CN101832819A - Method for synchronously measuring non-orthogonal polarization angle and elliptic polarization angle of dual-frequency laser - Google Patents

Abstract

The invention discloses a method for synchronously measuring a non-orthogonal polarization angle and an elliptic polarization angle of a dual-frequency laser, which belongs to the technical field of laser application. The method comprises the following steps of: forming the dual-frequency laser to be measured into optical beat frequency by using a polarizer, converting the optical beat frequency into an alternating current signal by using a photoelectric detecting circuit, and measuring an amplitude value of the alternating current signal by using an effective value converting circuit and an AD acquisition circuit; and rotating the polarizer, and solving the non-orthogonal polarization angle and the elliptic polarization angle of the dual-frequency laser to be measured at the same time by measuring a maximum value and a minimum value of the amplitude of the beat frequency. In the method, on the basis of a perfect theoretical model, the characteristics of non-orthogonal polarization and elliptical polarization of the dual-frequency laser are considered synthetically, so the measurement on the non-orthogonal polarization and the elliptical polarization are finished synchronously without theoretical measurement error; and an azimuth angle of a transmission axis of the polarizer does not need to be measured technically, so that the measurement error caused by angle measurement is avoided and high-precision measurement is more easily to realize.

Description

Nonopiateization of the polarization angle of double-frequency laser and polarization ellipse angle method for synchronously measuring

Technical field

The invention belongs to nonopiateization of the polarization angle and the polarization ellipse angle method for synchronously measuring in laser application technique field, particularly a kind of double-frequency laser.

Background technology

Dual-frequency laser source is the core component units of ultraprecise laser heterodyne interference measuring system, and its output laser comprises the light component of two different frequencies and polarization state, and the polarization characteristic of double-frequency laser is one of important parameter that characterizes the light source quality good or not.Imperfectization of double-frequency laser polarization characteristic comprises nonopiateization of polarization and polarization ellipseization, they are main sources of nonlinearity erron in the laser heterodyne interference measuring system, the measuring error of its introducing can reach several to tens of several nanometers, is seriously restricting the resolving power of measuring system.In order to realize the measurement resolution of nanometer scale, need as nonopiateization of polarization angle and polarization ellipse angle, carry out strict measurement to the polarization characteristic parameter of dual-frequency laser source.

The stokes parameter representation is to describe comprehensive, the most general method of light beam polarization state, by measure whole polarization characteristic parameters that stokes parameter can obtain tested light beam (Feng Weiwei. the stokes parameter of light polarization and degree of polarization intelligent measuring. the master of Qufu Normal University thesis), present business-like fall-off meter all is to be based upon on the light beam stokes parameter representation.Yet, this method is only applicable to monochromatic plane wave, be not suitable for the light beam situation of a plurality of wavelength and polarization state aliasing, the dual-frequency laser source in the laser heterodyne interference measuring system for example, when its output double-frequency laser departs from desirable linear polarization quadrature situation, technical can't be effectively the light component of two different frequencies the separation fully, thus also can't measure the polarization state of each frequency component independently.

Shanghai Optics and Precision Mechanics institute, Chinese Academy of Sciences executes will and really waits the people to detect nonopiateization of double-frequency zeeman laser device outgoing polarisation of light angle (Shi Zhiguo by the following method, vertical zeeman frequency stabilization research of Gong Jin duckweed .Uniphase 1007 type He-Ne laser tubes. the optics journal, 1993,13 (2): 102-106): double-frequency laser is formed optical beat after by polaroid, its amplitude V (θ) changes with the change of polaroid azimuth angle theta, measures two adjacent minimal value V of V (θ) _Min(θ ₁) and V _Min(θ ₂) corresponding angle θ ₁And θ ₂, can calculate nonopiateization of double-frequency laser polarization angle beta=pi/2-(θ ₂-θ ₁), the method has also defined the polarization separation degree P=V of tested light beam _Max(θ)/V _Min(θ).Yet, this method has following deficiency: one, this method only is only during for strict linearly polarized light correct at the light component of two different frequencies of double-frequency laser, perhaps only when the ovalization degree of the light component of two different frequencies is very little, just can obtain satisfactory approximation; Its two, this method need be known the azimuthal concrete numerical value of polarization of beat frequency amplitude minimal value correspondence, and the measuring accuracy of this angle value can be introduced measuring error to the calculating at nonopiateization of polarization angle; Its three, though this method has defined the polarization separation degree of tested double-frequency laser, do not provide the measurement approach of polarization ellipse angle.

