CN102042874B - Light intensity modulator-based far-field beam quality measuring device - Google Patents

Abstract

The invention discloses a light intensity modulator-based far-field beam quality measuring device, which consists of an imaging system, a light intensity modulator, a light intensity detector and a computer. Light beams are converged at the light intensity modulator through the imaging system, and light passing through the light intensity modulator enters the light intensity detector, is captured by the light intensity detector, and is finally output by the light intensity detector through the computer to reflect the numerical value of the beam quality. The beam quality is measured in a form of combining the light intensity detector and the light intensity modulator, the device has the characteristics of simple structure, easy manufacture, high speed, high response sensitivity, high detection precision and the like; and the numerical value can be used as a performance evaluation index for a real-time closed loop of a high-speed adaptive optical system.

Description

Far field beam quality measurement mechanism based on light intensity modulator

Technical field

The present invention relates to a kind of beam quality measurement mechanism, particularly a kind of far field beam quality measurement mechanism based on light intensity modulator.

Background technology

As everyone knows, inhomogeneous when the light intensity of incident beam, under the more weak situation of incident intensity, utilize traditional adaptive optics closed-loop policy of position, detection near field phase distortions such as Hartmann can't use.Thus; Piotr Piatrou and M.J.Booth etc. have successively proposed to utilize the far field light intensity to realize the ADAPTIVE OPTICS SYSTEMS closed loop at article " Beaconless stochastic parallel gradient descent laser beam control:numerical experiments, APPLIED OPTICS, 46 (27); 2007 " and " Wavefront sensorless adaptive optics for large aberrations; OPTICS LETTERS, 32,5 (2007) ".They have proposed a kind of new beam quality evaluation index in document, and point out to utilize this new evaluation index can accurate guidance ADAPTIVE OPTICS SYSTEMS closed loop, proofread and correct the position phase distortion of incident beam.All adopt CCD record far-field intensity distribution in the document, then utilize the method for software weighting to realize obtaining this new evaluation index.The problem that this acquisition methods brought is: on the one hand, because the normal CCD speed of detection is slower, the necessary in addition ranking operation time, the performance index of being obtained are bigger at interval, and the ADAPTIVE OPTICS SYSTEMS closed-loop bandwidth of forming thus is inevitable less; On the other hand, the CCD dynamic range is less, and the light intensity of surveying distributional difference before and after proofreading and correct is bigger, and it is too little and the zone that can't survey makes the performance index that finally calculate inaccurate to be easy to occur light intensity zone of saturation or light intensity.

Utilize hardware mode to realize the beam quality evaluation index that above-mentioned document is required at present, promptly

$V={\∫}_0^R{\∫}_0^{2\mathrm{\π}}{I}_{\mathrm{in}}(r,\mathrm{\θ})*D(r,\mathrm{\θ})\mathrm{rdrd\θ},---\left(a\right)$

Wherein, $D=\left\{\begin{array}{cc}1-\frac{r}{R},& r<R\\ 0,& R-r\&le;0\end{array}\right.,$

Only realize simple evaluation index calculating with pin hole; As; Mikhail A.Vorontsov utilizes pin hole hardware evaluation index to realize adaptive optics closed loop at a high speed at document " Adaptive optics based on analog parallel stochastic optimization:analysis and experimental demonstration; J.Opt.Soc.Am.17,1440,2000 ".Yet; Adopt pin hole to realize that simple evaluation index calculates, this hardware mode in essence just the beam quality evaluation index that provides of formula (a) find the solution a special case of mode, and Chen Bo etc. points out in document " point target imaging self-adaptive optical random paralleling gradient descent algorithm performance index and speed of convergence; optics journal; 29 (5), 2009 " after deliberation, is performance index with encircled power (evaluation index that promptly realizes with pin hole); The adaptive optics correcting result is absorbed in local minimum easily, rather than satisfies the global minimum that is corrected to optimal effectiveness.

Summary of the invention

The technical matters of device solves of the present invention is: overcome prior art and utilize CCD and software method of weighting to realize the drawback that exists when the beam quality evaluation index is obtained; Overcome utilize hardware evaluation index that pin hole realizes be absorbed in the characteristics of local minimum easily; A kind of high speed, sensitivity, accurate are provided; The beam quality measurement mechanism that is easy to realize is realized real-time closed-loop control at a high speed in order to cooperate ADAPTIVE OPTICS SYSTEMS.

