Method and device for adjusting poses of primary mirror and secondary mirror of beam shrinking system
By using theodolite mutual aiming and pinhole light source-assisted adjustment, the stability problem of primary and secondary mirror pose adjustment in the beam shrinking system was solved, realizing a high-precision and fast assembly and adjustment process, improving the system's anti-interference capability and reducing dependence on expensive equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-06
- Publication Date
- 2026-04-03
AI Technical Summary
In traditional beam-shrinking systems, the optical path is long and unstable during the orientation adjustment of the primary and secondary mirrors. The lack of reflective coating on the lenses leads to severe laser energy attenuation, making it impossible to form clear interference fringes and failing to meet the assembly and adjustment requirements.
Two theodolites are used to establish exit and incident references by mutual aiming. The positions and orientations of the primary and secondary mirrors are adjusted with the aid of reference marks and pinhole light sources. Precise alignment is achieved by combining a two-dimensional lifting platform, thus abandoning the traditional Zygo interferometer adjustment method.
It improves the stability and anti-interference ability of the assembly and adjustment process, reduces the dependence on expensive equipment, and ensures high-precision and fast assembly and adjustment results.
Smart Images
Figure CN121784985A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical precision assembly and adjustment technology, specifically to a method and apparatus for assembling and adjusting the position and orientation of primary and secondary mirrors in a beam-shrinking system. Background Technology
[0002] In laser parameter measurement systems, the beam diameter often needs to be adjusted to the corresponding size using a beam-shrinking system, depending on the size of the detector target surface. The pose adjustment of the primary and secondary mirrors in the beam-shrinking system is a crucial step in the assembly and adjustment of the entire optical system; the process must ensure that the poses of both the primary and secondary mirrors meet the design specifications.
[0003] The traditional approach to adjusting the pose of the primary and secondary lenses is as follows: The detection optical path is constructed using a Zygo interferometer and a plane mirror. The Zygo interferometer is set up at the light output port. The detection laser of the interferometer passes through the secondary mirror and the primary mirror to reach the plane mirror and return along the original optical path. After passing through the primary mirror and the secondary mirror again, it reaches the Zygo interferometer detector to form interference fringes. The misalignment of the primary mirror and the secondary mirror is analyzed by Zernike coefficient, and finally the pose adjustment of the primary mirror and the secondary mirror is completed.
[0004] Traditional assembly and adjustment methods have the following drawbacks: First, the actual optical path is relatively long, and the stability of the detection optical path system is poor; second, if the primary and secondary mirrors are not coated with reflective films, the reflectivity is only 4%, and the detection laser of the Zygo interferometer attenuates by hundreds of thousands after multiple reflections, making it impossible to form clear interference fringes. Therefore, the assembly and adjustment are limited and cannot meet the actual assembly and adjustment requirements. Summary of the Invention
[0005] The purpose of this invention is to provide a method and apparatus for adjusting the pose of primary and secondary mirrors in a beam shrinking system, thereby solving the technical problem of poor stability in the pose adjustment of primary and secondary mirrors in existing beam shrinking systems.
[0006] The solution of the present invention to the above-mentioned technical problems is as follows: A method for adjusting the pose of primary and secondary mirrors in a beam-contraction system includes the following steps: Reference establishment: Two reference marks are set at the theoretical positions of the optical axis of the beam-shrinking system. The first and second measuring devices are aligned with each other to establish an exit reference that coincides with the optical axis of the beam-shrinking system. Secondary mirror coarse adjustment: Adjust the second measuring device to the rear of the secondary mirror and switch the second measuring device to collimation mode. By adjusting the azimuth and pitch angle of the secondary mirror, make the secondary mirror self-aligned with the second measuring device to complete the coarse positioning of the secondary mirror's azimuth and pitch. Secondary mirror fine-tuning: Illuminate the pinhole light source located at the real focal point of the secondary mirror, switch the first measuring device to auto-collimation mode, and observe the pinhole image within the field of view of the first measuring device; eliminate defocus by adjusting the front and rear position of the secondary mirror to make the pinhole image clear; then adjust the azimuth and pitch angles of the secondary mirror to make the crosshairs of the first measuring device coincide with the pinhole image, thus completing the precise alignment of the secondary mirror with the emission reference. Reference transfer: Keeping the azimuth angle of the first measuring device unchanged, adjust its elevation angle to align with the second measuring device which has been raised to the height of the primary mirror; adjust the second measuring device so that the two are intersecting, thereby transferring the exit reference to the second measuring device and establishing the incident reference; Primary mirror coarse adjustment: Adjust the first measuring device to the rear of the primary mirror, switch the first measuring device to collimation mode, and adjust the azimuth and pitch angles of the primary mirror to make the primary mirror self-align with the first measuring device, thus completing the coarse positioning of the primary mirror's azimuth and pitch. Master mirror fine-tuning: Light up the pinhole light source, switch the second measuring device representing the incident reference to auto-collision mode, and observe the pinhole image in the field of view of the second measuring device; eliminate defocus by adjusting the front and rear position of the master mirror to make the pinhole image clear; then adjust the azimuth and pitch angles of the master mirror so that the crosshairs of the second measuring device coincide with the pinhole image, thus completing the precise alignment of the master mirror with the incident reference.
