CN110986824B - System and method for detecting surface shape of large-caliber convex free-form surface reflector - Google Patents
System and method for detecting surface shape of large-caliber convex free-form surface reflector Download PDFInfo
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- CN110986824B CN110986824B CN201911316403.6A CN201911316403A CN110986824B CN 110986824 B CN110986824 B CN 110986824B CN 201911316403 A CN201911316403 A CN 201911316403A CN 110986824 B CN110986824 B CN 110986824B
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Abstract
The invention discloses a system and a method for detecting the surface shape of a large-caliber convex free-form surface reflector, belonging to the technical field of advanced optical systems. The invention completes zero compensation to the free-form surface reflector by combining the curved surface calculation hologram with the spherical reflector. In order to realize the accurate alignment of the interferometer, the curved surface calculation hologram, the spherical reflector and the convex free-form surface reflector to be detected in the detection optical path, a corresponding functional area is designed on the curved surface calculation hologram, wherein the curved surface calculation hologram comprises a convex surface part interferometer alignment area and a plurality of diffraction areas such as a concave surface part main detection area, a projection cross line area, a spherical reflector alignment area and the like, and the areas are combined to ensure the accurate alignment of each optical element in the detection optical path and the measurement of the free-form surface shape result. The invention has the advantages of high detection precision, simple detection site environment and size requirement and the like, and provides guarantee for the manufacturing and development of modern advanced optical systems.
Description
Technical Field
The invention belongs to the technical field of advanced optical systems, and particularly relates to a system and a method for detecting the surface shape of a large-caliber convex free-form surface reflector.
Background
The free-form surface has the advantages of improving the image quality of an optical system, improving the design freedom of the optical system, simplifying the structure of the optical system and the like, is a core element of a modern optical system, and has been widely applied to optical systems of space cameras, lithography systems, display and imaging systems. In view of the advantages and wide applications of the free-form surface optical element, the surface shape of the reflecting mirror that does not meet the precision requirement may seriously affect the performance of the optical system, for example, for an imaging system, good image quality may not be obtained, for a lithography system, it may be difficult to obtain ultrahigh resolution, and the like, and it is very important to measure the surface shape of the surface of the element with high precision. Generally, as a means for testing the final surface shape of an optical mirror, interferometry is the basis for manufacturing optical elements with high precision.
The large-caliber convex free-form surface optical reflector has wide application in optical systems, and is generally used as a secondary mirror in the optical systems particularly for space camera optical systems and large-caliber telescope optical systems. For space cameras, the secondary mirror aperture is currently approaching the order of 1m, and for the Thirty Meter Telescope (TMT) and European extra Large Telescope (E-ELT) projects being built, the secondary mirror aperture is even exceeding 1.5 m. For the large-aperture optical convex reflector, a splicing measurement mode is generally adopted, but the mode has long detection time and many detection times, and meanwhile, the precision of a splicing algorithm can limit the reconstruction precision of the final mirror surface shape. The above difficulties bring limitations to the design and manufacture of related optical systems, and severely restrict the development and manufacture of related advanced optical systems. Therefore, the realization of the surface shape measurement of the large-caliber convex free-form surface reflector is one of the core steps in the development of modern advanced optical systems, and has important significance for the manufacture of the large-caliber convex free-form surface reflector.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a system and a method for detecting the surface shape of a large-caliber convex free-form surface reflector, aiming at solving the problem of low precision in detecting the surface shape of the large-caliber convex free-form surface reflector.
In order to achieve the aim, the invention provides a large-caliber convex free-form surface reflector mirror surface shape detection system, which comprises a convex free-form surface reflector to be detected, a curved surface calculation hologram, a spherical reflector and an interferometer;
the convex portion of the curved computational hologram comprises an interferometer alignment area (A1) and a convex obscuration reflection area (A2), the concave portion of the curved computational hologram comprises a spherical mirror alignment area (B1), a reticle projection area (B2) and a main detection area (B3);
the interferometer alignment area (A1) is used for precise alignment of the curved computational hologram with an interferometer;
the spherical mirror alignment area (B1) is used for precise alignment of the curved computational hologram with a spherical mirror.
