技术领域technical field
本发明属于光干涉测量仪器技术领域，特别是一种空间分光同轴斐索型同步移相干涉仪及其测量方法。The invention belongs to the technical field of optical interference measuring instruments, in particular to a space-splitting coaxial Fizeau type synchronous phase-shifting interferometer and a measuring method thereof.
背景技术Background technique
斐索型干涉仪采用被测光束与参考光束的共光路设计，除参考面外，干涉仪光学系统自身的像差对被测光束和参考光束的影响基本相同，绝大部分可相互抵消，因而斐索型干涉仪仅对参考面的精度要求高，而对系统波像差和其它元件的加工、装配精度要求较低。与泰曼格林型等非共光路干涉仪相比，斐索型干涉仪的设计和加工难度明显降低，因此成为大口径、大数值孔径光学元件面形检测的首选。The Fizeau interferometer adopts the common optical path design of the measured beam and the reference beam. Except for the reference surface, the aberration of the interferometer optical system itself has basically the same influence on the measured beam and the reference beam, and most of them can cancel each other out. Fizeau-type interferometers only have high requirements on the accuracy of the reference surface, but have lower requirements on the processing and assembly accuracy of the system wave aberration and other components. Compared with non-common optical path interferometers such as Tieman Green type, the design and processing difficulty of Fizeau type interferometer is significantly reduced, so it becomes the first choice for surface shape detection of large aperture and large numerical aperture optical components.
目前斐索型同步移相干涉仪主要有两种结构形式。一种是2004年4D公司Millerd等提出的倾斜参考镜结构(US7，057,738B2)，另一种是1989年Kuchel等提出(US4，872，755)，2006年Kimbrough等改进的短相干光源光程差匹配结构(Bradley T.Kimbrough.Pathmatchedvibration insensitive Fizeau interferometer.Ph.D dissertation，University of Arizona，2006)。前一种结构中参考面的倾斜使得测试光与参考光的共光路特性被部分破坏，从而引起相位测量误差，失去了斐索型干涉仪最大的优势。后一种结构通过前置辅助组件产生两束偏振态正交的光波同时照明主干涉仪，共形成6组干涉条纹。使用短时间相干长度的宽带照明光源，可使前置组件与干涉仪时间相干性匹配时，参考面与测试面干涉形成的被测干涉条纹对比度达到最大，同时其余5组附加条纹完全消失，从而实现同轴斐索同步移相干涉测量。然而其偏振移相采集模块的制作相对困难且成本高。此外，由于前置干涉组件与主干涉仪时间相干性匹配要实现光程差的绝对补偿，前置辅助组件中的可调反射镜移动范围要与参考镜到被测镜的距离相等，这使得前置辅助组件中可调反射镜的移动范围非常大，从而导致仪器结构庞大，难以小型化。At present, the Fizeau-type synchronous phase-shifting interferometer mainly has two structural forms. One is the tilted reference mirror structure (US7,057,738B2) proposed by 4D company Millerd et al. in 2004, the other is the short coherent light source optical path proposed by Kuchel et al. in 1989 (US4,872,755), and Kimbrough et al. in 2006 Differential matching structure (Bradley T. Kimbrough. Pathmatched vibration insensitive Fizeau interferometer. Ph. D dissertation, University of Arizona, 2006). The inclination of the reference plane in the former structure partially destroys the common optical path characteristics of the test light and the reference light, thus causing phase measurement errors and losing the greatest advantage of the Fizeau interferometer. The latter structure generates two beams of light waves with orthogonal polarization states through the front auxiliary component to illuminate the main interferometer at the same time, forming a total of 6 groups of interference fringes. Using a broadband illumination source with a short time coherence length can make the contrast of the measured interference fringes formed by the interference between the reference surface and the test surface reach the maximum when the time coherence of the front component and the interferometer is matched, and at the same time the remaining 5 groups of additional fringes disappear completely, thus Realize coaxial Fizeau synchronous phase-shifting interferometry. However, the fabrication of its polarization phase-shifting acquisition module is relatively difficult and costly. In addition, due to the time coherence matching between the pre-interference component and the main interferometer, the absolute compensation of the optical path difference must be realized, and the moving range of the adjustable mirror in the pre-assistant component must be equal to the distance from the reference mirror to the measured mirror, which makes The movable range of the adjustable reflector in the front auxiliary assembly is very large, which results in a bulky instrument structure and is difficult to miniaturize.
发明内容Contents of the invention
本发明的目的在于提供一种精度高、成本低、方便实用、可小型化的空间分光同轴斐索型同步移相干涉仪及其测量方法。The object of the present invention is to provide a high precision, low cost, convenient and practical, miniaturizable space splitting coaxial Fizeau type synchronous phase-shifting interferometer and its measuring method.