Far field beam quality measurement mechanism based on light intensity modulator of the present invention, the technical scheme of technical solution problem is: imaging system, light intensity modulator and the light intensity detector on optical axis, arranged in regular turn; The data input/output terminal of the output terminal of light intensity detector and computing machine is connected, and imaging system changes the incident beam that receives into convergent beam; Convergent beam and modulation that light intensity modulator will receive different beam qualities generate the output beam with different-energy size; Light intensity detector is caught the output beam after the modulation and is exported the numerical value of reflected collimated light beam quality; Computer acquisition light intensity detector output in order to the numerical value of reflected collimated light beam quality and in the display of computing machine, show.

Wherein, the modulating function D of described light intensity modulator (r, θ) statement is as follows:

$D=\left\{\begin{array}{cc}1-\frac{r}{R},& r<R\\ 0,& R-r\&le;0\end{array}\right.$ Or

$D=\left\{\begin{array}{cc}1,& r_{2k}<r<r_{2k+1}\mathrm{And\; r}<R\\ 0,& \mathrm{Others}\end{array}\right.$ Or

$D=\left\{\begin{array}{cc}1,& {\mathrm{\&theta;}}_{2k}<\mathrm{\&theta;}<{\mathrm{\&theta;}}_{2k+1}\mathrm{and\; r}<R\\ 0,& \mathrm{others}\end{array}\right.$

R, θ are to be the polar coordinate system on plane with the light intensity modulator front surface; R is the effective detecting area radius of light intensity detector; r _2kAnd θ _2kBe respectively light intensity modulator radially with angle design parameter, and 0＜r _2k＜R, 0＜θ _2k＜2 π, k are natural numbers.

Wherein, described imaging system is made up of monolithic or multi-disc lens.

Wherein, described light intensity detector is a kind of in ccd detector or photomultiplier or avalanche diode or the PIN pipe.

The present invention compared with prior art has following advantage:

(1) because the performance index that the present invention or employing M.J.Booth propose; Corresponding to modulating function D (r, first kind of expression-form θ), or on traditional pin hole beam quality evaluation index, revise; Corresponding to modulating function D (r; θ) second and third kind of expression-form makes beam quality evaluation index and spot radius be near-linear and changes, thereby utilizes the present invention to instruct the adaptive optics closed loop to be not easy to be absorbed in local minimum.

(2) the present invention can take three kinds of intensity modulation function D (r; θ) rather than only limit to M, J, the gradual change intensity modulation function that Booth etc. propose is as light intensity modulator; The two kinds of intensity modulation functions in back can be realized through micro-machined technology, and are simpler on the technology.

(3) method (must at first utilize the light distribution in the CCD sampling far field of relative muting sensitivity) of beam quality evaluation index is asked in software weighting different from the past; The present invention has used light intensity modulator; Luminous energy after light intensity modulator output has reflected the height of beam quality, therefore can directly adopt photomultiplier, snowslide diode etc. as sensitive detection parts.Because device has adopted these highly sensitive detectors, therefore, can realize detection to feeble signal, device possesses high sensitivity;

(4) based on the 3rd advantage; The present invention adopts photomultiplier, snowslide diode etc. as sensitive detection parts; Make that device need not the light intensity of surveying is calculated once more, therefore, the implementation method of the relative traditional software weighting of the speed of detection of device is greatly improved; In addition; Because it is constant that the gross energy of incident light can be thought, therefore suitably regulate the gross energy of incident intensity, can guarantee incident light before and after proofreading and correct all in the detector dynamic range; Saturated and the undetectable problem that occurs when avoiding adopting CCD to survey improves the accuracy of surveying.

Description of drawings

Fig. 1 is the far field beam quality measurement mechanism ADAPTIVE OPTICS SYSTEMS principle schematic based on light intensity modulator.

Fig. 2 is the gradation type light intensity modulator;

Fig. 3 is a circumference type light intensity modulator;

Fig. 4 is the radial mode light intensity modulator.

Embodiment

For making the object of the invention, technical scheme and advantage clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, to further explain of the present invention.

