collimator system is: , where F is the calculated focal length of the collimator system; The initial focal length of the Cassegrain mirror group; The focal length of the correction lens group is... .

[0012] Furthermore, the aperture of the correcting mirror group is smaller than the entrance pupil diameter of the Cassegrain mirror group; the entrance pupil diameter of the Cassegrain mirror group is equal to the aperture of the primary mirror; and the aperture of the correcting mirror group is greater than or equal to the exit pupil diameter of the Cassegrain mirror group.

[0013] Furthermore, the primary mirror is a concave reflector, and the secondary mirror is a convex reflector.

[0014] Furthermore, the primary mirror is a parabolic reflector, and the secondary mirror is a hyperboloid reflector.

[0015] Furthermore, when the light source of the collimator system is in one wavelength band, the correction lens group employs at least two optical lenses.

[0016] Furthermore, the correction lens assembly is detachably connected to the Cassegrain reflector assembly via a mechanical interface, which includes a positioning pin and a bolt fastening structure. The positioning pin is used to position the correction lens assembly, and the bolt fastening structure is used to fix the correction lens assembly.

[0017] The above technical solution achieves multi-focal-length switching through an integrated correction lens module. While ensuring beam collimation accuracy, it makes the system structure compact and allows for rapid and significant changes in focal length, enabling it to achieve superior measurement results in different working environments. Simultaneously, by adding a mechanical passive thermal compensation design to the mechanical structures of the primary and secondary mirrors, the thermal expansion effects of the primary mirror support, secondary mirror support, and truss structure are compensated.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) In terms of system compactness, the present invention makes the total axial length of the collimator system much smaller than that of the traditional Newtonian optical path by using the reflective folding design of the Cassegrain reflector group. Moreover, the total axial length increment of the collimator system after integrating the correction lens group is small, and the overall structure remains compact, solving the transportation and assembly problems caused by the long axis of the traditional refractive scheme.

[0020] (2) In terms of focal length switching efficiency, the present invention enables rapid integration of the correction lens group without recalibrating the coaxial state of the primary and secondary lenses, avoiding the complex process of replacing lenses or adjusting the spacing required by traditional reflective focusing, and significantly improving assembly and adjustment efficiency. At the same time, it supports the flexible replacement of multiple correction lens groups to meet the needs of different detection scenarios for multiple focal lengths.

[0021] (3) In terms of beam quality assurance, the present invention optimizes aberrations in short focal length mode by using the aspherical surface structure of the Cassegrain mirror group, and compensates for chromatic aberration and field curvature by using the achromatic design of the correction mirror group in long focal length mode, ensuring that the beam parallelism error is small in both modes and the MTF curve is close to the diffraction limit, thus meeting the image quality requirements of high-precision optical detection.

[0022] (4) Regarding the thermal stability of the focal length, the present invention improves the thermal stability of the focal length of the collimator system by adding a mechanical passive thermal compensation design to the mechanical structure of the primary and secondary mirrors and by compensating for the thermal expansion and contraction of the structure through the mutual compensation of the thermal expansion and contraction effect of the structure. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of a compact, large-diameter, variable-focal-length collimator system provided in an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of a mechanical passive thermal compensation structure provided in an embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram of a collimator system in short focal length mode provided in an embodiment of the present invention.

[0027] Figure 4 This is a schematic diagram of a collimator system in long focal length mode provided in an embodiment of the present invention.

[0028] Figure 5 The MTF curve in the short focal length (10mm) mode provided in the embodiment of the present invention.

[0029] Figure 6 The MTF curve in the long focal length (20mm) mode provided in the embodiment of the present invention.

