阅读说明：本技术 一种大曲率半径自由曲面镜面面形干涉测量装置及方法 (Large-curvature-radius free-form surface mirror surface shape interference measurement device and method ) 是由 闫力松 冀慧茹 晁联盈 莫言 马冬林 于 2019-08-08 设计创作，主要内容包括：本发明公开了一种大曲率半径自由曲面镜面面形干涉测量装置及方法。其中测量装置包括干涉仪、CGH、光学透镜,通过在CGH设置主检测区域、与光学透镜对准区域、与干涉仪对准区域、镜面基准区域及透镜基准区域五种衍射区域对装置中的光学器件之间的位置进行调整,从而保证了检测光路中各光学元件的精确对准；本发明通过利用光学透镜对检测光路长度进行缩短,同时结合计算全息元件对待测自由曲面反射镜进行零位补偿,解决了现有技术由于在检测大曲率半径光学元件时检测光路的光程较长而导致的对测量环境要求较高测量困难的问题,为现代先进光学系统的制造开发提供保证,具有检测精度高,检测场地环境及尺寸要求简单等优点。(The invention discloses an interference measurement device and method for a large-curvature radius free-form surface mirror surface shape. The measuring device comprises an interferometer, a CGH and an optical lens, and the position between optical devices in the device is adjusted by arranging five diffraction regions, namely a main detection region, an alignment region with the optical lens, an alignment region with the interferometer, a mirror surface reference region and a lens reference region in the CGH, so that the accurate alignment of each optical element in a detection light path is ensured; the invention shortens the length of the detection light path by using the optical lens, and simultaneously performs zero compensation on the free-form surface reflector to be detected by combining the calculation holographic element, solves the problem of difficult measurement with higher requirement on the measurement environment caused by longer optical path of the detection light path when detecting the optical element with large curvature radius in the prior art, provides guarantee for the manufacture and development of modern advanced optical systems, and has the advantages of high detection precision, simple requirements on the environment and the size of a detection field and the like.)

1. The interference measurement device for the surface shape of the free-form surface with the large curvature radius is characterized by comprising an interferometer, a CGH and an optical lens;

The CGH is used for receiving interference light sent by the interferometer, and after diffraction occurs, the interference light is converged by the optical lens and vertically incident on the free-form surface reflector to be detected, so that zero compensation detection is realized on the free-form surface reflector to be detected;

the optical lens is used for receiving the diffracted light sent by the CGH and converging the light to shorten the length of a detection light path.

2. The interferometry device for surface shape of a free-form surface with a large curvature radius according to claim 1, wherein the front and back surfaces of the optical lens are spherical surfaces, the curvature radius of the back surface is equal to the curvature radius of the vertex of the free-form surface reflector to be measured, and the back surface is the surface closer to the free-form surface reflector to be measured.

3. The large radius of curvature free-form specular surface shape interferometry device of claim 1, wherein the CGH comprises a main detection region, an alignment with optical lens region, an alignment with interferometer region, a specular reference region, a lens reference region.

4. the large radius of curvature free-form specular surface shape interferometry device of claim 3, wherein said main detection region is located in a central region of said CGH, and said optical lens alignment region and said interferometer alignment region are sequentially distributed outward; the mirror surface reference areas are uniformly distributed in the alignment area with the optical lens; the lens reference regions are uniformly distributed in the interferometer alignment region.

5. the large-curvature-radius free-form surface mirror surface shape interferometry device according to claim 3 or claim 4, wherein the main detection area is a zero compensation measurement area of the free-form surface mirror to be measured; the alignment area with the optical lens is used for realizing alignment of the CGH and the optical lens in interferometry; the interferometer alignment area is used for aligning the CGH with the interferometer; the mirror surface reference area is used for realizing the rough alignment of the free-form surface reflector to be detected in the detection light path; the lens reference area is used for coarse adjustment of the position of the optical lens.

