CN107631687B - Point source dystopy expands simultaneous phase-shifting fizeau interferometer and its measurement method - Google Patents
Point source dystopy expands simultaneous phase-shifting fizeau interferometer and its measurement method Download PDFInfo
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Abstract
The invention discloses a kind of point source dystopys to expand simultaneous phase-shifting fizeau interferometer and its measurement method.The interferometer includes pointolite array, striking rope type main interferometer and spectroscopic imaging component.Method are as follows: the identical spherical wave of four beams that pointolite array generates respectively enters main interferometer, by adjusting pointolite array on main interferometer collimator objective focal plane at a distance from optical axis, so that four collimation wavefront being emitted through main interferometer are incident on the difference of the angle on reference mirror, to introduce different phase-shift phases in interference of the plane of reference from test surfaces, the phase shifting interference of four width imaging clearlies is then obtained simultaneously on a CCD by spectroscopic imaging component.The present invention has the characteristics that at low cost, shock resistance is good, easily operated, can be used for the fields such as the real-time high-precision detection of optical element.
Description
Technical Field
The invention belongs to the technical field of optical interference measuring instruments, and particularly relates to a point source ectopic beam expanding synchronous phase shifting Fizeau interferometer and a measuring method thereof.
Background
The Fizeau interferometer is widely applied to the field of optical measurement, and the common optical path structure of the Fizeau interferometer enables the aberration of an optical system inside the interferometer to be offset in a measurement result, so that high-precision detection of an optical element is achieved. However, in the data acquisition process of the interferometer, environmental interference can destroy the phase shift accuracy, so that measurement errors are caused, and in severe cases, measurement cannot be even carried out. How to apply the fizeau interferometer to dynamic measurement in an unstable environment is a current research hotspot.
At present, the fizeau type synchronous phase-shifting interferometer mainly has two structural forms. One is the tilted reference mirror structure proposed by millard et al, 4D 2004 (US7, 057,738B2), the other is Kuchel et al, 1989 (US4, 872, 755), the 2006 Kimbrough et al improved short coherent light source optical path difference matching structure (Bradley t. In the former structure, the inclination of the reference surface causes the common-path characteristic of the test light and the reference light to be partially destroyed, thereby causing a phase measurement error and losing the greatest advantage of the fizeau type interferometer. The latter structure generates two light waves with orthogonal polarization states through the front auxiliary component and simultaneously illuminates the main interferometer, and 6 groups of interference fringes are formed in a conformal mode. By using the broadband illumination light source with short time coherence length, when the time coherence of the front-end assembly is matched with that of the interferometer, the contrast ratio of the interference fringes to be measured formed by the interference of the reference surface and the test surface reaches the maximum, and the other 5 groups of additional fringes completely disappear, so that the coaxial Fizeau synchronous phase-shifting interferometry is realized. However, since four adjacent pixels are used as a resolving unit to recover the phase, the spatial resolution is lost. In addition, due to the limitation of the fabrication process of the micro-polarization array, the resolution of the interferometer is further improved and a bottleneck is encountered. Moreover, for a large-aperture interferometer system, due to factors such as glass material manufacturing and mechanical support, optical uniformity errors caused by stress birefringence cannot be completely eliminated, and polarization aberration causes interference pattern contrast blurring and wavefront measurement errors.
Disclosure of Invention
The invention aims to provide a point source ectopic beam expanding synchronous phase shifting Fizeau interferometer and a measuring method thereof, which have the advantages of high precision, low cost, convenience, practicability and miniaturization.
The technical solution for realizing the purpose of the invention is as follows: a point source ectopic beam expanding synchronous phase shifting fizeau interferometer, comprising: pointolite array, main interferometer and beam split imaging subassembly, four bundles of the same spherical waves that pointolite array produced get into main interferometer respectively, then acquire four phase shift interferograms simultaneously on a CCD through beam split imaging subassembly, wherein:
the point light source array is used for generating four divergent spherical waves with the same complex amplitude but different spatial positions;
the main interferometer is a Fizeau interferometer, so that reference light reflected from a reference surface and test light reflected from a test surface form an interference field;
the spectral imaging component (13) is used for separating interference fields generated by the four light sources respectively reflected by the reference surface and the test surface on the CCD target surface and enabling the CCD target surface to be conjugated with the test surface.