As shown in Figure 1, comprising: imaging system 1, light intensity modulator 2, light intensity detector 3 and computing machine 4, Wavefront correctors of adaptive optics part 5.Imaging system 1, light intensity modulator 2 and the light intensity detector 3 on optical axis, arranged in regular turn; The data input/output terminal of the output terminal of light intensity detector 3 and computing machine 4 is connected, and imaging system 1 changes the incident beam that receives into convergent beam; Convergent beam and modulation that light intensity modulator 2 will receive different beam qualities generate the output beam with different-energy size; Light intensity detector 3 is caught the output beam after the modulation and is exported the numerical value of reflected collimated light beam quality; Computing machine 4 gather light intensity detectors 3 outputs in order to the numerical value of reflected collimated light beam quality and in the display of computing machine 4, show.

Incident beam gets into imaging system 1 behind Wavefront correctors of adaptive optics part 5; And focus on light intensity modulator 2 places; Light distribution after light intensity modulator 2 modulation will get into light intensity detector 3, and caught by light intensity detector 3, the light intensity data that is finally detected to computing machine 4 inputs by light intensity detector 3; Computing machine 4 according to the data computation efferent echo of input before corrector 5 required voltage numerical value and drive wave-front corrector 5 and proofread and correct the incident distorted wavefronts; Repeat above process, the numerical value of exporting until light intensity detector 3 satisfies predefined requirement, stops closed loop.Described imaging system 1 is made up of monolithic or multi-disc lens.Described light intensity detector 3 is a kind of in ccd detector or photomultiplier or avalanche diode or the PIN pipe.

2 pairs of incidents of light intensity modulator are assembled the modulating action of light intensity and can be represented with following formula:

I _out(r，θ)＝I _in(r，θ)*D(r，θ)， (1)

In the formula, I _OutIt is the light distribution after the modulation; I _InBe that incident intensity distributes; R, θ are to be the polar coordinate system on plane with light intensity modulator 2; D is a modulating function, and

$D=\left\{\begin{array}{cc}1-\frac{r}{R},& r<R\\ 0,& R-r\&le;0\end{array}\right.$ Or

$D=\left\{\begin{array}{cc}1,& r_{2k}<r<r_{2k+1}\mathrm{And\; r}<R\\ 0,& \mathrm{Others}\end{array}\right.$ Or

$D=\left\{\begin{array}{cc}1,& {\mathrm{\&theta;}}_{2k}<\mathrm{\&theta;}<{\mathrm{\&theta;}}_{2k+1}\mathrm{and\; r}<R\\ 0,& \mathrm{others}\end{array}\right.,$

R is light intensity detector 3 effective detecting area radiuses; K is a natural number; r _2kAnd θ _2kBe respectively light intensity modulator 2 radially with angle design parameter, and 0＜r _2k＜R, 0＜θ _2k＜2 π, k are natural numbers.Accompanying drawing 2, Fig. 3 and Fig. 4 are respectively 3 instances of intensity modulation function D, and Fig. 2 is the gradation type light intensity modulator, corresponding to first kind of expression-form of modulating function; Fig. 3 is a circumference type light intensity modulator, corresponding to second kind of expression-form of modulating function; Fig. 4 is the radial mode light intensity modulator, corresponding to the third expression-form of modulating function.

Thus, the beam quality evaluation index V that outputs to computing machine 4 through light intensity detector 3 can provide through following formula

$V={\&Integral;}_0^R{\&Integral;}_0^{2\mathrm{\&pi;}}{I}_{\mathrm{out}}(r,\mathrm{\&theta;})\mathrm{rdrd\&theta;}={\&Integral;}_0^R{\&Integral;}_0^{2\mathrm{\&pi;}}{I}_{\mathrm{in}}(r,\mathrm{\&theta;})*D(r,\mathrm{\&theta;})\mathrm{rdrd\&theta;}---\left(2\right).$

Light intensity modulator 2 can quantitative response beam quality numerical value height be based upon the incident intensity gross energy and remain unchanged or change under the less situation.And we know, incident beam focuses on back hot spot distribution size and the contained position of incident beam phase distortion size is directly related, and the hot spot distribution range that is produced after phase distortion bigger light beam so thus in the contained position of incident beam focuses on is also big more.For the height of reflected collimated light beam quality numerical value fast, people propose to utilize pin hole to collect the center energy as light intensity modulator, in order to the encircled energy V of reflection focal spot _c, this process can be described as:

