CN102221356A - Device and method for measuring laser incident angle by sinusoidally modulating multi-beam laser heterodyne secondary harmonics with Doppler galvanometer - Google Patents

Abstract

The invention discloses a device and method for measuring a laser incident angle by sinusoidally modulating multi-beam laser heterodyne secondary harmonics with a Doppler galvanometer, which relate to a device and method for measuring a laser incident angle and are used for solving the problems of poor quality of acquired laser difference frequency signals and low operating speed of signal processing during the measurement of the laser incident angle with the conventional laser heterodyne dynamic angle measuring method. The method comprises the following steps of: making a galvanometer perform simple harmonic oscillation; starting a laser; and continually acquiring electrical signals output by a photoelectric detector by using a signal processing system, processing an acquired difference frequency signal, and obtaining an incident angle to be detected according to a ratio coefficient of the frequency of a laser heterodyne signal to a refraction angle which is formed by laser entering a glass plate of which the thickness is known. The device has the advantages of high laser difference frequency signal quality and high operating speed of signal processing, and can be widely applied to ultra-precision measurement, detection, processing equipment and laser radar systems.

Description

The device and method of Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle

Technical field

The present invention relates to a kind of device and method of Laser Measurement incident angle.

Background technology

Accurate measurement of angle be the engineering field always demand side to the problem that solves.Along with science and technology development, Angle Measuring Equipment and measuring method are constantly weeded out the old and bring forth the new, as pin-point accuracy clinometer rule spare such as code-disc, permagnetic synchronous motor, laser scanner, inductosyn, spatial Fourier spectrometer and 4 quadrant detector angle measurement and utilize the extensive application of the angle-measuring equipment of these devices exploitations, provide the solution of a large amount of measurement of angle problems for engineering design and testing staff.Angle-measuring method comprises CCD optics angle-measuring method, PIP interferometry, imaging type grating autocollimation angle-measuring method, based on autocollimation angle-measuring method of Moire fringe etc.Utilize these methods generally all can not reach the requirement of pin-point accuracy measurement of angle.

Because characteristics such as the optics angle measurement is untouchable owing to having, precision is high and simple in structure enjoy people's attention, therefore use the method for optics angle measurement to obtain application more and more widely.Based on this, a kind of dynamic measuring angle algorithm that detects based on the multi-beam laser heterodyne has been proposed, not needing to be characterized in the directional information of index glass, can when satisfying precision, realize inclination angle detection on a large scale.

But there is the of poor quality and slow problem of arithmetic speed signal Processing of laser difference frequency signal of gathering in existing heterodyne dynamic measuring angle method when the Laser Measurement incident angle.

Summary of the invention

The present invention exists when the Laser Measurement incident angle and gathers the of poor quality and slow problem of arithmetic speed signal Processing of laser difference frequency signal in order to solve existing heterodyne dynamic measuring angle method, and the device and method of the Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle that proposes.

The device of Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle, it comprises H ₀Glass plate, convergent lens, photodetector and the signal processing system of solid state laser, polarizing beam splitter mirror PBS, quarter-wave plate, galvanometer, plane mirror, known thickness,

H ₀The linearly polarized light that solid state laser sends is incident to quarter-wave plate after polarizing beam splitter mirror PBS reflection, light beam after described quarter-wave plate transmission is incident to the light receiving surface of galvanometer, light beam through described vibration mirror reflected is sent to polarizing beam splitter mirror PBS once more after the quarter-wave plate transmission, light beam after this polarizing beam splitter mirror PBS transmission is incident to the reflecting surface of plane mirror, light beam after this plane reflection mirror reflection is incident to the glass plate front surface of known thickness, in the glass plate of light beam in this known thickness of the glass plate front surface transmission of this known thickness, after repeatedly reflecting, the glass plate rear surface of this known thickness and front surface obtain the multi beam reflected light, this multi beam reflected light all converges to by convergent lens on the photosurface of photodetector with light beam after the glass plate front surface reflection of this known thickness after the front surface transmission of the glass plate of this known thickness, and described photodetector output electric signal is given signal processing system.