[0030] In the figure, 1. Cassegrain mirror assembly; 11. Primary mirror; 12. Secondary mirror; 13. Primary mirror support; 14. Secondary mirror support; 15. Truss structure; 16. Thermal compensation component; 2. Correction mirror assembly; 21. First lens; 22. Second lens; 3. First focal plane; 4. Second focal plane; 100. Collimator system. Detailed Implementation

[0031] The terms “comprising” and “having”, and any variations thereof, in the specification, claims, and accompanying drawings of this invention are intended to cover a non-exclusive inclusion, such as a process, method, system, product, or apparatus that includes a series of steps or units, not necessarily limited to those explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0032] The present invention aims to propose a compact, large-aperture, variable-focal-length collimator system. By integrating a correction lens group, it achieves multi-focal-length switching. While ensuring the collimation accuracy of the beam, the collimator system has a compact structure and can quickly and significantly change the focal length, enabling the collimator system to achieve better measurement results in different working environments.

[0033] Please refer to the appendix. Figure 1 The collimator system 100 provided by this invention includes a Cassegrain mirror assembly 1, a corrector mirror assembly 2, and a thermal compensation component. The Cassegrain mirror assembly 1 and the corrector mirror assembly 2 are optically conjugate. The thermal compensation component is disposed inside the Cassegrain mirror assembly 1 to compensate for the thermal expansion effect of the Cassegrain mirror assembly 1. The corrector mirror assembly 2 is located near the focal plane in the output light path of the Cassegrain mirror assembly 1, and is detachably connected to the Cassegrain mirror assembly 1. The corrector mirror assembly 2 is used to collimate the short focal length parallel beam output from the Cassegrain mirror assembly 1 into a long focal length parallel beam, thereby overcoming the fixed focal length limitation.

[0034] Please refer to the appendix for details. Figure 3 The Cassegrain reflector assembly 1 includes a primary mirror 11 and a secondary mirror 12 arranged coaxially. The primary mirror 11 has a central aperture for forming a short focal length parallel beam. Both the primary mirror 11 and the secondary mirror 12 are reflectors, and they cooperate to achieve a light path folding effect by utilizing the light reflection characteristics, thereby compressing the total axial length of the collimator system 100. The Cassegrain reflector assembly 1 outputs a short focal length parallel beam with relatively low parallelism. Understandably, this invention uses a large-aperture Cassegrain reflector assembly 1, and the Cassegrain reflector assembly 1, with its coaxial reflective folding characteristics of the primary mirror 11 and the secondary mirror 12, can achieve a significant compression of the total axial length compared to a Newtonian light path. Therefore, the collimator system 100 of this invention simultaneously possesses a large aperture and a small total axial length. Taking a 10m focal length system as an example, the total axial length of the Cassegrain reflector group 1 is only 1 / 10 of that of a Newtonian optical path (about 1m to 2m), which avoids the volume defects of traditional refractive or Newtonian optical paths and greatly reduces the assembly and adjustment complexity and logistics transportation difficulty of the collimator system 100.

[0035] The primary mirror 11 is a concave reflector, and the secondary mirror 12 is a convex reflector. Specifically, the primary mirror 11 is a parabolic reflector with a light-transmitting aperture of 600mm, made of silicon carbide (SiC) material. The secondary mirror 12 is a hyperboloid reflector made of glass-ceramic material. The Cassegrain reflector assembly 1 optimizes aberrations through the aspherical surface structure of the primary mirror 11 and the secondary mirror 12. In this embodiment, the primary mirror 11 and the secondary mirror 12 together form a short focal length mode with a focal length of 10m. The first focal plane 3 is the theoretical focal plane of the collimator system 100 in the short focal length mode.

[0036] Please refer to the appendix for details. Figure 2 The Cassegrain mirror assembly 1 also includes a primary mirror support 13, a secondary mirror support 14, and a truss structure 15. The primary mirror support 13 supports the primary mirror 11, the secondary mirror support 14 supports the secondary mirror 12, and the truss structure 15 is disposed between the primary mirror support 13 and the secondary mirror support 14. A thermal compensation component 16 is disposed on the side of the secondary mirror support 14 away from the primary mirror support 13, and the thermal compensation component 16 is used to compensate for the thermal expansion effect of the primary mirror support 13, the secondary mirror support 14, and the truss structure 15. Understandably, the thermal expansion effect of the primary mirror support 13, the secondary mirror support 14, and the truss structure 15 will cause changes in the distance between the primary and secondary mirrors, resulting in a decrease in the parallelism of the emitted light rays, which in turn leads to a deviation between the actual focal length and the designed focal length of the collimator system 100. This invention improves the thermal stability of the collimator system at a focal length of 100 Å by adding thermal compensation components to the mechanical structure of the primary and secondary mirrors and compensating for the thermal expansion and contraction of the structure.