实现本发明目的技术解决方案为：一种空间分光同轴斐索型同步移相干涉仪，其特征在于，包括：点光源及其分光组件、主干涉仪和分光成像组件，由点光源发出的球面波经分光组件分成四束后进入主干涉仪，最后通过分光成像组件在一个CCD上同时获取四幅相移干涉图，其中：The technical solution to realize the object of the present invention is: a space-splitting coaxial Fizeau-type synchronous phase-shifting interferometer, characterized in that it includes: a point light source and its spectroscopic component, a main interferometer and a spectroscopic imaging component, and the light emitted by the point light source The spherical wave is divided into four beams by the spectroscopic component and then enters the main interferometer, and finally four phase-shifted interferograms are simultaneously acquired on a CCD by the spectroscopic imaging component, where:
所述点光源及其分光组件用于产生四个复振幅相同但空间位置不同的发散球面波；The point light source and its light splitting component are used to generate four diverging spherical waves with the same complex amplitude but different spatial positions;
所述主干涉仪为斐索型干涉仪，使从参考面反射回的参考光和测试面反射回的测试光形成干涉场；The main interferometer is a Fizeau type interferometer, so that the reference light reflected back from the reference surface and the test light reflected back from the test surface form an interference field;
所述分光成像组件用于将四个光源分别经参考面与测试面反射产生的干涉场在CCD靶面上分开，并且使得CCD靶面与测试面共轭。The spectroscopic imaging component is used to separate the interference fields generated by the reflection of the four light sources from the reference surface and the test surface on the CCD target surface, and make the CCD target surface and the test surface conjugate.
进一步地，所述分光组件包括顺次共光轴设置的会聚物镜、棋盘光栅和第一孔径光阑，所述第一孔径光阑滤出棋盘光栅的(±1，±1)级四束衍射光，并且滤除其它级次衍射光，所得的四束衍射光复振幅相同，并且分别位于正方形的四个顶点，该正方形的中心不在主干涉仪的光轴上，该正方形的边长d即相邻发散球面波的横向错位距离，d通过调整棋盘光栅与第一孔径光阑之间的距离lg来确定：Further, the light splitting assembly includes a converging objective lens, a checkerboard grating, and a first aperture stop that are sequentially arranged on common optical axes, and the first aperture stop filters out the (±1, ±1) order four-beam diffraction of the checkerboard grating light, and filter out other orders of diffracted light, the obtained four beams of diffracted light have the same complex amplitude, and are respectively located at the four vertices of the square, the center of the square is not on the optical axis of the main interferometer, and the side length d of the square is the phase The lateral dislocation distance of adjacent diverging spherical waves, d, is determined by adjusting the distance lg between the checkerboard grating and the first aperture stop:
d＝2λlg/Λd=2λlg /Λ
其中，λ为入射光波长，Λ为棋盘光栅的光栅周期。Among them, λ is the wavelength of the incident light, and Λ is the grating period of the checkerboard grating.
进一步地，所述主干涉仪包括顺次共光轴设置的分光膜、准直物镜、参考面和测试面，由点光源发出的球面波经分光组件分成四束后进入主干涉仪，进入主干涉仪的四束光分别由准直物镜扩束后顺序通过参考面和测试面，其中每束光分别被参考面和测试面反射形成参考光和测试光，参考光和测试光沿原路返回并由分光膜反射进入分光成像组件。Further, the main interferometer includes a spectroscopic film, a collimating objective lens, a reference surface, and a test surface arranged in sequence with a common optical axis. The four beams of the interferometer are respectively expanded by the collimator objective lens and sequentially pass through the reference surface and the test surface, where each beam is reflected by the reference surface and the test surface respectively to form a reference light and a test light, and the reference light and test light return along the original path And reflected by the spectroscopic film into the spectroscopic imaging component.
进一步地，所述分光成像组件包括顺次共光轴设置的第二孔径光阑、透镜阵列、成像物镜、CCD，所述透镜阵列紧贴第二孔径光阑，且二者位于主干涉仪所产生的参考光和测试光的焦面；Further, the spectroscopic imaging assembly includes a second aperture stop, a lens array, an imaging objective lens, and a CCD arranged in sequence on common optical axes, the lens array is close to the second aperture stop, and both are located at the main interferometer The focal planes of the generated reference and test beams;
第二孔径光阑滤出经参考面与测试面反射回来的四组参考光与测试光，并且滤除干扰光，该四组参考光与测试光分别经过透镜阵列中各个透镜的物方主点，成像物镜将经过透镜阵列的四组参考光与测试光准直成平行光，该平行光在CCD的靶面上形成四个分开的光斑。The second aperture diaphragm filters out the four groups of reference light and test light reflected back by the reference surface and the test surface, and filters out the interference light. The four groups of reference light and test light respectively pass through the object-side principal points of each lens in the lens array , the imaging objective collimates the four groups of reference light and test light passing through the lens array into parallel light, and the parallel light forms four separate light spots on the target surface of the CCD.
