CN114136465B - Instantaneous two-step phase-shift transverse shearing interferometry system and method - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
- G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
- G01J9/0215—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods by shearing interferometric methods
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
- G01B9/02011—Interferometers characterised by controlling or generating intrinsic radiation properties using temporal polarization variation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
- G01B9/02029—Combination with non-interferometric systems, i.e. for measuring the object
- G01B9/0203—With imaging systems
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/0209—Low-coherence interferometers
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Abstract
The invention relates to an instantaneous two-step phase-shift transverse shear interferometry system and method. The problems of complex light path, high debugging difficulty, high cost, complex structure, poor stability and extremely easy introduction of extra errors in the prior art are solved. The invention is characterized in that a laser emergent light source is reflected by a microscope objective and a lens through a reflecting mirror, and then reaches a tested element through standard mirroring of a beam splitting prism, and then is vertically incident into a first crystal polarization beam splitter after passing through a polarizer, two light waves are respectively split into four linearly polarized light beams in the vertical direction, so that the two-to-two shearing of four wave surfaces is realized, each pixel-level micro polarization unit on the phase mask is in one-to-one matching correspondence with a pixel point on the CCD camera target surface through a phase mask arranged in front of the CCD camera target surface, and each two pixel-level micro polarization units are spliced and combined into a super pixel, and the light transmission axes of two adjacent micro polarization units are respectively along the x-axis direction and the y-axis direction.
Description
Technical field:
the invention relates to the technical field of optical measurement, in particular to an instantaneous two-step phase-shift transverse shearing interferometry system and an instantaneous two-step phase-shift transverse shearing interferometry method.
The background technology is as follows:
the transverse shearing interference technology is to divide the wave front to be measured into two identical wave fronts to be measured with a certain transverse displacement in space through a certain optical-mechanical system. By applying the technology, the system error caused by adopting the standard wavefront in the optical interference is avoided, the structure of the system can be simplified to a certain extent, the influence of the test system on the precision of the optical element is reduced, and the measurement precision is improved.
In the prior art, the problems of inaccurate shearing quantity calculation, low surface shape reconstruction precision and the like caused by inaccurate shearing element resetting and too few shearing interference pattern sampling points still exist. There are many methods for realizing transverse shearing interference at present, for example, a Common-path compact wavefront diagnosis system based on a cross grating transverse shearing interferometer is proposed in a Common-path compact wavefront diagnosis system (Tong Ling, ect, "Common-path and compact wavefront diagnosissystem based on cross grating lateralshearing interferometer". Applied optics vol.53, issue 30, pp.7144-7152, 2014) which uses a cross grating as a shearing element and only allows diffraction light of + -1 order to pass through by using a mask plate to realize transverse shearing in x and y directions. The system has a simple structure and is easy to operate, but the requirements on the manufacturing precision of the grating are very high, and the transverse sampling resolution is low, so that the image resolution of the system is greatly limited.
A new method for measuring free-form surfaces based on a space phase-shifting transverse shear interferometry is proposed in a Single exposure free-form surface profiler (YONG BUM SEO, ect, "Single-shot freeform surface profiler" Vol.28, no.3/3February 2020,Optics Express,3401-3409). The shearing interference is realized by utilizing the birefringent crystal, but the optical path is built more complex, a non-common optical path system is adopted, the debugging difficulty is high, and additional errors are easy to generate; the patent 'phase-shifting transverse shearing interferometer (200710045147.2)', 'polarization phase-shifting double-shearing interference wave surface measuring instrument and detection method (200710047254.9)', and 'polarization phase-shifting double-shearing interference wave surface measuring instrument (200720075604.8)', describes a polarization phase-shifting double-shearing interference wave surface measuring instrument and detection method thereof, wherein a phase shifting system is formed by a fixed wave plate and a rotary analyzer, and shearing is realized by two parallel flat plates. The instrument has very high requirement on the positioning precision of a parallel flat plate, and phase shift is realized through a certain mechanical movement mechanism, so that the acquisition of an interference pattern is sensitive to the change of the system environment.