Further, the point light source array comprises a point light source, a first collimating objective lens, a chessboard grating, a first converging objective lens and an aperture diaphragm which are sequentially arranged coaxially, the aperture diaphragm filters out four beams of (+/-1 ) orders of diffraction light of the chessboard grating and filters out other orders of diffraction light, the complex amplitudes of the four beams of diffraction light are the same and are respectively positioned at four vertexes of a 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 transverse offset distance of adjacent divergent spherical waves:
d＝2λf2/Λ
wherein λ is the wavelength of incident light, f2Lambda is the grating period of the checkerboard grating for the focal length of the converging objective lens.
The main interferometer comprises a second collimating objective, a splitting film, a divergent objective, a third collimating objective, a reference surface and a test surface which are sequentially arranged in a coaxial manner, four beams of same spherical waves generated by a point light source array respectively enter the main interferometer, the four beams of light entering the main interferometer are firstly collimated by the collimating objective, then are expanded by the divergent objective and the third collimating objective, and finally sequentially pass through the reference surface and the test surface, wherein each beam of light is respectively reflected by the reference surface and the test surface to form reference light and test light, and the reference light and the test light return along the original path and are reflected by the splitting film to enter a splitting imaging assembly;
the divergent objective lens and the third collimating objective lens form a beam expanding system, and the optical zoom of the interference pattern is realized by changing the magnification of the beam expanding system.
Further, the split imaging component comprises a second convergent objective, a lens array, an imaging objective and a CCD which are sequentially arranged in a coaxial mode, and the position of the second convergent objective meets the following formula:
f4+f6-ls＞0
wherein f is4And f6Focal lengths of the divergent objective lens and the second convergent objective lens, respectively,/sIs the optical path between the divergent objective lens and the second convergent objective lens; the lens array is positioned on the focal plane of the second convergent objective lens;
the four groups of reference light and test light reflected by the reference surface and the test surface are converged by the second converging objective lens and then respectively pass through the object space principal point of each lens in the lens array, the four groups of reference light and test light passing through the lens array are collimated into parallel light by the imaging objective lens, and the parallel light forms four separated light spots on the target surface of the CCD.
Further, the focal length of the second converging objective lens satisfies the following equation:
f6＝f3dI/d
wherein f is3Is the focal length of the second collimator objective lens, dIThe diameter of each lens in the lens array.
Further, the lens array is a 2 × 2 negative lens array, and the focal length f of each negative lens is7Satisfy f7＝-dF#Wherein d is the transverse offset distance of the adjacent divergent spherical waves, F#Is the F-number of the beam after passing through the second converging objective.
Furthermore, the front focal plane of the imaging objective coincides with the image side main surface of the lens array, and the focal length f of the imaging objective8Satisfy f8≤LF#And/2, wherein L is the width of the CCD target surface.
