CN102221356B - 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

Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic is measured the device and method of laser incident angle

Technical field

The present invention relates to a kind of device and method of measuring laser incident angle.

Background technology

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

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

But there is the slow problem of arithmetic speed that laser difference frequency signal is of poor quality and signal is processed that gathers in existing heterodyne dynamic measuring angle method when measuring laser incident angle.

Summary of the invention

There is in order to solve existing heterodyne dynamic measuring angle method the slow problem of arithmetic speed that laser difference frequency signal is of poor quality and signal is processed that gathers in the present invention, and the Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic proposing is measured the device and method of laser incident angle when measuring laser incident angle.

Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic is measured the device of laser incident angle, and 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 again after 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 mirror reflection is incident to the glass plate front surface of known thickness, in glass plate through the light beam of the glass plate front surface transmission of this known thickness in this known thickness, after the glass plate rear surface of this known thickness and front surface multiple reflections, obtain multi beam reflected light, this multi beam reflected light through after the front surface transmission of the glass plate of this known thickness with glass plate front surface reflection through this known thickness after light beam all by convergent lens, converge on the photosurface of photodetector, described photodetector output electrical signals is to signal processing system.

The method of measuring the measurement device laser incident angle of laser incident angle based on above-mentioned Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic, it is realized by following steps:

First, the driving power of opening galvanometer makes galvanometer start to do simple harmonic oscillation; Meanwhile, open laser instrument;

Then by the electric signal of signal processing system continuous acquisition photodetector output, and the difference frequency signal collecting is processed, 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

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

θ ₀＝arcsin(nsinθ)

The refractive index of the glass plate that in formula, n is known thickness.

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

Feature and deficiency for traditional measuring system, the application has proposed a kind of method of measuring laser incident angle based on vibrating mirror sine modulation multi-beam laser heterodyne second harmonic, by add galvanometer 4 in light path, galvanometer 4 is done simple harmonic oscillation under sinusoidal drive signals effect, can carry out frequency modulation (PFM) to not inciding in the same time the light of its front surface, angle information to be measured is loaded in the difference on the frequency of heterodyne signal second harmonic, by Fourier, change and be easy to just can demodulate angle information to be measured, and measuring accuracy is high.Heterodyne technology and laser doppler technique are combined with, the advantage of two kinds of technology have well been applied in the detection of angle, make to modulate, detect, process simple.

Emulation proves, method is a kind of method of good non-cpntact measurement angle described in the application, can be applied in severe measurement environment.When taking measurement of an angle, adopting said method there is precision high, the advantage such as Linearity is good, and measuring speed is fast.Simulation result shows, the method is when measuring different angles, measuring error is less than 0.789677%, illustrate that the method application is feasible, reliable, can meet the requirement of tiny angle measurement, for many engineering fields provide good measurement means, can be widely used in laser radar, machinery, instrument and meter and electronics product manufacturing industry, there is good application prospect and value.

Accompanying drawing explanation

Fig. 1 is the structural representation that Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic of the present invention is measured the device of laser incident angle; 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 that in figure, curve table is shown into firing 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.

Embodiment

Embodiment one: present embodiment is described in conjunction with Fig. 1, described in present embodiment, the device of Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic measurement laser 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, light beam through described galvanometer 4 reflections is sent to polarizing beam splitter mirror PBS2 again after quarter-wave plate 3 transmissions, 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 glass plate 6 through the light beam of the glass plate 6 front surface transmissions of this known thickness in this known thickness, after glass plate 6 rear surfaces of this known thickness and front surface multiple reflections, obtain multi beam reflected light, this multi beam reflected light through after the front surface transmission of the glass plate 6 of this known thickness with glass plate 6 front surface reflections through this known thickness after light beam all by convergent lens 7, converge on the photosurface of photodetector 8, described photodetector 8 output electrical signals are to 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, the interference at infinity or on lens focal plane has contribution, so when interference is discussed, must consider multiple reflections and refraction effect, multi-beam laser should be discussed and interfere.

But, because laser reflects the optical mixing that transmits glass front after k time and k+1 time in reflected light and the glass rear surface of glass plate 6 front surfaces of known thickness, the amplitude of two difference frequency signals that produce differs 2～3 orders of magnitude, after Fourier transform, in order can to collect good laser difference frequency signal and to improve the arithmetic speed that signal is processed, so here we only consider that detected k secondary reflection transmits the E of front surface _kafter light and rear surface k+2 secondary reflection, transmit the E of front surface _k+2the humorous frequency difference of secondary that optical mixing produces.

