CN109163673B - A kind of multi-wavelength and the bisynchronous surface method for real-time measurement of phase shift interference and system - Google Patents
A kind of multi-wavelength and the bisynchronous surface method for real-time measurement of phase shift interference and system Download PDFInfo
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Abstract
The invention discloses a kind of multi-wavelength and the bisynchronous surface method for real-time measurement of phase shift interference and systems, it uses intervention module, it is divided phase shift module and CCD image-forming module, reference light and measurement light are first broken down into four road light sources and simultaneous phase-shifting 0 by light splitting phase shift module by it, pi/2, π, 3 pi/2s, tetra- road light source of phase shift Hou carries out interference and collects synchronous phase-shifted interference pattern by CCD image-forming module, parameter calibration is carried out to synchronous phase-shifted interference pattern before measurement, the parameter of calibration is the collected reference light in each channel, light intensity is measured relative to the 1st collected reference light in channel, the difference for the phase-shift phase that the phase-shift phase and the 1st channel that the ratio and each channel for measuring light intensity introduce introduce, the phase information of tested exemplar is further determined that using the parameter of calibration, to obtain the surface temporal structure of tested exemplar And improve the accuracy of measurement result.
Description
Technical Field
The invention belongs to the field of real-time measurement, and particularly relates to a multi-wavelength and phase-shift interference double-synchronization surface real-time measurement method and system.
Background
The geometric characteristics of the surface appearance and the structure of the sample piece are mainly formed by the technical processes of surface treatment, mechanical processing and the like, the external characteristics of the surface are reflected, and the method is an important quality index for manufacturing products and scientific research. Meanwhile, the surface appearance and structure are closely inseparable connected with the internal characteristics of the surface of the sample piece, such as residual stress, microscopic physical and mechanical characteristics and the like, and the method is an important representation of the dynamic characteristics of products and sample pieces.
The synchronous phase shift interference technology is a method for simultaneously obtaining a plurality of phase shift interference images and solving the surface topography of a measured sample. Compared with the traditional time phase shift interference method, the method has the main advantages of environmental vibration resistance, application in working occasions with severe environment, high measurement speed and capability of measuring dynamic samples. Although the synchronous phase shift technique can effectively reduce the influence of environmental vibration, other error terms are introduced, which mainly include the installation angle and retardation error of a wave plate, the installation angle error of a polaroid, the light intensity distribution unevenness and the phase error caused by a prism or a grating, the matching error of a plurality of interferograms and the like.
The existing synchronous phase-shifting interference technology has three relatively typical structures: a multi-camera or single-camera synchronous phase-shift interference system based on prism beam splitting is disclosed in the paper (Simultaneous phase-shift interferometer, ACL Kolioulos, International Society for Optics and Photonics,1992: 119-; a single-camera synchronous phase-shift interference system based on grating light splitting, a paper (Three channel-shifting interferometer using polarization and a diffusion mapping), HetwerA, Kranz J, Schwindower J, Optical Engineering,2000,39(4): 960-; one is a synchronous phase shift interference system based on a pixilated polarization mask or a phase delay mask, and US patent US7079251B2 discloses a method for analyzing and correcting errors of a multi-channel interference imaging system, wherein error influences such as image deformation, invalid pixel points, detector nonlinearity, inaccurate random phase shift and the like are considered in the method, but the description of a specific implementation scheme is also lacked. Therefore, research on optical path structure errors is mostly focused on theoretical analysis, the influence of each error source is quantitatively described, and the control mode of the errors is mostly dependent on selecting high-quality grade devices and improving mounting accuracy. Meanwhile, when the synchronous phase shift interference technology is applied to dynamic surface topography measurement, due to the limitation of the principle of the phase shift interference technology, the phase obtained by the algorithm solution is wrapped between-pi and pi, so that only continuous surfaces can be measured generally.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a multi-wavelength and phase-shift interference double-synchronization surface real-time measurement method and system, which adopt an interference module, a light splitting phase-shift module and a CCD imaging module to obtain four-channel synchronous phase-shift interference patterns, carry out parameter calibration on the synchronous phase-shift interference patterns collected by the CCD imaging module before measurement, and further determine the phase information of a measured sample by utilizing the calibrated parameters, thereby obtaining the surface instantaneous structure of the measured sample and improving the accuracy of the measurement result.
In order to achieve the above object, according to an aspect of the present invention, there is provided a real-time surface measurement method based on dual synchronization of multi-wavelength and phase-shift interference, specifically:
s1, decomposing incident light provided by a light source into mutually orthogonal reference light and measurement light;
s2, dividing the reference light and the measuring light into four paths, and then synchronously shifting the phases and interfering with each other;
s3, collecting four paths of optical signals after phase-shifting interference to obtain a synchronous phase-shifting interference pattern;
s4, calibrating parameters of the acquired synchronous phase shift interference pattern, which specifically comprises the following steps:
expressing the light intensity of the acquired synchronous phase-shifted interference pattern as
In the formula Io1And Ir1Representing the intensity of the measuring light and the intensity of the reference light of the first channel respectively,representing the measured phase, ko1、ko2、ko3Respectively representing the ratio of the measured light intensity collected by the second, third and fourth channels to the measured light intensity collected by the first channel, kr1、kr2、kr3Respectively representing the ratio of the reference light intensity collected by the second channel, the third channel and the fourth channel to the reference light intensity collected by the first channel, and delta gamma21、Δγ31、Δγ41Respectively representing the difference between the phase shift introduced by the second channel, the third channel and the fourth channel and the phase shift introduced by the 1 st channel;
the calibrated parameter values are respectively as follows: k is a radical ofo1、ko2、ko3、kr1、kr2、kr3、Δγ21、Δγ31And [ Delta ] gamma41；
S5, acquiring four paths of optical signals subjected to light splitting phase shifting interference by utilizing the steps S1-S3 to obtain a synchronous phase shifting interference pattern, and analyzing and processing to obtain a measurement phase of the measured sample so as to obtain a surface instantaneous structure of the measured sample.