As described in the patent "a prism-based lateral shearing interference spectrum imager and imaging method (202011643062.6)", a lateral shearing interference spectrum imager and imaging method based on right angle reflecting prisms are described, in which a tetrahedron prism is used to generate reference light and test light with a certain lateral displacement, and one of the right angle reflecting prisms is mounted on a one-dimensional shifter, through which the right angle reflecting prism can be controlled to move in the direction of its hypotenuse or right angle side to change the shearing amount, so that a certain movement mechanism support is required, so that the change of the environment will affect the measurement result. The realization of shearing in the system needs to ensure that the surface shape error and the space positioning error of the reflecting surface of the right-angle reflecting prisms reduce the measurement precision of the system under a certain space posture.
The problems of the prior art are as follows: the interference method for realizing the multidirectional transverse shearing has the advantages of complex light path, high debugging difficulty, high cost, complex structure, poor stability and extremely easy introduction of additional errors, and two or more light paths are required to be built for realizing the multidirectional shearing.
The invention comprises the following steps:
the invention aims to provide an instantaneous two-step phase shift transverse shearing interferometry system and an instantaneous two-step phase shift transverse shearing interferometry method, so as to solve the problems of complex optical path, high debugging difficulty, high cost, complex structure, poor stability and extremely easy introduction of additional errors in the prior art.
In order to achieve the above object, the technical solution of the present invention is as follows: the instantaneous two-step phase shift transverse shearing interferometry system comprises a laser light source 1, a lens 2, an objective lens 3 and a plane reflector 4 which are sequentially arranged on an optical axis, a measured optical element 5, a standard mirror 6, a beam splitting prism 7, a polarizer 8, a first crystal polarization beam splitter 9, a first lambda/4 wave plate 10, a second crystal polarization beam splitter 11, a second lambda/4 wave plate 12, a pixel-level phase mask 13 and a CCD camera 14 which are coaxially arranged, wherein the CCD camera 14 is connected with a computer; the light transmission axis of the polarizer 8 forms 45 degrees relative to the x-axis direction, the included angle between the fast axis direction of the first lambda/4 wave plate and the positive direction of the x-axis is 45 degrees, the included angle between the optical axis direction of the first crystal polarization beam splitter 9 and the positive direction of the x-axis is 45 degrees when the first crystal polarization beam splitter 9 is horizontally placed, the second crystal polarization beam splitter 11 is orthogonally placed, and the included angle between the fast axis direction of the second lambda/4 wave plate and the positive direction of the x-axis is 90 degrees; the phase mask 13 is arranged in front of the target surface of the CCD camera 14 and is consistent with the target surface in size, each pixel-level micro-polarization unit on the phase mask 13 is in one-to-one matching correspondence with a pixel point on the target surface of the CCD camera 14, each two pixel-level micro-polarization units are spliced and combined into a super pixel, and the light transmission shafts of two adjacent micro-polarization units are respectively along the x-axis direction and the y-axis direction; the two crystal polarization beam splitters are birefringent crystals.
The measuring method adopting the instantaneous two-step phase-shift transverse shearing interference device comprises the following steps: the object 5 is arranged on the outgoing side of a standard mirror 6 on the main optical axis
(1) The incident light reflected by the measured piece 5 is imaged on a beam splitting prism 7 through a standard mirror 6, and is incident to a first crystal polarization beam splitter 9 after passing through a polarizer 8;
(2) the two horizontal light waves emitted from the first crystal polarization beam splitter 9 are changed into two circularly polarized light beams with opposite rotation directions after passing through the first lambda/4 wave plate 10, and the left circularly polarized light beam and the right circularly polarized light beam are formed into four linearly polarized light beams after being vertically split by the second crystal polarization beam splitter 11;
(3) the linearly polarized light emitted in the step (2) passes through the second lambda/4 wave plate 12, and the four emitted linearly polarized light are respectively changed into two groups (two beams of left-handed and two beams of right-handed) of circularly polarized light with opposite rotation directions;
(4) the light waves emitted in the step (3) interfere after passing through the phase mask 13 in front of the target surface of the CCD camera 14, the micro-polarization units of each pixel level on the phase mask 13 are in one-to-one matching correspondence with each pixel point on the imaging panel of the CCD camera 14, the micro-polarization units of every two pixel levels are spliced and combined into a super pixel, the light transmission shaft angles of two adjacent micro-polarization units are respectively along the x-axis direction and the y-axis direction, phase shift interference occurs after the light waves pass through the phase mask 13, and a transverse sheared polarization interference original image is obtained by the CCD camera 14.
