CN104748671A - Nonlinear error correcting method and device for angular displacement type single-frequency laser interferometer - Google Patents

Abstract

The invention provides a nonlinear error correcting method and device for an angular displacement type single-frequency laser interferometer, and belongs to the technical field of laser measurement. The method comprises the step of performing separating measurement for two-way measurement light beam strength through a light switch; extracting nonlinear error parameters in the related light signals; correcting DC deviation error and non-uniform amplitude of an orthogonal signal and other errors. With the adoption of the method and the device, the technical effects of extracting the nonlinear error parameters in the angular displacement type single-frequency laser interferometer as startup and quickly correcting the nonlinear error in the angular displacement type single-frequency laser interferometer on real time can be achieved.

Description

Angular displacement single frequency laser interferometer nonlinearity erron modification method and device

Technical field

The invention belongs to laser measuring technique field, relate generally to a kind of angular displacement single frequency laser interferometer nonlinearity erron modification method and device.

Background technology

Along with the development of ultra precise measurement technology, Fast Ultra-Precision Measurement obtains to be paid close attention to and research widely, in fields such as accurate and ultraprecise machining, microelectronics equipment, nanometer technology industrial equipment and defence equipments, the monitoring of micrometric displacement parts, mobile platform and litho machine angle variable quantity becomes more and more important.Angular displacement laser interferometer, and can relative pivot angle in kinetic measurement campaign because higher measuring accuracy, has become the conventional means of modern angular displacement precision measurement.Angular displacement laser interferometer is actually the linear displacement laser interferometer linear displacement laser interferometer on monochromatic light road being modified into multi-pass, by measuring two the light path relative optical path changes obtained and then the variable quantity obtaining the target anglec of rotation.Therefore, angular displacement laser interferometer is the derivative schemes that linear displacement laser interferometer is measured, and its measuring accuracy depends on the measuring accuracy of linear displacement laser interferometer.Compared to double frequency linear displacement laser interferometer, displacement of the lines single frequency laser interferometer has that structure is simple, processing of circuit easily, to multiple advantages such as the requirement of environment are lower, its measuring speed is unrestricted in principle, because of but the Main Means in high speed linear measure longimetry field.But nonlinearity erron is the key issue of restraining line displacement single frequency laser interferometer precision always.

1981, Heydemann proposes to utilize the ellipse fitting method of least square method obtain the nonlinearity erron parameter in interference signal and then revise (P.L.M.Heydemann to nonlinearity erron, Determination and correction ofquadrature fringe measurement errors in interferometers.Appl.Opt.1981,20:3382-3384); The graduate Dai of German federal physical technique proposes to utilize ADC detect the peak-to-valley value extract real-time nonlinearity erron parameter of each channel signal of four-way displacement of the lines single frequency laser interferometer and make correction (Dai, G.-L. to it; Pohlenz, F.; Danzebrink, H.-U.; Hasche, K.; Wilkening, G.Improving the performance of interferometers in metrological scanningprobe microscopes.Meas.Sci.Technol.2004,15:444-450), real-time Heydemann modification method is called.But these methods above-mentioned generally all need target mirror displacement to reach λ/2 just can make signal nonlinearity erron parameter and identifying more accurately, when target mirror displacement is less than λ/2, the data discrete recorded is higher, cannot make accurate identification to nonlinearity erron parameter, the effect thus revised is bad.

2012, Rerucha proposes the method by modulated laser light source frequency, realize identification (the Rerucha S of single frequency laser interferometer nonlinearity erron parameter under quasistatic, Buchta Z, Sarbort M, et al.Detection of interference phase bydigital computation of quadrature signals in homodyne laser interferometry.Sensors, 2012,12 (10): 14095-14112), but this method needs to add and can modulate LASER Light Source, and identification needs the regular hour.

Summary of the invention

When two target mirror displacement of the lines differences are less than λ/2 for above-mentioned Heydemann modification method cannot accurately identify nonlinearity erron parameter and revise, and modulation of source method identification nonlinearity erron needs the problem can modulating LASER Light Source, the present invention proposes and have developed a kind of angular displacement single frequency laser interferometer nonlinearity erron modification method based on photoswitch and device, reaches and can realize angular displacement single frequency laser interferometer start i.e. acquisition nonlinearity erron parameter and the object making correction when angle displacement measurement.