As a further improvement of the present invention, step S2 is to perform splitting, phase shifting and interference on the reference light and the measurement light by using the splitting phase shift module, wherein, the light splitting phase shift module comprises an achromatic 1/4 wave plate, three light splitting and splitting modules and four analyzers, wherein the light transmission directions of the four analyzers are respectively set to be 0, pi/4, pi/2 and 3 pi/4, the reference light and the measuring light sequentially pass through an achromatic 1/4 wave plate, a one-component and two-component light module, two one-component and two-component light modules sequentially arranged on the same plane and four analyzers sequentially arranged on the same plane, so as to change the reference light and the measuring light into circularly polarized light with opposite rotation directions and divide the circularly polarized light and the measuring light into four symmetrical optical signals in parallel, and the phase shifts generated on the four optical signals are respectively 0, pi/2, pi and 3 pi/2.
As a further improvement of the invention, the phase is measuredThe expression of (a) is:
A＝(kr1ko2-kr2ko1)I1-(ko2-kr2)I2+(ko1-kr1)I3
B＝(kr1ko3-kr3ko1)I1-(ko3-kr3)I2+(ko1-kr1)I4
wherein,A. b, a, B, c and d are coefficients.
As a further improvement of the invention, the phase is measuredRepresenting the actual phaseThe amount of phase shift Deltay introduced with respect to the first channel1Sum, Δ γ1The value of (A) exceeds a preset error range, and the surface height information of the sample is
As a further improvement of the invention, the multi-wavelength light source is utilized to realize the measurement range expansion of the height of the measuring point, which specifically comprises the following steps:
obtaining interference phase phi of red, green and blue colors by using color LED as light sourceR，φG，φBCalculating the equivalent wavelength λ of red and green lightsRGAnd green-blue equivalent wavelength lambdaGBCorresponding equivalent phase phiRG＝φR-φGAnd phiGB＝φG-φB；
mRG、mGBRespectively an integer periodic series of two equivalent wavelength phases satisfying mRG≥mGBThe equation (lambda) is obtained by a finite element method under the condition that the equation is more than or equal to 0RG/2)*mRG+φRGλRG/4π＝(λGB/2)*mGB+φGBλGBM in 4 piRGAnd mGBWill be m of the minimum solutionRGSubstituted L ═ λRG/2)*mRG+φRGλRGA value of/4 pi to L;
substituting L into equation L ═ (λ)R/2)*mR+φ'RλR/4π、L＝(λG/2)*mG+φG'λG(λ) 4 π and L ═ LB/2)*mB+φB'λBPhi of/4 pi, hereR'、φG' and phiB' defining phi for the modified interference phases of the three colors red, green and blue, respectivelyR'∈(-π,π)、φG'∈(-π,π)、φB' ∈ (- π, π) and mR、mGAnd mBIs an integer, m of which is obtainedR、mG、mB；
M is to beR、mG、mBSubstituted into LR＝(λR/2)*mR+φRλR/4π、LG＝(λG/2)*mG+φGλG/4π、LB＝(λB/2)*mB+φBλBL is 4. pi. to obtainR、LGAnd LBAnd averaging the values, wherein the obtained average value is the height of the measured point.
In order to achieve the above object, according to another aspect of the present invention, there is provided a multi-wavelength and phase-shift interference double-synchronous surface real-time measurement system, which includes a light source, an interference module, a spectral phase shift module and a CCD imaging module, wherein the interference module is configured to decompose incident light provided by the light source into mutually orthogonal reference light and measurement light, the spectral phase shift module is configured to decompose the reference light and the measurement light into four paths, and then synchronously shift phases and interfere with each other, the CCD imaging module is configured to collect four paths of optical signals after phase-shift interference to obtain a synchronous phase-shift interference pattern, and perform analysis processing to obtain a measurement phase of a sample to be measured, so as to obtain a surface transient structure of the sample to be measured,
the synchronous phase shift interference pattern collected by the CCD imaging module is subjected to parameter calibration before measurement, and the parameter calibration specifically comprises the following steps:
expressing the light intensity of the synchronous phase-shifted interference pattern as
In the formula Io1And Ir1Respectively representing the intensity of the measuring light and the intensity of the reference light of the first channel of the CCD imaging module,representing the measured phase, ko1、ko2、ko3Respectively representing the ratio of the measured light intensity collected by the second, third and fourth channels of the CCD imaging module to the measured light intensity collected by the first channel of the CCD imaging module, kr1、kr2、kr3Respectively representing the ratio of the reference light intensity collected by the second, third and fourth channels of the CCD imaging module to the reference light intensity collected by the first channel of the CCD imaging module, delta gamma21、Δγ31、Δγ41Respectively representing the difference between the phase shift quantity introduced by the second, third and fourth channels of the CCD imaging module and the phase shift quantity introduced by the first channel of the CCD imaging module;
the calibrated parameter values are respectively as follows: k is a radical ofo1、ko2、ko3、kr1、kr2、kr3、Δγ21、Δγ31And [ Delta ] gamma41。
As a further improvement of the present invention, in step S2, the reference light and the measurement light are split, phase-shifted and interfered by the split phase shift module, wherein the split phase shift module includes an achromatic 1/4 wave plate, three splitting and splitting modules and four analyzers, the light transmission directions of the four analyzers are set to be 0, pi/4, pi/2 and 3 pi/4 respectively, the reference light and the measurement light sequentially pass through the achromatic 1/4 wave plate, one splitting module, two splitting modules sequentially disposed on the same plane and four analyzers sequentially disposed on the same plane, so as to convert the reference light and the measurement light into circularly polarized light with opposite rotation directions and to be divided into symmetrical four optical signals in parallel, and the phase shifts generated for the four optical signals are 0, pi/2, pi and 3 pi/2 respectively.