[0007] Furthermore, the method for adjusting the pose of the primary and secondary mirrors of the beam-shrinking system also includes the following steps: Preparation for installation and adjustment: Reserve polishing areas on the rear surfaces of the primary and secondary mirrors; initially install the primary and secondary mirrors in their theoretical positions; install a small hole with flocculent edges at the real focal point of the secondary mirror.
[0008] Further specifying, both the first measuring device and the second measuring device are theodolites, and the reference mark is a crosshair tool.
[0009] Further specifying, the mutual aiming of the first measuring device and the second measuring device includes the following steps: Adjust the pitch direction of the two theodolites to the horizontal plane, and use a two-dimensional lifting platform to adjust the height of the two theodolites so that the two theodolites can thread their respective crosshairs.
[0010] To further define it, the pinhole image being clear specifically means that the flocculent material at the edge of the pinhole image is clear and sharp.
[0011] Further specifying, adjusting the second measuring device to make them interlock includes the following steps: The elevation direction of the second measuring device was adjusted to be horizontal while keeping the azimuth angle unchanged. Align the first measuring device by changing the pitch angle of the second measuring device; Then, by adjusting the azimuth angle of the second measuring device, the two devices can be aligned to be intersected.
[0012] An assembly and adjustment device for the pose of primary and secondary mirrors of a beam shrinking system is used to implement the assembly and adjustment method for the pose of primary and secondary mirrors of the beam shrinking system, comprising a first measuring device, a second measuring device, a pinhole, a primary mirror, a secondary mirror, and a two-dimensional lifting platform. The bottoms of both the first and second measuring devices are connected to a two-dimensional lifting platform. The small hole is located at the common real focal point of the primary and secondary mirrors, and a light source is provided on the small hole.
[0013] Furthermore, the edge of the pinhole is provided with flocculent material to assist in judging whether the pinhole image is clear.
[0014] Furthermore, the beam-shrinking system's primary and secondary mirror orientation adjustment device also includes two reference marks, which are used to coordinate with the first and second measuring devices to establish an exit reference that coincides with the optical axis of the beam-shrinking system.
[0015] Furthermore, both the rear surface of the primary mirror and the rear surface of the secondary mirror have reserved polishing areas for self-alignment between the primary mirror and the first measuring device and between the secondary mirror and the second measuring device.
[0016] The beneficial effects of this invention are as follows: 1. This invention abandons the traditional approach of adjusting the pose of the primary and secondary mirrors of the beam-shrinking system using a Zygo interferometer and a plane mirror. Instead, it adopts a new approach of using two theodolites to align the output reference with the incident reference. This not only completely solves the technical bottleneck of severe energy attenuation caused by multiple reflections of the laser on the uncoated primary and secondary mirrors, thus preventing the formation of effective interference fringes, but also significantly improves the anti-interference capability and overall stability of the assembly process against long optical path vibrations, while reducing the dependence on expensive large-scale testing equipment.
[0017] 2. The present invention provides an ideal reflective surface for self-collimation adjustment by pre-reserving polished areas on the rear surfaces of the primary and secondary mirrors. A small hole light source with flocculent edges is set at the real focal point of the secondary mirror, making it intuitive and accurate to judge defocus and adjust the front and rear positions of the lens by observing the clarity of the flocculent material. The use of crosshair fixtures as reference marks, combined with a two-dimensional lifting platform to accurately adjust the height of the measuring device and perform the through-hole operation, ensures the accuracy and repeatability of reference establishment and transfer. Under the premise of ensuring high assembly and adjustment accuracy, the difficulty of assembly and adjustment is greatly reduced and the assembly and adjustment cycle is shortened. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the coarse adjustment operation of the secondary mirror in this invention; Figure 2 This is a schematic diagram of the secondary mirror fine-tuning operation of the present invention; Figure 3 This is a schematic diagram of the reference transfer operation of the present invention; Figure 4 This is a schematic diagram of the primary mirror coarse adjustment operation of the present invention; Figure 5 This is a schematic diagram of the primary mirror fine-tuning operation of the present invention; Figure 6 This is a structural diagram of the assembly and adjustment device for the primary and secondary mirror poses of the beam-shrinking system of the present invention.