进一步地，所述透镜阵列为2×2负透镜阵列，每个负透镜的焦距f1满足f1＝-dF#，其中d为相邻发散球面波的横向错位距离，F#为主干涉仪中准直物镜的F数。Further, the lens array is a 2×2 negative lens array, and the focal length f1 of each negative lens satisfies f1 =-dF# , where d is the lateral dislocation distance of adjacent diverging spherical waves, and F# is the main interferometer The F-number of the collimating objective lens.
进一步地，所述成像物镜的前焦面与透镜阵列的像方主面重合，成像物镜的焦距f2满足f2≤LF#/2，其中L为CCD靶面的宽度。Further, the front focal plane of the imaging objective lens coincides with the image-side main surface of the lens array, and the focal length f2 of the imaging objective lens satisfies f2 ≤ LF# /2, where L is the width of the CCD target surface.
进一步地，所述CCD的靶面与主干涉仪中测试面共轭，CCD的靶面与成像物镜像方主面之间的距离l为l＝f2+f22/dF#。Further, the target surface of the CCD is conjugate to the test surface in the main interferometer, and the distance l between the target surface of the CCD and the main surface of the imaging object mirror is l=f2 +f22 /dF# .
一种基于权利要求1所述空间分光同轴斐索型同步移相干涉仪的测量方法，其特征在于，包括以下步骤：A measurement method based on the space-splitting coaxial Fizeau type synchronous phase-shifting interferometer according to claim 1, characterized in that it comprises the following steps:
步骤1，点光源通过分光组件产生四个复振幅相同但空间位置不同的发散球面波，该四个发散球面波分别位于正方形的四个顶点，该正方形的中心不在主干涉仪的光轴上，将被测件置于主干涉仪中作为测试面，调整测试面使其与参考面平行，使得CCD上同时获取四幅相移干涉图；Step 1. The point light source generates four diverging spherical waves with the same complex amplitude but different spatial positions through the light splitting component. The four diverging spherical waves are respectively located at the four vertices of the square, and the center of the square is not on the optical axis of the main interferometer. Place the DUT in the main interferometer as the test surface, and adjust the test surface to be parallel to the reference surface, so that four phase-shifted interferograms can be obtained on the CCD at the same time;
步骤2，令x、y分别为所述正方形中心与主干涉仪光轴之间距离在水平、竖直方向上的投影长度，且满足y＝2x＝πf32/2Dk或者x＝2y＝πf32/2Dk，调节测试面与参考面之间的距离D为D＝πf32/4xk或者D＝πf32/4yk，得到相移量依次递增π/2的四幅干涉图，其中f3为准直物镜的焦距，k＝2π/λ为波矢，λ为入射光波长；Step 2, let x and y be the projected lengths of the distance between the center of the square and the optical axis of the main interferometer in the horizontal and vertical directions respectively, and satisfy y=2x=πf32 /2Dk or x=2y=πf32 /2Dk, adjust the distance D between the test surface and the reference surface as D=πf32 /4xk or D=πf32 /4yk, and obtain four interferograms with phase shifts increasing by π/2 successively, where f3 is the focal length of the collimating objective lens, k=2π/λ is the wave vector, and λ is the wavelength of the incident light;
步骤3，从一帧CCD图像上提取出四幅干涉图，通过移相算法对四幅干涉图进行处理，恢复出测试面的面形或波像差。Step 3, extract four interferograms from one frame of CCD image, process the four interferograms by phase-shift algorithm, and restore the surface shape or wave aberration of the test surface.
进一步地，步骤1所述CCD上同时获取四幅相移干涉图，忽略常数相移因子-2Dk，每幅干涉图的相移量δ(r)满足：Further, four phase-shift interferograms are simultaneously acquired on the CCD described in step 1, ignoring the constant phase-shift factor -2Dk, and the phase shift δ(r) of each interferogram satisfies:
δ(r)＝Dk(r/f3)2δ(r)=Dk(r/f3 )2
其中，D为参考面与测试面之间的距离，k＝2π/λ为波矢，为发散球面波到主干涉仪光轴之间的错位距离，f3为主干涉仪中准直物镜的焦距。Among them, D is the distance between the reference surface and the test surface, k=2π/λ is the wave vector, is the misalignment distance between the diverging spherical wave and the optical axis of the main interferometer, and f3 is the focal length of the collimating objective lens in the main interferometer.