Object of the present invention is achieved through the following technical solutions:

A kind of angular displacement single frequency laser interferometer nonlinearity erron antidote, the method step is as follows:

(1) opening angle displacement laser interferometer, is positioned at the photoswitch S on two-way measuring beam _m1, S _m2switch to open mode simultaneously; Frequency stabilized laser Emission Lasers, be polarized Amici prism to be separated, folded light beam is parallel to each other with transmitted light beam after corner cube mirror reflection, two-way light beam is all successively by quarter wave plate, photoswitch, return after catoptron reflection again, again by after quarter wave plate, polarization state by after half-twist, incident polarization Amici prism; Be separated into by four-way detection system the coherent light that phase place differs pi/2 successively from the orthogonal level of polarization splitting prism outgoing and the polarized light of vertical polarization;

(2) S is made _m1switch to open mode, simultaneously S _m2switch to closed condition; This light switch S _m2corresponding measuring beam is blocked, photoswitch S _m1corresponding measuring beam irradiates No. four detectors normal through original optical path and produces photo-signal, stores the strength signal I of No. four detectors _m11, I _m12, I _m13, I _m14;

(3) S is made _m2switch to open mode, simultaneously S _m1switch to closed condition; This light switch S _m1corresponding measuring beam is blocked, photoswitch S _m2corresponding measuring beam irradiates No. four detectors normal through original optical path and produces photo-signal, stores the strength signal I of No. four detectors _m21, I _m22, I _m23, I _m24;

(4) two photoswitch S are made _m1, S _m2again switch to open mode, now two-way measuring beam all can normal through photoswitch S simultaneously _m1, S _m2, angular displacement single frequency laser interferometer normally works, and completes the measurement to target angle displacement; Signal now on No. four detectors is the superposition of direct current signal and AC signal, the coherent signal I that storage detector exports ₁, I ₂, I ₃, I ₄;

(5) following computing is done to the strength signal of No. four detectors stored and the coherent signal of output

$I_x=\frac{(I_1-I_{m11}-I_{m21})-(I_3-I_{m13}-I_{m23})}{2(\sqrt{I_{m11}{I}_{m21}}+\sqrt{I_{m13}{I}_{m23}})}$

$I_y=\frac{(I_2-I_{m12}-I_{m22})-(I_4-I_{m14}-I_{m24})}{2(\sqrt{I_{m12}{I}_{m22}}+\sqrt{I_{m14}{I}_{m24}})}$

Remove the DC component of each passage in four-way angular displacement single frequency laser interferometer, correct Amplitude Ration, obtain without direct current biasing error etc. amplitude orthogonal signal; Laser instrument Output of laser wavelength λ represents, the spacing of two-way measuring beam in target is L _d, and then the value of angular displacement can trying to achieve measured target is:

$\mathrm{\Δ\α}=\arctan \left[\frac{\arctan (I_x/I_y)\mathrm{\λ}}{4\mathrm{\π}{L}_d}\right].$

A kind of angular displacement single frequency laser interferometer nonlinearity erron correcting device, the emitting light path of frequency stabilized laser (1) configures polarization splitting prism A, quarter wave plate B successively and measures catoptron A, described quarter wave plate B is positioned at x, y plane, and it is coaxial with polarization splitting prism A, quarter wave plate B quick shaft direction and y-axis are at 45 ° counterclockwise, and described measurement catoptron A is parallel with quarter wave plate B; The reflected light path of described polarization splitting prism A configures quarter wave plate A and corner cube mirror successively, and described quarter wave plate A is positioned at y, z-plane, and coaxial with polarization splitting prism A, and quarter wave plate A quick shaft direction and y-axis are at 45 ° clockwise; Allocating and measuring catoptron B on the reflected light path of described corner cube mirror, described measurement catoptron B and measurement catoptron A are configured on measured target abreast; 1/2 wave plate, depolarization Amici prism and polarization splitting prism B is configured successively at the opposite side portion place being positioned at corner cube mirror of described polarization splitting prism A, described 1/2 wave plate is positioned at y, z-plane, and coaxial with polarization splitting prism A, 1/2 wave plate quick shaft direction becomes 22.5 ° clockwise with y-axis; Described polarization splitting prism B and depolarization Amici prism are parallel to each other and coaxial, photodetector A and photodetector device B respectively on the transmitted light path and reflected light path of described polarization splitting prism B; The reflected light path of described depolarization Amici prism once configures quarter wave plate C and polarization splitting prism C, and described quarter wave plate C is positioned at x, y plane, and coaxial with depolarization Amici prism, and quarter wave plate C quick shaft direction and y-axis are at 45 ° counterclockwise; Photodetector C and photodetector D is configured on polarization splitting prism C transmitted light path and reflected light path respectively; The bottom surface of described polarization splitting prism A, B, C, depolarization Amici prism and corner cube mirror is all positioned at x, z-plane, and coplanar; Photoswitch A and measurement catoptron B is parallel to each other and is configured in corner cube mirror coaxially and measures between catoptron B; Photoswitch B and measurement catoptron A is parallel to each other and is configured in quarter wave plate B coaxially and measures between catoptron A.