People such as the Gao Sai of Tsing-Hua University are on the basis that the beat frequency amplitude detects, the measurement model and the measurement means (Gao Sai at nonopiateization of the polarization angle and the polarization ellipse angle of double-frequency laser have been set up, Yin Chunyong, Guo Jihua. the experimental study of double reflecting film two-frequency He-Ne laser instrument dual frequency characteristics and polarization characteristic. optical technology, 2006,26 (6): 529-531).Aspect measurement model, this method has carried out nonopiateization of polarization and the polarization ellipse characteristic of double-frequency laser to consider that independently promptly under the situation of not considering polarization ellipseization nonopiateization of polarization angle is measured, vice versa; Aspect measurement means, the metering system at nonopiateization of polarization angle is with above to execute the approach that will really waits the people to take similar in this method, and the polarization ellipse angle is then by formula ρ=tg ^-1(V _Min/ 2V _Max) calculating, wherein V _MinAnd V _MaxBe the minimal value and the maximum value of beat frequency amplitude.Yet, this method has the deficiency of two aspects: on the one hand, the consideration that this method has been carried out nonopiateization of polarization of double-frequency laser and polarization ellipse characteristic independently, separated artificially, but these two kinds of imperfectization of polarization characteristics are simultaneous often in practical situation, therefore this method is short of on measurement model to some extent, and also can only the accurate approximate value of right and wrong, the particularly measurement at polarization ellipse angle can have bigger error based on the result of calculation that the imperfection model draws; On the other hand, this method still needs to measure the position angle of the pairing analyzer light transmission shaft of beat frequency extreme point technically, thus the measuring error that can't avoid measurement of angle to introduce.

In sum, based on the light polarization method for expressing of stokes parameter and corresponding measuring method thereof and be not suitable for dual-frequency laser source, and that existing imperfectization of the double-frequency laser polarization characteristic measuring method that detects based on the beat frequency amplitude remains on theoretical model is further perfect, also comes with some shortcomings technically.

Summary of the invention

Deficiency at existing measuring method, the present invention proposes a kind of nonopiateization of polarization angle and polarization ellipse angle method for synchronously measuring of double-frequency laser, its objective is that the measurement for imperfectization of dual-frequency laser source polarization characterisitic parameter provides a kind of based on the high-precision measuring method that improves theoretical model technically.

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

A kind of nonopiateization of polarization angle of double-frequency laser and polarization ellipse angle method for synchronously measuring, this method may further comprise the steps:

(1) be f with frequency ₁And f ₂, nonopiateization of polarization angle is that β, polarization ellipse angle are that the tested double-frequency laser of ρ forms optical beat signal after by polarizer, its frequency is | f ₂-f ₁|, amplitude is that (α), wherein α is the position angle of polarizer light transmission shaft to A for β, ρ;

(2) the described optical beat signal of step (1) is received and is converted to ac signal by the photodetection circuit, and its frequency is | f ₂-f ₁|, amplitude is A _e(β, ρ, α)=(α), wherein k is the gain of photodetection circuit to kA for β, ρ;

(3) the described ac signal of step (2) enters the AC value change-over circuit, and this change-over circuit output voltage is the effective value of input exchange signal, promptly

Its numerical value is measured by the AD Acquisition Circuit;

(4) rotatory polarization device changes its light transmission shaft azimuth angle alpha, and AC value change-over circuit output voltage changes with the α angle, maximum value U occurs _Max1, U _Max2With minimal value U _Min, U wherein _Max1〉=U _Max2