进一步地，步骤3所述移相算法为随机移相算法或者四步移相算法。Further, the phase-shifting algorithm described in step 3 is a random phase-shifting algorithm or a four-step phase-shifting algorithm.
本发明与现有技术相比，其显著优点在于：(1)可实现同轴斐索同步移相干涉测量；(2)仅用一个普通点光源即可实现移相，成本较低；(3)无需其它偏振元件，结构紧凑；(4)测试过程简单，调整方便，对环境的要求较低，使测试更容易实现。Compared with the prior art, the present invention has significant advantages in that: (1) coaxial Fizeau synchronous phase shifting interferometry can be realized; (2) phase shifting can be realized with only one common point light source, and the cost is low; (3) ) No other polarization components are needed, and the structure is compact; (4) The test process is simple, easy to adjust, and has low requirements on the environment, making the test easier to implement.
附图说明Description of drawings
图1是本发明空间分光同轴斐索型同步移相干涉仪的结构示意图。Fig. 1 is a schematic structural diagram of a space-splitting coaxial Fizeau-type synchronous phase-shifting interferometer of the present invention.
图2是点光源存在横向偏移导致准直光产生倾斜的光路示意图。Fig. 2 is a schematic diagram of the optical path in which the collimated light is tilted due to the lateral offset of the point light source.
图3是倾斜光入射在干涉光场间引入相移的示意图。Fig. 3 is a schematic diagram of oblique light incidence introducing a phase shift between interfering light fields.
图4是四个点光源与准直物镜焦点的相对位置示意图。Fig. 4 is a schematic diagram of the relative positions of the four point light sources and the focal point of the collimating objective lens.
图中：1、点光源；2、分光组件；3、会聚物镜；4、棋盘光栅；5、第一孔径光阑；6、分光膜；7、准直物镜；8、参考面；9、测试面；10、分光成像组件；11、第二孔径光阑；12、透镜阵列；13、成像物镜；14、CCD。In the figure: 1. Point light source; 2. Beam splitting component; 3. Converging objective lens; 4. Checkerboard grating; 5. First aperture stop; 6. Beam splitting film; 7. Collimating objective lens; 10. Spectroscopic imaging component; 11. Second aperture stop; 12. Lens array; 13. Imaging objective lens; 14. CCD.
具体实施方式Detailed ways
结合图1，本发明空间分光同轴斐索型同步移相干涉仪，其特征在于，包括：点光源1及其分光组件2、主干涉仪和分光成像组件10，由点光源1发出的球面波经分光组件分成四束后进入主干涉仪，最后通过分光成像组件10在一个CCD14上同时获取四幅相移干涉图，其中：In conjunction with FIG. 1 , the spatial spectroscopic coaxial Fizeau type synchronous phase-shifting interferometer of the present invention is characterized in that it includes: a point light source 1 and its spectroscopic component 2, a main interferometer and a spectroscopic imaging component 10, and the spherical surface emitted by the point light source 1 After the wave is divided into four beams by the spectroscopic component, it enters the main interferometer, and finally four phase-shifted interferograms are simultaneously acquired on a CCD14 through the spectroscopic imaging component 10, wherein:
(1)所述点光源1及其分光组件2用于产生四个复振幅相同但空间位置不同的发散球面波；(1) The point light source 1 and its light splitting assembly 2 are used to generate four divergent spherical waves with the same complex amplitude but different spatial positions;
所述分光组件2包括顺次共光轴设置的会聚物镜3、棋盘光栅4和第一孔径光阑5，所述第一孔径光阑5滤出棋盘光栅4的(±1，±1)级四束衍射光，并且滤除其它级次衍射光，所得的四束衍射光复振幅相同，并且分别位于正方形的四个顶点，该正方形的中心不在主干涉仪的光轴上，该正方形的边长d即相邻发散球面波的横向错位距离，d通过调整棋盘光栅4与第一孔径光阑5之间的距离lg来确定：The spectroscopic assembly 2 includes a converging objective lens 3, a checkerboard grating 4, and a first aperture stop 5 arranged on a common optical axis in sequence, and the first aperture stop 5 filters out (±1, ±1) levels of the checkerboard grating 4 Four beams of diffracted light, and other orders of diffracted light are filtered out, the obtained four beams of diffracted light have the same complex amplitude, and are respectively located at the four vertices of the square, the center of the square is not on the optical axis of the main interferometer, and the side length of the square is d is the lateral dislocation distance of adjacent diverging spherical waves, and d is determined by adjusting the distance lg between the checkerboard grating 4 and the first aperture stop 5:
d＝2λlg/Λd=2λlg /Λ
其中，λ为入射光波长，Λ为棋盘光栅4的光栅周期。Wherein, λ is the wavelength of the incident light, and Λ is the grating period of the checkerboard grating 4 .