As a further improvement of the inventionMeasuring the phaseThe expression of (a) is:
A＝(kr1ko2-kr2ko1)I1-(ko2-kr2)I2+(ko1-kr1)I3
B＝(kr1ko3-kr3ko1)I1-(ko3-kr3)I2+(ko1-kr1)I4
wherein,A. b, a, B, c and d are coefficients.
As a further improvement of the invention, the phase is measuredRepresenting the actual phaseThe amount of phase shift Deltay introduced with respect to the first channel1Sum, Δ γ1The value of (A) exceeds a preset error range, and the surface height information of the sample is
As a further improvement of the invention, the multi-wavelength light source is utilized to realize the measurement range expansion of the height of the measuring point, which specifically comprises the following steps:
obtaining interference phase phi of red, green and blue colors by using color LED as light sourceR，φG，φBCalculating the equivalent wavelength λ of red and green lightsRGAnd green-blue equivalent wavelength lambdaGBCorresponding equivalent phase phiRG＝φR-φGAnd phiGB＝φG-φB；
mRG、mGBRespectively an integer periodic series of two equivalent wavelength phases satisfying mRG≥mGBThe equation (lambda) is obtained by a finite element method under the condition that the equation is more than or equal to 0RG/2)*mRG+φRGλRG/4π＝(λGB/2)*mGB+φGBλGBM in 4 piRGAnd mGBWill be m of the minimum solutionRGSubstituted L ═ λRG/2)*mRG+φRGλRGA value of/4 pi to L;
substituting L into equation L ═ (λ)R/2)*mR+φ'RλR/4π、L＝(λG/2)*mG+φG'λG(λ) 4 π and L ═ LB/2)*mB+φB'λBPhi of/4 pi, hereR'、φG' and phiB' defining phi for the modified interference phases of the three colors red, green and blue, respectivelyR'∈(-π,π)、φG'∈(-π,π)、φB' ∈ (- π, π) and mR、mGAnd mBIs an integer, m of which is obtainedR、mG、mB；
M is to beR、mG、mBSubstituted into LR＝(λR/2)*mR+φRλR/4π、LG＝(λG/2)*mG+φGλG/4π、LB＝(λB/2)*mB+φBλBL is 4. pi. to obtainR、LGAnd LBAnd averaging the values, wherein the obtained average value is the height of the measured point.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
1. according to the multi-wavelength and phase-shift interference double-synchronization surface real-time measurement method and system, the interference module, the light splitting phase-shift module and the CCD imaging module are adopted to obtain the four-channel synchronous phase-shift interference pattern, the synchronous phase-shift interference pattern collected by the CCD imaging module is subjected to parameter calibration before measurement, the precision of the measured phase of the measured sample is improved, and therefore the surface instantaneous structure of the measured sample is obtained and the accuracy of the measurement result is improved.
2. The invention relates to a multi-wavelength and phase-shift interference double-synchronous surface real-time measurement method and a system, which are characterized in that the phase shift delta gamma introduced to a 1 st channel1Presetting PV value error range, and when the PV value error range exceeds the preset error, determining delta gamma1Removed from the measured phase values, thereby further reducing the error in the measured phase.
3. The invention relates to a multi-wavelength and phase shift interference double-synchronous surface real-time measurement method and a system thereof, which are characterized in that a multi-wavelength light source is introduced for measurement, an equivalent wavelength is introduced, and an integer periodic series of the equivalent wavelength is further obtained by finite element calculation, so that the integer periodic series of the multi-wavelength is obtained by reverse calculation, the measurement range is effectively expanded to the length of half wavelength of the integer equivalent wavelength by utilizing the height information of a sample to be measured of the integer periodic series of the multi-wavelength, and the measurement resolution and the measurement precision of a single wavelength are kept.
Drawings
FIG. 1 is a schematic structural diagram of a multi-wavelength and phase-shift interference double-synchronization surface real-time measurement system according to an embodiment of the present invention;
in all the figures, the same reference numerals denote the same features, in particular: the device comprises a 1-light source, a 2-collimating lens group, a 3-light collecting lens, a 4-small hole, a 5-collimating lens, a 6-polarizer, a 7-depolarization beam splitter prism, an 8-Michelson interference module, a 9-objective lens, a 10-polarization beam splitter prism, an 11-reference plane mirror, a 12-sample to be tested, a 13-dispersion phase shift module, a 14-achromatic 1/4 wave plate, a 15-rectangular prism, a 16-analyzer array, a 17-achromatic lens and an 18-color CCD imaging module.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other. The present invention will be described in further detail with reference to specific embodiments.