6. An interference measurement method for the surface shape of a free-form surface mirror with a large curvature radius comprises the following steps:

S1, aligning the interferometer, the CGH, the optical lens and the free-form surface to be measured;

S2, compensating and diffracting interference light emitted by the interferometer through CGH, converging the interference light through an optical lens, and vertically emitting the light to the free-form surface to be measured;

and S3, the light path returns after being reflected by the free-form surface to be detected, returns to the interferometer again after passing through the optical lens and the CGH, and interferes with the reference light of the interferometer to obtain interference fringes under the zero fringe state, so that the surface shape result of the free-form surface to be detected is obtained.

7. The interferometry method for free-form mirror surface shape with large radius of curvature according to claim 6, wherein the step S1 comprises the steps of:

S11, adjusting the relative position between the CGH and the interferometer, so that light emitted by the interferometer returns to the interferometer after passing through an alignment area on the CGH, and forms interference fringes in a zero-fringe state with reference light of the interferometer, thereby completing alignment of the interferometer and the CGH;

s12, after the interferometer is aligned with the CGH, four CGH projection cross lines are formed behind the CGH along the light path direction, the optical lens is placed in the center of the four CGH projection cross lines, and coarse alignment of the optical lens, the interferometer and the CGH is completed;

S13, adjusting the position of the optical lens, enabling the light emitted by the interferometer to return to the interferometer after passing through the lens alignment area on the CGH and the optical lens, and forming a zero-fringe state interference fringe with the reference light of the interferometer, thereby completing the alignment of the interferometer, the CGH and the optical lens;

After the alignment of the S14, the interferometer, the CGH and the optical lens, four CGH projection cross lines are formed behind the optical lens along the direction of the light path, the free-form surface to be measured is placed in the center of the four CGH projection cross lines, and the rough alignment of the free-form surface to be measured in the light path is completed;

and S15, adjusting the position of the free-form surface to be measured, and finishing the accurate alignment of the interferometer, the CGH, the optical lens and the free-form surface to be measured when the free-form surface formed in the interferometer detects that interference fringes become sparse and even zero fringes.

Technical Field

the invention belongs to the field of optical detection, and particularly relates to a large-curvature-radius free-form surface mirror surface shape interference measurement device and 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 the optical system based on the free-form surface becomes an important direction of the development of the modern high-performance optical system, the manufacturing requirement of the high-precision free-form surface optical element comes with the application research, and the high-precision measurement of the free-form surface is the basis of the manufacturing of the high-precision free-form surface optical element, is one of the core steps in the development of the advanced optical system, and has important significance for the manufacturing of the advanced optical system.

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 optical element with Large curvature radius is widely applied in optical systems, for example, the curvature radius of the vertex of a primary mirror of a European extreme Telescope (E-ELT) reaches 84m magnitude, and if a traditional compensation detection method is adopted, the detection optical path length is not less than 84 m. The larger the length of the detection light path is, the higher the requirement on the size of a detection field is, and meanwhile, the more strict the requirements on detection environments such as vibration and airflow disturbance are, the higher the detection difficulty is.

in summary, it is an urgent need to solve the above-mentioned problems to provide a simple and convenient large-curvature radius free-form surface hybrid compensation mirror surface shape interferometry device and method with low requirements for measurement environment.

Disclosure of Invention

aiming at the defects of the prior art, the invention aims to provide a large-curvature-radius free-form surface mirror surface shape interference measurement device and method, and aims to solve the problem that in the prior art, the measurement is difficult due to the fact that the optical path length of a detection optical path is long when an optical element with a large curvature radius is detected.

In order to achieve the above object, the present invention provides, in one aspect, an interferometric device for measuring a surface shape of a free-form surface with a large radius of curvature, including an interferometer, a Computer Generated Hologram (CGH), and an optical lens;

The CGH is used for receiving interference light sent by the interferometer, and after diffraction occurs, the interference light is converged by the optical lens and then vertically incident on the free-form surface reflector to be detected, so that zero compensation detection is realized on the free-form surface reflector to be detected;

The optical lens is used for receiving the diffracted light sent by the CGH and converging the light to shorten the length of a detection optical path.