Based on the method for the measurement device laser incident angle of above-mentioned Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle, it is realized by following steps:

At first, the driving power of opening galvanometer makes galvanometer begin to do simple harmonic oscillation; Simultaneously, open laser instrument;

Electric signal by signal processing system continuous acquisition photodetector output then, and the difference frequency signal that collects handled, according to the relation at the refraction angle of the glass plate of frequency and known thickness:

f＝Kcosθ

Obtain the refraction angle θ that laser is incident to the glass plate of known thickness:

cosθ＝f/K

F is the frequency of heterodyne signal in the formula, and K is the scale-up factor at the refraction angle of the frequency f of heterodyne signal and the glass plate that laser is incident to known thickness, thereby obtains incident angle θ to be measured ₀Size be:

θ ₀＝arcsin(nsinθ)

N is the refractive index of the glass plate of known thickness in the formula.

Described measurement mechanism of the application and method not only have the traditional optical angle measurement technique have untouchable, precision is high and advantages of simple structure and simple, also has the outstanding advantage of the fast operation of the high and signal Processing of the laser difference frequency signal quality of collection.

Characteristics and deficiency at traditional measuring system, the application has proposed a kind of method based on galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle, by in light path, adding galvanometer 4, galvanometer 4 is done simple harmonic oscillation under the sinusoidal drive signals effect, can carry out frequency modulation (PFM) to the light that difference incides its front surface constantly, angle information to be measured is loaded in the difference on the frequency of heterodyne signal second harmonic, be easy to just can demodulate angle information to be measured by Fourier's variation, and measuring accuracy is high.Heterodyne technology and laser doppler technique are used in combination, the advantage of two kinds of technology well have been applied in the detection of angle, make modulation, detect, handle simple.

Emulation proves, the described method of the application is a kind of method of good non-cpntact measurement angle, can be applied on the abominable measurement environment.When taking measurement of an angle, adopting said method has the precision height, advantage such as Linearity is good, and measuring speed is fast.Simulation result shows, this method is when measuring different angles, measuring error is less than 0.789677%, illustrate that it is feasible, reliable that this method is used, can satisfy the minute angle Testing requirement, for many engineerings field provides good measurement means, can be widely used in laser radar, machinery, instrument and meter and the electronic product manufacturing industry, have good application prospect and value.

Description of drawings

Fig. 1 is the structural representation of the device of Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle of the present invention; Fig. 2 is multi-beam laser principle of interference figure in the glass plate of known thickness; Fig. 3 different incidence angles is measured corresponding spectrogram, and the actual value of curve representation incident angle is followed successively by 4.0mrad, 4.5mrad, 5.0mrad, 5.5mrad, 6.0mrad, 6.5mrad, 7.0mrad, 7.5mrad from right to left among the figure.

Embodiment

Embodiment one: present embodiment is described in conjunction with Fig. 1, the device of the described Doppler's galvanometer of present embodiment Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle comprises glass plate 6, convergent lens 7, photodetector 8 and the signal processing system 9 of H0 solid state laser 1, polarizing beam splitter mirror PBS2, quarter-wave plate 3, galvanometer 4, plane mirror 5, known thickness

The linearly polarized light that H0 solid state laser 1 sends is incident to quarter-wave plate 3 after polarizing beam splitter mirror PBS2 reflection, light beam after described quarter-wave plate 3 transmissions is incident to the light receiving surface of galvanometer 4, after quarter-wave plate 3 transmissions, be sent to polarizing beam splitter mirror PBS2 once more through described galvanometer 4 beam reflected, light beam after this polarizing beam splitter mirror PBS2 transmission is incident to the reflecting surface of plane mirror 5, light beam after these plane mirror 5 reflections is incident to glass plate 6 front surfaces of known thickness, in the glass plate 6 of light beam in this known thickness of the glass plate 6 front surface transmissions of this known thickness, after repeatedly reflecting, glass plate 6 rear surfaces of this known thickness and front surface obtain the multi beam reflected light, this multi beam reflected light all converges on the photosurface of photodetector 8 by convergent lens 7 with light beam after glass plate 6 front surface reflections of this known thickness after the front surface transmission of the glass plate 6 of this known thickness, and described photodetector 8 output electric signal are given signal processing system 9.Because light beam can constantly reflect and reflect (as shown in Figure 2) between the front and rear surfaces of the glass plate of known thickness, and this reflection and refraction for reflected light and transmitted light at infinity or the interference on the lens focal plane contribution is all arranged, so when interference is discussed, must consider repeatedly reflection and refraction effect, multi-beam laser promptly should be discussed interfere.