Fig. 1 is a schematic structural diagram of a multi-wavelength and phase-shift interference double-synchronization surface real-time measurement system according to an embodiment of the present invention. As shown in fig. 1, the multi-wavelength and phase-shift interference double-synchronization surface real-time measurement system includes a light source 1, a collimating lens group 2 (a condenser lens 3, a pinhole 4, a collimator lens 5), a polarizer 6, a depolarizing beam splitter 7, a michelson interference module 8 (an objective lens 9, a polarizing beam splitter 10, a reference plane mirror 11, a sample to be measured 12), a beam splitting phase shift module 13 (an achromatic 1/4 wave plate 14, a depolarizing beam splitter 7, a rectangular prism 15, an analyzer array 16), an achromatic lens 17, and a color CCD imaging module 18, in this embodiment, the light source is a color light source, light generated from the light source 1 is collected by the condenser lens 3, passes through the pinhole 4 and the collimator lens 5 to obtain collimated light, enters the polarizer 6, passes through the polarizer 6 to become collimated linearly polarized light, and is reflected by the depolarizing beam splitter 7 to enter the michelson interference, the Michelson interference module 8 comprises an objective lens 9, a polarization beam splitter prism 10, a reference plane mirror 11 and a sample piece to be measured 12, wherein polarized light passing through the objective lens 9 is divided into two parts by the polarization beam splitter prism 10; wherein the reflected s component is reflected by the reference flat mirror 11 as reference light; the transmitted p-component is reflected by the surface of the sample 12 to be measured to obtain the measured surface topography and structure information thereof, and becomes the measurement light. The two reflected lights converge on the splitting plane of the polarization splitting prism 10, pass through the objective lens 9 and the depolarization splitting prism 7, enter the splitting phase shift module 13, and generate synchronous phase shift interference. When a multicolor light source (such as an RGB combined light source or a white light source) is adopted for illumination and a color camera is used for interference pattern acquisition, synchronous interference patterns of R, G, B three wave bands can be obtained simultaneously through channel decomposition of the color camera, and double synchronization of multi-wavelength and phase-shift interference is realized. The multi-wavelength interference technology can effectively expand the measuring range of single-wavelength phase shift interference, the four-channel synchronous phase shift interference technology can realize real-time measurement, and the synchronous realization of the two can form a large-range real-time interference system.
The spectral phase shift module 13 is composed of an achromatic 1/4 wave plate 14, 3 broadband depolarizing beam splitters 7, 3 rectangular prisms 15, and an analyzer array 16. One broadband depolarization beam splitting prism and one right-angle prism are combined to form one beam splitting and splitting module. The reference and measurement light first pass through achromatic 1/4 wave plate 14, forming circularly polarized light of opposite handedness. Then, the light sequentially passes through the 1 one-to-two light splitting module and the 2 one-to-two light splitting module to become parallel and symmetrical four-path light. The four paths of light then pass through analyzer arrays with polarization directions of 0, pi/4, pi/2 and 3 pi/4 respectively to realize that the phase shifts generated on the four paths of light signals are 0, pi/2, pi and 3 pi/2 respectively, and finally four interference patterns with different phase shift amounts are formed. The interference pattern is imaged on an imaging target surface of a CCD imaging module 18 through an achromatic lens 17, a synchronous phase-shifting interference pattern is obtained by a computer, and the instantaneous morphology and structure of the surface are obtained through computer analysis processing and phase reconstruction.
The multi-wavelength and phase shift interference double-synchronous surface real-time measuring system has the following measuring principle:
according to the principle of polarized light phase-shift interference, the measuring light and the reference light which are respectively incident to the measuring system areAndwherein A iso(x, y) represents the amplitude of the measuring light, Ar(x, y) represents the reference light amplitude,in order to measure the phase of the light,the phases of the reference light are perpendicular in their polarization direction.
If the included angle between the fast axis of the 1/4 wave plate and the x-axis is pi/4, and the included angle between the polarization direction of the light transmitted through the analyzer and the x-axis is β, the distribution of the interference light intensity is:
i (x, y) represents the interference pattern finally acquired by the camera,is the phase to be determined.
It is known that where the analyzer performs a phase modulation, a fixed phase shift 2 β can be introduced between the measurement light and the reference light when β changes, β depending on the design of the phase shift cellThe four paths of interference phase shifts are respectively 0, pi/2, pi and 3 pi/2 after being sequentially 0, pi/4, pi/2 and 3 pi/4. Setting:Io(x, y) and Ir(x, y) represents the intensity of the measuring light and the intensity of the reference light, respectively, and the expression of the four-path interference signal is (for convenience of expression, the coordinates (x, y) in the formula are omitted, and the same is used below):
the phase distribution to be measured is obtained according to the four-step phase shift method as follows:
the distribution of the phase reflects the instantaneous surface morphology and structure of the measured sample, and if the obtained interference phase range is within a half wavelength, the relationship between the surface height information and the phase distribution of the measured sample is shown as the following formula:
wherein z (x, y) is height information of the appearance of the measured surface, and lambda is the wavelength of light wave. When the phase wrapping range exceeds half wavelength, the phase needs to be unwrapped, and the obtained unwrapped phase phi (x, y) is obtained in the formula (4)Instead of phi (x, y), the range of height values obtained by this method is (-lambda/4, lambda/4).
However, the above calculation is only for an ideal system, i.e. the orthogonal measuring light and reference light are uniformly distributed into four channels, and the phase shift introduced by the four channels is exactly pi/2 apart from each other, but in practical cases, the distribution of the measuring light and reference light in the four channels is not uniform, and the phase shift introduced by the four channels is not exactly pi/2 apart, so the actual interference light intensity is expressed as:
in the formula IoiAnd Iri(i 1-4) represents the respective measured light intensity and reference light intensity of the four channels, respectively, and Δ γ1～Δγ4Respectively, represent the amount of phase shift actually introduced by the four channels.
In the above formula of interference light intensity, only I1～I4Is a known amount, Ioi、Iri、Δγi(i is 1 to 4) andare all unknown quantities. If the unknowns are independent of each other, it is obviously not possible to find the phase to be measured. However, for practical systems, after both the structure and the device have been determined, it is determined for the measurement light Ioi(I1-4) and a reference beam IriThe distribution of (I-1-4) should be fixed, i.e. the measurement light Ioi(i＝1～4) And reference light IriAnd (i is 1-4) in a fixed proportional relation. The specific ratio can be obtained by respectively measuring the reference light intensity and the measured light intensity, the calculated proportionality coefficient can be stored as the inherent parameter of the system, and only direct calling is needed for each measurement. Order to
Ir4:Ir3:Ir2:Ir1＝kr3:kr2:kr1:1
Io4:Io3:Io2:Io1＝ko3:ko2:ko1:1
kr1,kr2,kr3Respectively representing the ratio of the reference light intensity collected by the second, third and fourth channels of the CCD imaging module to the reference light intensity collected by the first channel of the CCD imaging module, ko1,ko2,ko3Respectively representing the ratio of the measured light intensity collected by the second channel, the third channel and the fourth channel of the CCD imaging module to the measured light intensity collected by the first channel of the CCD imaging module.
