CN103234461A - Novel laser interference length measuring method - Google Patents

Abstract

The invention discloses a new laser interference length measurement method belonging to the technical field of optical measurement. Specifically, the measured object is fixedly connected with the photodetector, and by adopting the principle of time series interferometry, using the computer image processing method, the time series intensity map is directly received by the photodetector for a period of time, and stored in the computer; In computer processing, after filtering a series of interference intensities, inverse Fourier transform is performed on them, and dewrapping processing is performed to finally obtain continuous phases, and then phase expansion is performed to obtain displacement information of objects; The object to be measured is fixedly connected to the photodetector, no complex interference optical path is required, no expensive dual-frequency laser generator is required, the optical path is simple, the length value at any time can be measured, the measurement cost is low, and there is dual-frequency laser measurement Strong anti-interference ability and high signal-to-noise ratio.

Description

A kind of new laser interference length-measuring method

Technical field

The invention belongs to field of optical measuring technologies, particularly a kind of new laser interference length-measuring method.Relate in particular to the rectangular method of survey that computer time, sequence image was measured with the laser measurement ohject displacement.

Background technology

Traditional interfere measurement technique has very high measuring accuracy, and under the repressed situation of noise, the repeatability of measurement is also fine, but has the smaller limitation of measurable scope.Address this problem the two kinds of methods that mainly contain: the one, by use long wavelength's infrared light supply, but after adopting infrared light supply, all optical elements of interference system all will change the optical material that adapts to infrared light into, and light path is difficult for building; Method two is the method that adopts dual-wavelength measurement, and the method construct by the light wave fields stack goes out the bigger effective wavelength of wavelength the displacement of measured object is measured.