[0037] Furthermore, considering that both the truss structure 15 and the primary mirror support 13 have stringent requirements for strength, stiffness, machinability, and coefficient of thermal expansion, the range of selectable materials is limited. Based on the reasonable selection of the material for the secondary mirror support 14, this invention adds a thermal compensation component 16 behind the secondary mirror support 14. When the thermal compensation condition formula is satisfied: At this time, mechanical passive thermal compensation can be achieved, thereby ensuring that the change in the distance between the primary and secondary mirrors is minimal after temperature changes.

[0038] ,in, and These are the coefficient of thermal expansion and axial length of the truss structure 15, respectively. and These are the coefficient of thermal expansion and axial length of the thermal compensation structure 16, respectively. and These are the coefficient of thermal expansion and axial length of the secondary mirror support 14, respectively. and These are the coefficient of thermal expansion and axial length of the primary mirror support 13, respectively. This refers to the change in ambient temperature. The change in the distance between the primary and secondary mirrors caused by the thermal expansion effect of the truss structure 15; The change in the distance between the primary and secondary mirrors caused by the thermal expansion effect of the thermal compensation structure 16; The change in the distance between the primary and secondary mirrors caused by the thermal expansion effect of the secondary mirror support 14; This refers to the change in the distance between the primary and secondary mirrors caused by the thermal expansion effect of the primary mirror support 13. Understandably, through the above structural design, the thermal expansion effects of different components are synergistically offset, achieving stable control of the distance between the primary and secondary mirrors under temperature changes; that is, regardless of temperature changes, the distance between the primary and secondary mirrors will not be affected.

[0039] It should be noted that the coefficients of thermal expansion and axial lengths of the truss structure 15, secondary mirror support 14, and primary mirror support 13, as well as the coefficient of thermal expansion of the thermal compensation component 16, are all pre-set known quantities. Therefore, the axial length of the thermal compensation component 16 can be obtained according to the above-mentioned thermal compensation condition formula. In this embodiment, the mechanical passive heat dissipation design of the Cassegrain reflector group is based on the requirements of component strength, stiffness, and thermal characteristics. The primary mirror support 13 is made of Invar steel with a very small coefficient of thermal expansion, the secondary mirror support 14 is made of titanium alloy, and the truss structure 15 connecting the primary and secondary mirrors is made of silicon nitride. At the same time, in order to reduce the axial length of the thermal compensation component 16, this embodiment selects a thermal compensation component 16 with a larger coefficient of thermal expansion (e.g., 6061 aluminum alloy and titanium alloy). According to calculation and analysis, only an increase of approximately 15 mm in the axial length of the thermal compensation component 16 is needed to keep the distance between the primary and secondary mirrors approximately constant under temperature changes, effectively controlling the influence of temperature on the parallelism of the output beam of the collimator system 100, thereby improving the detection accuracy of the collimator system 100. Understandably, in some feasible embodiments, the truss structure 15, thermal compensation component 16, secondary mirror support component 14, and primary mirror support component 13 may also be made of other suitable materials, which are not limited here.

