CN102927969B - Detection method of change of micro inclination angle of index mirror in interferometer provided with plane mirror as index mirror - Google Patents

Abstract

The invention discloses a detection method of change of a micro inclination angle of an index mirror in an interferometer provided with a plane mirror as the index mirror. The detection method comprises the following steps of: carrying out direct current removal and normalization on laser interference light intensity data on a transmission surface detector and a reflection surface detector to obtain data, figuring up initial phase differences of THL, RHL, THR and RHR to obtain thetaL and thetaR respectively, on the basis of the THL and the THR, carrying out phase compensation on the RHL and the RHR by utilizing the thetaL and the thetaR, carrying out inverse trigonometric computation on the compensated RHL and RHR alternatively so as to obtain a phase difference deltatheta of a signal, adjusting the phase of the deltatheta so as to obtain a phase theta, and inverting the actual micro inclination angle alpha of the index mirror by utilizing the physical relationship of the inclination angle corresponding to the theta; and figuring up an average value of the inclination angles in the time duration of 1/fmin, solving an inclined center of the micro inclination angle, and measuring the change of the micro inclination angle around the inclined center. According to the detection method provided by the invention, 0.2 micro-radian can be realized, and the measured frequency is 0.1-200 Hz.

Description

Level crossing does the detection method of the micro-change of pitch angle of index glass in the interferometer of index glass

Technical field

The present invention relates to geometric angle measuring technique, be specifically related to a kind of measuring method of micro-change of pitch angle of index glass, be mainly used in the measurement of dynamic micro-change of pitch angle of the interferometer midplane mirror index glass of porch (Porch Swing) structure.

Background technology

Interferometer is tight optical instrument, the interference modulations efficiency of instrument, and interferogram quality, spectrogram quality is very easily subject to the impact of instrument platform vibration or index glass self scanning motion.Adopting in the interferometer of porch structure, due to the resiliency supported that is supported for of index glass, even also carrying out micro-rocking freely when index glass stops, difference slightly when this micro-center of rocking and scanning motion.For obtaining the optimum signal-noise ratio at zero optical path difference place, need to detect micro-center of rocking at zero optical path difference place, and utilize Dynamic Calibration Technique to maintain the oscillation centre that index glass moves in the time of zero optical path difference.In addition, debuging in process of index glass also needs the rolling dynamic characteristic of index glass itself to make and measure assessment.The measurement changing for ultralow frequency, micro-angle is at present subject to measuring method restriction, cannot accurately measure.

Conventionally in the interferometer of porch structure, conventionally introduce a set of reference laser interferometer of light path altogether, tilt with the motion of measuring index glass for the benchmark that sampling interferogram is provided to instrument.Fig. 1 is main optical path and reference laser light path and the detection principle schematic diagram of the interferometer of this structure.Catoptron is introduced in main interference light path with reference to laser, becomes linearly polarized light through polarizer laser signal, and linearly polarized laser is two bundles in beam splitter punishment, and a Reuter crosses after λ/8 slide again and to reflect through index glass that to become its light intensity of circularly polarized light be I _fm, it is I that another bundle maintains its light intensity of original polarization state after index glass reflection _sm, two-beam is finally at beam splitter place and bundle.Have when the polarization beam splitter prism between the component of identical polarization direction and interfere, prism is divided into the interference light of horizontal vertical direction of vibration transmitted light and the reflected light of phasic difference pi/2 simultaneously, finally in the detector face of transmission plane and reflecting surface, be converted into electric signal, then after amplifying by trans-impedance amplifier, carry out signal and process computing.

Transmission plane detector is T face, and reflecting surface detector is R face.Index glass vergence direction two-dimensional quadrature is decomposed, and only taking horizontal direction as example, vertical direction by that analogy.Transmission plane detector horizontal direction is called T _hL, T _hR, reflecting surface detector is R _hL, R _hR.Consider the non-ideal characteristic of each road signal, horizontal direction transmission plane and reflecting surface are respectively surveyed the signal that unit sees and are respectively:

Wherein: for getting real part computing.I=I _fm+ I _smit is the constant light intensity that arrives detector.I _fmfor the light intensity after horizontal glass reflection, I _smfor the light intensity after index glass reflection.I '=I _fmi _smfor the light intensity through ovennodulation.V _oPDrepresent that optical path difference speed is the twice of index glass physical motion speed herein.λ is reference laser wavelength.θ _land θ _rrepresent respectively in orthogonality relation two pairs of detectors because optics error, the detector fixing phase place that interval error, the mechanical rigging error etc. of unit are introduced mutually changes.α represents the physics inclination angle of index glass.Δ θ (α) represents that the dynamic phasing that the inclination of index glass is introduced changes.M (α) represents degree of modulation.