Traditional double-frequency laser interferometry technology is to be a special kind of skill that the basis is measured with the double-frequency laser interference principle.Two-frequency laser interferometer is by U.S. HP(Hewlett-Packard) company initiative and obtain patent, first is HP5500A, puts on market in 1970.The range of HP5500A is 61m, and precision is 5*10 ⁷, measuring speed is 330mm/s.Behind 5500A, Hewlett-Packard Corporation has also developed 5501A, 5525A, 5526A, 5527A, 5528A and 5529A.The measurement display (5508A) of the 5528A laser measurement system of the early development eighties has adopted micro processor controls, has increased the dirigibility of measuring, and has made things convenient for the user.The highest measurement speed that the 5528A double frequency is measured laser system is 18.3m/min, and linear measurement range is 40m.First two-frequency laser interferometer of China developed jointly by China National Measuring Science Research Inst. and Shaaxi Mechanical Engineering College, identifies by country in April, 1976; Shanghai Optics and Precision Mechanics institute, Chinese Academy of Sciences executed the will fruit in 1993, Wang Runwen has invented a kind of laser system with double frequence, have laser frequency and can carry out tuningly along the beat frequency curve, long working life, manufacturing, installation, debugging and maintenance have the advantage of simplicity and reliability ^[1]The Wu of Inst. of Physics, CAS made peace in 2004, Hou Yanxue, Ma Haiqiang has invented a kind of method and device of measuring low light level light source beat frequency, a kind of method and device of measuring low light level light source beat frequency disclosed, by being divided into two bundles behind the laser attenuation, respectively through two single-photon detectors of input behind the interference filter, secondary conversion device when wherein directly entering behind one tunnel process discriminating amplifier, first through delay line behind another road process discriminating amplifier, secondary conversion device when importing again; Signal with time-to-amplitude conversion instrument output is input into MCA then, through being accumulated in the beat frequency data that can obtain light source under the time domain on the MCA, through obtaining the beat frequency of low light level light source under the frequency domain behind the numerical value Fourier analysis, can not rely under the situation of spectrum analyzer, beat frequency to low light level light source is measured, and is not subjected to the restriction of the response time of detector and prime amplifier again ^[2]The Liu Gang of Tsing-Hua University in 2004, Zhang Shulian, Zhu Jun, Li Yan have invented a kind of Doppler anemometer based on self-mixing interference effect, and this knotmeter is by light source, and measure portion and signal are handled 3 parts and are formed.What its system source was used is two-frequency laser, and the measure portion of self-mixed interference system is that system's exocoel has been placed a quarter-wave plate, the polarization direction of this wave plate quick shaft direction and two polarized lights presss from both sides 45 respectively, light beam is advanced one back and forth at exocoel like this, and its polarization direction will become original vertical direction.When not having Doppler shift, to have only a spectral line on the power spectrum of laser instrument, and when Doppler shift exists, original spectral line on the power spectrum will become two, article two, the direction of the positive and negative representation speed of the difference of the corresponding beat signal of spectral line, the distance between two spectral lines can be converted into the size of speed, and the designed self-mixed interference knotmeter of this invention is that a kind of compact conformation is simple, the cost performance height, and be easy to realize the speed measuring device of velocity reversal identification ^[3]The Wang Ji of AVIC I Beijing Changcheng Institute of Metrology ﹠ Measurement (CIMM) had invented a kind of double-frequency laser interferometry apparatus in 2008.Light source light splitting light path is divided into the laser that two bundles have frequency difference with incident light source, enters the measurement light path part; After measuring catoptron and reference mirror two secondary reflections realization optics times journey, the photelectric receiver that is received signal section by 90 ° of phase differential receives, and has used acousto-optic shift frequency device, and measuring light and reference light are separated from the beginning, avoids frequency alias; Also adopt polarization spectro, polarization reception technique in addition, obtain good contrast, the interference signal that subdivision accuracy is high ^[4]Old of Institutes Of Technology Of Zhejiang in 2009 forever, Zhang Enzheng, Yan Liping, Tao Yang, Zhou Yanjiang has invented a kind of based on the linearity of double frequency principle of interference and the measuring method of position thereof, this measuring method adopts two-frequency laser output to contain the laser beam of orhtogonal linear polarizaiton light through common spectroscope light splitting, the light splitting of depolarization Amici prism, the wollaston prism beam splitting, the right-angle prism reflection, wollaston prism transmission, polarization splitting prism light splitting, the analyzer beat frequency finally obtains embodying one tunnel reference signal and the two-way measuring-signal of change in optical path length.This measuring method has been utilized dichroism and the polarization characteristic of optical device, formed based on the double light path of difference interference principle and measured structure, measure when having realized linearity and position thereof by the optical path difference of measuring double light path, have the measuring accuracy of nano level linearity and position thereof ^[5]The Huo Yu of Tsing-Hua University crystalline substance in 2010, Zhang Yanyan, He Shufang, the Gong Ke invention proposes a kind of double-frequency laser Doppler velocity measurement method, this method comprises generation double-frequency laser bundle, be divided into two double frequency light beams, respectively as measuring beat signal to generate with reference to beat signal and measuring beam to generate with reference to light beam; To and measure beat signal and carry out mixing with reference to beat signal, with the beat signal that obtains being directly proportional with the movement velocity of object to be measured; According to the beat signal that the movement velocity with the object that tests the speed is directly proportional, calculate the movement velocity of object to be measured.This invention can improve the highest measured speed of double-frequency laser Doppler velocity measurement method greatly, enlarges the speed range ^[6]

Traditional dual-frequency laser measurement principle is to be (ν by two bundle frequencies different laser frequency synthesis ₁-ν ₂) beat signal, this signal is the equal of a carrier signal, when measured object moves, can cause Doppler shift amount Δ ν signal, is that carrier wave is carried out warbled displacement signal, Δ ν comprises displacement information, and then demodulates actual displacement.

Summary of the invention

The object of the present invention is to provide a kind of new laser interference length-measuring method, it is characterized in that, this surveys the laser that rectangular method uses two bundle wavelength to approach very much, stack by light wave fields, construct the bigger effective wavelength of wavelength ratio, be used for the measurement to measured object, wherein, the length of surveying is the distance that movable photodetector moves;

Specifically be that measured object and photodetector are connected firmly, by adopting the principle of time series interferometry, utilize the Computer Image Processing method, directly by behind the time series intensity map of photodetector in reception a period of time, be stored in the computing machine; In Computer Processing, a series of interference strengths are carried out filtering after, again it is done inverse Fourier transform, go parcel to handle, finally obtain continuous phase, carry out phase unwrapping again, draw the displacement information of object; Concrete steps are as follows:

1) laser instrument of selecting two optical maser wavelengths to approach very much shines on the light splitting plain film with 45 ° of incident angles respectively;