(5) by the extreme voltage U that measures _Max1, U _Max2And U _Min, nonopiateization of the polarization angle of calculating tested double-frequency laser

With the polarization ellipse angle $\mathrm{\&rho;}=(1/2)\arccos [(\sqrt{U_{\max 1}^2-{\mathrm{<figure-callout\; id="2"\; label="U\; min"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\min }^{}}+\sqrt{U_{\max 2}^2-U_{\min }^2})/(U_{\max 1}+U_{\max 2})].$

The present invention has following characteristics and good result:

(1) method synthesis among the present invention has been considered nonopiateization of polarization and two kinds of imperfect polarization characteristics of polarization ellipseization of double-frequency laser, measurement to the two is finished synchronously, resulting nonopiateization of polarization angle and polarization ellipse angle are to separate accurately, and existing method is separated these two kinds of imperfect polarization characteristics, independently measure, what obtain is separating of being similar to, so the method among the present invention has higher measuring accuracy in theory;

(2) method among the present invention only needs the maximum value and the minimal value of the detection laser amplitude of beat, promptly can accurately find the solution nonopiateization of the polarization angle and the polarization ellipse angle of tested double-frequency laser, do not need to measure the position angle of the pairing polarizer light transmission shaft of extreme point, thereby avoided the measuring error that measurement of angle is introduced in the existing method, so the method among the present invention technically also has higher measuring accuracy.

Description of drawings

Fig. 1 is a double-frequency laser polarization state synoptic diagram

Fig. 2 is a double-frequency laser polarization state measurement mechanism schematic diagram

Fig. 3 is that double-frequency laser beat frequency amplitude is with the azimuthal change curve of polarizer

Among the figure, two different frequencies of 1 and 2 double-frequency lasers and light component, 3 polarizers, 4 photodetection circuit, 5 AC value change-over circuits, the 6AD Acquisition Circuit of polarization state.

Embodiment

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

Fig. 1 is a double-frequency laser polarization state synoptic diagram, and the double-frequency laser among the figure includes the light component 1 and 2 of two different frequencies and polarization state, and the frequency of their correspondences is designated as f respectively ₁And f ₂In the practical application, because the restriction of various non-ideal factors, the polarization state of double-frequency laser departs from desirable linear polarization quadrature, as shown in Figure 1,1 and 2 is strict linearly polarized light, but have the elliptically polarized light of polarization ellipse angle ρ, and wherein 1 is right-handed elliptical polarization light, 2 is left-handed elliptically polarized light.In addition, the angle of 1 and 2 main shafts neither be strict 90 °, their polarization non-orthogonal angles is designated as β.

For simplicity, get the x coordinate axis and overlap (choosing of coordinate axis do not influence The ultimate results) with 1 main shaft, then 1 Jones matrix can be expressed as

$E_1=R_1\left[\begin{array}{c}\cos \mathrm{\&rho;exp}\left[i\left(2\mathrm{\&pi;}{f}_{1}t\right)\right]\\ \sin \mathrm{\&rho;exp}\left[i(2\mathrm{\&pi;}{f}_{1}t+\mathrm{\&pi;}/2)\right]\end{array}\right]$

The phase place pi/2 shows that 1 is right-handed elliptical polarization light in the formula, R ₁It is 1 major axis radius.For 2, it can be regarded as by 1 and be rotated counterclockwise angle pi/2-β and obtain, and can get according to the Rotating Transition of Coordinate formula

${\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">E</figure-callout>}}_2={\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">R</figure-callout>}}_2\left[\begin{array}{cc}\cos (\mathrm{\&pi;}/2-\mathrm{\&beta;})& -\sin (\mathrm{\&pi;}/2-\mathrm{\&beta;})\\ \sin (\mathrm{\&pi;}/2-\mathrm{\&beta;})& \cos (\mathrm{\&pi;}/2-\mathrm{\&beta;})\end{array}\right]\left[\begin{array}{c}\cos \mathrm{\&rho;exp}\left[j\left(2\mathrm{\&pi;}{f}_{2}t\right)\right]\\ \sin \mathrm{\&rho;exp}\left[j(2\mathrm{\&pi;}{f}_{2}t-\mathrm{\&pi;}/2)\right]\end{array}\right]$