[0019] In the diagram, 1-First theodolite; 2-Second theodolite; 3-Primary mirror; 4-Secondary mirror; 5-Light source. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0021] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0022] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.
[0023] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0024] Example 1 This invention provides a method for adjusting the pose of primary and secondary mirrors in a beam-shrinking system, comprising the following steps: Preparation for installation and adjustment: Reserve polishing areas on the back surfaces of the primary and secondary mirrors; initially install the primary and secondary mirrors in their theoretical positions; install a small hole with flocculent edges at the real focal point of the secondary mirror.
[0025] Reference establishment: Two reference marks are set at the theoretical positions of the optical axis of the beam-shrinking system. The first and second measuring devices are aligned with each other to establish an exit reference that coincides with the optical axis of the beam-shrinking system. Secondary mirror coarse adjustment: Adjust the second measuring device to the rear of the secondary mirror and switch the second measuring device to collimation mode. By adjusting the azimuth and pitch angles of the secondary mirror, make the secondary mirror self-aligned with the second measuring device to complete the coarse positioning of the secondary mirror's azimuth and pitch. Secondary mirror fine-tuning: Illuminate the pinhole light source located at the real focal point of the secondary mirror, switch the first measuring device to auto-collimation mode, and observe the pinhole image within the field of view of the first measuring device; eliminate defocus by adjusting the front and rear position of the secondary mirror to make the pinhole image clear; then adjust the azimuth and pitch angles of the secondary mirror to make the crosshairs of the first measuring device coincide with the pinhole image, thus completing the precise alignment of the secondary mirror with the exit reference. Reference transfer: Keep the azimuth angle of the first measuring device unchanged, adjust its elevation angle to align with the second measuring device that has been raised to the height of the primary mirror; adjust the second measuring device so that the two are intersecting, thereby transferring the exit reference to the second measuring device and establishing the incident reference; Primary mirror coarse adjustment: Adjust the first measuring device to the back of the primary mirror, switch the first measuring device to collimation mode, and adjust the azimuth and pitch angles of the primary mirror to make the primary mirror self-aligned with the first measuring device, thus completing the coarse positioning of the primary mirror's azimuth and pitch. Master mirror fine-tuning: Turn on the pinhole light source, switch the second measuring device representing the incident reference to auto-collision mode, and observe the pinhole image in the field of view of the second measuring device; eliminate defocus by adjusting the front and back position of the master mirror to make the pinhole image clear; then adjust the azimuth and pitch angles of the master mirror to make the crosshairs of the second measuring device coincide with the pinhole image, thus completing the precise alignment of the master mirror with the incident reference.
[0026] The first and second measuring devices are both theodolites, namely the first theodolite and the second theodolite, and the reference mark is a crosshair fixture. Therefore, when establishing the reference, two crosshair fixtures are placed at both ends of the theoretical position of the optical axis of the beam-shrinking system. The pitch direction of the first and second theodolites is adjusted to the earth level. The two-dimensional lifting platform is used to adjust the first and second theodolites to the height of the crosshairs and pass the two crosshairs through the center. The first and second theodolites are aligned with each other and the azimuth angle is zeroed.
[0027] refer to Figure 1During the coarse adjustment of the secondary mirror, the second theodolite is set behind the secondary mirror 4. The height of the second theodolite is raised to be opposite the rear surface of the secondary mirror 4 using a two-dimensional lifting platform. Then the second theodolite is switched to collimation mode, and the azimuth and pitch angles of the secondary mirror 4 are adjusted until the polished part of the rear surface of the secondary mirror 4 and the second theodolite are self-aligned. At this time, the azimuth and pitch angles of the secondary mirror 4 are coarsely positioned.
[0028] refer to Figure 2 During the fine-tuning of the secondary mirror, use light source 5 to illuminate the pinhole. At this time, the first theodolite represents the emission reference. Switch the first theodolite to autocollimation mode and observe the pinhole image in the field of view of the first theodolite. If the flocculent material at the edge of the pinhole image is blurry, it indicates that the secondary mirror 4 is out of focus. Adjust the front and back position of the secondary mirror 4 until the flocculent material at the edge of the pinhole is clear and sharp. Then observe the position of the crosshairs and the light spot of the eyepiece of the first theodolite. Adjust the azimuth and pitch angle of the secondary mirror until the crosshairs coincide with the pinhole image. At this time, the secondary mirror 4 coincides with the emission reference, and the fine-tuning of the secondary mirror is completed.