But, because the optical mixing that transmit glass front of laser after the reflected light of glass plate 6 front surfaces of known thickness and the reflection of glass rear surface k time are with k+1 time, the amplitude of two difference frequency signals that produce differs 2～3 orders of magnitude, through after the Fourier transform, in order to collect laser difference frequency signal and the arithmetic speed that improves signal Processing preferably, so here we only consider that the k secondary reflection that is detected transmits the E of front surface _kTransmit the E of front surface behind light and the rear surface k+2 secondary reflection _K+2The humorous frequency difference of the secondary that optical mixing produced.

Embodiment two: present embodiment and embodiment one difference are that described signal processing system 9 is made up of wave filter 9-1, prime amplifier 9-2, modulus converter A/D and digital signal processor DSP, the electric signal that described wave filter 9-1 exports the photodetector 8 that receives carries out sending to prime amplifier 9-2 after the filtering, signal after prime amplifier 9-2 amplifies is exported to modulus converter A/D, and the digital signal after described modulus converter A/D will be changed sends to digital signal processor DSP.Other composition is identical with embodiment one with connected mode.

Embodiment three: present embodiment and embodiment one or two differences are that described galvanometer 4 is Doppler's galvanometer, and the simple harmonic oscillation equation of described galvanometer 4 is:

x(t)＝x ₀cos(ω _ct)

The rate equation of galvanometer 4 is:

v(t)＝-ω _cx ₀sin(ω _ct)

In the formula, parameter ω ₀Be laser angular frequency, parameter x ₀Be the amplitude of galvanometer vibration, parameter ω _cBe the angular frequency of galvanometer, c is the light velocity; T is the time.Other composition is identical with embodiment one or two with connected mode.

Embodiment four: the method for the measurement device laser incident angle that takes measurement of an angle based on embodiment one described Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic, it is realized by following steps:

At first, the driving power of opening galvanometer 4 makes galvanometer 4 begin to do simple harmonic oscillation; Simultaneously, the H0 solid state laser 1;

Electric signal by the output of signal processing system 9 continuous acquisition photodetectors 8 then, and the difference frequency signal that collects handled, according to the relation at the refraction angle of the glass plate 6 of frequency and known thickness:

f＝Kcosθ

Obtain the refraction angle θ that laser is incident to the glass plate 6 of known thickness:

cosθ＝f/K

F is the frequency of heterodyne signal in the formula, and K is the scale-up factor at the refraction angle of the frequency f of heterodyne signal and the glass plate 6 that laser is incident to known thickness, thereby obtains incident angle θ to be measured ₀Size be:

θ ₀＝arcsin(nsinθ)

N is the refractive index of the glass plate 6 of known thickness in the formula.

Embodiment five: present embodiment and embodiment four differences are the electric signal by 8 outputs of signal processing system 9 continuous acquisition photodetectors, and the difference frequency signal that collects handled, obtain the incident angle θ of the glass plate 6 of known thickness ₀Process in, the frequency f of heterodyne signal and scale-up factor K adopt following method to obtain:

Because the optical mixing that transmit glass front of laser after the glass plate 6 rear surfaces reflection of the reflected light of glass plate 6 front surfaces of known thickness and known thickness k time is with k+1 time, produce the difference frequency signal that two amplitudes differ 2～3 orders of magnitude, the humorous frequency difference of the described secondary of said method is the E of the glass plate 6 rear surface k secondary reflections of known thickness _kWith the E behind the glass plate 6 rear surface k+2 secondary reflections of known thickness _K+2What optical mixing produced;