(2)所述主干涉仪为斐索型干涉仪，使从参考面反射回的参考光和测试面反射回的测试光形成干涉场；(2) the main interferometer is a Fizeau type interferometer, so that the reference light reflected back from the reference surface and the test light reflected back from the test surface form an interference field;
所述主干涉仪包括顺次共光轴设置的分光膜6、准直物镜7、参考面8和测试面9，由点光源1发出的球面波经分光组件分成四束后进入主干涉仪，进入主干涉仪的四束光分别由准直物镜7扩束后顺序通过参考面8和测试面9，其中每束光分别被参考面8和测试面9反射形成参考光和测试光，参考光和测试光沿原路返回并由分光膜6反射进入分光成像组件10。The main interferometer includes a spectroscopic film 6, a collimating objective lens 7, a reference surface 8, and a test surface 9 arranged on a common optical axis in sequence. The spherical wave emitted by the point light source 1 is divided into four beams by the light splitting assembly and then enters the main interferometer. The four beams of light entering the main interferometer are respectively expanded by the collimating objective lens 7 and pass through the reference surface 8 and the test surface 9 sequentially, wherein each beam of light is respectively reflected by the reference surface 8 and the test surface 9 to form a reference light and a test light, and the reference light And the test light returns along the original path and is reflected by the spectroscopic film 6 into the spectroscopic imaging component 10 .
(3)所述分光成像组件10用于将四个光源分别经参考面与测试面反射产生的干涉场在CCD靶面上分开，并且使得CCD靶面与测试面共轭。(3) The spectroscopic imaging component 10 is used to separate the interference fields generated by the reflection of the four light sources from the reference surface and the test surface on the CCD target surface, and make the CCD target surface and the test surface conjugate.
所述分光成像组件10包括顺次共光轴设置的第二孔径光阑11、透镜阵列12、成像物镜13、CCD14，所述透镜阵列12紧贴第二孔径光阑11，且二者位于主干涉仪所产生的参考光和测试光的焦面；第二孔径光阑11滤出经参考面与测试面反射回来的四组参考光与测试光，并且滤除干扰光，该四组参考光与测试光分别经过透镜阵列12中各个透镜的物方主点，成像物镜13将经过透镜阵列12的四组参考光与测试光准直成平行光，该平行光在CCD14的靶面上形成四个分开的光斑。The spectroscopic imaging assembly 10 includes a second aperture stop 11, a lens array 12, an imaging objective lens 13, and a CCD 14 arranged on a common optical axis in sequence. The lens array 12 is close to the second aperture stop 11, and both are located at the main The focal plane of the reference light and the test light produced by the interferometer; the second aperture stop 11 filters out the four groups of reference light and test light reflected by the reference surface and the test surface, and filters out the interfering light, the four groups of reference light The test light and the test light respectively pass through the object-side principal points of each lens in the lens array 12, and the imaging objective lens 13 collimates the four groups of reference light and the test light passing through the lens array 12 into parallel light, and the parallel light forms four groups of light on the target surface of the CCD14. separate spots.
所述透镜阵列12为2×2负透镜阵列，每个负透镜的焦距f1满足f1＝-dF#，其中d为相邻发散球面波的横向错位距离，F#为主干涉仪中准直物镜7的F数。The lens array 12 is a 2×2 negative lens array, and the focal length f1 of each negative lens satisfies f1 =-dF# , where d is the lateral misalignment distance of adjacent diverging spherical waves, and F# is the center point of the main interferometer The F number of the straight objective lens 7.
所述成像物镜13的前焦面与透镜阵列12的像方主面重合，成像物镜13的焦距f2满足f2≤LF#/2，其中L为CCD14靶面的宽度。The front focal plane of the imaging objective lens 13 coincides with the image-side main surface of the lens array 12, and the focal length f2 of the imaging objective lens13 satisfies f2≤LF# /2 , where L is the width of the target surface of the CCD14.
所述CCD14的靶面与主干涉仪中测试面9共轭，CCD14的靶面与成像物镜13像方主面之间的距离l为l＝f2+f22/dF#。The target surface of the CCD 14 is conjugate to the test surface 9 in the main interferometer, and the distance l between the target surface of the CCD 14 and the main image-side surface of the imaging objective lens 13 is l=f2 +f22 /dF# .