Furthermore, the target surface of the CCD is conjugated with the testing surface in the main interferometer, and the distance l between the target surface of the CCD and the image side main surface of the imaging objective is equal to f8+f8 2/dF#。
A measurement method based on the point source ectopic beam expanding synchronous phase shifting fizeau interferometer in claim 1, comprising the following steps:
step 1, a point light source array generates four divergent spherical waves with the same complex amplitude but different spatial positions, the four divergent spherical waves are respectively positioned at four vertexes of a square, the center of the square is not positioned on an optical axis of a main interferometer, a tested piece is placed in the main interferometer to be used as a test surface, and the test surface is adjusted to be parallel to a reference surface, so that four phase-shift interferograms are simultaneously obtained on a CCD;
step 2, let Δ x and Δ y be the projection 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 that Δ x ═ 4m +1) λ f3 2f5 2/8lDf4 2、Δy＝(2n+1)λf3 2f5 2/4lDf4 2Or Δ x ═ 2m +1) λ f3 2f5 2/4lDf4 2、Δy＝(4n+1)λf3 2f5 2/8lDf4 2Obtaining four interference patterns with sequentially increasing pi/2 phase shift amount; wherein (m, n) is an integer, λ is the wavelength of incident light, f3、f4And f5The focal lengths of the second collimating objective lens, the divergent objective lens and the third collimating objective lens are respectively, D is the distance between the reference surface and the test surface, and l is the distance between the target surface of the CCD and the image side main surface of the imaging objective lens;
step 3, extracting four interference patterns from a frame of CCD image, processing the four interference patterns through a phase-shifting algorithm, and recovering the surface shape or wave aberration of the test surface;
and 4, continuously acquiring multiple frames of CCD images, respectively extracting wave aberration, and then calculating an average value to obtain the final test surface shape or wave aberration.
Further, four phase-shift interferograms are simultaneously acquired on the CCD in the step 1, and the phase shift amount delta (r) of each interferogram satisfies the following condition:
wherein,is the offset distance between the divergent spherical wave and the optical axis of the main interferometer.
Compared with the prior art, the invention has the remarkable advantages that: (1) the coaxial Fizeau synchronous phase-shifting interferometry can be realized, the phase shifting can be realized only by using one common point light source, and the cost is lower; (2) the distance between the point light source arrays and the diameter of the imaging lens array are variable, so that system errors can be effectively inhibited, and the detection resolution and precision are improved; (3) optical zooming can be realized by replacing the beam expanding system; (4) other polarization elements are not needed, and the structure is compact; the test process is simple, the adjustment is convenient, the requirement on the environment is lower, and the test is easier to realize.
Drawings
Fig. 1 is a schematic structural diagram of a point source ectopic beam expanding synchronous phase shifting fizeau interferometer.
Fig. 2 is a schematic diagram of the light path of collimated light resulting from the lateral shift of the point light source.
FIG. 3 is a schematic illustration of oblique light incidence introducing a phase shift between interfering light fields.
Fig. 4 is a diagram illustrating relative positions of four point light sources and the focal points of the collimator objective.
In the figure: 1. an array of point light sources; 2. a point light source; 3. a first collimating objective lens; 4. grating on the chessboard; 5. a first converging objective lens; 6. an aperture diaphragm; 7. a second collimator objective; 8. a light splitting film; 9. a divergent objective lens; 10. a third collimating objective lens; 11. a reference mirror; 12. testing the mirror; 13. a spectroscopic imaging assembly; 14. a second converging objective lens; 15. a lens array; 16. an imaging objective lens; 17. a CCD.
Detailed Description
With reference to fig. 1, the point source ectopic beam expanding synchronous phase shifting fizeau interferometer of the present invention comprises: the system comprises a point light source array 1, a main interferometer and a spectral imaging assembly 13, wherein four beams of same spherical waves generated by the point light source array 1 respectively enter the main interferometer, and then four phase-shift interferograms are simultaneously acquired on a CCD17 through the spectral imaging assembly 13, wherein:
(1) the point light source array 1 is used for generating four divergent spherical waves with the same complex amplitude but different spatial positions;
the point light source array 1 comprises a point light source 2, a first collimating objective lens 3, a chessboard grating 4, a first converging objective lens 5 and an aperture diaphragm 6 which are sequentially arranged coaxially, the aperture diaphragm 6 filters out four beams of (+/-1 ) diffraction light of the chessboard grating 4 and other orders of diffraction light, the complex amplitudes of the four beams of diffraction light are the same and are respectively positioned at four vertexes of a square, the center of the square is not on the optical axis of a main interferometer, and the side length d of the square is the transverse dislocation distance of adjacent divergent spherical waves
d＝2λf2/Λ
Wherein λ is the wavelength of incident light, f2Lambda is the focal length of the first polymer mirror 5 and lambda is the grating period of the checkerboard grating 4.