2) through transmission and the reflex of light splitting plain film, two bundle laser stacking add as a branch of synthetic laser, and the laser beam after the stack is by collimating and beam expanding system, and collimating expands;

3) shine directly on the photodetector that connects firmly with measured object through the laser behind the collimator and extender, when measured object is subjected to displacement, the process record that photodetector will receive the ohject displacement in a period of time gets off, acquisition contains the seasonal effect in time series receiving light power intensity of ohject displacement information, is stored on the computing machine;

4) computing machine carries out Fourier transform to the time series light intensity intensity data that photodetector obtains, obtain light intensity intensity spectrum figure, and spectrogram is carried out filtering, inverse Fourier transform obtains phase place, carry out after phase place goes the data of wrapping up to handle, finally obtain the information of ohject displacement.

Described laser alignment beam-expanding system is made up of spatial filter 4 and convex lens 5.

The measurement range of described laser interference length-measuring depends on the coherent length of the laser instrument that uses, to determine object shift length at any time.

The invention has the beneficial effects as follows:

1. the present invention adopts measured object and photodetector is connected firmly, and does not need complicated optical interference circuit, does not need expensive double-frequency laser generating means, is that a kind of light path is simple, measures the low measuring method of cost;

2. by making the very stack of approaching laser of two wavelength, synthesize a measurable frequency synthesis of frequency, can directly detect by photodetector, have the antijamming capability of dual-frequency laser measurement strong, the advantage that signal to noise ratio (S/N ratio) is high;

3. the time series interferometry can record the length value of any time, and the length value of object is carried out dynamic test rather than only measures the initial displacement value and the end shift value;

4. image process method is handled at phase place, finally obtains shift value, compares with the method for traditional record striped, and precision is higher, and along with the development of Electro-Optical Sensor Set, the space that can improve can be bigger;

5. the present invention is non-cpntact measurement, has higher measurement sensitivity and precision.

Description of drawings

Fig. 1 is the index path of time series interferometry ohject displacement.

Among the figure: (1) laser instrument A, (2) laser instrument B, (3) light splitting plain film, (4) spatial filter, (5) convex lens, (6) photodetector, (7) measured object, (8) computing machine.

Embodiment

The invention provides a kind of new laser interference length-measuring method.This surveys the laser that rectangular method uses two bundle wavelength to approach very much, by the stack of light wave fields, constructs the bigger effective wavelength of wavelength ratio, is used for the measurement to measured object, and wherein, the length of surveying is the distance that movable photodetector moves; Along with the appearance of equipment such as big capacity computer, high-speed CCD, make that interior record Serial No. image has become reality at certain time intervals, so the time series interference length-measuring is developed.The time series interference length-measuring is that the overall process of whole ohject displacement is noted, and uses the phase information of Fourier transform technology extract displacement body then, observes each some change in displacement in time on the object.The invention will be further described below in conjunction with accompanying drawing and example.

As shown in Figure 1, specifically be that measured object and photodetector are connected firmly, by adopting the principle of time series interferometry, utilize the Computer Image Processing method, directly by behind the time series intensity map of photodetector in reception a period of time, be stored in the computing machine; In Computer Processing, from a series of interference strength figure, choose arbitrarily a bit, it is done Fourier transform, after carrying out filtering, again it is done inverse Fourier transform, go parcel to handle, finally obtain continuous phase, carry out phase unwrapping again, draw the displacement information of object

The rectangular method of survey of the present invention is A laser instrument 1 and the B laser instrument 2 that light source adopts optical maser wavelength to approach.A laser instrument 1 and B laser instrument 2 quadrature arrangement, the laser beam light splitting plain film 3 that the two sends after light splitting plain film 3 is crossed in the light beam transmission of A laser instrument 1, is superposed to beam of laser with the laser beam of the B laser instrument 2 of light splitting plain film 3 reflection.Laser after the stack is through the laser alignment beam-expanding system of spatial filter 4 and convex lens 5 compositions, synthetic laser behind the collimator and extender shines directly into the photodetector 6 that connects firmly with measured object 7, when measured object 7 is subjected to displacement, photodetector 6 will receive the process record that measured object is subjected to displacement the ohject displacement in the time period and get off, the laser signal that contains ohject displacement information of record, and transfer signals to the processing of carrying out interference strength figure on the computing machine 8, the time series light intensity intensity data that obtains carries out Fourier transform, obtain light intensity intensity spectrum figure, and spectrogram carried out filtering, inverse Fourier transform obtains phase place, carry out after phase place goes the data of wrapping up to handle, finally obtain the information of ohject displacement.