The present invention has following characteristics and good result:

(1) compared to Heydemann modification method, owing to only needing switches light on off state can obtain nonlinearity erron parameter, thus start can be extracted the nonlinearity erron parameter in the measurement of angular displacement single frequency laser interferometer and then be revised nonlinearity erron.

(2) extracting the error correcting method of nonlinearity erron parameter compared to modulated light source, without the need to modulating LASER Light Source, reducing the requirement of angular displacement single frequency laser interferometer to light source.

(3) due to the parameter of nonlinearity erron can be extracted in advance, and then rebuild the orthogonal signal of angular displacement single frequency laser interferometer, run without the need to doing complex mathematical again to the data obtained, reduce the requirement of system to hardware.

Accompanying drawing explanation

Fig. 1 is angular displacement single frequency laser interferometer nonlinearity erron correcting device General allocation structure schematic diagram;

In figure, piece number illustrates: 1, frequency stabilized laser, 2, polarization splitting prism A, 3, quarter wave plate A, 4, corner cube mirror, 5 photoswitch A, 6, measure catoptron B, 7, measured target, 8, measure catoptron A, 9, photoswitch B, 10, quarter wave plate B, 11, 1/2 wave plate, 12, depolarization Amici prism, 13, polarization splitting prism B, 14, photodetector A, 15, photodetector B, 16, quarter wave plate C, 17, polarization splitting prism C, 18, photodetector C, 19, photodetector D.

Embodiment

Below in conjunction with accompanying drawing, the embodiment of the present invention is described in detail.

A kind of angular displacement single frequency laser interferometer nonlinearity erron correcting device, the emitting light path of frequency stabilized laser 1 configures polarization splitting prism A2, quarter wave plate B10 successively and measures catoptron A8, described quarter wave plate B10 is positioned at x, y plane, and it is coaxial with polarization splitting prism A2, quarter wave plate B10 quick shaft direction and y-axis are at 45 ° counterclockwise, and described measurement catoptron A8 is parallel with quarter wave plate B10; The reflected light path of described polarization splitting prism A2 configures quarter wave plate A3 and corner cube mirror 4 successively, and described quarter wave plate A3 is positioned at y, z-plane, and coaxial with polarization splitting prism A2, and quarter wave plate A3 quick shaft direction and y-axis are at 45 ° clockwise; Allocating and measuring catoptron B6 on the reflected light path of described corner cube mirror 4, described measurement catoptron B6 and measurement catoptron A8 are configured on measured target 7 abreast; 1/2 wave plate 11, depolarization Amici prism 12 and polarization splitting prism B13 is configured successively at the opposite side portion place being positioned at corner cube mirror 4 of described polarization splitting prism A2, described 1/2 wave plate 11 is positioned at y, z-plane, and coaxial with polarization splitting prism A2,1/2 wave plate 11 quick shaft direction becomes 22.5 ° clockwise with y-axis; Described polarization splitting prism B13 and depolarization Amici prism 12 are parallel to each other and coaxial, photodetector A14 and photodetector device B15 respectively on the transmitted light path and reflected light path of described polarization splitting prism B13; The reflected light path of described depolarization Amici prism 12 once configures quarter wave plate C16 and polarization splitting prism C17, described quarter wave plate C16 is positioned at x, y plane, and coaxial with depolarization Amici prism 12, quarter wave plate C16 quick shaft direction and y-axis are at 45 ° counterclockwise; Photodetector C18 and photodetector D19 is configured on polarization splitting prism C17 transmitted light path and reflected light path respectively; Described polarization splitting prism A2, B13, C17, depolarization Amici prism 12 are all positioned at x, z-plane with the bottom surface of corner cube mirror 4, and coplanar; It is characterized in that: photoswitch A5 and measurement catoptron B6 is parallel to each other and is configured in corner cube mirror 4 coaxially and measures between catoptron B6; Photoswitch B9 and measurement catoptron A8 is parallel to each other and is configured in quarter wave plate B10 coaxially and measures between catoptron A8; Wherein, the position of 1/2 wave plate 11 and quarter wave plate C16 can exchange, and quick shaft direction is constant; Described measurement catoptron A8 and measurement catoptron B6 comprises level crossing, prism of corner cube.