[0040] Please refer to the appendix for details. Figure 4A correction lens group 2 is integrated on the optical basic unit composed of the Cassegrain mirror group 1. The correction lens group 2 is located between the secondary mirror 12 and the first focal plane 3. The correction lens group 2 is an independent modular lens group. When the correction lens group and the Cassegrain mirror group work together, they form a long focal length mode. The second focal plane 4 is the theoretical focal plane of the collimator system 100 in the long focal length mode. The correction lens group 2 performs secondary collimation on the short focal length parallel beam with relatively low parallelism output from the Cassegrain mirror group 1, providing collimated light with higher parallelism, which is suitable for precision measurement conditions. It can be understood that by transferring the optical power switching function from the Cassegrain mirror group 1 to the transmissive correction lens group 2, this invention flexibly expands the various focal length combinations of the correction lens group 2 without changing the fixed parameters of the Cassegrain mirror group 1. This avoids the dependence of traditional reflective focusing on high-cost aspherical mirrors, reduces the maintenance cost of the collimator system 100, and ensures the stability and maintainability of the collimator system 100.

[0041] The optical power of Cassegrain mirror group 1 is positive, while the optical power of corrector mirror group 2 is negative. The optical power design of corrector mirror group 2 is optically conjugate to that of Cassegrain mirror group 1. Optical power and focal length are inversely related, which is determined by the optical power matching formula. To achieve focal length switching of the collimator system 100, where F is the calculated focal length of the collimator system 100; The initial focal length of the Cassegrain mirror group 1; To correct the focal length of lens group 2, In this embodiment, the focal length range of the collimator system 100 is 10m to 20m, and the initial focal length of the Cassegrain mirror group 1 is... =10m. That is to say, before the integrated correction mirror group 2, the focal length of the collimator system 100 is equal to the initial focal length of the Cassegrain mirror group 1, i.e., F= =10m; to switch the focal length F of the collimator system 100 to 20m, an integrated focal length filter is required. With the correction lens group 2 having a focal length of -20m, the collimator system 100 has a focal length F = 10 * (-20) / (10 - 20) = 20m, achieving a doubling of the focal length. Understandably, the collimator system 100 can achieve this by integrating different focal lengths... The corrective lens group 2 enables switching between different focal lengths F. It should be noted that the focal length range of the collimator system 100 can be set according to actual needs and is not limited here.

[0042] Please refer to the appendix again. Figure 1 The correction lens group 2 includes one or more optical lenses, corresponding to the attached... Figure 1In the series 21, 22 to 2n, where n represents the total number of optical lenses, the correction lens group 2 is configured to achieve focal length switching of the collimator system 100 by assembling optical lenses of different powers and numbers. In this embodiment, the correction lens group 2 adopts a double-lens combination (such as a double-separated structure or a double-cemented structure, which is not limited here) consisting of a first lens 21 and a second lens 22. The first lens 21 and the second lens 22 are made of crown glass and flint glass, respectively. In long focal length mode, chromatic aberration and field curvature are compensated by the glass material design of the correction lens group 2. It should be noted that when the system light source is monochromatic light, that is, the wavelength is one value, there is no chromatic aberration, and there is no need to compensate for chromatic aberration, and the correction lens group 2 may include only one lens; when the system light source is in a single band, such as the visible light band (380-780nm), chromatic aberration design is required, and the correction lens group 2 needs to use two or more lenses to correct chromatic aberration and other aberrations.

[0043] The corrective lens group 2 and the back plate (not shown) of the primary lens 1 are detachably connected via a mechanical flange (i.e., a mechanical interface). The mechanical interface includes a locating pin and a bolt fastening structure. The locating pin is used to achieve high-precision positioning of the corrective lens group 2, and the bolt fastening structure is used to fix the corrective lens group 2. Understandably, the locating pin and bolt fastening structure ensure that the corrective lens group 2 is installed in the same position each time, guaranteeing the repeatability of the corrective lens group 2's positioning accuracy. This eliminates the need to recalibrate the coaxial state of the primary and secondary lenses, avoiding the complex process of replacing lenses or adjusting the spacing required in traditional reflective focusing, and significantly improving assembly efficiency.