[0029] refer to Figure 3 During the reference transfer, the first theodolite and the second theodolite are aligned with each other to transfer the outgoing reference to the incoming reference.
[0030] Specifically, raise the second theodolite to the height of the primary mirror 3. At this point, the first theodolite coincides with the emission reference, and the azimuth angle of the first theodolite remains unchanged. Change the elevation angle to align with the second theodolite. First, adjust the elevation direction of the second theodolite to be horizontal while keeping its azimuth angle unchanged. Then, change the elevation angle of the second theodolite to align with the first theodolite. Both theodolites are switched to auto-collision mode. Finally, adjust the azimuth of the second theodolite to make the two theodolites interlock. At this point, the emission reference can be transferred to the second theodolite.
[0031] Similarly, refer to Figure 4 During the coarse adjustment of the primary mirror, raise the first theodolite to the height of the rear surface of the primary mirror 3, adjust the pitch direction of the first theodolite to the horizontal, and switch the first theodolite to the collimation mode; then adjust the azimuth and pitch angle of the primary mirror 3, and coordinate with the polished surface of the rear surface of the primary mirror 3 to auto-align with the first theodolite. At this time, the azimuth and pitch angle of the primary mirror 3 can complete the coarse positioning of the primary mirror 3.
[0032] refer to Figure 5 When fine-tuning the primary mirror, use light source 5 to illuminate the pinhole. At this time, the second theodolite represents the incident reference. Specifically, switch the second theodolite to autocollimation mode, and then observe the pinhole image in the field of view of the second theodolite. If the flocculent material at the edge of the pinhole image is blurry, it indicates that the primary mirror 3 is out of focus. Adjust the front and back position of the primary mirror 3 until the flocculent material at the edge of the pinhole is clear and sharp. Then observe the position of the crosshairs and the light spot of the second theodolite eyepiece, and adjust the azimuth and pitch angle of the primary mirror until the crosshairs coincide with the pinhole image. At this time, the primary mirror coincides with the incident reference, and the setup is complete.
[0033] Example 2 refer to Figure 6 This embodiment provides an assembly and adjustment device for the pose of primary and secondary mirrors in a beam-shrinking system, used to implement the assembly and adjustment method for the pose of primary and secondary mirrors in a beam-shrinking system described in Embodiment 1. The device includes a first measuring device, a second measuring device, a pinhole, a primary mirror 3, a secondary mirror 4, and a two-dimensional lifting platform. The first measuring device is illustrated using a first theodolite 1 as an example, and the second measuring device is illustrated using a second theodolite 2 as an example. The bottoms of both the first and second measuring devices are connected to the two-dimensional lifting platform, which can move up and down and forward and backward, enabling the two theodolites to move in a vertical plane. The pinhole is located at the common real focal point of the primary mirror 3 and the secondary mirror 4, and a light source 5 is provided on the pinhole to form a point light source. Flocculent material is provided at the edge of the pinhole to assist in judging whether the pinhole image is clear. Polished areas are reserved on the rear surfaces of both the primary mirror 3 and the secondary mirror 4 to complete the self-alignment of the primary mirror with the first measuring device and the secondary mirror with the second measuring device.
[0034] The setup and adjustment device for the primary and secondary mirror positions of the beam shrinking system also includes two reference marks. The reference marks are used to coordinate with the first and second measuring devices to establish an exit reference that coincides with the optical axis of the beam shrinking system.
[0035] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0036] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.