A kind of angular displacement single frequency laser interferometer nonlinearity erron modification method, the method step is as follows:

(1) opening angle displacement laser interferometer, makes it normally to work.During interference, the Electric Field Distribution of two bundle laser can be expressed as follows:

(2) S is made _m1switch to open mode, simultaneously S _m2switch to closed condition; This light switch S _m2corresponding measuring beam is blocked, photoswitch S _m1corresponding measuring beam irradiates No. four detectors normal through original optical path and produces photo-signal, only has S in the signal now on No. four detectors _m1the signal of corresponding measuring beam, for:

In formula, α is detector photoelectric transformation efficiency; K represents probe access, k=1, and 2,3,4; Cosine square be 1/2 at the mean value in laser optical frequency cycle, then final output photoelectric stream can be expressed as

$I_{m1k}=\frac{1}{2}\mathrm{\α}{E}_{m10k}^2;$

(3) S is made _m1switch to closed condition, simultaneously S _m2switch to open mode; This light switch S _m1corresponding measuring beam is blocked, photoswitch S _m2corresponding measuring beam irradiates No. four detectors normal through original optical path and produces photo-signal, only has S in the signal now on No. four detectors _m2the signal of corresponding measuring beam, for:

$I_{m2k}=\frac{1}{2}\mathrm{\α}{E}_{m20k}^2;$

(4) two photoswitch S are made _m1, S _m2again switch to open mode, now two-way measuring beam all can normal through photoswitch S simultaneously _m1, S _m2, angular displacement single frequency laser interferometer normally works, and completes the measurement to target angle displacement; Signal now on No. four detectors is the coherent signal of two-way measuring beam, and the built-up radiation field on detector photosensitive unit is:

Light detecting device is all square-law detector, and the photocurrent of the output of detector is:

In formula, first and second is equivalent to the DC component that detecting device exports; Section 3 be two-way measuring beam with frequency item, its mean value is zero; Section 4 is difference frequency term, and two light frequencies are equal, and thus final output photoelectric stream can be expressed as:

The AC signal of Section 3 in formula needed for linear displacement laser interferometer measurement, detector photocurrent expression formula in the step of contrast (1) (2) can be found out, can be obtained the DC component in final coherent light signal by control optical switch status, the AC signal that final each road detector obtains is:

AC signal after normalization is:

(5) final quadrature signal does following computing

$I_x=\frac{(I_1-I_{m11}-I_{m21})-(I_3-I_{m13}-I_{m23})}{2(\sqrt{I_{m11}{I}_{m21}}+\sqrt{I_{m13}{I}_{m23}})}$

$I_y=\frac{(I_2-I_{m12}-I_{m22})-(I_4-I_{m14}-I_{m24})}{2(\sqrt{I_{m12}{I}_{m22}}+\sqrt{I_{m14}{I}_{m24}})};$

Then can remove the DC component of each passage in four-way angular displacement single frequency laser interferometer, obtain without direct current biasing error etc. amplitude orthogonal signal; Laser instrument Output of laser wavelength λ represents, the spacing of two-way measuring beam in target is L _d, and then the value of angular displacement can trying to achieve measured target is:

$\mathrm{\Δ\α}=\arctan \left[\frac{\arctan (I_x/I_y)\mathrm{\λ}}{4\mathrm{\π}{L}_d}\right].$

Claims (4)

1. an angular displacement single frequency laser interferometer nonlinearity erron modification method, is characterized in that: described method step is as follows:

(1) opening angle displacement laser interferometer, is positioned at the photoswitch S on two-way measuring beam _m1, S _m2switch to open mode simultaneously; Frequency stabilized laser Emission Lasers, be polarized Amici prism to be separated, folded light beam is parallel to each other with transmitted light beam after corner cube mirror reflection, two-way light beam is all successively by quarter wave plate, photoswitch, return after catoptron reflection again, again by after quarter wave plate, polarization state by after half-twist, incident polarization Amici prism; Be separated into by four-way detection system the coherent light that phase place differs pi/2 successively from the orthogonal level of polarization splitting prism outgoing and the polarized light of vertical polarization;

(2) S is made _m1switch to open mode, simultaneously S _m2switch to closed condition; This light switch S _m2corresponding measuring beam is blocked, photoswitch S _m1corresponding measuring beam irradiates No. four detectors normal through original optical path and produces photo-signal, stores the strength signal I of No. four detectors _m11, I _m12, I _m13, I _m14;

(3) S is made _m2switch to open mode, simultaneously S _m1switch to closed condition; This light switch S _m1corresponding measuring beam is blocked, photoswitch S _m2corresponding measuring beam irradiates No. four detectors normal through original optical path and produces photo-signal, stores the strength signal I of No. four detectors _m21, I _m22, I _m23, I _m24;