[0044] The corrector lens group 2 avoids beam obstruction through a pupil connection design. This pupil connection design ensures that the aperture of the corrector lens group 2 is greater than or equal to the exit pupil diameter of the Cassegrain reflector group 1, resulting in a principal ray transmittance ≥95% and peripheral ray vignetting ≤5%. Furthermore, the aperture of the corrector lens group 2 is significantly smaller than the entrance pupil diameter of the collimator system 100, reducing the manufacturing difficulty and risk of the corrector lens group 2, and minimizing the increase in the overall axial length of the collimator system 100 after integrating the corrector lens group 2, thus maintaining a compact overall structure. In this embodiment, the total axial length of the collimator system 100 before integrating the corrector lens group 2 is ≤1.01m (e.g., 1008mm), and the total axial length of the collimator system 100 after integrating the corrector lens group 2 is ≤1.1m (e.g., 1084mm), having minimal impact on the original system's total axial length. It should be noted that since the primary mirror of the Cassegrain reflector group is the aperture stop of the collimator system 100, the aperture (i.e., effective aperture) of the primary mirror is the entrance pupil diameter of the collimator system 100. In this embodiment, the aperture of the primary mirror 12 is 600 mm, so the entrance pupil diameter of the collimator system 100 is also 600 mm. The aperture of the correction mirror group 2 is ≤50 mm, meaning the aperture of the correction mirror group 2 is less than 1 / 5 of the entrance pupil diameter of the collimator system 100.

[0045] Please refer to the appendix for details. Figures 5 to 6 Tables 1 to 2 Figure 5 Table 1 illustrates the MTF curves and corresponding parameter descriptions in short focal length mode. Figure 6 Table 2 illustrates the MTF curves and corresponding parameter descriptions in long focal length mode. In short focal length mode, the optical system's MTF@20 lp / mm ≥ 0.64; in long focal length mode, the optical system's MTF@20 lp / mm ≥ 0.35, both approaching the diffraction limit. Understandably, MTF (Modulation Transfer Function) describes the transmission capability of the collimator system 100 for objects at different spatial frequencies (unit: lp / mm, i.e., line pairs per millimeter). The higher the MTF value, the higher the collimated beam angle accuracy and the better the wavefront quality output by the collimator system 100. Here, it refers to the fact that at a spatial frequency of 20 lp / mm, the MTF reaches 0.64 and 0.35 respectively, both close to the diffraction limit, indicating that the collimated beam angle accuracy output by the collimator system 100 of this invention is close to the theoretical optimum.

[0046] Table 1. MTF curve parameters in short focal length (10mm) mode.

[0047]

[0048] Table 2. MTF curve parameters in telephoto (20mm) mode.

[0049]

[0050] It should be noted that:

[0051] First, in terms of system compactness, the present invention makes the total axial length of the collimator system much smaller than that of the traditional Newtonian optical path through the reflective folding design of the Cassegrain reflector group. Furthermore, the correction lens group used to change the focal length of the collimator system adopts modular integration of small-diameter lens groups, which makes the increase in the total axial length of the collimator system after the integration of the correction lens group small, and the overall structure remains compact, thus solving the transportation and assembly problems caused by the long axis of the traditional refractive scheme.

[0052] Secondly, regarding focal length switching efficiency, this invention designs the correction lens group as an independent module, enabling rapid integration via a mechanical interface. This eliminates the need to recalibrate the coaxial state of the primary and secondary lenses, avoiding the complex process of replacing lenses or adjusting spacing required in traditional reflective focusing systems, thus significantly improving assembly and adjustment efficiency. Furthermore, the modular design supports flexible replacement of multiple correction lens groups, meeting the diverse focal length requirements of different testing scenarios.

[0053] Third, in terms of beam quality assurance, this invention optimizes aberrations independently for each focal length mode by combining the Cassegrain reflector group and the integrated correction lens group into the overall system: in the short focal length mode, aberrations are optimized through the aspherical surface structure of the reflector, and in the long focal length mode, aberrations are compensated for by the achromatic design of the correction lens group. This ensures that the beam parallelism error is small in both modes, and the MTF curve is close to the diffraction limit, meeting the image quality requirements of high-precision optical detection.