When laser with incident angle θ ₀Incident field during glass plate 6 front surfaces of oblique incidence known thickness is

E (t)=E _lExp (i ω ₀T) formula 1

The simple harmonic oscillation equation of galvanometer 4

X (t)=x ₀Cos (ω _cT) formula 2

The rate equation of galvanometer 4 is

V (t)=-ω _cx ₀Sin (ω _cT) formula 3

Because the motion of galvanometer 4, catoptrical frequency becomes

ω=ω ₀(1-2 ω _cx ₀Sin (ω _cT)/c) formula 4

Above-mentioned various in, parameter ω ₀Be laser angular frequency, parameter x ₀Be the amplitude of galvanometer 4 vibrations, parameter ω _cBe the angular frequency of galvanometer 4, c is the light velocity;

Then t-l/c arrives the reflection light field of glass plate 6 front surfaces of known thickness constantly and is:

E ₀(t)=α E _lExp{i[ω ₀(1-2 ω _cx ₀Sin (ω _c(t-l/c))/c) formula 5

(t-l/c)+ω ₀x ₀cos(ω _c(t-l/c))/c]}

In the formula, parameter alpha ₀=r, r are the reflection coefficient of the glass plate 6 of known thickness.L is the light path of galvanometer 4 to glass plate 6 front surfaces of known thickness, E _lBe the amplitude constant;

, obtain the expression formula that m restraints transmitted light and write as following form respectively in difference constantly and after transmiting the glass plate 6 of known thickness through the light of glass plate 6 transmissions of known thickness by glass plate 6 rear surfaces of known thickness reflection m time:

E ₁(t)＝α ₁E _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-(l+2ndcosθ)/c))/c)

(t-(l+2ndcosθ)/c)+ω ₀x ₀cos(ω _c(t-(l+2ndcosθ)/c))/c]}

E ₂(t)＝α ₂E _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-(l+4ndcosθ)/c))/c)

(t-(l+4ndcosθ)/c)+ω ₀x ₀cos(ω _c(t-(l+4ndcosθ)/c))/c]}

E ₃(t)＝α ₃E _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-(l+6ndcosθ)/c))/c)

(t-(l+6ndcos θ)/c)+ω ₀x ₀Cos (ω _c(t-(l+6ndcos θ)/c))/c] } formula 6

·

·

·

E _m(t)＝α _mE _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-(l+2mndcosθ)/c))/c)

(t-(l+2mndcosθ)/c)+ω ₀x ₀cos(ω _c(t-(l+2mndcosθ)/c))/c]}

Wherein, parameter alpha ₁=β β ' r ' ..., α _m=β β ' r ' ^(2m-1)β is the transmission coefficient of glass plate 6 front surfaces of known thickness, transmission coefficient when β ' goes out the glass plate 6 of known thickness for transmittance, r ' is the catoptrical reflection coefficient of glass plate 6 inner front and rear surfaces of known thickness, the refraction angle when θ is a light beam light from glass plate 6 front surfaces of surrounding medium incident known thickness, the subscript m value is 0,1,2 ..., n is the refractive index of the glass plate 6 of known thickness, and d is the thickness of the glass plate 6 of known thickness;

Total light field that photodetector 8 receives is expressed as:

E (t)=E ₀(t)+E ₁(t)+... + E _m(t) formula 7

Then the photocurrent of photodetector 8 outputs can be expressed as:

$I=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{1}{Z}\underset{S}{\∫\∫}\frac{1}{2}[E_0\left(t\right)+E_1\left(t\right)+...+E_m\left(t\right)+...]{[E_0\left(t\right)+E_1\left(t\right)+...+E_m\left(t\right)+...]}^{*}\mathrm{ds}$ Formula 8

Wherein, parameter e is an electron charge, and parameter Z is the intrinsic impedance of photodetector 8 surface dielectrics, and parameter η is a quantum efficiency, and parameter S is the area of photodetector 8 photosurfaces, and parameter h is a Planck's constant, and parameter v is a laser frequency, * number expression complex conjugate;