$={\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">R</figure-callout>}}_2\left[\begin{array}{c}\cos \mathrm{\&rho;}\sin \mathrm{\&beta;exp}\left[j\left(2\mathrm{\&pi;}{f}_{2}t\right)\right]-\sin \mathrm{\&rho;}\cos \mathrm{\&beta;exp}\left[j(2\mathrm{\&pi;}{f}_{2}t-\mathrm{\&pi;}/2)\right]\\ \cos \mathrm{\&rho;}\cos \mathrm{\&beta;exp}\left[j\left(2\mathrm{\&pi;}{f}_{2}t\right)\right]+\sin \mathrm{\&rho;}\sin \mathrm{\&beta;exp}\left[j(2\mathrm{\&pi;}{f}_{2}t-\mathrm{\&pi;}/2)\right]\end{array}\right]$

Phase place-pi/2 shows that 2 is left-handed elliptically polarized lights in the formula, R ₂It is 2 major axis radius.

Fig. 2 is a double-frequency laser polarization state measurement mechanism schematic diagram, comprises polarizer 3, photodetection circuit 4, AC value change-over circuit 5, AD Acquisition Circuit 6.Tested double-frequency laser forms optical beat by polarizer 3 backs, receive and be converted into ac signal by photodetection circuit 4, this ac signal enters AC value change-over circuit 5, the output voltage of AC value change-over circuit 5 is the effective value of input exchange signal, and this effective value voltage is measured by AD Acquisition Circuit 6.

As shown in Figure 1, the angle of the light transmission shaft of polarizer 3 and x axle is α, and then double-frequency laser is by behind the polarizer 3, and the optical field distribution on its light transmission shaft direction is

E＝[cosα?sinα].(E ₁+E ₂)

＝R ₁[cosρcosαexp(i2πf ₁t)+sinρsinαexp(i2πf ₁t+π/2)]+

＝R ₂[cosρsin(α+β)exp(i2πf ₂t)-sinρcos(α+β)exp(i2πf ₂t-π/2)]

Transmitted light intensity is I=E.E ^*, transmitted light is received by photodetection circuit 4, and the alternating component in its output signal is

$I_A=k\&CenterDot;R_1\&CenterDot;R_2\left\{2\right[{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&rho;}\cos \mathrm{\&alpha;}\sin (\mathrm{\&alpha;}+\mathrm{\&beta;})+{\sin }^2\mathrm{\&rho;}\sin \mathrm{\&alpha;}\cos (\mathrm{\&alpha;}+\mathrm{\&beta;})\left]\cos \right[2\mathrm{\&pi;}(f_1-f_2)t]$

$+2\cos \mathrm{\&rho;}\sin \mathrm{\&rho;}[-\cos \mathrm{\&alpha;}\cos (\mathrm{\&alpha;}+\mathrm{\&beta;})+\sin \mathrm{\&alpha;}\sin (\mathrm{\&alpha;}+\mathrm{\&beta;})]\cos [2\mathrm{\&pi;}(f_1-f_2)t+\mathrm{\&pi;}/2]\}$

$=k\&CenterDot;R_1\&CenterDot;R_2\left\{\right[\sin (2\mathrm{\&alpha;}+\mathrm{\&beta;})+\sin \mathrm{\&beta;}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&rho;}\left]\cos \right[2\mathrm{\&pi;}(f_1-f_2)t]$

$+\sin 2\mathrm{\&rho;}\cos (2\mathrm{\&alpha;}+\mathrm{\&beta;})\sin \left[2\mathrm{\&pi;}(f_1-f_2)t\right]\}$