Narrate the concept of synthetic wavelength according to existing theory in conjunction with the present invention: suppose that the A laser instrument 1 of use and two bundle Wavelength of Laser of B laser instrument 2 are respectively λ _aAnd λ _bλ wherein _aλ _bThe phase value of the each point that use face battle array photodetector detects is:

λ=λ _aThe time, φ _1a, φ _2a, φ _3a... φ _Ka

λ=λ _bThe time, φ _1b, φ _2b, φ _3b... φ _Kb

K is that the efficiently sampling of one dimension direction is counted, if interference fringe is closeer, make the phase change of consecutive point greater than 2 π, then the position that records of the single wavelength of above-mentioned usefulness mutually value all have the 2 π integral multiple saltus step problems that can't proofread and correct immediately, the pass between they and the actual light path difference L is:

$L_i=[\frac{{\mathrm{\&phi;}}_{\mathrm{ia}}}{2\mathrm{\&pi;}}+m]{\mathrm{\&lambda;}}_a$ $L_i=[\frac{{\mathrm{\&phi;}}_{\mathrm{<figure-callout\; id="2"\; label="ib"\; filenames="HDA00003151144900011.png"\; state="\{\{state\}\}">ib</figure-callout>}}}{2\mathrm{\&pi;}}+n]{\mathrm{\&lambda;}}_b$

I is i sampled point in the formula; M, nm', n' corresponds respectively to λ _a, λ _bStriped integer level time.

With the light path of i adjacent pixels i+1 and be

$L_{i+1}=[\frac{{\mathrm{\&phi;}}_{(i+1)a}}{2\mathrm{\&pi;}}+m^{\&prime;}]{\mathrm{\&lambda;}}_a$ $L_{i+1}=[\frac{{\mathrm{\&phi;}}_{(i+1)\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA00003151144900011.png"\; state="\{\{state\}\}">b</figure-callout>}}}{2\mathrm{\&pi;}}+n^{\&prime;}]{\mathrm{\&lambda;}}_b$

Make Δ L=L _I+1-L _iΔ φ _{(i+1) a}=φ _{(i+1) a}-φ _IaΔ φ _{(i+1) b}=φ _{(i+1) b}-φ _Ib

Pass between they and the actual light path difference is:

$\mathrm{\&Delta;L}=[\frac{\mathrm{\&Delta;}{\mathrm{\&phi;}}_{(i+1)a}}{2\mathrm{\&pi;}}+(m^{\&prime;}-m)]{\mathrm{\&lambda;}}_a$ $\mathrm{\&Delta;L}=[\frac{\mathrm{\&Delta;}{\mathrm{\&phi;}}_{(i+1)\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA00003151144900011.png"\; state="\{\{state\}\}">b</figure-callout>}}}{2\mathrm{\&pi;}}+(n^{\&prime;}-n)]{\mathrm{\&lambda;}}_b$

Suppose that fringe order difference between any two adjacent pixels is to λ _aAnd λ _bIdentical, namely m-m'=n-n' can get

In the formula: The effective wavelength that is called dual wavelength namely is equivalent to use wavelength to be

Laser carry out interferometry.The essence of dual-wavelength measurement is with effective wavelength λ _EqReplace original single wavelength, when use two the bundle Wavelength of Laser (frequency) relatively near the time, can generate the bigger effective wavelength of a branch of wavelength ratio.