Reissue to orderΔγ21＝Δγ2-Δγ1,Δγ31＝Δγ3-Δγ1,Δγ41＝Δγ4-Δγ1，Representing the sum of the phase to be measured and the amount of phase shift introduced by the first channel, DeltaGamma21～Δγ41Respectively representing the difference between the phase shift introduced by the second, third and fourth channels and the phase shift introduced by the first channel, which can be called as relative phase shift, then the corresponding actual interference light intensity equation becomes,
in fixed systems by Delta Gamma21～Δγ41Also constant, or solved in advance and stored as a parameter intrinsic to the system. The specific mode is as follows:
phase-shifted interference signals for any one channel:
the reference mirror or the measured piece is driven by the piezoelectric ceramics to move at a constant step pitch (for example, delta h is 10nm), a series of interference light intensity graphs are synchronously acquired, and the equal-phase-shift interval of the position of each pixel point (x, y) in a view field can be obtainedData of variations in intensity of interference, i.e.
InAnd (x, y) represents the interference light intensity detected by a certain pixel point when the piezoelectric ceramic drives the reference mirror or the measured sample to move the nth step.
Assuming λ is 620nm, the phase shift interval introduced by each step of moving the piezoelectric ceramic is as followsAfter moving about 31 steps, the interference light intensity of the pixel point changes for a period, and the 31 light intensity data points of the pixel point are subjected to Fourier fitting by utilizing matlab, so that the initial phase of a fitting curve can be obtained, namely the phase difference corresponding to the initial height informationPhase difference Δ γ caused by sum optical path structureiThe sum of (x, y);
order toRepresenting the initial phase distribution of the ith optical path obtained by fitting
Wherein, Δγ21(x,y)～Δγ41(x, y) represents the difference between the amount of phase shift introduced by the 2 nd, 3 rd and 4 th channels and the amount of phase shift introduced by the first channel, respectively.
And calculating all pixel points on the whole surface in the whole view field of each channel to obtain a real phase difference value distribution value. Thus, the actual system of interference equations is further expressed as:
further obtaining:
wherein,
A＝(kr1ko2-kr2ko1)I1-(ko2-kr2)I2+(ko1-kr1)I3
B＝(kr1ko3-kr3ko1)I1-(ko3-kr3)I2+(ko1-kr1)I4
note that, here, it is found thatThat is, the final productIs to find the phaseAnd the amount of phase shift introduced by the first channel (in fact, as can be seen from the derivation of the formula, the first channel here can be any of the 4 channels). If Δ γ1Is uniform over the measurement field of view, in general Δ γ1(even. DELTA. gamma.)2～4) Is uniform over the entire field of view of the interferogram, the degree of uniformity being judged using the PV value. A threshold value delta (> 0) can be set ifThen can be directly handledAs a phase distribution of the sample surface, byObtaining the height information of the surface of the sample; otherwise, the slave is also requiredSubtracting the obtained data to obtain the phase distribution of the real ground surface, wherein the relative height information of the sample surface is
As a preferred embodiment of the present invention, in order to expand the measuring range of the large-range high-precision surface real-time measuring system based on the above dual synchronization of multi-wavelength and phase shift interference, specifically, the method includes:
for the color interferogram obtained by the illumination of the color light source and the collection of the color CCD, since R, G, B interferograms of three components can be obtained by color channel decomposition, the interference phases phi of the three colors red, green and blue can be obtained based on the phase calculation process (the calibration process is performed three times, corresponding to R, G, B components obtained by the color interferogram decomposition, respectively)R，φG，φBCalculating the equivalent wavelength λ of red and green lightsRGAnd green-blue equivalent wavelength lambdaGBCorresponding equivalent phase phiRG＝φR-φGAnd phiGB＝φG-φB；
mRG、mGBRespectively an integer periodic series of two equivalent wavelength phases satisfying mRG≥mGBThe equation (lambda) is obtained by a finite element method under the condition that the equation is more than or equal to 0RG/2)*mRG+φRGλRG/4π＝(λGB/2)*mGB+φGBλGBM in 4 piRGAnd mGBWill be m of the minimum solutionRGSubstituted L ═ λRG/2)*mRG+φRGλRGA value of/4 pi to L;
substituting L into equation L ═ (λ)R/2)*mR+φ'RλR/4π、L＝(λG/2)*mG+φG'λG(λ) 4 π and L ═ LB/2)*mB+φB'λBPhi of/4 pi, hereR'、φG' and phiB' defining phi for the modified interference phases of the three colors red, green and blue, respectivelyR'∈(-π,π)、φG'∈(-π,π)、φB' ∈ (- π, π) and mR、mGAnd mBIs an integer, m of which is obtainedR、mG、mB；
M is to beR、mG、mBSubstituted into LR＝(λR/2)*mR+φRλR/4π、LG＝(λG/2)*mG+φGλG/4π、LB＝(λB/2)*mB+φBλBL is 4. pi. to obtainR、LGAnd LBAnd averaging the values, wherein the obtained average value is the height of the measured point.