Zero passage detection is filled out impulse method (referring to " Fourier transform spectrometer collimation error detecting technology ", Sun Fang, Dai Zuoxiao etc., infrared and laser engineering, 2006,10, be 92-96) by interference signal DC filtering, amplitude limiting amplifier circuit, is then converted into square-wave signal by zero cross detection circuit, in conjunction with the direction of index glass motion, obtain the one dimension inclination angle of index glass.This detection method precision is higher, but needs the directional information of index glass, however index glass in the time turning to district or index glass in the time of quasi-static micro-rocking, cannot carry out real-time continuous measurement because directional information is indefinite.And detect (referring to " technical research of the high-accuracy dynamic measuring angle on a large scale of space fourier spectrometer " based on instantaneous laser optical power, Huajian, Wei Huan east literary composition etc., photoelectric project, 2009,10,36-10) dynamic measuring angle algorithm, although do not need the directional information of index glass, can realize the continuous detecting at inclination angle in a big way, but measuring accuracy can only reach 0.03 radian, the method also cannot be measured the tiny inclination angle variation of index glass in the time of micro-rocking simultaneously.

Summary of the invention

The invention provides a kind of detection method of the new dynamic micro-change of pitch angle detecting based on phase relation between laser interference signal, exist on the basis of error at the detector signal taking into full account and actual light path, signal is re-established to mathematical model, first the phase error between imperfect measuring-signal is also carried out the phase compensation of signal, then carries out the computing of signal.Introduced the key technique that measuring technique ultimate principle and algorithm are realized, detection technique provided by the invention can realize amplitude precision and reach 0.2 microradian and frequency and be low to moderate the detection of dynamic micro-change of pitch angle of 1Hz simultaneously.

For realizing such object, under above-mentioned I and M (α) are constant condition, in the signal that (1) to (4) is described, I regards DC quantity as, and 2M (α) √ I ' regards the range value A of interchange as.First measure I and A Zhi Ze tetra-road signals are rewritten as:

Be normalized and first remove direct current I for formula (5) to the signal of (8), then divided by amplitude A, and represent each road signal with real part, order (5) to (8) can be transformed to desirable sine and cosine:

Record (9) and (11), the zero-crossing timing interval t of (10) and (12) _l, t _r, calculate θ L=t _l/ T _s, θ _r=t _r/ T _s, R _hLand R _hRwith reference to T _hLwith T _hRcarrying out phase compensation, to obtain (13) (14) as follows:

For (9) (13), (10) (14), choose be worth separately [0.707,0.707] carry out inverse trigonometric function calculating and to result of calculation carry out periodicity adjust obtain with difference be θ _δ+ Δ θ (α), utilizes the physical relation of the corresponding index glass inclination alpha of phase place, detector pitch d, laser wavelength lambda be finally inversed by the tiny inclination angle of the actual single measurement of index glass calculating mean value as the inclination center that is the micro-inclination angle of index glass, test constantly index glass is around dynamic micro-change of pitch angle at inclination center.

Concrete implementation step is as follows:

1) signal normalization.Transmission plane, reflecting surface detector Ge road signal are carried out obtaining interference signal (9) (11) (10) (12) after filtering direct current, amplitude normalization two pairs of the left and right in orthogonality relation of survey record detector T _hLwith R _hLbe signal, the T of formula (9) (11) _hRwith R _hRbe the signal of formula (10) (12), the zero crossing time interval is designated as t _land t _r.

3) initial phase difference of orthogonal signal calculates, and sampling time interval is known as T _s, calculate two pairs of the left and right detector T in orthogonality relation with chronometry _hLwith R _hL, T _hRwith R _hRinitial phase difference be designated as respectively θ _l=t _l/ T _s, θ _r=t _r/ T _s.

4) phase compensation of orthogonal signal.Utilize θ _land θ _r, to carrying out phase compensation in the laser interference signal of orthogonality relation accordingly, (9) compensate (11): [R _hL-T _hLsin (θ _l)]/cos (θ _l) become (13), (10) compensate (12): [R _hR-T _hRsin (θ _r)]/cos (θ _r) become (13), obtain having transmission plane and the reflecting surface signal pair of desirable orthogonal property: (9) and (13); (10) with (14).