(4) two photoswitch S are made _m1, S _m2again switch to open mode, now two-way measuring beam all can normal through photoswitch S simultaneously _m1, S _m2, angular displacement single frequency laser interferometer normally works, and completes the measurement to target angle displacement; Signal now on No. four detectors is the superposition of direct current signal and AC signal, the coherent signal I that storage detector exports ₁, I ₂, I ₃, I ₄;

(5) following computing is done to the strength signal of No. four detectors stored and the coherent signal of output

$I_x=\frac{(I_1-I_{m11}-I_{m21})-(I_3-I_{m13}-I_{m23})}{2(\sqrt{I_{m1}{I}_{m21}}+\sqrt{I_{m13}{I}_{m23}})}$

$I_y=\frac{(I_2-I_{m12}-I_{m22})-(I_4-I_{m1}-I_{m24})}{2(\sqrt{I_{m12}{I}_{m22}}+\sqrt{I_{m14}{I}_{m24}})}$

The DC component of each passage in four-way angular displacement single frequency laser interferometer can be removed, correct Amplitude Ration, obtain without direct current biasing error etc. amplitude orthogonal signal; Laser instrument Output of laser wavelength λ represents, air refraction is n, and the spacing of two-way measuring beam in target is L _d, and then the value of angular displacement can trying to achieve measured target is:

$\mathrm{\Δ\α}=\arctan \left[\frac{\arctan (I_x/I_y)\mathrm{\λ}}{4\mathrm{\πn}{L}_d}\right].$

2. an angular displacement single frequency laser interferometer nonlinearity erron correcting device, the emitting light path of frequency stabilized laser (1) configures polarization splitting prism A (2), quarter wave plate B (10) successively and measures catoptron A (8), described quarter wave plate B (10) is positioned at x, y plane, and it is coaxial with polarization splitting prism A (2), quarter wave plate B (10) quick shaft direction and y-axis at 45 ° counterclockwise, described measurement catoptron A (8) is parallel with quarter wave plate B (10); The reflected light path of described polarization splitting prism A (2) configures quarter wave plate A (3) and corner cube mirror (4) successively, described quarter wave plate A (3) is positioned at y, z-plane, and coaxial with polarization splitting prism A (2), quarter wave plate A (3) quick shaft direction and y-axis at 45 ° clockwise; Allocating and measuring catoptron B (6) on the reflected light path of described corner cube mirror (4), described measurement catoptron B (6) and measurement catoptron A (8) are configured on measured target (7) abreast; 1/2 wave plate (11), depolarization Amici prism (12) and polarization splitting prism B (13) is configured successively at the opposite side portion place being positioned at corner cube mirror (4) of described polarization splitting prism A (2), described 1/2 wave plate (11) is positioned at y, z-plane, and coaxial with polarization splitting prism A (2), 1/2 wave plate (11) quick shaft direction becomes 22.5 ° clockwise with y-axis; Described polarization splitting prism B (13) and depolarization Amici prism (12) are parallel to each other and coaxial, photodetector A (14) and photodetector device B (15) respectively on the transmitted light path and reflected light path of described polarization splitting prism B (13); At reflected light path last time configuration quarter wave plate C (16) and the polarization splitting prism C (17) of described depolarization Amici prism (12), described quarter wave plate C (16) is positioned at x, y plane, and coaxial with depolarization Amici prism (12), quarter wave plate C (16) quick shaft direction and y-axis at 45 ° counterclockwise; Photodetector C (18) and photodetector D (19) is configured on polarization splitting prism C (17) transmitted light path and reflected light path respectively; Described polarization splitting prism A, B, C (2,13,17), depolarization Amici prism (12) are all positioned at x, z-plane with the bottom surface of corner cube mirror (4), and coplanar; It is characterized in that: photoswitch A (5) and measurement catoptron B (6) are parallel to each other and are configured in corner cube mirror (4) coaxially and measure between catoptron B (6); Photoswitch B (9) and measurement catoptron A (8) are parallel to each other and are configured in quarter wave plate B (10) coaxially and measure between catoptron A (8).

3. angular displacement single frequency laser interferometer nonlinearity erron correcting device according to claim 2, is characterized in that: the position of described 1/2 wave plate (11) and quarter wave plate C (16) can exchange, and quick shaft direction is constant.

4. angular displacement single frequency laser interferometer nonlinearity erron correcting device according to claim 2, is characterized in that: described measurement catoptron A (8) and measurement catoptron B (6) comprise level crossing, prism of corner cube.