本发明基于空间分光同轴斐索型同步移相干涉仪的测量方法，包括以下步骤：The present invention is based on the measurement method of the spatial spectroscopic coaxial Fizeau type synchronous phase-shifting interferometer, comprising the following steps:
步骤1，点光源通过分光组件产生四个复振幅相同但空间位置不同的发散球面波，该四个发散球面波分别位于正方形的四个顶点，该正方形的中心不在主干涉仪的光轴上，将被测件置于主干涉仪中作为测试面，调整测试面使其与参考面平行，使得CCD上同时获取四幅相移干涉图；所述CCD上同时获取四幅相移干涉图，忽略常数相移因子-2Dk，每幅干涉图的相移量δ(r)满足：Step 1. The point light source generates four diverging spherical waves with the same complex amplitude but different spatial positions through the light splitting component. The four diverging spherical waves are respectively located at the four vertices of the square, and the center of the square is not on the optical axis of the main interferometer. Place the DUT in the main interferometer as the test surface, adjust the test surface to be parallel to the reference surface, so that four phase-shifted interferograms are simultaneously acquired on the CCD; four phase-shifted interferograms are simultaneously acquired on the CCD, ignoring the constant phase The shift factor -2Dk, the phase shift δ(r) of each interferogram satisfies:
δ(r)＝Dk(r/f3)2δ(r)=Dk(r/f3 )2
其中，D为参考面与测试面之间的距离，k＝2π/λ为波矢，为发散球面波到主干涉仪光轴之间的错位距离，f3为主干涉仪中准直物镜的焦距。Among them, D is the distance between the reference surface and the test surface, k=2π/λ is the wave vector, is the misalignment distance between the diverging spherical wave and the optical axis of the main interferometer, and f3 is the focal length of the collimating objective lens in the main interferometer.
步骤2，令x、y分别为所述正方形中心与主干涉仪光轴之间距离在水平、竖直方向上的投影长度，且满足y＝2x＝πf32/2Dk或者x＝2y＝πf32/2Dk，调节测试面与参考面之间的距离D为D＝πf32/4xk或者D＝πf32/4yk，得到相移量依次递增π/2的四幅干涉图，其中f3为准直物镜的焦距，k＝2π/λ为波矢，λ为入射光波长；Step 2, let x and y be the projected lengths of the distance between the center of the square and the optical axis of the main interferometer in the horizontal and vertical directions respectively, and satisfy y=2x=πf32 /2Dk or x=2y=πf32 /2Dk, adjust the distance D between the test surface and the reference surface as D=πf32 /4xk or D=πf32 /4yk, and obtain four interferograms with phase shifts increasing by π/2 successively, where f3 is the focal length of the collimating objective lens, k=2π/λ is the wave vector, and λ is the wavelength of the incident light;
步骤3，从一帧CCD图像上提取出四幅干涉图，通过移相算法对四幅干涉图进行处理，恢复出测试面的面形或波像差；所述移相算法为随机移相算法或者四步移相算法。Step 3, extract four interferograms from one frame of CCD image, process the four interferograms through a phase-shifting algorithm, and restore the surface shape or wave aberration of the test surface; the phase-shifting algorithm is a random phase-shifting algorithm or a four-phase Phase shift algorithm.
实施例1Example 1
本发明空间分光同轴斐索型同步移相干涉仪光路结构如图1所示，包括了，The optical path structure of the space-split coaxial Fizeau type synchronous phase-shifting interferometer of the present invention is shown in Figure 1, including,
1)点光源1及其分光组件2用于产生四个复振幅相同但空间位置不同的发散球面波。分光组件包括会聚物镜3、棋盘光栅4、第一孔径光阑5。点光源1经过会聚物镜3与棋盘光栅4后产生多个衍射级次，第一孔径光阑5用于滤出棋盘光栅4的(±1，±1)级四只光，并且滤除其它级次衍射光。这四个点光源分别位于正方形的四个顶点，且其所构成的正方形的中心不在主干涉仪的光轴上。正方形的边长d可以通过调整棋盘光栅4与第一孔径光阑5之间的距离lg来改变。满足d＝2λlg/Λ，其中λ为入射光波长，Λ为光栅周期。1) The point light source 1 and its light splitting component 2 are used to generate four diverging spherical waves with the same complex amplitude but different spatial positions. The beam splitting assembly includes a converging objective lens 3 , a checkerboard grating 4 , and a first aperture stop 5 . The point light source 1 produces multiple diffraction orders after passing through the converging objective lens 3 and the checkerboard grating 4. The first aperture stop 5 is used to filter out the (±1, ±1) order four lights of the checkerboard grating 4, and filter out other orders Sub-diffracted light. The four point light sources are respectively located at the four vertices of the square, and the center of the square formed by them is not on the optical axis of the main interferometer. The side length d of the square can be changed by adjusting the distance lg between the checkerboard grating 4 and the first aperture stop 5 . Satisfy d=2λlg /Λ, where λ is the wavelength of the incident light, and Λ is the grating period.