[0037] 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; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for adjusting the pose of primary and secondary mirrors in a beam-shrinking system, characterized in that, Includes the following steps: Reference establishment: Two reference marks are set at the theoretical positions of the optical axis of the beam-shrinking system. The first and second measuring devices are aligned with each other to establish an exit reference that coincides with the optical axis of the beam-shrinking system. Secondary mirror coarse adjustment: Adjust the second measuring device to the rear of the secondary mirror and switch the second measuring device to collimation mode. By adjusting the azimuth and pitch angle of the secondary mirror, make the secondary mirror self-aligned with the second measuring device to complete the coarse positioning of the secondary mirror's azimuth and pitch. Secondary mirror fine-tuning: Illuminate the pinhole light source located at the real focal point of the secondary mirror, switch the first measuring device to auto-collimation mode, and observe the pinhole image within the field of view of the first measuring device; eliminate defocus by adjusting the front and rear position of the secondary mirror to make the pinhole image clear; then adjust the azimuth and pitch angles of the secondary mirror to make the crosshairs of the first measuring device coincide with the pinhole image, thus completing the precise alignment of the secondary mirror with the emission reference. Reference transfer: Keep the azimuth angle of the first measuring device unchanged, and adjust its elevation angle to align with the second measuring device that has been raised to the height of the main mirror; Adjust the second measuring device so that the two are interlocked, thereby transferring the exit reference to the second measuring device and establishing the incident reference; Primary mirror coarse adjustment: Adjust the first measuring device to the rear of the primary mirror, switch the first measuring device to collimation mode, and adjust the azimuth and pitch angles of the primary mirror to make the primary mirror self-align with the first measuring device, thus completing the coarse positioning of the primary mirror's azimuth and pitch. Primary mirror fine-tuning: Light up the pinhole light source, switch the second measuring device representing the incident reference to auto-collimation mode, and observe the pinhole image in the field of view of the second measuring device; By adjusting the front and rear positions of the primary mirror to eliminate defocus and make the pinhole image clear; then by adjusting the azimuth and pitch angles of the primary mirror to make the crosshairs of the second measuring device coincide with the pinhole image, the primary mirror is precisely aligned with the incident reference.
2. The method for adjusting the pose of the primary and secondary mirrors in the beam-shrinking system according to claim 1, characterized in that, The method for adjusting the pose of the primary and secondary mirrors of the beam-shrinking system also includes the following steps: Preparation for installation and adjustment: Reserve polishing areas on the rear surfaces of the primary and secondary mirrors; initially install the primary and secondary mirrors in their theoretical positions; install a small hole with flocculent edges at the real focal point of the secondary mirror.
3. The method for adjusting the pose of the primary and secondary mirrors in the beam-shrinking system according to claim 1, characterized in that, Both the first measuring device and the second measuring device are theodolites, and the reference mark is a crosshair tool.
4. The method for adjusting the pose of the primary and secondary mirrors in the beam-shrinking system according to claim 3, characterized in that, The mutual aiming of the first measuring device and the second measuring device includes the following steps: Adjust the pitch direction of the two theodolites to the horizontal plane, and use a two-dimensional lifting platform to adjust the height of the two theodolites so that the two theodolites can thread their respective crosshairs.
5. The method for adjusting the pose of the primary and secondary mirrors in the beam-shrinking system according to claim 2, characterized in that, The pinhole image being clear specifically means that the flocculent material at the edge of the pinhole image is clear and sharp.
6. The method for adjusting the pose of the primary and secondary mirrors in the beam-shrinking system according to claim 1, characterized in that, Adjusting the second measuring device so that the two are interlocked includes the following steps: The elevation direction of the second measuring device was adjusted to be horizontal while keeping the azimuth angle unchanged. Align the first measuring device by changing the pitch angle of the second measuring device; Then, by adjusting the azimuth angle of the second measuring device, the two devices can be aligned to be intersected.
7. A device for adjusting the pose of primary and secondary mirrors in a beam-shrinking system, characterized in that, The assembly and adjustment method for realizing the pose of the primary and secondary mirrors of the beam-shrinking system according to any one of claims 1 to 6 includes a first measuring device, a second measuring device, a pinhole, a primary mirror, a secondary mirror, and a two-dimensional lifting platform. The bottoms of both the first and second measuring devices are connected to a two-dimensional lifting platform. The small hole is located at the common real focal point of the primary and secondary mirrors, and a light source is provided on the small hole.
8. The device for adjusting the pose of primary and secondary mirrors in a beam-shrinking system according to claim 7, characterized in that, The edge of the pinhole is provided with flocculent material to assist in judging whether the pinhole image is clear.
9. The device for adjusting the pose of primary and secondary mirrors in a beam-shrinking system according to claim 7, characterized in that, The beam-shrinking system's primary and secondary mirror orientation adjustment device also includes two reference marks. These reference marks are used to coordinate with the first and second measuring devices to establish an exit reference that coincides with the optical axis of the beam-shrinking system.
10. The device for adjusting the pose of primary and secondary mirrors in a beam-shrinking system according to claim 7, characterized in that, Both the rear surfaces of the primary mirror and the secondary mirror have pre-reserved polished areas to facilitate self-alignment between the primary mirror and the first measuring device, and between the secondary mirror and the second measuring device.