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

Embodiment three: present embodiment and embodiment one or two differences are that described galvanometer 4 is Doppler 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 formula, parameter ω ₀for laser angular frequency, parameter x ₀for the amplitude of galvanometer vibration, parameter ω _cfor the angular frequency of galvanometer, c is the light velocity; T is the time.Other composition and connected mode are identical with embodiment one or two.

Embodiment four: the method for the measurement device laser incident angle that the Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic based on described in embodiment one takes measurement of an angle, it is realized by following steps:

First, the driving power of opening galvanometer 4 makes galvanometer 4 start to do simple harmonic oscillation; Meanwhile, H0 solid state laser 1;

Then by the electric signal of signal processing system 9 continuous acquisition photodetectors 8 outputs, and the difference frequency signal collecting is processed, 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

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

θ ₀＝arcsin(nsinθ)

The refractive index of the glass plate 6 that in formula, n is known thickness.

Embodiment five: present embodiment and embodiment four differences are by the electric signal of signal processing system 9 continuous acquisition photodetector 8 outputs, and the difference frequency signal collecting is processed, obtain the incidence angle θ of the glass plate 6 of known thickness ₀process in, the frequency f of heterodyne signal and Proportional coefficient K are to adopt following method to obtain:

Because laser reflects the optical mixing that transmits glass front after k time and k+1 time in the reflected light of glass plate 6 front surfaces and the glass plate of known thickness 6 rear surfaces of known thickness, produce the difference frequency signal that two amplitudes differ 2～3 orders of magnitude, the E of the glass plate 6 rear surface k secondary reflections that the humorous frequency difference of secondary described in said method is known thickness _kwith the E after the glass plate 6 rear surface k+2 secondary reflections of known thickness _k+2optical mixing produces;

When laser is with incidence angle θ ₀incident field during glass plate 6 front surface 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

Due to 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 ₀for laser angular frequency, parameter x ₀for the amplitude of galvanometer 4 vibrations, parameter ω _cfor the angular frequency of galvanometer 4, c is the light velocity;

T-l/c constantly arrives the reflection light field of glass plate 6 front surfaces of known thickness 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 formula, parameter alpha ₀=r, the reflection coefficient of the glass plate 6 that r is known thickness.L is that galvanometer 4 is to the light path of glass plate 6 front surfaces of known thickness, E _lfor amplitude constant;

Through the light of glass plate 6 transmissions of known thickness, in the same time by glass plate 6 rear surfaces reflections m time of known thickness and do not transmiting after the glass plate 6 of known thickness, obtain the expression formula that m restraints transmitted light and write respectively as following form:

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 ' transmits the glass plate 6 of known thickness for light, the catoptrical reflection coefficient of the inner front and rear surfaces of glass plate 6 that r ' is known thickness, refraction angle when θ is light beam light from glass plate 6 front surface of surrounding medium incident known thickness, subscript m value is 0,1,2 ..., n is the refractive index of the glass plate 6 of known thickness, the thickness of the glass plate 6 that d is 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

The photocurrent of photodetector 8 outputs can be expressed as:

$I=\frac{\mathrm{\&eta;e}}{\mathrm{hv}}\frac{1}{Z}\underset{S}{\&Integral;\&Integral;}\frac{1}{2}[E_0\left(t\right)+E_1\left(t\right)+...+E_m\left(t\right)+...]{[E_0\left(t\right)+E_1\left(t\right)+...+E_m\left(t\right)+...]}^{*}\mathrm{<figure-callout\; id="8"\; label="ds\; Formula"\; filenames="HDA0000065397520000011.png"\; state="\{\{state\}\}">ds</figure-callout>}$ Formula 8

Wherein, parameter e is electron charge, and parameter Z is the intrinsic impedance of photodetector 8 surface dielectrics, and parameter η is quantum efficiency, and parameter S is the area of photodetector 8 photosurfaces, and parameter h is Planck's constant, and parameter v is laser frequency, represents complex conjugate No. *;