$V_c=\underset{d}{\&Integral;}{I}_{\mathrm{in}}(r,\mathrm{\&theta;})\mathrm{rdrd\&theta;}---\left(3\right)$

Wherein, d is a light intensity modulator, i.e. the transparent zone territory of pin hole.For simplifying analytic process, suppose that far-field spot is evenly distributed, light spot energy distributes and is expressed from the next:

$I_{\mathrm{in}}=\frac{I_{\mathrm{sum}}}{{r_d}^2}\mathrm{circ}\left(r\right);---\left(4\right)$

Circ (r) is a circle function, and r≤r _d, I _SumIt is the gross energy of hot spot; So

$V_c={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{r_1}\frac{I_{\mathrm{sum}}}{r_d^2}\mathrm{circ}\left(r\right)\mathrm{rdrd\&theta;}=I_{\mathrm{sum}}\frac{\mathrm{\&pi;}{r_1}^2}{r_d^2}.---\left(5\right)$

Spot radius r _d≤R, r ₁It is the radius of the logical light part of pin hole.This shows, along with spot radius r _dIncrease, the encircled energy V of focal spot _cBe quick downtrending and distribute, the simulation result of this result and Chen Bo etc. is corresponding to, and Chen Bo etc. also spells out, and when there was the Changing Pattern of this quick decline in performance index, the adaptive optics closed loop of guidance was absorbed in local minimum easily thus.In order to address this problem, M.J.Booth etc. have proposed a kind of new beam quality evaluation index V promptly:

$V={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{r_d}{I}_{\mathrm{in}}(r,\mathrm{\&theta;})*(1-\frac{r}{R})\mathrm{rdrd\&theta;}---\left(6\right)$

Equally, with formula (4) substitution formula (6), obtain new beam quality evaluation index and be:

$V=\mathrm{\&pi;}{I}_{\mathrm{sum}}(1-\frac{2}{3R}{r}_d)---\left(7\right)$

Be not difficult to find that at this time beam quality evaluation index V is with spot radius r _dIncrease be linear trends of change, this result is also consistent with the simulation result of Chen Bo etc., Chen Bo etc. also spell out apparatus to be had the performance index of linear Changing Pattern to instruct the adaptive optics closed loop to be not easy to be absorbed in the part to be worth most.

In order to obtain the linear changing relation between performance index and the spot radius, we also can be through simply revising to arrive this linear relationship traditional pin performance evaluation device.We have known that pin performance evaluation is output as:

$V_c={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{r_1}\frac{I_{\mathrm{sum}}}{r_d^2}\mathrm{circ}\left(r\right)\mathrm{rdrd\&theta;}=I_{\mathrm{sum}}\frac{\mathrm{\&pi;}{r_1}^2}{r_d^2}---\left(8\right)$

Wherein circ (r) is a circle function, when we when the radial direction of light intensity modulator increases some endless belt, following formula becomes:

$V_c={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{r_1}\frac{I_{\mathrm{sum}}}{r_d^2}\mathrm{circ}\left(r\right)\mathrm{rdrd\&theta;}+{\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_{r_2}^{r_3}\frac{I_{\mathrm{sum}}}{r_d^2}\mathrm{circ}\left(r\right)\mathrm{rdrd\&theta;}+...+{\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_{r_{2k}}^{r_{2k+1}}\frac{I_{\mathrm{sum}}}{r_d^2}\mathrm{circ}\left(r\right)\mathrm{rdrd\&theta;}$

$=I_{\mathrm{sum}}\frac{\mathrm{\&pi;}{r_1}^2}{r_d^2}+I_{\mathrm{sum}}\frac{\mathrm{\&pi;}(r_3^2-r_2^2)}{r_d^2}+...+I_{\mathrm{sum}}\frac{\mathrm{\&pi;}(r_{2k+1}^2-r_{2k}^2)}{r_d^2}---\left(9\right)$

Wherein, r wherein ₁Be the radius of center pit, r ₂And r ₃Be respectively the inside radius and the external radius of first endless belt; r _2kAnd r _2k+1The inside radius and the external radius that refer to the k endless belt respectively, and r _2k+1≤r _d

If satisfied

following formula so becomes

V _c＝I _sumπ(1-r _d/C) (10)