The electric current of intermediate frequency that arrangement obtains the heterodyne second harmonic signal is:

$I_{\mathrm{if}}=\frac{\mathrm{\ηe}}{2\mathrm{hv}}\frac{1}{Z}\underset{s}{\∫\∫}\underset{p=0}{\overset{\∞}{\mathrm{\Σ}}}\underset{j=p+2}{\overset{\∞}{\mathrm{\Σ}}}(E_p\left(t\right){E_j}^{*}\left(t\right)+{E_p}^{*}\left(t\right)E_j\left(t\right))\mathrm{ds}$ Formula 9

With formula 5 and formula 6 substitution formula 9, net result is:

$I_{\mathrm{IF}}=\frac{\mathrm{\&eta;e}}{\mathrm{hv}}\frac{\mathrm{\&pi;}}{\mathrm{<figure-callout\; id="0"\; label="Z\; E"\; filenames="HDA0000065397520000021.png"\; state="\{\{state\}\}">Z</figure-callout>}}{E}_{}^{}{}_0^2\underset{p=0}{\overset{m-1}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{m-p}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{j+p}{\mathrm{\&alpha;}}_j\cos [\frac{8\mathrm{nd}\cos {\mathrm{\&theta;\&omega;}}_0{\mathrm{\&omega;}}_c^2{x}_0}{c^2}t+\frac{2{\mathrm{\&omega;}}_c{x}_0}{c}-\frac{4\mathrm{nd}{\mathrm{\&omega;}}_0\cos \mathrm{\&theta;}}{c}$

Formula 10

$-\frac{8\mathrm{nd}\cos \mathrm{\&theta;}{\mathrm{\&omega;}}_0{\mathrm{\&omega;}}_c^2{x}_0(l+2\mathrm{pnd}\cos \mathrm{\&theta;})}{c^3}]$

Ignore 1/c ³Event after be reduced to:

$I_{\mathrm{IF}}=\frac{\mathrm{\&eta;e}}{\mathrm{hv}}\frac{\mathrm{\&pi;}}{\mathrm{<figure-callout\; id="0"\; label="Z\; E"\; filenames="HDA0000065397520000021.png"\; state="\{\{state\}\}">Z</figure-callout>}}{E}_{}^{}{}_0^2\underset{p=0}{\overset{m-1}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{m-p}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{j+p}{\mathrm{\&alpha;}}_j\cos (\frac{8\mathrm{nd}\cos {\mathrm{\&theta;\&omega;}}_0{\mathrm{\&omega;}}_c^2{x}_0}{c^2}t+\frac{{2\mathrm{\&omega;}}_0{x}_0-4\mathrm{nd}{\mathrm{\&omega;}}_0\cos \mathrm{\&theta;}}{c})$ Formula 11

Wherein, p and j are nonnegative integer;

According to formula 9, the frequency of heterodyne second harmonic signal is designated as:

$f=8\mathrm{nd}\cos {\mathrm{\&theta;\&omega;}}_0{\mathrm{\&omega;}}_c^2{x}_0/\left({2\mathrm{\&pi;c}}^2\right)=4\mathrm{nd}\cos {\mathrm{\&theta;\&omega;}}_0{\mathrm{\&omega;}}_c^2{x}_0/\left({\mathrm{\&pi;c}}^2\right)=K\cos \mathrm{\&theta;}$ Formula 12

Learn that according to formula 11 and formula 12 frequency of interference signal and the glass plate of known thickness 6 refraction angle θ are inversely proportional to, scale-up factor is:

$K=4\mathrm{nd}{\mathrm{\&omega;}}_0{\mathrm{\&omega;}}_c^2{x}_0/\left({\mathrm{\&pi;c}}^2\right)$ Formula 13

Emulation experiment:

Get H ₀Solid state laser 1 wavelength X=2050nm, this laser is to eye-safe; Refractive index n=1.493983 of the glass plate 6 of known thickness generally, glass plate 6 thickness of known thickness are 2cm; The photosurface aperture of photodetector 8 is R=1mm, and the sensitivity of photodetector 8 is 1A/W.The amplitude x of galvanometer 4 ₀=0.0001m.Utilize MATLAB emulation to obtain multi-beam laser heterodyne second harmonic and measure different incidence angles θ ₀Corresponding multi-beam laser heterodyne second harmonic signal Fourier transform frequency spectrum as shown in Figure 3, as can be seen from Figure 3, along with the increase of incident angle, the relative position of frequency spectrum reduces to the increase frequency that the low frequency direction moves promptly along with angle.Under the constant situation of glass plate 6 thickness of known thickness, scale-up factor K is a constant, because frequency f is f=Kcos θ=Kcos (arcsin (sin θ with scale-up factor K pass ₀/ n)), laser incident angle θ ₀With the frequency f relation of being inversely proportional to, promptly as incident angle θ ₀During increase, frequency f reduces thereupon, and the relative position of frequency spectrum moves to the low frequency direction, and Fig. 3 has verified the correctness of front theoretical analysis well.Need to prove that because heterodyne detection is a kind of detection mode of nearly diffraction limit, detection sensitivity is high, so the signal to noise ratio (S/N ratio) of Fig. 3 multi-beam laser heterodyne second harmonic signal is very high.

Utilize above-mentioned Sine Modulated multi-beam laser heterodyne second harmonic mensuration, continuous analog eight groups of data, obtained different incidence angles θ ₀Simulation result, as shown in table 1.

Table 1 different incidence angles θ ₀Actual value and simulation value

Need to prove: utilize the emulation experiment data of table 1, finally the maximum relative error that can obtain the analogue value is less than 0.789677%, and the measuring accuracy of this method is very high as can be seen.Simultaneously, analyze data and it can also be seen that systematic error that environment brings and reading error are negligible in emulation, the error in the emulation experiment mainly comes from trueness error after the Fast Fourier Transform (FFT) (FFT) and the round-off error in the computation process.

Characteristics and deficiency at traditional measuring system, the application has proposed a kind of method that takes measurement of an angle based on galvanometer Sine Modulated multi-beam laser heterodyne second harmonic, by in light path, adding galvanometer 4, galvanometer 4 is done simple harmonic oscillation under the sinusoidal drive signals effect, can carry out frequency modulation (PFM) to the light that difference incides its front surface constantly, angle information to be measured is loaded in the difference on the frequency of heterodyne signal second harmonic, be easy to just can demodulate angle information to be measured by Fourier's variation, and measuring accuracy is high.Heterodyne technology and laser doppler technique are used in combination, the advantage of two kinds of technology well have been applied in the detection of angle, make modulation, detect, handle simple.

Emulation proves, the described method of the application is a kind of method of good non-cpntact measurement angle, can be applied on the abominable measurement environment.When taking measurement of an angle, adopting said method has the precision height, advantage such as Linearity is good, and measuring speed is fast.Simulation result shows, this method is when measuring different angles, measuring error is less than 0.789677%, illustrate that it is feasible, reliable that this method is used, can satisfy the minute angle Testing requirement, for many engineerings field provides good measurement means, can be widely used in laser radar, machinery, instrument and meter and the electronic product manufacturing industry, have good application prospect and value.

Above content be in conjunction with concrete preferred implementation to further describing that the present invention did, can not assert that concrete enforcement of the present invention is confined to these explanations.For this person of an ordinary skill in the technical field, without departing from the inventive concept of the premise, can also make some simple deduction or replace, all should be considered as belonging to the definite scope of patent protection of claims that the present invention submits to.