Further preferably, the front and rear surfaces of the optical lens are spherical surfaces, and the curvature radius of the rear surface is equal to the vertex curvature radius of the free-form surface reflector to be measured, and the rear surface is the surface closer to the free-form surface reflector to be measured.

Further preferably, the CGH includes five kinds of diffractive optical regions of a main detection region, an alignment region with an optical lens, an alignment region with an interferometer, a mirror reference region, and a lens reference region.

Further preferably, the main detection area is located in the central area of the CGH, and an alignment area with the optical lens and an alignment area with the interferometer are sequentially distributed outwards; the mirror surface reference areas are uniformly distributed in the alignment area with the optical lens; the lens reference areas are uniformly distributed in the area aligned with the interferometer.

further preferably, the main detection area is a zero compensation measurement area of the free-form surface reflector to be detected; the alignment area with the optical lens is used for realizing the alignment of the CGH and the optical lens in the interferometry; the alignment area with the interferometer is used for aligning the CGH with the interferometer; the mirror surface reference area is used for realizing the rough alignment of the free-form surface reflector to be detected in the detection light path; the lens reference area is used for coarse adjustment of the position of the optical lens.

The invention provides a large curvature radius free-form surface mirror surface shape interference measurement method on the other hand, which comprises the following steps:

s1, aligning the interferometer, the CGH, the optical lens and the free-form surface reflector to be measured;

S2, compensating and diffracting interference light emitted by the interferometer through CGH, converging the interference light through an optical lens, and vertically emitting the light to the free-form surface reflector to be measured;

And S3, the light path returns back through the original path after being reflected by the free-form surface reflector to be detected, returns back to the interferometer after passing through the optical lens and the CGH, interferes with the reference light of the interferometer to obtain interference fringes under the zero fringe state, and further obtains the surface shape result of the free-form surface reflector to be detected.

Further preferably, the method for aligning the interferometer, the CGH, the optical lens and the free-form surface mirror to be measured in step S1 includes the following steps:

s11, adjusting the relative position between the CGH and the interferometer, so that light emitted by the interferometer returns to the interferometer after passing through an alignment area on the CGH, and forms interference fringes in a zero-fringe state with reference light of the interferometer, thereby completing alignment of the interferometer and the CGH;

S12, after the interferometer is aligned with the CGH, four CGH projection cross lines are formed behind the CGH along the light path direction, the optical lens is placed in the center of the four CGH projection cross lines, and coarse alignment of the optical lens, the interferometer and the CGH is completed;

s13, adjusting the position of the optical lens, enabling the light emitted by the interferometer to return to the interferometer after passing through the lens alignment area on the CGH and the optical lens, and forming a zero-fringe state interference fringe with the reference light of the interferometer, thereby completing the alignment of the interferometer, the CGH and the optical lens;

S14, after alignment of the interferometer, the CGH and the optical lens, four CGH projection cross lines are formed behind the optical lens along the direction of the light path, and the free-form surface reflector to be measured is placed in the center of the four CGH projection cross lines to complete rough alignment of the free-form surface reflector to be measured in the light path;

And S15, adjusting the position of the free-form surface reflector to be measured, and finishing the accurate alignment of the interferometer, the CGH, the optical lens and the free-form surface reflector to be measured when the free-form surface detection interference fringes formed in the interferometer become sparse and even zero fringes.

Through the technical scheme, compared with the prior art, the invention can obtain the following beneficial effects:

1. The invention provides a large-curvature radius free-form surface mirror surface shape interference measurement method, which shortens the length of a detection light path by using an optical lens, and simultaneously performs zero compensation on a free-form surface reflector to be detected by combining a calculation holographic element, thereby solving the problem of high measurement difficulty in the prior art caused by long light path of the detection light path when a large-curvature radius optical element is detected.