Further, the front and back surfaces of the curved surface computer generated hologram are spherical surfaces.
Further, the interferometer alignment area (A1) is located at the center of the convex portion of the curved computational hologram.
Further, the spherical mirror alignment region (B1) is located at the periphery of the primary detection region (B3).
The invention also provides a detection method based on the large-caliber convex free-form surface reflector mirror surface shape detection system, which comprises the following steps:
s1, using the interferometer alignment area (A1) to complete the alignment of the curved surface computation hologram and the interferometer;
s2, placing a spherical reflector, and adjusting the position of the spherical reflector to accurately align the interferometer, the spherical reflector and the curved surface calculation hologram;
s3, placing the convex free-form surface reflector in the center of four cross lines formed behind the curved surface calculation hologram to finish the rough alignment of the convex free-form surface reflector in the light path, and forming corresponding interference fringes in the interferometer through the main detection area (B3);
s4, adjusting the position of the convex free-form surface reflector to enable the free-form surface detection interference fringes formed in the interferometer to be close to a zero fringe state as much as possible;
and S5, measuring a wave aberration result corresponding to the convex free-form surface reflector, adjusting the accurate position of the convex free-form surface reflector by combining the wave aberration, and performing zero compensation measurement on the convex free-form surface reflector.
Further, the step S1 includes: adjusting the relative position between the curved surface calculation hologram and the interferometer, so that light rays emitted by the interferometer return to the interferometer after passing through the interferometer alignment area (A1) and form interference fringes with reference light of the interferometer; and continuously adjusting the relative position of the curved surface calculation hologram and the interferometer, and adjusting the interference fringes to a zero fringe state.
Further, the step S2 includes: placing the spherical reflector and adjusting the position of the spherical reflector, so that light rays emitted by the interferometer are reflected to the spherical reflector through the convex surface part of the curved surface calculation hologram and then reflected to the convex surface of the curved surface calculation hologram by the spherical reflector, are reflected by the alignment area (B1) of the spherical reflector and then return to the interferometer along the original path, and form interference fringes with reference light of the interferometer; and continuously adjusting the position of the spherical reflector until the interference fringes change into a zero fringe state.
Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:
(1) the invention combines the curved surface calculation hologram with the spherical surface reflector for use, realizes zero compensation of the convex free-form surface reflector in a mixed compensation mode, thereby completing full-aperture interference measurement of the large-aperture convex free-form surface reflector, not only improving the detection precision, but also having simple requirements on the environment and the size of a detection field and strong operability, and providing a guarantee for the manufacturing and development of modern advanced optical systems.
(2) According to the invention, by designing a plurality of corresponding functional areas on the curved surface calculation hologram, the accurate alignment of each optical element in the detection light path is ensured together, and the accurate obtaining of the final convex free-form surface shape result is further ensured.
Drawings
FIG. 1 is a schematic diagram of a mirror surface shape interference detection optical path of a large-aperture convex free-form surface reflector;
FIGS. 2(a) and 2(b) are schematic diagrams of the distribution of the convex and concave areas of the CGH, respectively;
FIG. 3 is an interferogram of the corresponding position after alignment of the CGH with the interferometer;
fig. 4 is a schematic diagram of the relationship between the CGH projection reticle and the large-caliber convex free-form surface reflector.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention discloses a method for carrying out full-aperture compensation measurement on a convex free-form surface reflector based on a spherical reflector and a curved surface calculation hologram, which solves the problem of difficulty in full-aperture interference measurement of the mirror surface of a large-aperture convex free-form surface reflector. The method realizes zero compensation of the convex free-form surface reflector by combining the curved surface calculation hologram with the spherical reflector. And in order to realize the accurate alignment of the interferometer, the curved surface calculation hologram, the spherical reflector and the convex free-form surface reflector to be measured in the detection optical path, a corresponding functional area is designed on the curved surface calculation hologram, wherein the curved surface calculation hologram comprises four diffraction areas which are respectively an interferometer alignment area positioned on a convex part and a main detection area positioned on a concave part, a cross line projection area and a spherical reflector alignment area, and the four areas jointly ensure the accurate alignment of each optical element in the detection optical path and the accurate measurement of a free-form surface shape result.