Claims (5)

1. the device of Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle is characterized in that it comprises H ₀The glass plate (6) of solid state laser (1), polarizing beam splitter mirror PBS (2), quarter-wave plate (3), galvanometer (4), plane mirror (5), known thickness, convergent lens (7), photodetector (8) and signal processing system (9),

H ₀The linearly polarized light that solid state laser (1) sends is incident to quarter-wave plate (3) after polarizing beam splitter mirror PBS (2) reflection, light beam after described quarter-wave plate (3) transmission is incident to the light receiving surface of galvanometer (4), after quarter-wave plate (3) transmission, be sent to polarizing beam splitter mirror PBS (2) once more through described galvanometer (4) beam reflected, light beam after this polarizing beam splitter mirror PBS (2) transmission is incident to the reflecting surface of plane mirror (5), light beam after this plane mirror (5) reflection is incident to glass plate (6) front surface of known thickness, in the glass plate (6) of light beam in this known thickness of glass plate (6) the front surface transmission of this known thickness, after repeatedly reflecting, glass plate (6) rear surface of this known thickness and front surface obtain the multi beam reflected light, this multi beam reflected light all converges on the photosurface of photodetector (8) by convergent lens (7) with light beam after glass plate (6) front surface reflection of this known thickness after the front surface transmission of the glass plate (6) of this known thickness, and described photodetector (8) output electric signal is given signal processing system (9).

2. the device of Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle according to claim 1, it is characterized in that described signal processing system (9) is by wave filter (9-1), prime amplifier (9-2), analog to digital converter (A/D) and digital signal processor (DSP) are formed, the electric signal that described wave filter (9-1) is exported the photodetector (8) that receives carries out sending to prime amplifier (9-2) after the filtering, signal after prime amplifier (9-2) amplifies is exported to analog to digital converter (A/D), and the digital signal after described analog to digital converter (A/D) will be changed sends to digital signal processor (DSP).

3. the device of Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle according to claim 1 and 2 is characterized in that described galvanometer (4) is Doppler's galvanometer, and the simple harmonic oscillation equation of described Doppler's galvanometer is:

x(t)＝x ₀cos(ω _ct)

The rate equation of Doppler's galvanometer is:

v(t)＝-ω _cx ₀sin(ω _ct)

In the formula, parameter ω ₀Be laser angular frequency, parameter x ₀Be the amplitude of galvanometer (4) vibration, parameter ω _cBe the angular frequency of galvanometer (4), c is the light velocity, and t is the time;

4. based on the method for the measurement device laser incident angle of the described Doppler's galvanometer of claim 1 Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle, it is characterized in that it is realized by following steps:

At first, the driving power of opening galvanometer (4) makes galvanometer (4) begin to do simple harmonic oscillation; Simultaneously, open H ₀Solid state laser (1);

Electric signal by signal processing system (9) continuous acquisition photodetector (8) output then, and the difference frequency signal that collects handled, according to the relation at the refraction angle of the glass plate (6) of frequency and known thickness:

f＝Kcosθ

Obtain the refraction angle θ that laser is incident to the glass plate (6) of known thickness:

cosθ＝f/K

F is the frequency of heterodyne signal in the formula, and K is the scale-up factor at the refraction angle of the frequency f of heterodyne signal and the glass plate (6) that laser is incident to known thickness, thereby obtains incident angle θ to be measured ₀Size be:

θ ₀＝arcsin(nsinθ)

N is the refractive index of the glass plate (6) of known thickness in the formula.

5. the method for Doppler's galvanometer Sine Modulated multi-beam laser heterodyne second harmonic Laser Measurement incident angle according to claim 4, it is characterized in that electric signal by signal processing system (9) continuous acquisition photodetector (8) output, and the difference frequency signal that collects handled, obtain the incident angle θ of the glass plate (6) of known thickness ₀Process in, the frequency f of heterodyne signal and scale-up factor K adopt following method to obtain:

Because the optical mixing that transmit glass front of laser after glass plate (6) the rear surface reflection of the reflected light of glass plate (6) front surface of known thickness and known thickness k time is with k+1 time, produce the difference frequency signal that two amplitudes differ 2～3 orders of magnitude, the humorous frequency difference of the described secondary of said method is the E of glass plate (6) the rear surface k secondary reflection of known thickness _kWith the E behind glass plate (6) the rear surface k+2 secondary reflection of known thickness _K+2What optical mixing produced;

When laser with incident angle θ ₀Incident field during the glass plate of oblique incidence known thickness (6) front surface is