Through the three-wavelength interference phase analysis, the measurement range is effectively expanded to an integral number of half-wavelength lengths of equivalent wavelength, and the measurement resolution and precision of single wavelength are reserved. When the method is used for solving the optimal integer period solution, the inaccurate calculation caused by phase shift errors can be avoided, and meanwhile, the threshold for judging whether the optimal solution is in a micron order can be determined, so that the interference level solution is scientific, has high confidence coefficient, and is high in calculation speed.
As a preferred embodiment of the present invention, a real-time surface measurement method with dual synchronization of multi-wavelength and phase-shift interference specifically comprises:
s1, decomposing incident light provided by a light source into mutually orthogonal reference light and measurement light;
s2, decomposing the reference light and the measuring light into four paths, and then synchronously shifting the phases (0, pi/2, pi and 3 pi/2) and interfering with each other;
the method specifically comprises the following steps: the light splitting and phase shifting module is used for splitting, phase shifting and interfering reference light and measuring light, and comprises an achromatic 1/4 wave plate, three light splitting and splitting modules and four polarization analyzers, the light transmission directions of the four polarization analyzers are respectively set to be 0, pi/4, pi/2 and 3 pi/4, the reference light and the measuring light sequentially pass through an achromatic 1/4 wave plate, one light splitting and splitting module, two light splitting and splitting modules sequentially placed on the same plane and four polarization analyzers sequentially placed on the same plane, the light splitting and phase shifting module is used for converting the reference light and the measuring light into circularly polarized light with opposite rotation directions, then parallelly splitting the circularly polarized light into symmetrical four paths of optical signals, and the phase shifts generated on the four paths of optical signals are respectively 0, pi/2, pi and 3 pi/2.
S3, collecting four paths of optical signals after phase-shifting interference to obtain a synchronous phase-shifting interference pattern;
s4, calibrating parameters of the acquired synchronous phase shift interference pattern, which specifically comprises the following steps:
expressing the light intensity of the acquired synchronous phase-shifted interference pattern as
In the formula Io1And Ir1Representing the intensity of the measuring light and the intensity of the reference light of the first channel respectively,representing the measured phase, ko1、ko2、ko3Respectively representing the ratio of the measured light intensity collected by the second, third and fourth channels to the measured light intensity collected by the first channel, kr1、kr2、kr3Are respectively provided withRepresenting the ratio of the reference light intensity collected by the second, third and fourth channels to the reference light intensity collected by the first channel, Delta gamma21、Δγ31、Δγ41Respectively representing the difference between the phase shift introduced by the second channel, the third channel and the fourth channel and the phase shift introduced by the 1 st channel;
the calibrated parameter values are respectively as follows: k is a radical ofo1、ko2、ko3、kr1、kr2、kr3、Δγ21、Δγ31And [ Delta ] gamma41；
The method specifically comprises the following steps:
phase-shifted interference signals for any one channel:
the reference mirror or the measured piece is driven by the piezoelectric ceramics to move at a constant step pitch (for example, delta h is 10nm), a series of interference light intensity graphs are synchronously acquired, and the equal-phase-shift interval of the position of each pixel point (x, y) in a view field can be obtainedData of variations in intensity of interference, i.e.
InAnd (x, y) represents the interference light intensity detected by a certain pixel point when the piezoelectric ceramic drives the reference mirror or the measured sample to move the nth step.
Assuming λ is 620nm, the phase shift interval introduced by each step of moving the piezoelectric ceramic is as followsAfter moving about 31 steps, the interference light intensity of the pixel point changes for one period, and mat is utilizedlab performs Fourier fitting on the 31 light intensity data points of the pixel point to obtain an initial phase of a fitting curve, namely, the phase difference corresponding to the initial height informationPhase difference Δ γ caused by sum optical path structureiThe sum of (x, y);
order toRepresenting the initial phase distribution of the ith optical path obtained by fitting
Wherein, Δγ21(x,y)～Δγ41(x, y) represents the difference between the amount of phase shift introduced by the 2 nd, 3 rd and 4 th channels and the amount of phase shift introduced by the first channel, respectively.
S5, acquiring the synchronous phase shift interference pattern of the measured sample by utilizing the steps S1-S3, and analyzing and processing the synchronous phase shift interference pattern of the measured sample by utilizing the calibrated parameter value to obtain the measurement phase of the measured sample, thereby obtaining the surface instantaneous structure of the measured sample.