2)主干涉仪，所述主干涉仪为斐索型干涉仪，使分别从参考面和测试面反射回的两束光波形成干涉场，所述主干涉仪包括分光膜6、准直物镜7、参考面8和测试面9，进入主干涉仪的四支光经分别由所述准直物镜7扩束后顺序通过参考面8和置于参考面后方的测试面9，经测试面9反射返回，再由分光膜6反射进入分光成像组件10。2) the main interferometer, the main interferometer is a Fizeau type interferometer, so that the two beams of light waves reflected back from the reference surface and the test surface respectively form an interference field, and the main interferometer includes a spectroscopic film 6 and a collimating objective lens 7 , the reference surface 8 and the test surface 9, the four lights that enter the main interferometer pass through the reference surface 8 and the test surface 9 placed behind the reference surface in sequence after being expanded by the collimating objective lens 7 respectively, and are reflected by the test surface 9 It returns and is reflected by the spectroscopic film 6 into the spectroscopic imaging component 10 .
3)分光成像组件10，用于将四个光源分别经参考面8与测试面9反射产生的干涉场在CCD14靶面上分开，并且使得CCD14靶面与测试面9共轭。分光成像组件10包括第二孔径光阑11、透镜阵列12、成像物镜13、CCD14。其中第二孔径光阑11用于滤出经参考面8与测试面9反射回来的四组参考光与测试光，并且滤出其它干扰光。透镜阵列12紧贴第二孔径光阑11，且位于反射光束的焦面。四组反射参考光与测试光分别经过各个透镜的物方主点。透镜阵列12为2×2负透镜阵列，其每一个透镜的作用相当于场镜。焦距f1满足f1≈-dF#。其中F#为准直物镜7的F数。成像物镜13用于将经过透镜阵列12的四组参考光与测试光准直成平行光，并且使得在CCD14靶面上的四组光斑是分开的。成像物镜13的前焦面与透镜阵列12的像方主面重合。成像物镜13的焦距满足f2≤LF#/2，其中L为CCD14靶面的宽度。CCD14的靶面与测试面9共轭，与成像物镜13像方主面之间的距离近似为l＝f+f2/dF#。3) The spectroscopic imaging component 10 is used to separate the interference field generated by the reflection of the four light sources from the reference surface 8 and the test surface 9 on the CCD14 target surface, and make the CCD14 target surface and the test surface 9 conjugate. The spectroscopic imaging assembly 10 includes a second aperture stop 11 , a lens array 12 , an imaging objective lens 13 , and a CCD 14 . The second aperture stop 11 is used to filter out the four sets of reference light and test light reflected by the reference surface 8 and the test surface 9 , and to filter out other interference lights. The lens array 12 is close to the second aperture stop 11 and is located at the focal plane of the reflected light beam. The four groups of reflected reference light and test light respectively pass through the object space principal point of each lens. The lens array 12 is a 2×2 negative lens array, and each lens acts as a field lens. The focal length f1 satisfies f1 ≈-dF# . Wherein F# is the F number of the collimating objective lens 7. The imaging objective lens 13 is used to collimate the four groups of reference light and the test light passing through the lens array 12 into parallel light, and separate the four groups of light spots on the target surface of the CCD 14 . The front focal plane of the imaging objective lens 13 coincides with the image side principal plane of the lens array 12 . The focal length of the imaging objective lens 13 satisfies f2 ≤ LF# /2, where L is the width of the target surface of the CCD 14 . The target surface of the CCD 14 is conjugate to the test surface 9 , and the distance between it and the main image-side surface of the imaging objective lens 13 is approximately l=f+f2 /dF# .
所述空间分光同轴斐索型同步移相干涉仪原理如下：The principle of the spatial spectroscopic coaxial Fizeau type synchronous phase-shifting interferometer is as follows:
如图2所示，当位于准直物镜7前焦面的点光源与其焦点存在一个横向错位距离r时，经过准直物镜7后的光束与光轴存在一个角度θ＝r/f3，其中f3为准直物镜7的焦距。从而在被参考面8与测试面9反射所产生的干涉场中引入一个常数相移量。如图3所示，根据几何光学性质其相移量为δ(r)＝k(AD-AB-BC)＝-2Dcosθ，由于θ很小，在小角度近似可以得到δ(r)＝Dk(r/f3)2，这里忽略了一个常数相移因子-2Dk，其中D为参考面与测试面之间的距离，k＝2π/λ为波矢。As shown in Figure 2, when there is a lateral misalignment distance r between the point light source on the front focal plane of the collimating objective lens 7 and its focal point, there is an angle θ=r/f3 between the light beam passing through the collimating objective lens 7 and the optical axis, where f3 is the focal length of the collimating objective lens 7 . Therefore, a constant phase shift is introduced into the interference field generated by the reflection of the reference surface 8 and the test surface 9 . As shown in Figure 3, according to the geometrical optics properties, its phase shift is δ(r)=k(AD-AB-BC)=-2Dcosθ, since θ is very small, it can be approximated at small angles as δ(r)=Dk( r/f3 )2 , a constant phase shift factor -2Dk is ignored here, where D is the distance between the reference surface and the test surface, and k=2π/λ is the wave vector.