2. The invention provides a large-curvature radius free-form surface mirror surface shape interference measuring device, which adjusts the position between optical devices in the device by arranging five diffraction regions, namely a main detection region, an alignment region with an optical lens, an alignment region with an interferometer, a mirror surface reference region and a lens reference region, in a CGH (compact surface H), thereby ensuring the accurate alignment of each optical element in a detection light path, ensuring the accuracy of a measurement result and avoiding introducing extra aberration in the surface shape interference detection result.

drawings

FIG. 1 is a schematic diagram of an interferometric device for measuring the surface shape of a free-form surface with a large curvature radius according to the present invention;

FIG. 2 is a schematic view of the distribution of CGH regions provided by the present invention;

FIG. 3 is an interferogram of a CGH provided by the present invention after alignment with an interferometer;

FIG. 4 is a schematic diagram of the relationship between the projection reticle of the CGH and the position of the optical lens according to the present invention;

FIG. 5 is a schematic diagram of the relationship between the CGH projection reticle and the free-form surface reflector to be measured according to the present invention.

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 order to achieve the above object, in one aspect, the present invention provides an interferometric device for measuring a surface shape of a free-form surface with a large radius of curvature, as shown in fig. 1, including an interferometer 1, a CGH2, an optical lens 3;

wherein, the interferometer 1 is used for sending interference light; specifically, the interference light sent by the interferometer 1 may be a standard spherical wave;

The CGH2 is used for receiving interference light sent by the interferometer 1, after diffraction occurs, diffraction wavefront is converged by the optical lens 3 and then vertically incident on the free-form surface reflector 4 to be detected, so that zero compensation detection is realized on the free-form surface reflector 4 to be detected;

The optical lens 3 is used for receiving the diffracted light sent by the CGH2 and converging the light to shorten the length of the detection optical path. Specifically, the front and rear surfaces of the optical lens 3 are spherical surfaces, and the surface close to the free-form surface reflector to be measured is taken as the rear surface, and the curvature radius of the rear surface is equal to the vertex curvature radius of the free-form surface reflector 4 to be measured, so that the diffracted light can be normally incident on the free-form surface reflector to be measured along the normal direction of the free-form surface reflector to be measured after passing through the optical lens 3.

specifically, taking the circular CGH shown in fig. 2 as an example, the CGH includes five diffractive optical areas, namely a main detection area, an alignment area with an optical lens, an alignment area with an interferometer, a mirror reference area, and a lens reference area, for ensuring accurate alignment of each optical element in a detection optical path, and avoiding introducing additional aberration in an interference detection result. The reticle frequency distribution in each region is different, wherein the main detection region is positioned in the central region of the CGH, and an alignment region with the optical lens and an alignment region with the interferometer are distributed outwards in sequence; in the embodiment, the number of the mirror surface reference areas is 4, and the mirror surface reference areas are respectively and uniformly distributed in the alignment area with the optical lens; there are 4 lens reference areas, which are uniformly distributed in the alignment area of the interferometer. Specifically, the main detection area is a zero compensation measurement area of the free-form surface reflector to be detected; the alignment area with the optical lens is used for realizing the alignment of the CGH and the optical lens in the interferometry; the alignment area with the interferometer is used for aligning the CGH with the interferometer; the mirror surface reference area is used for realizing the rough alignment of the free-form surface reflector to be detected in the detection light path; the lens reference area is used for coarse adjustment of the position of the optical lens.

the invention provides a large curvature radius free-form surface mirror surface shape interference measurement method on the other hand, which comprises the following steps:

s1, aligning the interferometer, the CGH, the optical lens and the free-form surface reflector to be measured; in particular, since the free-form surface detection apparatus involves four optical elements, i.e., an interferometer, a CGH, an optical lens, and a free-form surface, misalignment in the alignment of the optical elements introduces additional aberration in the interference detection result, so that they need to be accurately aligned.

S2, compensating and diffracting interference light emitted by the interferometer through CGH, converging the interference light through an optical lens, and vertically emitting the light to the free-form surface reflector to be measured; specifically, the compensation element CGH can compensate the free-form surface reflector to be measured, and diffracted light generated after the interference light passes through the compensation element CGH can be normally incident on the free-form surface reflector to be measured along the normal direction of the free-form surface reflector to be measured after passing through the optical lens and can return back in an original path, so that the generated interference pattern is ensured to only contain surface shape deviation information of the free-form surface reflector to be measured. Specifically, the optical path can greatly shorten the optical path under the convergence action of the optical lens, and specifically, the optical path length is shortened to be within 1/5 of the length of the curvature radius of the vertex of the free-form surface reflector to be detected, so that the problems of high measurement difficulty and the like caused by long optical path of the detection optical path and high requirement on the measurement environment can be effectively avoided when the optical element with large curvature radius is detected.