The measuring method of the present invention will be described with reference to specific examples. Fig. 1 shows a surface shape interference detection light path diagram of a large-aperture convex free-form surface reflector, in which a spherical reflector and a curved surface calculation hologram are required to perform full-aperture compensation measurement on a free-form surface in interference detection, so as to realize zero detection, that is, each incident light ray is incident along the normal of the free-form surface reflector and exits along the normal. Specifically, four optical elements including a convex free-form surface reflector 1 to be detected, a curved surface calculation hologram 2, a spherical reflector 3 and an interferometer 4 are involved in a detection light path, wherein the front surface and the rear surface of the curved surface calculation hologram are spherical surfaces.
The misalignment of the optical elements in the optical path causes additional aberration to be introduced into the detection result, and therefore, in order to ensure accurate alignment between the optical elements during detection, a corresponding alignment area is designed on the curved surface computer hologram 2, the alignment area is shown in fig. 2, an interferometer alignment area a1 and a convex obscuration reflection area a2 are designed on the convex surface portion of the curved surface computer hologram, and a spherical mirror alignment area B1, a reticle projection area B2 and a main detection area B3 are designed on the concave surface portion of the curved surface computer hologram. The interferometer alignment area A1 is located at the center of the convex part of the curved computational hologram to complete the precise alignment of the curved computational hologram 2 with the interferometer 4; a spherical mirror alignment area B1 is located at the periphery of the main detection area B3 for accurate alignment of the curved computational hologram 2 with the spherical mirror 3.
During detection, firstly, the precise alignment of the curved surface calculation hologram 2 and the interferometer 4 is completed by using the interferometer alignment area A1: by adjusting the relative position (including three-dimensional translation and inclination) between the curved surface calculation hologram 2 and the interferometer 4, the light emitted by the interferometer 4 is reflected by the interferometer alignment area a1 and returns to the interferometer 4, and forms an interference fringe with the interferometer reference light, the relative position between the curved surface calculation hologram and the interferometer is continuously adjusted, the interference fringe is adjusted to a zero fringe state (the interference fringe is completely black or completely white, as shown in fig. 3), and at this time, the interferometer 4 and the curved surface calculation hologram 2 complete accurate alignment.
After the alignment of the interferometer 4 and the curved surface calculation hologram 2 is completed, the spherical reflector 3 is placed and the position of the spherical reflector 3 is adjusted, at the moment, light rays emitted by the interferometer 4 are reflected to the spherical reflector 3 through the convex part of the curved surface calculation hologram 2 and then reflected to the convex surface of the curved surface calculation hologram 2 through the spherical reflector alignment area B1 positioned on the concave surface of the curved surface calculation hologram, the light rays are returned to the interferometer 4 along the original path after being reflected, interference fringes are formed with interferometer reference light, the position of the spherical reflector 3 is continuously adjusted, the interference fringes are adjusted to be in a zero fringe state, and at the moment, the interferometer 4, the spherical reflector 3 and the curved surface calculation hologram 2 are accurately aligned.