(2) The main interferometer is a Fizeau interferometer, so that reference light reflected from a reference surface and test light reflected from a test surface form an interference field;
the main interferometer comprises a second collimating objective 7, a light splitting film 8, a divergent objective 9, a third collimating objective 10, a reference surface 11 and a test surface 12 which are sequentially arranged in a coaxial manner, four beams of same spherical waves generated by a point light source array 1 respectively enter the main interferometer, the four beams of light entering the main interferometer are firstly collimated by the first collimating objective 7, then are expanded by the divergent objective 9 and the collimating objective 10, and finally sequentially pass through the reference surface 11 and the test surface 12, wherein each beam of light is respectively reflected by the reference surface 11 and the test surface 12 to form reference light and test light, and the reference light and the test light return along the original path and are reflected by the light splitting film 8 to enter a light splitting imaging assembly 13.
The divergent objective lens 9 and the third collimator objective lens 10 form a beam expanding system, and the magnification of the beam expanding system is changed to realize optical magnification variation of the interference pattern.
(3) The spectral imaging component 13 is used for separating interference fields generated by the four light sources respectively reflected by the reference surface and the test surface on the CCD target surface, and enabling the CCD target surface and the test surface to be conjugated.
The spectroscopic imaging assembly 13 comprises a second convergent objective lens 14, a lens array 15, an imaging objective lens 16 and a CCD17 which are sequentially arranged coaxially, wherein the position of the second convergent objective lens 14 satisfies the requirement
f4+f6-ls＞0
Wherein f is4And f6Focal lengths of the divergent objective lens 9 and the second convergent objective lens 14, l, respectivelysIs the optical path between the divergent objective 9 and the second convergent objective 14; the lens array 15 is located in the focal plane of the second converging objective 14;
the four groups of reference light and test light reflected by the reference surface and the test surface are converged by the second converging objective lens 14 and then pass through the object space principal point of each lens in the lens array 15, the four groups of reference light and test light passing through the lens array 15 are collimated into parallel light by the imaging objective lens 16, and the parallel light forms four separated light spots on the target surface of the CCD 17.
The focal length of the second converging objective lens 14 satisfies
f6＝f3dI/d
Wherein f is3Is the focal length of the second collimator objective 7, dIThe diameter of each lens in the lens array 15.
The lens array 15 is a 2 × 2 negative lens array, each negative lens having a focal length f7Satisfy f7＝-dF#Wherein d is the transverse offset distance of the adjacent divergent spherical waves, F#Is the F-number of the beam after passing through the second converging objective 14.
The front focal plane of the imaging objective 16 coincides with the image-side main surface of the lens array 15, the focal length f of the imaging objective 168Satisfy f8≤LF#And/2, wherein L is the width of the target surface of the CCD 17.
The target surface of the CCD17 is conjugated with the test surface 12 in the main interferometer, and the distance l between the target surface of the CCD17 and the image side main surface of the imaging objective lens 16 is f8+f8 2/dF#。
The invention discloses a point source ectopic beam expanding synchronous phase shifting Fizeau interferometer-based measuring method, which comprises the following steps of:
step 1, a point light source array generates four divergent spherical waves with the same complex amplitude but different spatial positions, the four divergent spherical waves are respectively positioned at four vertexes of a square, the center of the square is not positioned on an optical axis of a main interferometer, a tested piece is placed in the main interferometer to be used as a test surface, and the test surface is adjusted to be parallel to a reference surface, so that four phase-shift interferograms are simultaneously obtained on a CCD; four phase shift interferograms are simultaneously acquired on the CCD, and the phase shift quantity delta (r) of each interferogram satisfies the following conditions:
wherein,is the offset distance between the divergent spherical wave and the optical axis of the main interferometer.