And S3, the light path returns back through the original path after being reflected by the free-form surface reflector to be detected, returns back to the interferometer after passing through the optical lens and the CGH, interferes with the reference light of the interferometer to obtain interference fringes under the zero fringe state, and further obtains the surface shape result of the free-form surface reflector to be detected.

specifically, the method for aligning the interferometer, the CGH, the optical lens, and the free-form surface mirror to be measured in step S1 includes the following steps:

s11, adjusting the relative position between the CGH and the interferometer to enable light rays emitted by the interferometer to return to the interferometer through an alignment area on the CGH and the interferometer and form interference fringes with reference light of the interferometer, continuously adjusting the relative position between the CGH and the interferometer, and adjusting the interference fringes to a zero fringe state, wherein the interference fringes are completely black or completely white, as shown in FIG. 3; when the interference fringes are completely black or white, the precise alignment of the interferometer and the CGH is completed; specifically, the relative position between the CGH and the interferometer may be adjusted by translating or tilting the CGH;

s12, after the interferometer and the CGH are accurately aligned, projecting through a lens reference area of the CGH, forming four CGH projection cross lines shown in figure 4 behind the CGH along the light path direction, placing an optical lens in the center of the four CGH projection cross lines formed behind the CGH, and completing coarse adjustment of the positions of the optical lens, the interferometer and the CGH;

s13, further adjusting the position of the optical lens, wherein light is emitted by the interferometer, reflected by the lens alignment area on the CGH and the front surface of the optical lens, passes through the lens alignment area again, returns to the interferometer, forms interference fringes with reference light of the interferometer, and then continuously adjusting the position of the optical lens to adjust the interference fringes to a zero fringe state, as shown in FIG. 3, at this time, the precise alignment of the interferometer, the CGH and the optical lens is completed;

S14, after the interferometer, the CGH and the optical lens are accurately aligned, projecting through a mirror surface reference area of the CGH, forming four CGH projection cross lines shown in figure 5 behind the optical lens along the direction of the light path, and placing the free-form surface reflector to be measured in the center of the four CGH projection cross lines to complete the rough alignment of the free-form surface reflector to be measured in the light path;

s15, forming corresponding interference fringes in the interferometer by the free-form surface reflector to be detected through the CGH main area, further adjusting the position of the free-form surface reflector to be detected, wherein the free-form surface detection interference fringes formed in the interferometer are sparse and even can obtain the condition of zero fringes, namely, the precise alignment of the interferometer, the CGH, the optical lens and the free-form surface reflector to be detected is realized. Specifically, the position of the free-form surface reflector to be measured can be adjusted by translating or inclining the free-form surface reflector to be measured.

the invention provides a large-curvature radius free-form surface mirror surface shape interference measurement device and a method, wherein five diffraction regions, namely a main detection region, an alignment region with an optical lens, an alignment region with an interferometer, a mirror surface reference region and a lens reference region, are arranged on a CGH (compact computer graphics) to adjust the positions of optical devices in the device, so that the accurate alignment of each optical element in a detection light path is ensured, and the introduction of extra aberration in an interference detection result is avoided; the invention shortens the length of the detection light path by using the optical lens, and simultaneously performs zero compensation on the free-form surface reflector to be detected by combining the calculation holographic element, compared with the prior art, the length of the light path is shortened to be within 1/5 of the length of the curvature radius of the vertex of the free-form surface reflector to be detected, thereby solving the problem of difficult measurement with higher requirement on the measurement environment caused by longer light path of the detection light path when detecting the optical element with large curvature radius in the prior art, and providing guarantee for the manufacturing and development of the modern advanced optical system.

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.