阅读说明：本技术 一种凸自由曲面反射镜面形测试方法 (method for testing surface shape of convex free-form surface reflector ) 是由 闫力松 冀慧茹 晁联盈 莫言 马冬林 于 2019-08-02 设计创作，主要内容包括：本发明属于先进光学系统技术领域,公开了一种凸自由曲面反射镜面形测试方法,能够构建由干涉仪、空间光调制器、球面反射镜、凸自由曲面反射镜组成的精确测试光路；其中,空间光调制器被划分为四种调制区域,分别用于对凸自由曲面反射镜进行测量、与干涉仪对准、与球面反射镜对准、以及投射十字线。本发明通过对测试光路的整体设计及光学元器件对准方式等进行改进,构建的精确测试光路能够基于混合补偿干涉测量凸自由曲面反射镜,与现有技术相比提供了一种新的测试思路,尤其能够有效解决大口径凸面干涉测量困难的问题,该方法通过利用球面反射镜提供会聚光路,同时结合空间光调制器对凸自由曲面反射镜完成零位补偿。(The invention belongs to the technical field of advanced optical systems, and discloses a convex free-form surface reflector surface shape testing method which can construct an accurate testing light path consisting of an interferometer, a spatial light modulator, a spherical reflector and a convex free-form surface reflector; the spatial light modulator is divided into four modulation regions, which are respectively used for measuring the convex free-form surface reflector, aligning with the interferometer, aligning with the spherical reflector and projecting the cross line. According to the method, the overall design of the test light path, the alignment mode of optical components and the like are improved, the constructed accurate test light path can be used for measuring the convex free-form surface reflector based on hybrid compensation interference, compared with the prior art, a new test thought is provided, and particularly the problem that the interference measurement of a large-caliber convex surface is difficult can be effectively solved.)

1. A convex free-form surface reflector surface shape testing method is characterized in that the method can construct an accurate testing light path consisting of four optical components, namely an interferometer, a spatial light modulator, a spherical reflector and a convex free-form surface reflector; the spatial light modulator is used as a compensation element, and is divided into four modulation areas which are respectively used as four diffraction optical areas, wherein the four diffraction optical areas are respectively used as a main detection area for aligning the spatial light modulator with the convex free-form surface reflector and carrying out measurement, a first area for aligning the spatial light modulator with the interferometer, a second area for aligning the spatial light modulator with the spherical reflector and at least four third areas which are used as cross line projection areas, and the third areas are distributed along the edge of the spatial light modulator;

The method specifically comprises the following steps:

(1) Alignment of the interferometer with the spatial light modulator: adjusting the relative positions of the interferometer and the spatial light modulator to enable light rays emitted by the interferometer to return to the interferometer after passing through a first area in the spatial light modulator, and forming interference fringes with reference light of the interferometer; then, continuously adjusting the relative positions of the interferometer and the spatial light modulator to adjust the interference fringes to a zero fringe state, so as to realize the accurate alignment of the interferometer and the spatial light modulator;

(2) aligning the spherical reflector: on the premise that the interferometer and the spatial light modulator are accurately aligned, adjusting the position of a spherical reflector at the rear end of the spatial light modulator to enable light rays emitted by the interferometer to pass through a second area in the spatial light modulator, reflect by the spherical reflector, return to the second area, return to the interferometer and form interference fringes with reference light of the interferometer; then, continuously adjusting the position of the spherical reflector to adjust the interference fringes to a zero fringe state, so as to realize the accurate alignment of the spherical reflector, the spatial light modulator and the interferometer;

(3) Rough alignment of the convex free-form surface reflector: on the premise that the spherical reflector is accurately aligned with the spatial light modulator and the interferometer, the convex free-form surface reflector is placed on the basis of at least four cross lines appearing at the rear end of the spherical reflector, so that the center of the convex free-form surface reflector is close to a central point surrounded by the cross lines, and therefore the rough alignment of the convex free-form surface reflector is completed;