Step 2, let Δ x and Δ y be the projection 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 that Δ x ═ 4m +1) λ f3 2f5 2/8lDf4 2、Δy＝(2n+1)λf3 2f5 2/4lDf4 2Or Δ x ═ 2m +1) λ f3 2f5 2/4lDf4 2、Δy＝(4n+1)λf3 2f5 2/8lDf4 2Obtaining four interference patterns with sequentially increasing pi/2 phase shift amount; wherein (m, n) is an integer, λ is the wavelength of incident light, f3、f4And f5The focal lengths of the second collimator objective lens 7, the divergent objective lens 9 and the third collimator objective lens 10 are respectively, D is the distance between the reference surface and the test surface, and l is the distance between the target surface of the CCD17 and the image side main surface of the imaging objective lens 16;
step 3, extracting four interference patterns from a frame of CCD image, processing the four interference patterns through a phase-shifting algorithm, and recovering the surface shape or wave aberration of the test surface; the phase-shifting algorithm is a random phase-shifting algorithm or a four-step phase-shifting algorithm.
And 4, continuously acquiring multiple frames of CCD images, respectively extracting wave aberration, and then calculating an average value to obtain the final surface shape or wave aberration of the test surface, so that the system error is inhibited, and the detection precision is improved.
Example 1
The light path structure of the point source ectopic beam expanding synchronous phase shifting Fizeau interferometer of the invention is shown in figure 1 and comprises,
1) the point light source array 1 is used to generate four divergent spherical waves with the same complex amplitude but different spatial positions. The point light source array 1 includes a point light source 2, a first collimating objective 3, a checkerboard grating 4, a first converging objective 5, and an aperture stop 6. The point light source 2 generates a plurality of diffraction orders after passing through the first collimating objective 3, the chessboard grating 4 and the first converging mirror 5, and the aperture diaphragm 6 is used for filtering four lights of the order (+/-1, +1) of the chessboard grating 4 and filtering diffracted lights of other orders. The four point light sources are respectively positioned at four vertexes of the square, and the center of the square formed by the four point light sources is not on the optical axis of the main interferometer. The length d of the square, i.e. the lateral offset d of adjacent diverging spherical waves, is 2 λ f2A/Λ, where λ is the wavelength of the incident light, f2Lambda is the focal length of the first polymer mirror 5 and lambda is the grating period of the checkerboard grating 4.
2) The interferometer comprises a second collimating objective 7, a spectroscopic film 8, a divergent objective 9, a third collimating objective 10, a reference surface 11 and a test surface 12, wherein four beams of light entering the interferometer are collimated by the second collimating objective 7, then expanded by the divergent objective 9 and the third collimating objective 10, and finally sequentially pass through the reference surface 11 and the test surface 12, each beam of light is reflected by the reference surface 11 and the test surface 12 respectively to form reference light and test light, and the reference light and the test light return along the original path and are reflected by the spectroscopic film 8 to enter a spectroscopic imaging assembly 13.