The method specifically comprises the following steps: measuring phaseThe expression of (a) is:
A＝(kr1ko2-kr2ko1)I1-(ko2-kr2)I2+(ko1-kr1)I3
B＝(kr1ko3-kr3ko1)I1-(ko3-kr3)I2+(ko1-kr1)I4
wherein,A. b, a, B, c and d are coefficients;
the obtained surface height information of the sample piece is
Measuring phaseRepresenting the actual phaseThe amount of phase shift Deltay introduced with respect to the first channel1Sum of if Δ γ1Is uniform over the measurement field of view, in general Δ γ1(even. DELTA. gamma.)2～4) Is uniform over the entire field of view of the interferogramThe degree of uniformity can be judged using the PV value. A threshold value delta (> 0) can be set ifThen can be directly handledAs a phase distribution of the sample surface, byObtaining the height information of the surface of the sample; otherwise, the slave is also requiredSubtracting the obtained data to obtain the phase distribution of the real ground surface, wherein the relative height information of the sample surface is
Obtaining interference phase phi of red, green and blue colors by using color LED as light sourceR，φG，φB(the calibration process needs to be executed three times and respectively corresponds to R, G, B three components obtained by decomposing the color interference pattern.) to calculate the equivalent wavelength lambda of the red light and the green lightRGAnd green-blue equivalent wavelength lambdaGBCorresponding equivalent phase phiRG＝φR-φGAnd phiGB＝φG-φB；
mRG、mGBRespectively an integer periodic series of two equivalent wavelength phases satisfying mRG≥mGBThe equation (lambda) is obtained by a finite element method under the condition that the equation is more than or equal to 0RG/2)*mRG+φRGλRG/4π＝(λGB/2)*mGB+φGBλGBM in 4 piRGAnd mGBWill be m of the minimum solutionRGSubstituted L ═ λRG/2)*mRG+φRGλRGA value of/4 pi to L;
substituting L into etcFormula L ═ λR/2)*mR+φ'RλR/4π、L＝(λG/2)*mG+φG'λG(λ) 4 π and L ═ LB/2)*mB+φB'λBPhi of/4 pi, hereR'、φG' and phiB' defining phi for the modified interference phases of the three colors red, green and blue, respectivelyR'∈(-π,π)、φG'∈(-π,π)、φB' ∈ (- π, π) and mR、mGAnd mBIs an integer, m of which is obtainedR、mG、mB；
M is to beR、mG、mBSubstituted into LR＝(λR/2)*mR+φRλR/4π、LG＝(λG/2)*mG+φGλG/4π、LB＝(λB/2)*mB+φBλBL is 4. pi. to obtainR、LGAnd LBAnd averaging the values, wherein the obtained average value is the height of the measured point.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A multi-wavelength and phase shift interference double-synchronous surface real-time measurement method is characterized by comprising the following steps:
s1, decomposing incident light provided by a light source into mutually orthogonal reference light and measurement light;
s2, dividing the reference light and the measuring light into four paths, and then synchronously shifting the phases and interfering with each other;
s3, collecting four paths of optical signals after phase-shifting interference to obtain a synchronous phase-shifting interference pattern;
s4, calibrating parameters of the acquired synchronous phase shift interference pattern, which specifically comprises the following steps:
expressing the light intensity of the acquired synchronous phase-shifted interference pattern as
In the formula Io1And Ir1Representing the intensity of the measuring light and the intensity of the reference light of the first channel respectively,representing the measured phase, ko1、ko2、ko3Respectively representing the ratio of the measured light intensity collected by the second, third and fourth channels to the measured light intensity collected by the first channel, kr1、kr2、kr3Respectively representing the ratio of the reference light intensity collected by the second channel, the third channel and the fourth channel to the reference light intensity collected by the first channel, and delta gamma21、Δγ31、Δγ41Respectively representing the difference between the phase shift introduced by the second channel, the third channel and the fourth channel and the phase shift introduced by the 1 st channel;
the calibrated parameter values are respectively as follows: k is a radical ofo1、ko2、ko3、kr1、kr2、kr3、Δγ21、Δγ31And [ Delta ] gamma41；
S5, acquiring four paths of optical signals subjected to light splitting phase shifting interference by utilizing the steps S1-S3 to obtain a synchronous phase shifting interference pattern, and analyzing and processing to obtain a measurement phase of the measured sample so as to obtain a surface instantaneous structure of the measured sample.
2. The real-time surface measurement method with dual synchronization of multi-wavelength and phase shift interference as claimed in claim 1, wherein step S2 utilizes a split phase shift module to split, phase shift and interfere the reference light and the measurement light, wherein the split phase shift module comprises an achromatic 1/4 wave plate, three dichroic modules and four analyzers, wherein the light transmission directions of the four analyzers are respectively set to 0, pi/4, pi/2 and 3 pi/4, the reference light and the measurement light sequentially pass through the achromatic 1/4 wave plate, one dichroic module, two dichroic modules sequentially disposed on the same plane and four analyzers sequentially disposed on the same plane, so as to realize that the reference light and the measurement light are changed into circularly polarized light with opposite rotation directions and are parallelly divided into symmetrical four optical signals, and the phase shifts generated on the four optical signals are respectively 0, pi/2, pi and 3 pi/2.
3. The real-time surface measurement method based on dual synchronization of multi-wavelength and phase-shift interference as claimed in claim 1, wherein the measurement phase is determined by the following stepsThe expression of (a) is:
wherein,A. b, a, B, c and d are coefficients.
4. The real-time surface measurement method based on dual synchronization of multi-wavelength and phase-shift interference as claimed in claim 3, wherein the measurement phase is determined by the following stepsRepresenting the actual phaseThe amount of phase shift Deltay introduced with respect to the first channel1Sum, Δ γ1The value of (A) exceeds a preset error range, and the surface height information of the sample is
5. The real-time surface measurement method based on dual synchronization of multi-wavelength and phase shift interference as claimed in claim 3 or 4, wherein the measurement range extension of the height of the measurement point is realized by using a multi-wavelength light source, specifically:
obtaining interference phase phi of red, green and blue colors by using color LED as light sourceR，φG，φBCalculating the equivalent wavelength λ of red and green lightsRGAnd green-blue equivalent wavelength lambdaGBCorresponding equivalent phase phiRG＝φR-φGAnd phiGB＝φG-φB；
λR、λGAnd λBRed, green and blue wavelengths, respectively; m isR、mGAnd mBInteger periodic series of red, green and blue light wavelength phases, respectively; m isRG、mGBRespectively an integer periodic series of two equivalent wavelength phases satisfying mRG≥mGBThe equation (lambda) is obtained by a finite element method under the condition that the equation is more than or equal to 0RG/2)*mRG+φRGλRG/4π＝(λGB/2)*mGB+φGBλGBM in 4 piRGAnd mGBWill be m of the minimum solutionRGSubstituted L ═ λRG/2)*mRG+φRGλRGObtaining an L value through the pi of/4;
substituting L into equation L ═ (λ)R/2)*mR+φ'RλR/4π、L＝(λG/2)*mG+φG'λG(λ) 4 π and L ═ LB/2)*mB+φB'λBPhi of/4 pi, hereR'、φG' and phiB' defining phi for the modified interference phases of the three colors red, green and blue, respectivelyR'∈(-π,π)、φG'∈(-π,π)、φB' ∈ (- π, π) and mR、mGAnd mBIs an integer, m of which is obtainedR、mG、mB；
M is to beR、mG、mBSubstituted into LR＝(λR/2)*mR+φRλR/4π、LG＝(λG/2)*mG+φGλG/4π、LB＝(λB/2)*mB+φBλBL is 4. pi. to obtainR、LGAnd LBAnd averaging the values, wherein the obtained average value is the height of the measured point.