After the precise alignment of the interferometer 4, the spherical mirror 3 and the curved computational hologram 2 is completed, four crosshairs are formed behind the curved computational hologram 2, as shown in fig. 4. The free-form surface mirror 1 is placed in the center of the four cross lines, at which time the rough alignment of the free-form surface mirror in the optical path is completed, which will form corresponding interference fringes in the interferometer 4 through the curved surface computer hologram main detection area B3. Then, the position (translation and inclination) of the convex free-form surface reflector 1 is further adjusted, the free-form surface detection interference fringes formed in the interferometer 4 become sparse and even can obtain the condition of zero fringes, at the moment, the accurate adjustment of the free-form surface reflector in the optical path is completed, the accurate alignment of the interferometer 4, the curved surface calculation hologram 2, the spherical reflector 3 and the convex free-form surface reflector 1 is realized, the wave aberration result corresponding to the free-form surface reflector can be measured at the moment, the accurate position of the free-form surface reflector is adjusted by combining the wave aberration, the zero compensation measurement of the large-caliber free-form surface reflector is realized, and the surface shape interference detection result of the large-caliber convex free-form surface reflector is finally obtained.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. A large-caliber convex free-form surface reflector mirror surface shape detection system is characterized by comprising a convex free-form surface reflector to be detected, a curved surface calculation hologram, a spherical reflector and an interferometer;
the convex portion of the curved computational hologram comprises an interferometer alignment area (A1) and a convex obscuration reflection area (A2), the concave portion of the curved computational hologram comprises a spherical mirror alignment area (B1), a reticle projection area (B2) and a main detection area (B3);
the interferometer alignment area (A1) is used for precise alignment of the curved computational hologram with an interferometer;
the spherical mirror alignment area (B1) is used for precise alignment of the curved computational hologram with a spherical mirror;
the front and back surfaces of the curved surface calculation hologram are spherical surfaces.
2. The large aperture convex freeform reflector topography detection system as claimed in claim 1, wherein said interferometer alignment area (a1) is located in the center of the convex portion of said curved computational hologram.
3. The large aperture convex freeform reflector profile inspection system of claim 1, wherein said spherical reflector alignment area (B1) is located at the periphery of said primary inspection area (B3).
4. The detection method of the large-caliber convex free-form surface reflector mirror surface shape detection system based on any one of claims 1 to 3, characterized by comprising the following steps:
s1, using the interferometer alignment area (A1) to complete the alignment of the curved surface computation hologram and the interferometer;
s2, placing a spherical reflector, and adjusting the position of the spherical reflector to accurately align the interferometer, the spherical reflector and the curved surface calculation hologram;
s3, placing the convex free-form surface reflector in the center of four cross lines formed behind the curved surface calculation hologram to finish the rough alignment of the convex free-form surface reflector in the light path, and forming corresponding interference fringes in the interferometer through the main detection area (B3);
s4, adjusting the position of the convex free-form surface reflector to enable the free-form surface detection interference fringes formed in the interferometer to be close to a zero fringe state as much as possible;
and S5, measuring a wave aberration result corresponding to the convex free-form surface reflector, adjusting the accurate position of the convex free-form surface reflector by combining the wave aberration, and performing zero compensation measurement on the convex free-form surface reflector.
5. The detection method according to claim 4, wherein the step S1 includes: adjusting the relative position between the curved surface calculation hologram and the interferometer, so that light rays emitted by the interferometer return to the interferometer after passing through the interferometer alignment area (A1) and form interference fringes with reference light of the interferometer; and continuously adjusting the relative position of the curved surface calculation hologram and the interferometer, and adjusting the interference fringes to a zero fringe state.
6. The detection method according to claim 4, wherein the step S2 includes: placing the spherical reflector and adjusting the position of the spherical reflector, so that light rays emitted by the interferometer are reflected to the spherical reflector through the convex surface part of the curved surface calculation hologram and then reflected to the convex surface of the curved surface calculation hologram by the spherical reflector, are reflected by the alignment area (B1) of the spherical reflector and then return to the interferometer along the original path, and form interference fringes with reference light of the interferometer; and continuously adjusting the position of the spherical reflector until the interference fringes change into a zero fringe state.
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