In the formula, phase place

K is the gain of photodetection circuit, and (β, ρ α) are the amplitude of beat frequency light signal, A to A _e(β, ρ, α)=(β, ρ are the amplitude of beat frequency electric signal α) to kA, make K=kR ₁R ₂, A then _e(β, ρ α) can be calculated by following formula

$A_e^2(\mathrm{\&beta;},\mathrm{\&rho;},\mathrm{\&alpha;})=K^2\{{[\sin (2\mathrm{\&alpha;}+\mathrm{\&beta;})+\sin \mathrm{\&beta;}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&rho;}]}^2+{\left[\sin 2\mathrm{\&rho;}\cos (2\mathrm{\&alpha;}+\mathrm{\&beta;})\right]}^2\}$

$=K^2[{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">cos</figure-callout>}}^{2}2\mathrm{\&rho;}{\sin }^2(2\mathrm{\&alpha;}+\mathrm{\&beta;})+2\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&rho;}\sin \mathrm{\&beta;}\sin (2\mathrm{\&alpha;}+\mathrm{\&beta;})-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">cos</figure-callout>}}^{2}2\mathrm{\&rho;}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&beta;}+1]$

Observe

Mathematic(al) representation, as can be known

Be the quadratic function of sin (2 alpha+beta), and sin (2 alpha+beta) ∈ [1,1], when sin (2 alpha+beta)=-during sin β/cos2 ρ, Obtain minimal value

$A_{e\mathrm{<figure-callout\; id="2"\; label="min"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">min</figure-callout>}}^2=K^2(1-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&beta;})(1-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">cos</figure-callout>}}^{2}2\mathrm{\&rho;})$

When sin (2 alpha+beta)=± 1,

Obtain two maximum value

$A_{e\max 1}^2=K^2{[1+\cos \left(2\mathrm{\&rho;}\right)\sin \mathrm{\&beta;}]}^2$

${\mathrm{<figure-callout\; id="2"\; label="A\; e\; max"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">A</figure-callout>}}_{e\max }^2=K^2{[1-\cos \left(2\mathrm{\&rho;}\right)\sin \mathrm{\&beta;}]}^2$

Because sin (2 alpha+beta) is the periodic function of polarizer 3 light transmission shaft azimuth angle alpha, its cycle is π, when polarizer rotation half cycle,

Obtain maximum value one time

A maximum value

And twice minimal value

Shown in the curve among Fig. 3 (, get β=5 ° among the figure, ρ=2 °) for the ease of observing.Correspondingly, maximum value also appears one time in the output voltage of AC value change-over circuit 5

A maximum value And twice minimal value

Substitution

With

Expression formula can obtain in the hope of separating

$\mathrm{\&beta;}=\arcsin \left(\frac{\sqrt{U_{\max 1}^2-U_{\min }^2}-\sqrt{U_{\max 2}^2-U_{\min }^2}}{U_{\max 1}+U_{\max 2}}\right)$

$\mathrm{\&rho;}=\frac{1}{2}\arccos \left(\frac{\sqrt{U_{\max 1}^2-{\mathrm{<figure-callout\; id="2"\; label="U\; min"\; filenames="HSA00000103468600011.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\min }^{}}+\sqrt{U_{\max 2}^2-U_{\min }^2}}{U_{\max 1}+U_{\max 2}}\right)$