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

$I_{\mathrm{if}}=\frac{\mathrm{\&eta;e}}{2\mathrm{hv}}\frac{1}{Z}\underset{s}{\&Integral;\&Integral;}\underset{p=0}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\underset{j=p+2}{\overset{\&infin;}{\mathrm{\&Sigma;}}}(E_p\left(t\right){E_j}^{*}\left(t\right)+{E_p}^{*}\left(t\right)E_j\left(t\right))\mathrm{<figure-callout\; id="9"\; label="ds\; Formula"\; filenames="HDA0000065397520000011.png"\; state="\{\{state\}\}">ds</figure-callout>}$ Formula 9

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

$I_{\mathrm{IF}}=\frac{\mathrm{\&eta;e}}{\mathrm{hv}}\frac{\mathrm{\&pi;}}{Z}{E}_0^2\underset{p=0}{\overset{m-1}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{m-p}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{j+p}{\mathrm{\&alpha;}}_j\cos [\frac{8\mathrm{nd}\cos {\mathrm{\&theta;\&omega;}}_0{\mathrm{\&omega;}}_c^2{x}_0}{c^2}t+\frac{2{\mathrm{\&omega;}}_c{x}_0}{c}-\frac{4\mathrm{nd}{\mathrm{\&omega;}}_0\cos \mathrm{\&theta;}}{c}$

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:

$I_{\mathrm{IF}}=\frac{\mathrm{\&eta;e}}{\mathrm{hv}}\frac{\mathrm{\&pi;}}{Z}{E}_0^2\underset{p=0}{\overset{m-1}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{m-p}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{j+p}{\mathrm{\&alpha;}}_j\cos (\frac{8\mathrm{nd}\cos {\mathrm{\&theta;\&omega;}}_0{\mathrm{\&omega;}}_c^2{x}_0}{c^2}t+\frac{{2\mathrm{\&omega;}}_0{x}_0-4\mathrm{nd}{\mathrm{\&omega;}}_0\cos \mathrm{\&theta;}}{c})$ 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

According to formula 11 and formula 12, learn, the frequency of interference signal and the glass plate of known thickness 6 refraction angle θ are inversely proportional to, and 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 ₀as shown in Figure 3, as can be seen from Figure 3, along with the increase of incident angle, the increase frequency that relative position of frequency spectrum moves along with angle to low frequency direction reduces corresponding multi-beam laser heterodyne second harmonic signal Fourier transform frequency spectrum.In the situation that glass plate 6 thickness of known thickness are constant, Proportional coefficient K is constant, because frequency f and Proportional coefficient K close, is f=Kcos θ=Kcos (arcsin (sin θ ₀/ n)), laser incident angle θ ₀with the frequency f relation that is inversely proportional to, work as incidence angle θ ₀during increase, frequency f reduces thereupon, and the relative position of frequency spectrum moves to low frequency direction, and Fig. 3 has verified the correctness of theoretical analysis above well.It should be noted 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 modulation 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

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

Feature and deficiency for traditional measuring system, the application has proposed a kind of method taking measurement of an angle based on vibrating mirror sine modulation multi-beam laser heterodyne second harmonic, by add galvanometer 4 in light path, galvanometer 4 is done simple harmonic oscillation under sinusoidal drive signals effect, can carry out frequency modulation (PFM) to not inciding in the same time the light of its front surface, angle information to be measured is loaded in the difference on the frequency of heterodyne signal second harmonic, by Fourier, change and be easy to just can demodulate angle information to be measured, and measuring accuracy is high.Heterodyne technology and laser doppler technique are combined with, the advantage of two kinds of technology have well been applied in the detection of angle, make to modulate, detect, process simple.

Emulation proves, method is a kind of method of good non-cpntact measurement angle described in the application, can be applied in severe measurement environment.When taking measurement of an angle, adopting said method there is precision high, the advantage such as Linearity is good, and measuring speed is fast.Simulation result shows, the method is when measuring different angles, measuring error is less than 0.789677%, illustrate that the method application is feasible, reliable, can meet the requirement of tiny angle measurement, for many engineering fields provide good measurement means, can be widely used in laser radar, machinery, instrument and meter and electronics product manufacturing industry, there is good application prospect and value.