3) The spectroscopic imaging assembly 13 is used for reflecting the four light sources respectively through the reference surface and the test surfaceThe interference field is split at the target surface of the CCD17 and makes the target surface of the CCD17 conjugate to the test surface 12. The spectroscopic imaging assembly 13 includes a second convergent objective 14, a lens array 15, an imaging objective 16, and a CCD17, which are sequentially arranged coaxially. Wherein the position of the second converging objective lens 14 satisfies f4+f6-ls> 0, wherein f4And f6Focal lengths of the divergent objective lens 9 and the second convergent objective lens 14, l, respectivelysIs the optical path between the divergent objective 9 and the second convergent objective 14; the lens array 15 is located in the focal plane of the second converging objective 14; the four groups of reference light and test light reflected by the reference surface and the test surface are converged by the second converging objective lens 14 and then pass through the object space principal point of each lens in the lens array 15, the four groups of reference light and test light passing through the lens array 15 are collimated into parallel light by the imaging objective lens 16, and the parallel light forms four separated light spots on the target surface of the CCD 17. The focal length of the second converging objective lens 14 satisfies f6＝f3dID, wherein f3Is the focal length of the second collimator objective 7, dIThe diameter of each lens in the lens array 15. The lens array 15 is a 2 × 2 negative lens array, each of which functions as a field lens and has a focal length f7Satisfy f7＝-dF#Wherein d is the transverse offset distance of the adjacent divergent spherical waves, F#Is the F-number of the beam after passing through the second converging objective 14. The imaging objective lens 16 is used to collimate the four sets of reference light and test light passing through the lens array 15 into parallel light and to separate the four sets of light spots on the target surface of the CCD 17. The front focal plane of the imaging objective 16 coincides with the image-side main surface of the lens array 15. The focal length of the imaging objective lens 16 satisfies f8≤LF#And/2, wherein L is the width of the target surface of the CCD 17. The target surface of the CCD17 is conjugate to the test surface 12 and is at a distance of approximately l to f from the image-side main surface of the imaging objective 168+f8 2/dF#。
The principle of the point source ectopic beam expanding synchronous phase shifting Fizeau interferometer is as follows:
as shown in FIG. 2, when the point light source located in the front focal plane of the second collimator objective 7 has a lateral offset distance r from its focal point, the light beam passing through the second collimator objective 7 has an angle with the optical axisθ＝r/f3The beam expansion angle through the divergent objective lens 9 and the third collimator objective lens 10 becomes θ' ═ rf4/f3f5Wherein f is3、f4And f5Which are the focal lengths of the second collimator objective 7, the divergent objective 9 and the third collimator objective 10, respectively. Thereby introducing a constant amount of phase shift in the interference field produced by reflection from the reference plane 11 and the test plane 12. As shown in fig. 3, the amount of phase shift is δ (r) ═ k (AD-AB-BC) ═ -2Dcos θ 'according to geometrical optical properties, and since θ' is small, δ (r) ═ 2 pi D (2-r) can be obtained by approximation at a small angle2f4 2/f3 2f5 2) And/λ, where D is the distance between the reference surface and the test surface.
For the point source ectopic beam expanding synchronous phase shifting fizeau interferometer, the point light source array 1 generates four point light sources with the same complex amplitude, as shown in fig. 4, the centers of the four point light sources are taken as the origin of coordinates, the coordinates of the front focus of the second collimator objective 7 are (Δ x, Δ y), without loss of generality, it is assumed that Δ x is greater than 0 and less than or equal to Δ y, and at this time, the difference between the phase shift amount of each point light source corresponding to the interferogram and the minimum phase shift amount thereof is, in order from small to large: 0. 4 π dD Δ xf4 2/λf3 2f5 2、4πdDΔyf4 2/λf3 2f5 2、4πdD(Δx+Δy)f4 2/λf3 2f5 2And reconstructing the phase by adopting a random phase shift algorithm. In particular, when (Δ x, Δ y) satisfies Δ x ═ 4m +1 λ f3 2f5 2/8lDf4 2，Δy＝(2n+1)λf3 2f5 2/4lDf4 2And when (m, n) is an integer, the difference between the phase shift amount of each interference pattern and the minimum phase shift amount of each interference pattern is 0, pi/2, pi and 3 pi/2 from small to large, and the phase is reconstructed by adopting a four-step phase shift algorithm.
The measurement steps of the point source ectopic beam expanding synchronous phase shifting Fizeau interferometer are as follows:
1) turning on the point light source 2 and waiting for it to stabilize;
2) placing a tested piece according to the Fizeau interferometer light path, opening a computer and interference pattern data processing software, and calling out interference fringes acquired in real time;
3) adjusting the distance between the test surface 12 and the reference surface 11 to be approximately λ f3 2f5 2/8Δxf4 2So that the four interference patterns generate about pi/2 phase shift quantity from small to large in sequence;
4) adjusting the position and the inclination state of the test surface 12 to minimize the stripes in the view field;
5) selecting the centers of the four interference patterns, and extracting the four interference patterns from a frame of CCD image;
6) and calculating the four interference patterns by a random phase-shifting algorithm or a four-step phase-shifting algorithm to recover the surface shape or wave aberration of the test surface.