By above-mentioned embodiment as can be known, method synthesis among the present invention has been considered nonopiateization of polarization and two kinds of imperfect polarization characteristics of polarization ellipseization of double-frequency laser, measurement to the two is finished synchronously, resulting nonopiateization of polarization angle and polarization ellipse angle are to separate accurately, and existing method is separated two kinds of imperfect polarization characteristics, independently measure, what obtain is separating of being similar to.At this point, illustrate in conjunction with Fig. 1: (1) as nonopiateization of polarization angle β=5 °, and the polarization ellipse angle is ρ=2 °, Theoretical Calculation normalization extreme value U _Max1(42.5 °)=1, U _Max1(132.5 °)=0.84006 and U _Min(90 °, 175 °)=0.06394 can get β '=pi/2-(175 °-90 °)=5 °, ρ '=tg by existing measuring method ^-1(U _Min/ 2U _Max1)=1.8310 °; (2) as nonopiateization of polarization angle β=5 °, the polarization ellipse angle is ρ=5 °, Theoretical Calculation normalization extreme value U _Max1(42.5 °)=1, U _Max1(132.5 °)=0.84193 and U _Min(90 °, 175 °)=0.15932 can get β '=pi/2-(175 °-90 °)=5 °, ρ '=tg by existing measuring method ^-1(U _Min/ 2U _Max1)=4.5546 °; (3) as nonopiateization of polarization angle β=5 °, the polarization ellipse angle is ρ=8 °, Theoretical Calculation normalization extreme value U _Max1(42.5 °)=1, U _Max1(132.5 °)=0.84538 and U _Min(90.25 °, 174.88 °)=0.25340 can get β '=pi/2-(174.88 °-90.25 °)=5.37 °, ρ '=tg by existing measuring method ^-1(U _Min/ 2U _Max1)=7.2203 °; (4) as nonopiateization of polarization angle β=5 °, the polarization ellipse angle is ρ=11 °, Theoretical Calculation normalization extreme value U _Max1(42.5 °)=1, U _Max1(132.5 °)=0.85047 and U _Min(90.25 °, 174.75 °)=0.34529 can calculate β '=pi/2-(174.75 °-90.25 °)=5.5 °, ρ '=tg according to current measuring methods ^-1(U _Min/ 2U _Max1)=9.7953 °.Have bigger measuring error by the existing as can be known measuring method of aforementioned calculation result in the measurement of polarization ellipse angle, when the polarization ellipse degree was big, also there was certain error in the measurement at nonopiateization of polarization angle.It should be noted that, above-mentioned result of calculation is not draw under there are not the situation of error in supposition amplitude and measurement of angle, yet nonetheless, result of calculation that existing measuring method obtains and actual value still have certain difference, this is because existing measuring method builds on the imperfection theoretical model, and there is not theoretic measuring error in the method among the present invention based on perfect theoretical model, therefore has higher measuring accuracy.

In addition, by above-mentioned embodiment as can be known, method among the present invention only needs the maximum value and the minimal value of the detection laser amplitude of beat, promptly can accurately find the solution nonopiateization of the polarization angle and the polarization ellipse angle of tested double-frequency laser, do not need to measure the position angle of the pairing polarizer light transmission shaft of extreme point, thereby avoided the measuring error that measurement of angle is introduced in the existing method, so the method among the present invention technically also has higher measuring accuracy.

Claims (1)

1. nonopiateization of the polarization angle of a double-frequency laser and polarization ellipse angle method for synchronously measuring is characterized in that this method may further comprise the steps:

(1) be f with frequency ₁And f ₂, nonopiateization of polarization angle is that β, polarization ellipse angle are that the tested double-frequency laser of ρ forms optical beat signal after by polarizer, its frequency is | f ₂-f ₁|, amplitude is that (α), wherein α is the position angle of polarizer light transmission shaft to A for β, ρ;

(2) the described optical beat signal of step (1) is received and is converted to ac signal by the photodetection circuit, and its frequency is | f ₂-f ₁|, amplitude is A _e(β, ρ, α)=(α), wherein k is the gain of photodetection circuit to kA for β, ρ;

(3) the described ac signal of step (2) enters the AC value change-over circuit, and this change-over circuit output voltage is the effective value of input exchange signal, promptly

Its numerical value is measured by the AD Acquisition Circuit;

(4) rotatory polarization device changes its light transmission shaft azimuth angle alpha, and AC value change-over circuit output voltage changes with the α angle, maximum value U occurs _Max1, U _Max2With minimal value U _Min, U wherein _Max1〉=U _Max2

(5) by the extreme voltage U that measures _Max1, U _Max2And U _Min, nonopiateization of the polarization angle of calculating tested double-frequency laser

With the polarization ellipse angle

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