[0054] Fourth, regarding the thermal stability of the focal length, this invention improves the thermal stability of the collimator system by adding a mechanical passive thermal compensation design to the mechanical structure of the primary and secondary lenses. Through the mutual compensation of the thermal expansion and contraction effects of the structure, the influence of temperature changes on the distance between the primary and secondary lenses is effectively reduced without introducing a complex mechanical structure.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A compact, large-diameter, variable-focal-length collimator system, characterized in that, The collimator system includes a Cassegrain mirror assembly, a corrector mirror assembly, and a thermal compensation component. The Cassegrain mirror assembly and the corrector mirror assembly are optically conjugate. The thermal compensation component is disposed inside the Cassegrain mirror assembly to compensate for the thermal expansion effect of the Cassegrain mirror assembly. The corrector mirror assembly is located on the side of the Cassegrain mirror assembly closer to the focal plane and is detachably connected to the Cassegrain mirror assembly. The Cassegrain mirror assembly includes a primary mirror and a secondary mirror arranged coaxially. The corrector mirror assembly is used to collimate the short-focal-length parallel beam output by the Cassegrain mirror assembly into a long-focal-length parallel beam. The corrector mirror assembly includes one or more optical lenses, and is configured to equip different powers and different numbers of optical lenses to achieve focal length switching of the collimator system.

2. The compact, large-diameter, variable-focal-length collimator system as described in claim 1, characterized in that, The Cassegrain reflector assembly further includes a primary mirror support, a secondary mirror support, and a truss structure. The truss structure is disposed between the primary mirror support and the secondary mirror support. The thermal compensation component is disposed on the side of the secondary mirror support away from the primary mirror support. The thermal compensation component is used to compensate for the thermal expansion effect of the primary mirror support, the secondary mirror support, and the truss structure.

3. The compact, large-diameter, variable-focal-length collimator system as described in claim 2, characterized in that, The thermal compensation component satisfies the thermal compensation condition formula: ;in, and These are the coefficient of thermal expansion and the axial length of the truss structure, respectively. and These are the coefficient of thermal expansion and the axial length of the thermal compensation structure, respectively. and These are the coefficient of thermal expansion and the axial length of the secondary mirror support, respectively. and These are the coefficient of thermal expansion and the axial length of the primary mirror support, respectively.

4. The compact, large-diameter, variable-focal-length collimator system as described in claim 1, characterized in that, The optical power of the Cassegrain reflector group is positive, and the optical power of the correction mirror group is negative.

5. A compact, large-diameter, variable-focal-length collimator system as described in claim 3, characterized in that, The optical power matching formula for the collimator system is: , where F is the calculated focal length of the collimator system; The initial focal length of the Cassegrain mirror group; The focal length of the correction lens group is... .

6. A compact, large-diameter, variable-focal-length collimator system as described in claim 1, characterized in that, The aperture of the correcting mirror group is smaller than the entrance pupil diameter of the Cassegrain mirror group; the entrance pupil diameter of the Cassegrain mirror group is equal to the aperture of the primary mirror; the aperture of the correcting mirror group is greater than or equal to the exit pupil diameter of the Cassegrain mirror group.

7. A compact, large-diameter, variable-focal-length collimator system as described in claim 1, characterized in that, The primary mirror is a concave reflector, and the secondary mirror is a convex reflector.

8. A compact, large-diameter, variable-focal-length collimator system as described in claim 1, characterized in that, The primary mirror is a parabolic reflector, and the secondary mirror is a hyperboloid reflector.

9. A compact, large-diameter, variable-focal-length collimator system as described in claim 1, characterized in that, When the light source of the collimator system is in one wavelength band, the correction lens group uses at least two optical lenses.

10. A compact, large-diameter, variable-focal-length collimator system as described in claim 1, characterized in that, The correction mirror assembly is detachably connected to the Cassegrain reflector assembly via a mechanical interface. The mechanical interface includes a positioning pin and a bolt fastening structure. The positioning pin is used to position the correction mirror assembly, and the bolt fastening structure is used to fix the correction mirror assembly.

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