(4) The accurate alignment step of the convex free-form surface reflector: the light emitted by the interferometer passes through a main detection area in the spatial light modulator, is reflected by a spherical reflector, a convex free-form surface reflector and the spherical reflector again, returns to the main detection area, finally returns to the interferometer, and forms interference fringes with reference light of the interferometer; by utilizing the interference fringes, the position of the convex free-form surface reflector is adjusted to make the interference fringes become sparse, so that the convex free-form surface reflector and other optical components in the test optical path can be accurately aligned to obtain an accurately constructed accurate test optical path;

(5) And (4) based on the accurate test light path obtained in the step (4), utilizing the main detection area to realize surface shape measurement of the convex free-form surface reflector.

2. The convex free-form surface mirror surface shape testing method according to claim 1, wherein in the step (4), the making of the interference fringes sparse is preferably a making of the interference fringes to a zero-fringe state.

3. The method for testing the shape of a convex free-form surface mirror according to claim 1, wherein for the spatial light modulator, the main detection region, the first region, and the second region are arranged and distributed from inside to outside in sequence around the common circle center; at least four of the third regions are each located within the second region and these third regions are evenly distributed along the edge of the spatial light modulator.

4. The method for testing the surface shape of a convex free-form surface reflecting mirror according to claim 1, wherein the diameter of the convex free-form surface reflecting mirror is 100mm or more.

5. The method for testing the shape of a convex freeform surface mirror according to any one of claims 1 to 4, wherein the number of the third areas is preferably an even number.

6. the method for testing the shape of a convex freeform surface reflector according to any one of claims 1 to 5, wherein the number of said third areas is preferably four.

Technical Field

the invention belongs to the technical field of advanced optical systems, and particularly relates to a convex free-form surface reflector surface shape testing method.

Background

With the progress of national technology, the fields of space detection, ground remote sensing, aviation, aerospace, illumination, display and the like put forward higher requirements on the aspects of light weight, miniaturization, system image quality optimization and the like of an optical system. The free-form surface is applied to the optical system, so that the optimization degree of freedom of the system can be improved, the design residual error of the optical system and the number of optical elements are reduced, and the structure of the optical system is simplified while the image quality of the system is improved. The advantages enable an optical system designer to break through the concept of the traditional optical system according to the special requirements of the design parameters of the optical system and apply the free-form surface to a brand new system design scheme. Therefore, the free-form surface optical system has the advantages of reducing the number of optical elements, improving the imaging quality, meeting the requirement of light weight and the like. At present, the free-form surface is successfully applied to optical systems such as space cameras, lighting optics, helmet display and the like. The application research of optical systems based on free-form surfaces has become an important direction for the development of modern high-performance optical systems, and the manufacturing requirement of high-precision free-form surface optical elements is met, while the high-precision measurement of the free-form surfaces is the basis for manufacturing the high-precision free-form surface optical elements. The interferometry is used as a general final precision detection method of an optical element, and the ideal state of the interferometry is to realize zero detection of the element to be detected.

The convex free-form surface, especially the large-caliber convex free-form surface with the diameter more than or equal to 100mm, needs the large-caliber convergent light beam to be incident on the surface of the free-form surface reflector to complete the interference measurement due to the particularity of the geometric form, and in view of the limitation of factors such as the existing detection equipment and device method, the large-caliber convergent light beam is difficult to generate, the practical difficulty in the detection brings the limitation to the design of the related optical system, and the development and the manufacture of the advanced optical system with the large radius of curvature are seriously restricted. 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 the advanced optical system, and has important significance for the manufacture of the advanced optical system.