In summary, the point source ectopic beam expanding synchronous phase shifting fizeau interferometer of the invention uses the lateral offset of the four point light sources and the optical axis to introduce the phase shift in the interference field of the reference light and the test light, and recovers the phase through a frame of image, thereby realizing dynamic measurement. Because the distance between the point light source arrays and the diameter of the imaging lens array are variable, the system error can be effectively inhibited, and the detection resolution and precision are improved. Optical zoom can be realized by replacing the beam expanding system. Because no polarization element, PZT phase shift element and the like are introduced, the cost is low, the structure is compact, and the miniaturization is easy to realize. In addition, the test process is simple, the adjustment is convenient, the requirement on the environment is lower, and the test is easier to realize.
Claims (2)
1. The utility model provides a measurement method based on point source dystopy expands synchronous phase shifting Fizeau interferometer of moving, its characterized in that, point source dystopy expands synchronous phase shifting Fizeau interferometer of moving includes pointolite array (1), main interferometer and beam split imaging subassembly (13), and four the same spherical waves of bundle that pointolite array (1) produced get into main interferometer respectively, then acquire four phase shifting interferograms simultaneously on a CCD (17) through beam split imaging subassembly (13), wherein:
the point light source array (1) is used for generating four divergent spherical waves with the same complex amplitude but different spatial positions;
the main interferometer is a Fizeau interferometer, so that reference light reflected from a reference surface and test light reflected from a test surface form an interference field;
the light splitting imaging component (13) is used for splitting interference fields generated by the four light sources respectively reflected by the reference surface and the test surface on the CCD target surface and enabling the CCD target surface to be conjugated with the test surface;
the method comprises the following steps:
step 1, a point light source array generates four divergent spherical waves with the same complex amplitude but different spatial positions, the four divergent spherical waves are respectively positioned at four vertexes of a square, the center of the square is not positioned on an optical axis of a main interferometer, a tested piece is placed in the main interferometer to be used as a test surface, and the test surface is adjusted to be parallel to a reference surface, so that four phase-shift interferograms are simultaneously obtained on a CCD;
step 2, enabling the delta x and the delta y to be the projection lengths of the distance between the center of the square and the optical axis of the main interferometer in the horizontal direction and the vertical direction respectively, and meeting the requirementsOr Δ x ═ 2m +1) λ f3 2f5 2/4lDf4 2、Δy＝(4n+1)λf3 2f5 2/8lDf4 2Obtaining four interference patterns with sequentially increasing pi/2 phase shift amount; where m, n are integers, λ is the wavelength of the incident light, f3、f4And f5The focal lengths of the second collimating objective lens (7), the divergent objective lens (9) and the third collimating objective lens (10) are respectively, D is the distance between the reference surface and the test surface, and l is the distance between the target surface of the CCD (17) and the image side main surface of the imaging objective lens (16);
step 3, extracting four interference patterns from a frame of CCD image, processing the four interference patterns through a phase-shifting algorithm, and recovering the surface shape or wave aberration of the test surface;
and 4, continuously acquiring multiple frames of CCD images, respectively extracting wave aberration, and then calculating an average value to obtain the final test surface shape or wave aberration.
2. The method for measuring the point source ectopic beam expanding synchronous phase shifting Fizeau interferometer according to claim 1, wherein four phase shifting interferograms are simultaneously obtained on the CCD in step 1, and the phase shifting amount δ (r) of each interferogram satisfies the following condition:
wherein,is the offset distance between the divergent spherical wave and the optical axis of the main interferometer.
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| CN105928455A (en) * | 2016-05-20 | 2016-09-07 | 南京理工大学 | Spatial beam splitting coaxial Fizeau type synchronous phase-shift interferometer and measuring method thereof |
| CN106017307A (en) * | 2016-05-20 | 2016-10-12 | 南京法珀仪器设备有限公司 | Quasi full compensation laser feedback interferometer |
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