6. A multi-wavelength and phase-shift interference double-synchronous surface real-time measuring system comprises a light source, an interference module, a light splitting phase shift module and a CCD imaging module, wherein the interference module is used for splitting incident light provided by the light source into mutually orthogonal reference light and measuring light, the light splitting phase shift module is used for splitting the reference light and the measuring light into four paths and then synchronously shifting the phase and interfering the four paths respectively, the CCD imaging module is used for collecting four paths of optical signals after phase-shift interference to obtain a synchronous phase-shift interference pattern and analyzing and processing the synchronous phase to obtain a measuring phase of a measured sample so as to obtain a surface instantaneous structure of the measured sample,
the synchronous phase shift interference pattern collected by the CCD imaging module is subjected to parameter calibration before measurement, and the parameter calibration specifically comprises the following steps:
expressing the light intensity of the synchronous phase-shifted interference pattern as
In the formula Io1And Ir1Respectively representing the intensity of the measuring light and the intensity of the reference light of the first channel of the CCD imaging module,representing the measured phase, ko1、ko2、ko3Respectively representing the ratio of the measured light intensity collected by the second, third and fourth channels of the CCD imaging module to the measured light intensity collected by the first channel of the CCD imaging module, kr1、kr2、kr3Respectively representing parameters collected by the second, third and fourth channels of the CCD imaging moduleThe ratio of the reference intensity to the reference intensity collected by the first channel of the CCD imaging module, Delta gamma21、Δγ31、Δγ41Respectively representing the difference between the phase shift quantity introduced by the second, third and fourth channels of the CCD imaging module and the phase shift quantity introduced by the first channel of the CCD imaging module;
the calibrated parameter values are respectively as follows: k is a radical ofo1、ko2、ko3、kr1、kr2、kr3、Δγ21、Δγ31And [ Delta ] gamma41。
7. The system of claim 6, wherein step S2 is to split, phase shift and interfere the reference light and the measurement light by using a split phase shift module, wherein the split phase shift module comprises an achromatic 1/4 wave plate, three dichroic modules and four analyzers, the light transmission directions of the four analyzers are respectively set to 0, pi/4, pi/2 and 3 pi/4, the reference light and the measurement light sequentially pass through the achromatic 1/4 wave plate, one dichroic module, two dichroic modules sequentially disposed on the same plane and four analyzers sequentially disposed on the same plane, so as to change the reference light and the measurement light into circularly polarized light with opposite rotation directions and to divide the circularly polarized light into symmetrical four optical signals in parallel, and the phase shifts generated for the four optical signals are respectively 0, pi/2, pi and 3 pi/2.
8. The system of claim 6, wherein the measurement phase is synchronized by the dual synchronization of multi-wavelength and phase shift interferometryThe expression of (a) is:
wherein,A. b, a, B, c and d are coefficients.
9. The system of claim 8, wherein the measurement phase is synchronized by the dual synchronization of multi-wavelength and phase shift interferometryRepresenting the actual phaseThe amount of phase shift Deltay introduced with respect to the first channel1Sum, Δ γ1The value of (A) exceeds a preset error range, and the surface height information of the sample is
10. The real-time surface measurement system based on dual synchronization of multi-wavelength and phase shift interference as claimed in claim 8 or 9, wherein the multi-wavelength light source is used to realize the measurement range extension of the height of the measurement point, specifically:
obtaining interference phase phi of red, green and blue colors by using color LED as light sourceR，φG，φBCalculating the equivalent wavelength λ of red and green lightsRGAnd green-blue equivalent wavelength lambdaGBCorresponding equivalent phase phiRG＝φR-φGAnd phiGB＝φG-φB；
λR、λGAnd λBRed, green and blue wavelengths, respectively; m isR、mGAnd mBInteger periodic series of red, green and blue light wavelength phases, respectively; m isRG、mGBRespectively an integer periodic series of two equivalent wavelength phases satisfying mRG≥mGBThe equation (lambda) is obtained by a finite element method under the condition that the equation is more than or equal to 0RG/2)*mRG+φRGλRG/4π＝(λGB/2)*mGB+φGBλGBM in 4 piRGAnd mGBWill be m of the minimum solutionRGSubstituted L ═ λRG/2)*mRG+φRGλRGObtaining an L value through the pi of/4;
substituting L into equation L ═ (λ)R/2)*mR+φ'RλR/4π、L＝(λG/2)*mG+φG'λG(λ) 4 π and L ═ LB/2)*mB+φB'λBPhi of/4 pi, hereR'、φG' and phiB' defining phi for the modified interference phases of the three colors red, green and blue, respectivelyR'∈(-π,π)、φG'∈(-π,π)、φB' ∈ (- π, π) and mR、mGAnd mBIs an integer, m of which is obtainedR、mG、mB；
M is to beR、mG、mBSubstituted into LR＝(λR/2)*mR+φRλR/4π、LG＝(λG/2)*mG+φGλG/4π、LB＝(λB/2)*mB+φBλBL is 4. pi. to obtainR、LGAnd LBAnd averaging the values, wherein the obtained average value is the height of the measured point.
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