对于所述的空间分光同轴斐索型同步移相干涉仪而言，点光源1通过分光组件2产生四个复振幅相同的点光源，如图4所示，以四个点光源的中心为坐标原点，准直物镜7的前焦点的坐标为(x,y)，不失一般性，我们假设0＜x≤y，此时每个点光源对应干涉图的相移量与其最小相移量之间差值从小到大依次为：0、2dDk/f32x、2dDk/f32y、2dDk/f32(x+y)，采用随机移相算法重构相位。特别的，当(x,y)满足y＝2x＝πf32/2Dk时，每幅干涉图的相移量与其最小相移量之间差值从小到大依次为0、π/2、π、3π/2，采用四步移相算法重构相位。For the space-splitting coaxial Fizeau-type synchronous phase-shifting interferometer, the point light source 1 generates four point light sources with the same complex amplitude through the light splitting component 2, as shown in Figure 4, with the centers of the four point light sources as The origin of the coordinates, the coordinates of the front focus of the collimating objective lens 7 are (x, y), without loss of generality, we assume that 0<x≤y, at this time the phase shift of each point light source corresponding to the interferogram and its minimum phase shift The difference between them is as follows from small to large: 0, 2dDk/f32 x, 2dDk/f32 y, 2dDk/f32 (x+y), and the random phase shift algorithm is used to reconstruct the phase. In particular, when (x, y) satisfies y=2x=πf32 /2Dk, the difference between the phase shift of each interferogram and its minimum phase shift is 0, π/2, π from small to large , 3π/2, using a four-step phase-shifting algorithm to reconstruct the phase.
使用上述空间分光同轴斐索型同步移相干涉仪测量的步骤为：The measurement steps of using the above-mentioned spatial spectroscopic coaxial Fizeau-type synchronous phase-shifting interferometer are as follows:
1)打开点光源1并待其稳定；1) Turn on point light source 1 and wait for it to stabilize;
2)按斐索干涉仪光路放置被测件，打开计算机及干涉图数据处理软件，调出实时采集到的干涉条纹；2) Place the test piece according to the optical path of the Fizeau interferometer, open the computer and the interferogram data processing software, and call out the interference fringes collected in real time;
3)调节测试面9与参考面8之间的距离约为πf32/4xk，使得四幅干涉图之间从小到大依次产生约π/2相移量；3) Adjust the distance between the test surface 9 and the reference surface 8 to be about πf32 /4xk, so that the four interferograms generate about π/2 phase shifts in order from small to large;
4)调整测试面9的位置和倾斜状态，使视场内条纹最少；4) Adjust the position and inclination of the test surface 9 to minimize fringes in the field of view;
5)选取四幅干涉图的中心，在一帧CCD图像上提取出四幅干涉图；5) Select the centers of the four interferograms, and extract four interferograms on one frame of CCD image;
6)通过随机移相算法或者四步移相算法，对四幅干涉图进行计算，恢复出测试面面形或波像差。6) Calculate the four interferograms through the random phase shift algorithm or the four-step phase shift algorithm to recover the test surface shape or wave aberration.
综上所述，本发明空间分光同轴斐索型同步移相干涉仪，利用四个点光源与光轴的横向偏移在参考光与测试光的干涉场中引入相移，通过一帧图像恢复相位，实现了动态测量。由于没有偏振元件以及PZT等移相元件的引入，其成本低，结构紧凑，易于实现小型化。此外，测试过程简单，调整方便，对环境的要求较低，使测试更容易实现。To sum up, the space-splitting coaxial Fizeau type synchronous phase-shifting interferometer of the present invention uses four point light sources and the lateral offset of the optical axis to introduce a phase shift in the interference field of the reference light and the test light, and through a frame of image Recovering the phase realizes the dynamic measurement. Since there is no polarizing element and the introduction of phase shifting elements such as PZT, its cost is low, its structure is compact, and it is easy to realize miniaturization. In addition, the test process is simple, easy to adjust, and has low requirements on the environment, making the test easier to implement.
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