Compared with the prior art, the invention has the beneficial effects that:
(1) The method is simple to operate, the measurement system does not need any mechanical movement, and the instantaneous two-step phase shift transverse shearing interference pattern with fixed phase shift can be synchronously obtained through single exposure.
(2) In the process of acquiring the shearing interference pattern, the shearing interference and the synchronous phase shift are realized through a common-path optical system, the method is suitable for wave surface measurement of low-coherence light, two or more optical paths are not required to be established, and the system is simple to debug.
(3) The invention utilizes the pixel phase mask plate to realize the simultaneous acquisition of two transverse shearing interference patterns with fixed phase shift, can realize the transient interference measurement of wave surfaces without using expensive piezoelectric transducers, linear converters and other mechanical phase shift mechanisms, has strong anti-interference capability, improves the measurement speed and reduces the measurement cost.
(4) Synchronous phase shift is realized by adopting a pixel-level micro-polarization unit array, and the method is simple and reliable and has high calculation efficiency.
(5) The shearing quantity of the polarization crystal beam splitter is fixed, so that the problem of calculating the shearing quantity is avoided, and the calculating error is reduced.
Description of the drawings:
FIG. 1 is a schematic diagram of a system for implementing instantaneous two-step phase-shifting transverse shear interferometry.
FIG. 2 is a schematic diagram of two crystal polarizing beam splitters implementing transient two-step phase shift transverse shear interference.
Fig. 3 is a schematic diagram of a pixel phase mask corresponding to pixel points on a CCD detector one by one and a direction of a micro polarization unit array at a pixel level thereof.
Fig. 4 is a polarization interference original acquired by a CCD camera after passing through a mask.
Fig. 5 is a graph of two transverse shearing interference fringes with a fixed phase shift obtained after a mask patterning process.
The reference numerals are explained as follows:
the device comprises a laser light source 1, a lens 2, an objective lens 3, a plane reflecting mirror 4, a measured optical element 5, a standard mirror 6, a beam splitting prism 7, a polarizer 8, a first crystal polarization beam splitter 9, a first lambda/4 wave plate 10, a second crystal polarization beam splitter 11, a second lambda/4 wave plate 12, a pixel phase mask 13 and a CCD camera 14.
The specific embodiment is as follows:
the present invention will be described in detail with reference to the accompanying drawings and examples.
The invention has the core idea that the instantaneous two-step phase shift transverse shearing is realized by combining and synchronizing two crystal polarization beam splitters with a double refraction effect.
Referring to fig. 1, the instantaneous two-step phase shift transverse shearing interferometry system provided by the invention comprises a laser light source 1, a lens 2, an objective lens 3 and a plane reflector 4 which are arranged on an optical axis, a measured optical element 5, a standard mirror 6, a beam splitting prism 7, a polarizer 8, a first crystal polarization beam splitter 9, a first lambda/4 wave plate 10, a second crystal polarization beam splitter 11, a second lambda/4 wave plate 12, a pixel-level phase mask 13 and a CCD camera 14 which are coaxially arranged on a main optical axis in sequence, wherein the CCD camera 14 is connected with a computer; the angle of the polarizer 8 is 45 degrees relative to the x-axis direction, the included angle between the fast axis direction of the first lambda/4 wave plate and the positive direction of the x-axis is 45 degrees, the included angle between the optical axis direction of the first crystal polarization beam splitter 9 and the positive direction of the x-axis is 45 degrees when the first crystal polarization beam splitter 9 is horizontally placed, the second crystal polarization beam splitter 11 is orthogonally placed, and the included angle between the fast axis direction of the second lambda/4 wave plate and the positive direction of the x-axis is 90 degrees; the phase mask 13 is arranged in front of the target surface of the CCD camera 14 and is consistent with the target surface in size, each pixel-level micro-polarization unit on the phase mask 13 is in one-to-one matching correspondence with a pixel point on the target surface of the CCD camera 14, each two pixel-level micro-polarization units are spliced and combined into a super pixel, and the light transmission shafts of two adjacent micro-polarization units are respectively along the x-axis direction and the y-axis direction.