E (t)=E _lExp (i ω ₀T) formula 1

The simple harmonic oscillation equation of galvanometer (4)

X (t)=x ₀Cos (ω _cT) formula 2

The rate equation of galvanometer (4) is

V (t)=-ω _cx ₀Sin (ω _cT) formula 3

Because the motion of galvanometer (4), catoptrical frequency becomes

ω=ω ₀(1-2 ω _cx ₀Sin (ω _cT)/c) formula 4

Above-mentioned various in, parameter ω ₀Be laser angular frequency, parameter x ₀Be the amplitude of galvanometer (4) vibration, parameter ω _cBe the angular frequency of galvanometer (4), c is the light velocity, and t is the time;

Then t-l/c arrives the reflection light field of glass plate (6) front surface of known thickness constantly and is:

E ₀(t)＝αE _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-l/c))/c)

Formula 5

(t-l/c)+ω ₀x ₀cos(ω _c(t-l/c))/c]}

In the formula, parameter alpha ₀=r, r are the reflection coefficient of the glass plate (6) of known thickness; L is the light path of galvanometer (4) to glass plate (6) front surface of known thickness, and El is the amplitude constant;

, obtain the light field that m restraints transmitted light and be respectively in difference constantly and after transmiting the glass plate (6) of known thickness through the light of glass plate (6) transmission of known thickness by the glass plate of known thickness (6) rear surface reflection m time:

E ₁(t)＝α ₁E _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-(l+2ndcosθ)/c))/c)

(t-(l+2ndcosθ)/c)+ω ₀x ₀cos(ω _c(t-(l+2ndcosθ)/c))/c]}

E ₂(t)＝α ₂E _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-(l+4ndcosθ)/c))/c)

(t-(l+4ndcosθ)/c)+ω ₀x ₀cos(ω _c(t-(l+4ndcosθ)/c))/c]}

E ₃(t)＝α ₃E _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-(l+6ndcosθ)/c))/c)

(t-(l+6ndcos θ)/c)+ω ₀x ₀Cos (ω _c(t-(l+6ndcos θ)/c))/c] } formula 6

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E _m(t)＝α _mE _lexp{i[ω ₀(1-2ω _cx ₀sin(ω _c(t-(l+2mndcosθ)/c))/c)

(t-(l+2mndcosθ)/c)+ω ₀x ₀cos(ω _c(t-(l+2mndcosθ)/c))/c]}

Wherein, parameter alpha ₁=β β ' r ' ..., α _m=β β ' r ' ^(2m-1)β is the transmission coefficient of glass plate (6) front surface of known thickness, transmission coefficient when β ' goes out the glass plate (6) of known thickness for transmittance, r ' is the catoptrical reflection coefficient of the inner front and rear surfaces of glass plate (6) of known thickness, the refraction angle when θ is a light beam from glass plate (6) front surface of surrounding medium incident known thickness, the subscript m value is 0,1,2 ..., n is the refractive index of the glass plate (6) of known thickness, and d is the thickness of the glass plate (6) of known thickness;

Total light field that photodetector (8) receives is expressed as:

E (t)=E ₀(t)+E ₁(t)+... + E _m(t) formula 7

Then the photocurrent of photodetector (8) output can be expressed as:

Formula 8

Wherein, parameter e is an electron charge, and parameter Z is the intrinsic impedance of photodetector (8) surface dielectric, parameter η is a quantum efficiency, and parameter S is the area of photodetector (8) photosurface, and parameter h is a Planck's constant, parameter v is a laser frequency, * number expression complex conjugate;

The electric current of intermediate frequency that arrangement obtains the heterodyne second harmonic signal is:

Formula 9

With formula 5 and formula 6 substitution formula 9, net result is:

Formula 10

Ignore 1/c ³Event after be reduced to:

Formula 11

Wherein, p and j are nonnegative integer;

According to formula 9, the frequency of heterodyne second harmonic signal is designated as:

Formula 12

Learn that according to formula 11 and formula 12 frequency of interference signal and the glass plate of known thickness (6) incident angle are inversely proportional to, scale-up factor is:

Formula 13.

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