Wherein, C is greater than r _dConstant.We just can obtain the performance index characteristic similar with formula (7) like this.Same reason, the logical light area of also can be on the angle of light intensity modulator suitable increase, i.e. umbrella shape transparent zone territory, the angle in every zone is from θ _2kTo θ _2k+1, radially from 0 to r _dThereby, the output of original pin hole light intensity modulator is modified to:

$V_c={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{r_1}\frac{I_{\mathrm{sum}}}{r_d^2}\mathrm{circ}\left(r\right)\mathrm{rdrd\&theta;}+{\&Integral;}_{{\mathrm{\&theta;}}_2}^{{\mathrm{\&theta;}}_3}{\&Integral;}_0^{r_d}\frac{I_{\mathrm{sum}}}{r_d^2}\mathrm{circ}\left(r\right)\mathrm{rdrd\&theta;}+...+{\&Integral;}_{{\mathrm{\&theta;}}_{2k}}^{{\mathrm{\&theta;}}_{2k+1}}{\&Integral;}_0^{r_d}\frac{I_{\mathrm{sum}}}{r_d^2}\mathrm{circ}\left(r\right)\mathrm{rdrd\&theta;}$

$=I_{\mathrm{sum}}\frac{\mathrm{\&pi;}{r_1}^2}{r_d^2}+I_{\mathrm{sum}}({\mathrm{\&theta;}}_3-{\mathrm{\&theta;}}_2)+...+I_{\mathrm{sum}}({\mathrm{\&theta;}}_{2k+1}-{\mathrm{\&theta;}}_{2k})---\left(11\right)$

Wherein, θ ₂And θ ₃Be respectively the start angle and the angle at the end in first umbrella shape transparent zone territory;

θ _2kAnd θ _2k+1Be the start angle and the angle at the end in k umbrella shape transparent zone territory.

We can obtain the performance index characteristic of (10) formula equally as

.

Describing above is to be used to realize the present invention and embodiment; Scope of the present invention should not described by this and limit; It should be appreciated by those skilled in the art,, all belong to claim of the present invention and come restricted portion in any modification that does not depart from the scope of the present invention or local replacement.

Claims (3)

1. based on the far field beam quality measurement mechanism of light intensity modulator, it is characterized in that comprising imaging system (1), light intensity modulator (2) and the light intensity detector (3) on optical axis, arranged in regular turn; The output terminal of light intensity detector (3) is connected with the data input/output terminal of computing machine (4), and imaging system (1) changes the incident beam that receives into convergent beam; Convergent beam and modulation that light intensity modulator (2) will receive different beam qualities generate the output beam with different-energy size; Light intensity detector (3) is caught the output beam after the modulation and is exported the numerical value of reflected collimated light beam quality; Computing machine (4) gather light intensity detector (3) output in order to the numerical value of reflected collimated light beam quality and in the display of computing machine (4), show;

The modulating function D of described light intensity modulator (2) (r, θ) statement is as follows:

$D=\left\{\begin{array}{cc}1-\frac{r}{R}& ,r<R\\ 0& ,R-r\&le;0\end{array}\right.$ Or

$D=\left\{\begin{array}{ccc}1& ,r_{2k}<r<r_{2k+1}\mathrm{And}& r<R\\ 0& ,\mathrm{Others}& \end{array}\right.$ Or

$D=\left\{\begin{array}{ccc}1& ,{\mathrm{\&theta;}}_{2k}<\mathrm{\&theta;}<{\mathrm{\&theta;}}_{2k+1}\mathrm{and}& r<R\\ 0& ,\mathrm{others}& \end{array}\right.$

R, θ are to be the polar coordinate system on plane with light intensity modulator (2) front surface; R is an effectively detecting area radius of light intensity detector (3); r _2kAnd θ _2kBe respectively light intensity modulator (2) radially with angle design parameter, and 0＜r _2k＜R, 0＜θ _2k＜2 π, k are natural numbers.

2. the far field beam quality measurement mechanism based on light intensity modulator according to claim 1, it is characterized in that: described imaging system (1) is made up of monolithic or multi-disc lens.

3. the far field beam quality measurement mechanism based on light intensity modulator according to claim 1, it is characterized in that: described light intensity detector (3) is a ccd detector, or photomultiplier, or avalanche diode, or the PIN pipe.

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