By the concept of effective wavelength as can be known, the light wave fieldss of the synthetic effective wavelength of two bundle laser can be expressed as:

E _eq=A _eqcos[ω _eqt-k _eqΔz+φ]

Therefore, the light intensity that receives

$I_{\mathrm{eq}}={A_{\mathrm{<figure-callout\; id="2"\; label="eq"\; filenames="HDA00003151144900011.png"\; state="\{\{state\}\}">eq</figure-callout>}}}^2{\cos }^2({\mathrm{\&omega;}}_{\mathrm{eq}}t-k_{\mathrm{eq}}\mathrm{\&Delta;z}\left(t\right)+\mathrm{\&phi;})$

$=\frac{1}{2}{A_{\mathrm{eq}}}^2[1+\cos 2({\mathrm{\&omega;}}_{\mathrm{eq}}t-k_{\mathrm{eq}}\mathrm{\&Delta;z}\left(t\right)+\mathrm{\&phi;})]---\left(1\right)$

Wherein, A _EqBe the amplitude of effective wavelength, ω _EqBe the temporal frequency of effective wavelength, k _EqBe the spatial frequency of effective wavelength, φ is initial phase, and might as well establish it is 0, and Δ z (t) is the warping function of measured object.By the method for time series interferometry, utilize Fourier transformation method that the measured object displacement function is extracted, and then can observe the displacement information of measured object intuitively.

After measured object carries out continuous motion, cause the time modulation variation of laser intensity on the photodetector, this process is received by photodetector, and light intensity signal is noted.The measured object displacement intensity data that photodetector is obtained carries out Fourier transform, and deal with data can obtain spectrogram, and spectrogram is carried out can obtaining after filtering, the inverse Fourier transform variation of phase place, and namely total phase changing capacity can be obtained.Because the frequency of two bundle laser is known, equivalent Wavelength of Laser λ _EqBe known, so ω _EqAnd k _EqAlso be known, and total phase place change by formula (1) as can be known, Δ φ=2 (ω _EqT-k _EqΔ z) can obtain by Fourier transform method, therefore can obtain the actual displacement Δ z of object in the certain hour

List of references

[1] Shi Zhiguo; Wang Runwen. laser system with double frequence: Chinese .93112556.1[P] .1994-07-20.

[2] Wu Lingan; Hou Yanxue; Ma Haiqiang. a kind of method and device of measuring low light level light source beat frequency: Chinese .200410046006.9[P] .2005.02.23

[3] Liu Gang; Zhang Shulian; Zhu Jun; Li Yan. based on the self-mixed interference Doppler anemometer of two-frequency laser: Chinese .200410009261.6[P] .2005-03-16.

[4] Wang Ji. double-frequency laser interferometry apparatus: Chinese .200810117028.8[P] .2009-04-22.

[5] Chen Benyong; Zhang Enzheng; Yan Liping; Tao Yang; Zhou Yanjiang. based on the linearity of double frequency principle of interference and the measuring method of position thereof: Chinese .200910100065.2[P] .2009-11-18

[6] Huo Yujing; Zhang Yanyan; He Shufang; Gong Ke. a kind of double-frequency laser Doppler velocity measurement method and device: Chinese .201010220246.1[P] .2010-11-17.

Claims (3)

1. A new laser interference length measurement method, characterized in that the length measurement method uses two laser beams with very close wavelengths, and through the superposition of optical wave fields, an equivalent wavelength with a relatively large wavelength is constructed for measuring The measurement of the object, wherein, the measured length is the moving distance of the movable photodetector; the specific steps are as follows: 1) Select two lasers with very close laser wavelengths, and irradiate them on the spectroscopic flat film at an incident angle of 45°; 2) After the transmission and reflection of the spectroscopic flat film, the two laser beams are superimposed into a synthetic laser beam, and the superimposed laser beam is collimated and expanded through the collimation beam expansion system; 3) The laser beam after collimation and expansion is directly irradiated on the photodetector fixedly connected with the measured object. When the measured object is displaced, the photodetector will record the process of receiving the displacement of the object within a period of time, and obtain The received light intensity of the time series containing the object displacement information is stored on the computer; 4) The computer performs Fourier transform on the time-series light intensity data obtained by the photodetector to obtain the light intensity spectrum diagram, and filters the spectrum diagram, inverse Fourier transform to obtain the phase, and performs phase unwrapping data processing Finally, the information about the displacement of the object is finally obtained. 2. A new laser interferometric length measurement method according to claim 1, characterized in that the laser collimation and beam expansion system consists of a spatial filter 4 and a convex lens 5. 3. A new method of laser interferometric length measurement according to claim 1, characterized in that the measuring range of said laser interferometric length measurement depends on the coherence length of the laser used to measure the displacement length of the object at any time .

Images