5) to orthogonal interference signal value in two couple of [0.707,0.707] the inverse trigonometric function computing that hockets.Acos (R _hL)-acos (T _hL) or acos (R _hR)-acos (R _hL) to the phase difference θ of respective signal.

6) periodicity of carrying out the phase difference θ that inverse trigonometric function computing obtains is entered to horizontal phasing control, change 2 π that deduct that are greater than 2 π for phase place, phase place changes 2 π that will add that are less than-2 π and obtains true phase theta.

7) utilize the physical relation of the corresponding index glass inclination alpha of phase theta, detector pitch d, laser wavelength lambda: be finally inversed by the tiny inclination angle of the actual single measurement of index glass

8) t is recorded in continuous coverage _ninferior single inclination angle value α _i(measurement time t=1/f _min=t _nt _s, f _minfor minimum measurement of dip angle frequency), calculating mean value inclination center taking this numerical value as the micro-inclination angle of index glass, test constantly is around micro-change of pitch angle at inclination center.

Embodiment:

The application of the present invention in laser interferometer, laser instrument adopts semiconductor laser, and its wavelength is 852nm, optical path difference speed V _oPD=1.46cm/s, is simple signal at the laser interference signal that at the uniform velocity section produces, detector pitch d=5.2mm.Sample frequency f _s=100khz, equivalent sampling time interval T _s=10 μ s.T in one-shot measurement process _l=10 μ s and t _r=25 μ s.Equivalence θ _l=0.1rad and θ _r=0.25rad.Utilize θ _land θ _rrespectively the signal of (11) and (13) is compensated, angle inverting is periodically adjusted and is obtained θ, and utilizes inclination center while finally calculating 0.1Hz individual microradian, once dynamically tiny inclination angle changes α=0.8 microradian, and measuring noise is <=0.2 microradian.Successfully realize the detection of the dynamic micro-change of pitch angle that is less than 1 microradian.

Brief description of the drawings

Fig. 1 is interferometer reference path of the present invention, metering circuit schematic diagram.

Fig. 2 is the process flow diagram of measuring method of the present invention.

Claims (1)

1. level crossing does a detection method for the micro-change of pitch angle of index glass in the interferometer of index glass, it is characterized in that comprising the steps:

1) to transmission plane, reflecting surface detector Ge road signal data: the left T of transmission level _hLwith the left R of reflection levels _hL, the right T of transmission level _hRwith the right R of reflection levels _hRcarry out filtering direct current and amplitude normalization, measure the T in orthogonality relation _hLwith R _hL, T _hRwith R _hRthe zero crossing time interval: t _land t _r, wherein t _lfor T _hLwith R _hLthe zero crossing time interval, t _rfor T _hRwith R _hRthe zero crossing time interval;

3) setting sampling time interval is T _s, calculate T _hLwith R _hL, T _hRwith R _hRinitial phase difference be respectively: θ _l=t _l/ T _s, θ _r=t _r/ T _s;

4) with T _hL, T _hRfor benchmark, to R _hL, R _hRutilize respectively θ _land θ _rcarry out phase compensation:

R _HL＝[R _HL-T _HLsin(θ _L)]/cos(θ _L)，

R _HR＝[R _HR-T _HRsin(θ _R)]/cos(θ _R)，

Obtain having the new signal pair of desirable orthogonal property: T _hLwith R _hL, T _hRwith R _hR;

5) to new signal to T _hLwith R _hL, T _hRwith R _hRchoose separately and after the value of [0.707,0.707], hocket inverse trigonometric function computing and be the poor phase difference θ that obtains;

6) periodicity of phase difference θ is entered to horizontal phasing control, change 2 π that deduct that are greater than 2 π for phase place, 2 π that will add that phase place variation is less than-2 π obtain true phase theta;

7) the actual tiny inclination angle of index glass of calculating single measurement d is for measuring T _hLdetector and measurement T _hRthe spacing of detector, the wavelength that λ is reference laser;

8) t is recorded in continuous coverage _ninferior single inclination angle value α _i, Measuring Time is t=1/f _min=t _nt _s, f _minfor minimum measurement of dip angle frequency, calculating mean value:

$\stackrel{\&OverBar;}{\mathrm{\&alpha;}}=\underset{i=0}{\overset{t_n}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_i/t_n$

Inclination center taking this numerical value as the micro-inclination angle of index glass, test constantly is around inclination center micro-change of pitch angle.