Disclosure of Invention

aiming at the defects or improvement requirements in the prior art, the invention aims to provide a convex free-form surface reflector surface shape testing method, wherein the overall design of a testing light path, the alignment mode of optical components and the like are improved, and the constructed accurate testing light path can measure the convex free-form surface reflector based on hybrid compensation interference; in addition, in order to realize the accurate alignment of the interferometer, the spatial light modulator, the spherical optical reflector and the convex free-form surface reflector to be detected in the detection light path, the accurate alignment of each optical element in the detection light path and the measurement of the surface shape result of the convex free-form surface reflector are jointly ensured by designing a corresponding functional area on the spatial light modulator, the surface shape detection result obtained by the measurement is based on the zero compensation measurement of the convex free-form surface reflector, a non-common path error is not substituted, and the detection result is directly consistent with the surface shape result of the mirror surface.

in order to achieve the above object, according to the present invention, there is provided a method for testing the surface shape of a convex free-form surface reflector, characterized in that the method is capable of constructing an accurate test optical path composed of four optical components, i.e., an interferometer, a spatial light modulator, a spherical reflector, and a convex free-form surface reflector; the spatial light modulator is used as a compensation element, and is divided into four modulation areas which are respectively used as four diffraction optical areas, wherein the four diffraction optical areas are respectively used as a main detection area for aligning the spatial light modulator with the convex free-form surface reflector and carrying out measurement, a first area for aligning the spatial light modulator with the interferometer, a second area for aligning the spatial light modulator with the spherical reflector and at least four third areas which are used as cross line projection areas, and the third areas are distributed along the edge of the spatial light modulator;

The method specifically comprises the following steps:

(1) Alignment of the interferometer with the spatial light modulator: adjusting the relative positions of the interferometer and the spatial light modulator to enable light rays emitted by the interferometer to return to the interferometer after passing through a first area in the spatial light modulator, and forming interference fringes with reference light of the interferometer; then, continuously adjusting the relative positions of the interferometer and the spatial light modulator to adjust the interference fringes to a zero fringe state, so as to realize the accurate alignment of the interferometer and the spatial light modulator;

(2) Aligning the spherical reflector: on the premise that the interferometer and the spatial light modulator are accurately aligned, adjusting the position of a spherical reflector at the rear end of the spatial light modulator to enable light rays emitted by the interferometer to pass through a second area in the spatial light modulator, reflect by the spherical reflector, return to the second area, return to the interferometer and form interference fringes with reference light of the interferometer; then, continuously adjusting the position of the spherical reflector to adjust the interference fringes to a zero fringe state, so as to realize the accurate alignment of the spherical reflector, the spatial light modulator and the interferometer;

(3) Rough alignment of the convex free-form surface reflector: on the premise that the spherical reflector is accurately aligned with the spatial light modulator and the interferometer, the convex free-form surface reflector is placed on the basis of at least four cross lines appearing at the rear end of the spherical reflector, so that the center of the convex free-form surface reflector is close to a central point surrounded by the cross lines, and therefore the rough alignment of the convex free-form surface reflector is completed;

(4) The accurate alignment step of the convex free-form surface reflector: the light emitted by the interferometer passes through a main detection area in the spatial light modulator, is reflected by a spherical reflector, a convex free-form surface reflector and the spherical reflector again, returns to the main detection area, finally returns to the interferometer, and forms interference fringes with reference light of the interferometer; by utilizing the interference fringes, the position of the convex free-form surface reflector is adjusted to make the interference fringes become sparse, so that the convex free-form surface reflector and other optical components in the test optical path can be accurately aligned to obtain an accurately constructed accurate test optical path;

(5) And (4) based on the accurate test light path obtained in the step (4), utilizing the main detection area to realize surface shape measurement of the convex free-form surface reflector.

in a further preferred embodiment of the present invention, in the step (4), the interference fringes are thinned, preferably by being adjusted to a zero-fringe state.

As a further preferred aspect of the present invention, in the spatial light modulator, the main detection region, the first region, and the second region are arranged and distributed from inside to outside in sequence around the common center of circle; at least four of the third regions are each located within the second region and these third regions are evenly distributed along the edge of the spatial light modulator.

In a further preferred embodiment of the present invention, the convex free-form surface mirror has a diameter of 100mm or more.

as a further preferred aspect of the present invention, the number of the third regions is preferably an even number.