Above content is in conjunction with concrete preferred implementation further description made for the present invention, can not assert that specific embodiment of the 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. Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic is measured the device of laser incident angle, it is characterized in that it comprises H ₀solid state laser (1), polarizing beam splitter mirror PBS(2), glass plate (6), convergent lens (7), photodetector (8) and the signal processing system (9) of quarter-wave plate (3), galvanometer (4), plane mirror (5), known thickness,

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

2. Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic according to claim 1 is measured the device of laser incident angle, 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) form, described wave filter (9-1) carries out sending to prime amplifier (9-2) after filtering to the electric signal of the photodetector receiving (8) output, signal after prime amplifier (9-2) amplifies is exported to analog to digital converter (A/D), described analog to digital converter (A/D) sends to digital signal processor (DSP) by the digital signal after conversion.

3. Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic according to claim 1 and 2 is measured the device of laser incident angle, it is characterized in that described galvanometer (4) is Doppler galvanometer, and the simple harmonic oscillation equation of described Doppler galvanometer is:

x(t)=x ₀cos(ω _ct)

The rate equation of Doppler galvanometer is:

v(t)=-ω _cx ₀sin(ω _ct)

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

4. based on Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic claimed in claim 1, measure the method for the measurement device laser incident angle of laser incident angle, it is characterized in that it is realized by following steps:

First, the driving power of opening galvanometer (4) makes galvanometer (4) start to do simple harmonic oscillation; Meanwhile, open H ₀solid state laser (1);

Then by the electric signal of signal processing system (9) continuous acquisition photodetector (8) output, and the difference frequency signal collecting is processed, according to the relation at the refraction angle of the glass plate of frequency and known thickness (6):

f=Kcosθ

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

cosθ=f/K

In formula, f is the frequency of heterodyne signal, 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 incidence angle θ to be measured ₀size be:

θ ₀=arcsin(nsinθ)

The refractive index of the glass plate that in formula, n is known thickness (6).

5. the method for measuring the measurement device laser incident angle of laser incident angle based on Doppler vibrating mirror sine modulation multi-beam laser heterodyne second harmonic according to claim 4, it is characterized in that by the electric signal of signal processing system (9) continuous acquisition photodetector (8) output, and the difference frequency signal collecting is processed, obtain the incidence angle θ of the glass plate (6) of known thickness ₀process in, the frequency f of heterodyne signal and Proportional coefficient K are to adopt following method to obtain:

Because laser reflects the optical mixing that transmits glass front after k time and k+1 time at the reflected light of glass plate (6) front surface of known thickness and glass plate (6) rear surface of known thickness, produce the difference frequency signal that two amplitudes differ 2～3 orders of magnitude, the E of glass plate (6) the rear surface k secondary reflection that the humorous frequency difference of secondary of said method is known thickness _kwith the E after glass plate (6) the rear surface k+2 secondary reflection of known thickness _k+2optical mixing produces;

When laser is with incidence angle θ ₀the incident field during 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

Due to 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 ₀for laser angular frequency, parameter x ₀for the amplitude of galvanometer (4) vibration, parameter ω _cfor the angular frequency of galvanometer (4), c is the light velocity, and t is the time;

T-l/c constantly arrives the reflection light field of glass plate (6) front surface of known thickness 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 formula, parameter alpha ₀=r, the reflection coefficient of the glass plate that r is known thickness (6); L is that galvanometer (4) is to the light path of glass plate (6) front surface of known thickness, E _lfor amplitude constant;

Through the light of glass plate (6) transmission of known thickness, in the same time by the glass plate of known thickness (6) rear surface reflection m time and do not transmiting after the glass plate (6) of known thickness, obtain the light field that m restraints transmitted light and be respectively:

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 ' transmits the glass plate (6) of known thickness for light, the catoptrical reflection coefficient of the inner front and rear surfaces of the glass plate that r ' is known thickness (6), refraction angle when θ is light beam from glass plate (6) front surface of surrounding medium incident known thickness, subscript m value is 0,1,2 ..., n is the refractive index of the glass plate (6) of known thickness, the thickness of the glass plate that d is known thickness (6);

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

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

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

formula 8

Wherein, parameter e is electron charge, and parameter Z is the intrinsic impedance of photodetector (8) surface dielectric, parameter η is quantum efficiency, and parameter S is the area of photodetector (8) photosurface, and parameter h is Planck's constant, parameter v is laser frequency, represents complex conjugate No. *;

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

formula 9

By 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

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

formula 13.

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