The measuring process of the system is as follows: the laser 1 emits a light source, the light source is reflected by the reflecting mirror 4 through the beam splitting prism 7 and the standard mirror 6 to reach the tested element 5 through the beam expansion and collimation system realized by the microscope objective 2 and the lens 3. The test wavefront returned from the surface of the tested element 5 is vertically incident into the first crystal polarization beam splitter 9 after passing through the polarizer 8, and the crystal polarization beam splitter has a double refraction characteristic, so that the test wavefront is horizontally split into two linearly polarized lights with a certain transverse displacement and mutually perpendicular vibration directions, namely o light and e light when exiting. The two light waves pass through the first lambda/4 wave plate 10, and the included angle between the fast axis direction and the positive x axis direction of the lambda/4 wave plate 10 is 45 degrees, so that the incident two linearly polarized light beams are respectively changed into left-handed circularly polarized light and right-handed circularly polarized light. The circularly polarized light vertically irradiates on the second crystal polarization beam splitter 11, and after being split by the crystal polarization beam splitter 11, the two circularly polarized light beams are split into four linearly polarized light beams in the vertical direction again respectively, so that the two shearing of four wave surfaces is realized. The included angle between the fast axis direction of the second lambda/4 wave plate and the positive direction of the x-axis is 90 degrees, the split light waves pass through the second lambda/4 wave plate 12 to generate phase delay, and referring to fig. 3, through a phase mask 13 installed in front of the target surface of a CCD camera 14, micro polarization units of each pixel level on the phase mask 13 are in one-to-one matching correspondence with pixel points on the target surface of the CCD camera 14, and micro polarization units of every two pixel levels are spliced and combined into a super pixel, and the light transmission axes of two adjacent micro polarization units are respectively along the x-axis direction and the y-axis direction.
The principle analysis of the invention is as follows:
two linearly polarized lights with transverse displacement, namely o light and e light, are emitted from the crystal polarization beam splitter; when the light exits, the phase difference between the o light and the e light is as follows:
wherein lambda is the operating wavelength of the crystal polarization beam splitter, n o 、n e Refractive indices of o light and e light respectively emitted from the crystal polarization beam splitter, L o 、L e Optical paths of o light and e light, L o 、L e Can be calculated from the crystal thickness.
After the outgoing light passes through the phase mask 13, when passing through the micro-polarization unit with the polarization direction of 0 °, the jones vector expressions of the four light waves outgoing from the second crystal polarization beam splitter 11 are respectively:
E 2 ＝0(3)
E 4 ＝0(5)
when passing through a micro polarization unit having a polarization direction of 90 °, the jones vector expressions of the four light waves emitted from the second crystal polarization beam splitter 11 are respectively:
E 1 ＝0(6)
E 3 ＝0(8)
the four light waves pass through the pixel-level micro polarization unit array to generate phase shift interference, wherein when passing through the micro polarization unit with the polarization transmission direction of 0 DEG, E is used for 1 And E is 3 The superposition of these two light waves produces interference, and the light intensity expression of the interference pattern can be expressed as:
when passing through a micro-polarization unit with a 90 DEG polarization direction, the light passes through E 2 And E is 4 The two light waves are overlapped to generate interference, and the light intensity expression of the interference pattern can be expressed as：
Wherein in the formulas (10) and (11),for the initial phase carried by the surface of the element to be measured, delta c The phase difference between the o light and the e light emitted by the crystal polarization beam splitter is specifically given by the formula (1).
The instantaneous two-step phase-shift transverse shearing interferometry method provided by the invention is adopted to arrange the measured piece 5 on the outgoing side of the standard mirror 6 on the main optical axis, and comprises the following steps:
(1) the incident light reflected by the measured piece 5 is imaged on a beam splitting prism 7 through a standard mirror 6, and is incident to a first crystal polarization beam splitter 9 after passing through a polarizer 8;
(2) the two horizontal light waves emitted from the first crystal polarization beam splitter 9 are changed into two circularly polarized light beams with opposite rotation directions after passing through the first lambda/4 wave plate 10, and the left circularly polarized light beam and the right circularly polarized light beam are formed into four linearly polarized light beams after being vertically split by the second crystal polarization beam splitter 11;
(3) the linearly polarized light emitted in the step (2) passes through the second lambda/4 wave plate 12, and the four emitted linearly polarized light are respectively changed into two groups (two beams of left-handed and two beams of right-handed) of circularly polarized light with opposite rotation directions;
(4) the light waves emitted in the step (3) interfere after passing through the phase mask 13 in front of the CCD camera 14 target surface, each pixel-level micro-polarization unit on the phase mask 13 is in one-to-one matching correspondence with each pixel point on the CCD camera 14 imaging panel, each two pixel-level micro-polarization units are spliced and combined into a super pixel, and the light transmission shafts of two adjacent micro-polarization units are respectively along the x-axis direction and the y-axis direction. The light wave passes through the phase mask 13 and then phase shift interference occurs, and a transverse shearing polarized interference original image is obtained by the CCD camera 14.