As a further preferred aspect of the present invention, the number of the third regions is preferably four.

through the technical scheme, compared with the prior art, the interference measurement of the surface shape of the convex free-form surface reflector is realized based on the mixed compensation mode of combining the spatial light modulator and the spherical optical reflector, and the method is particularly suitable for the large-caliber convex free-form surface reflector (certainly, also suitable for the small-caliber convex free-form surface reflector). The invention designs a mixed compensation detection light path (namely a test light path), introduces a spatial light modulator and an optical spherical reflector, modulates the phase of incident light through the spatial light modulator, provides a convergent light beam by combining the spherical reflector, and can complete zero compensation (namely, enabling light to normally enter along each point of the surface of the free-form surface reflector and simultaneously to normally exit) on a convex free-form surface reflector (especially a large-caliber convex free-form surface reflector).

The invention adopts the concave spherical reflector to provide the converged light beam, has small manufacturing difficulty of the concave spherical reflector, and solves the problem that the prior art is difficult to provide the large-caliber converged light beam to the convex free-form surface reflector, especially the large-caliber convex free-form surface reflector. According to the invention, the spatial light modulator is combined with the spherical reflector, so that the zero compensation measurement of the convex free-form surface reflector to be measured is completed while the large-caliber convergent light beam is realized; the zero compensation measurement can ensure that no non-common-path error is substituted in the surface shape detection result, and the detection result is directly consistent with the surface shape result of the mirror surface.

The misalignment in the alignment of the optical elements can introduce extra aberration in the interference detection result, and in order to ensure the accurate alignment of each optical element in an interference detection light path, functional regions are planned and designed in the spatial light modulator, namely four diffraction regions including four regions, namely a main measurement region (namely, a main detection region and a main region), a spatial light modulator and interferometer alignment region (namely, a first region), a spatial light modulator and spherical mirror alignment region (namely, a second region) and a spatial light modulator projection cross line region (namely, a third region); the main measurement area can be used for completing compensation measurement of the convex free-form surface reflector and further used for surface shape testing; the first area is used for finishing the alignment of the interferometer and the spatial light modulator in the detection light path; the second area is used for finishing the alignment of the spherical reflector and the spatial light modulator in the detection light path; the third area with at least four numbers can correspondingly project at least four cross lines around the convex free-form surface reflector to be detected, so that the rough alignment of the position of the convex free-form surface reflector to be detected in the detection optical path is conveniently realized. By utilizing the design and the mutual matching of the functional areas and the design based on the integral alignment step of the method, the accurate alignment of each optical element in the detection light path and the measurement of the surface shape result of the convex free-form surface reflector are ensured together, and the method is particularly suitable for measuring the full-aperture surface shape of the large-aperture convex free-form surface reflector.

according to the built light path, the interferometer and the spatial light modulator, the position of the spatial light modulator and the spherical reflector in the light path and the position of the spatial light modulator and the position of the convex free-form surface reflector in the light path are sequentially arranged, so that the alignment of the detection light path can be completed, and the zero compensation surface shape measurement of the convex free-form surface reflector can be realized.

In conclusion, the invention can complete the interference measurement of the convex free-form surface reflector, is particularly suitable for the large-caliber convex free-form surface reflector with the diameter more than or equal to 100mm, provides guarantee for the manufacturing and development of modern advanced optical systems, and has the advantages of high detection precision, simple requirements on detection site environment and size and the like.

Drawings

Fig. 1 is a schematic diagram of a convex free-form surface hybrid compensation detection optical path.

fig. 2 is a schematic diagram of the distribution of the planning region of the spatial light modulator.

Fig. 3 (a) and (b) are schematic diagrams of interference diagrams of corresponding positions after the spatial light modulator is aligned with the interferometer.

Fig. 4 is a schematic diagram of a position relationship between a projection reticle of the spatial light modulator and the convex free-form surface reflector to be measured.

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.

As shown in fig. 1, an interference detection light path diagram (especially suitable for a large-diameter convex free-form surface) of a convex free-form surface reflector according to the present invention is shown, in the interference detection, light rays in a detection light path need to be converged by a spherical reflector to provide a convergent light beam required for detecting the convex free-form surface, and a compensation element spatial light modulator needs to be used to compensate the convex free-form surface reflector to implement zero compensation detection on the free-form surface reflector (so-called zero compensation detection, that is, each incident light ray is incident along a normal of the free-form surface reflector and exits along a normal). The detection light path of the convex free-form surface reflector relates to four optical elements of an interferometer, a spatial light modulator, a spherical reflector and the convex free-form surface reflector. The misalignment in the alignment of the optical elements may introduce extra aberration in the interference detection result, and in order to ensure the precise alignment of each optical element in the interference detection optical path, it is necessary to design corresponding functional regions on the spatial light modulator, and the functional regions are distributed as shown in fig. 2.

The spatial light modulator includes four diffractive optical regions, which are a main detection region, an alignment region with the interferometer (i.e., a first region), an alignment region with the spherical mirror (i.e., a second region), and a reticle projection region (i.e., a third region). The main detection area is a convex free-form surface reflector zero compensation measurement area and can be used for finally measuring the surface shape of the free-form surface reflector; the alignment area of the interferometer and the spatial light modulator is used for aligning the spatial light modulator and the interferometer, when in detection, the relative position (including three-dimensional translation and inclination) between the spatial light modulator and the interferometer is adjusted, so that light rays emitted by the interferometer return to the interferometer after passing through the alignment area of the spatial light modulator and the interferometer, interference fringes are formed with reference light of the interferometer, the relative position between the spatial light modulator and the interferometer is continuously adjusted, and the interference fringes are adjusted to be in a zero fringe state (the interference fringes are completely black or completely white, as shown in (a) and (b) in figure 3; after the interferometer and the spatial light modulator are accurately aligned, a spherical reflector is placed in a light path, light is emitted through the interferometer by adjusting the position of the spherical reflector, is reflected by a spatial light modulator and a spherical reflector alignment area on the spatial light modulator and the spherical reflector, returns to the spatial light modulator and the spherical reflector alignment area, returns to the interferometer and forms interference fringes with reference light of the interferometer, and the interference fringes are adjusted to a zero fringe state (the interference fringes at corresponding positions are completely black or completely white as shown in (a) and (b) in fig. 3) by continuously adjusting the reflection position of the spherical reflector;

After the precise alignment of the interferometer, the spatial light modulator and the spherical reflector is completed, four cross lines are formed based on the projected cross line area on the spatial light modulator, as shown in fig. 4, the convex free-form surface reflector is placed near the center of the four cross lines (for example, the distance between the center of the convex free-form surface reflector and the central point surrounded by the cross lines does not exceed the preset distance maximum value requirement, the preset distance maximum value can be flexibly set, of course, the two centers can also be directly overlapped with each other), at this time, the rough alignment of the convex free-form surface reflector in the light path is completed, the corresponding interference fringes are formed in the interferometer through the main area of the spatial light modulator, and the detection interference fringes of the free-form surface formed in the interferometer become sparse or even can obtain the condition of zero fringes through further adjusting the positions (such as translation and inclination) of the convex free-form surface reflector, at the moment, the precise adjustment of the free-form surface reflector in the optical path is finished, namely, the precise alignment of the interferometer, the spatial light modulator, the spherical reflector and the convex free-form surface reflector is realized, the surface shape detection result of the convex free-form surface reflector can be obtained through interferometry, the non-common-path error is not substituted in the surface shape detection result, and the detection result is directly consistent with the surface shape result of the mirror surface.

The components (such as a spatial light modulator and the like) adopted in the test light path can be directly commercially available components; in addition, the division of the four modulation regions on the spatial light modulator can be self-programmed by referring to the prior art such as a product manual.

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.