Referring to FIG. 5, the transverse shearing polarization interference original image obtained by the invention is subjected to corresponding mask image taking processingTwo transverse shearing interference fringe patterns a and b can be synchronously obtained, and a certain fixed phase shift amount is arranged between the two obtained interference patternsWherein delta c The phase difference between the o light and the e light emitted by the crystal polarization beam splitter is specifically given by the formula (1).
Claims (3)
1. An instantaneous two-step phase-shifting transverse shear interferometry system, characterized by: the device comprises a laser light source (1), a lens (2), an objective lens (3) and a plane reflecting mirror (4) which are sequentially arranged on an optical axis, and further comprises a measured optical element (5), a standard mirror (6), a beam splitting prism (7), a polarizer (8), a first crystal polarization beam splitter (9), a first lambda/4 wave plate (10), a second crystal polarization beam splitter (11), a second lambda/4 wave plate (12), a pixel-level phase mask plate (13) and a CCD camera (14), wherein the measured optical element, the standard mirror (6), the beam splitting prism (7), the polarizer (8), the first crystal polarization beam splitter (9), the second lambda/4 wave plate (12), and the CCD camera (14) are connected with a computer; the light transmission axis of the polarizer (8) forms 45 degrees relative to the x-axis direction, the included angle between the fast axis direction of the first lambda/4 wave plate and the positive direction of the x-axis is 45 degrees, the included angle between the light axis direction of the first crystal polarization beam splitter (9) and the positive direction of the x-axis is 45 degrees when the first crystal polarization beam splitter is horizontally placed, the second crystal polarization beam splitter (11) is orthogonally placed with the first crystal polarization beam splitter, and the included angle between the fast axis direction of the second lambda/4 wave plate and the positive direction of the x-axis is 90 degrees; the phase mask (13) is arranged in front of the target surface of the CCD camera (14) and is consistent with the target surface in size, the micro-polarization units of each pixel level on the phase mask (13) are in one-to-one matching correspondence with pixel points on the target surface of the CCD camera (14), the micro-polarization units of every two pixel levels are spliced and combined into a super pixel, and the light transmission shafts of two adjacent micro-polarization units are respectively along the x-axis direction and the y-axis direction.
2. An instantaneous two-step phase-shifting transverse shear interferometry system according to claim 1, wherein: the first crystal polarization beam splitter (9) and the second crystal polarization beam splitter (11) are birefringent crystals.
3. A measurement method employing the instantaneous two-step phase-shifting transverse shear interferometry system of claim 1, characterized by: the method comprises the following steps: the measured optical element (5) is arranged on the emergent side of a standard mirror (6) on the main optical axis;
(1) the incident light reflected by the tested optical element (5) is imaged on a beam splitting prism (7) through a standard mirror (6), and is incident to a first crystal polarization beam splitter (9) after passing through a polarizer (8);
(2) two horizontal light waves emitted from the first crystal polarization beam splitter (9) are changed into two circularly polarized light beams with opposite rotation directions after passing through the first lambda/4 wave plate (10), and the left circularly polarized light beam and the right circularly polarized light beam are formed into four linearly polarized light beams after being vertically split by the second crystal polarization beam splitter (11);
(3) the linearly polarized light emitted in the step (2) passes through a second lambda/4 wave plate (12), and the four emitted linearly polarized light are respectively changed into two groups of circularly polarized light with opposite rotation directions, wherein two groups of circularly polarized light with opposite rotation directions are left-handed and the other two groups of circularly polarized light are right-handed;
(4) the light waves emitted in the step (3) are interfered after passing through a phase mask (13) in front of a target surface of a CCD camera (14), micro-polarization units of each pixel level on the phase mask (13) are in one-to-one matching correspondence with each pixel point on an imaging panel of the CCD camera (14), the micro-polarization units of every two pixel levels are spliced and combined into a super pixel, the angles of light transmission axes of two adjacent micro-polarization units are respectively along the x-axis direction and the y-axis direction, phase shift interference occurs after the light waves pass through the phase mask (13), and a transverse shearing polarization interference original image is obtained by the CCD camera (14).
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