CN101482502B - Single-pulse measurement method for nonlinear refraction of materials - Google Patents

Abstract

The invention discloses a single-pulse measurement method of material non-linearity refraction. A phase object is added in the detection light-path. The material non-linearity refraction is determined by measuring the non-linearity transmittance of a far-field aperture under the action of single-pulse. The single-pulse measurement method has features of simple light-path, simple data processing, single-pulse measurement, no need of moving sampler, simultaneous measurement of size and symbol of the non-linearity refraction, accurate measurement result, greatly reduced measurement cost.

Description

The method of single-pulse measurement nonlinear refraction coefficient of materials

Technical field

The present invention relates to a kind of method of measuring the optical nonlinear refraction of material, belong to non-linear photon and learn material and nonlinear optics field of information processing.

Background technology

Along with the develop rapidly of art such as optical communication and optical information processing, the research of nonlinear optical material becomes more and more important.The realization of functions such as optical logic, optics memory, optical transistor, photoswitch and phase place complex conjugate mainly depends on the progress of nonlinear optical material.

The optical nonlinearity measuring technique is one of gordian technique of research nonlinear optical material.Measuring method commonly used has Z scanning, 4f system coherent imaging technology, Mach-Zehnder interferometric method, four-wave mixing, the non-linear interferometric method of third harmonic, elliptic polarization method, phase object Z-scan etc.Z scan method (MansoorSheik-Bahae, Ali A.Said, Tai-Hui Wei wherein; David J.Hagan; E.W.Van Stryland. " Sensitive measurement of optical nonlinearities using a single beam ", IEEEJ.Quantum Elect, 26; 760-769 (1990)) light path is simple, highly sensitive, is that at present the most frequently used single beam is measured the material optical non-linear method.But in this measuring method, sample need move in the laser propagation direction, and needs laser repeatedly to excite, and is inapplicable to the material of film and easy damaged.Phase object Z-scan (Junyi Yang and Yinglin Song; " Direct observation of thetransient thermal lensing effect using the PO Z-scan " Vol.34; No.2; Doc.ID 100701) be on the basis of traditional Z-scanning, add in the position of the front focal plane of lens that a phase object realizes.Compare with traditional Z-scanning, the result of measured nonlinear refraction coefficient of materials has become unimodal or single paddy characteristic curve by the peak valley characteristic curve of traditional Z-scanning.But the same with traditional Z-scanning, this measuring method also needs sample the moving of laser propagation direction, and needs laser repeatedly to excite, and damages material easily.

4f phase coherence imaging system (G.Boudebs and S.Cherukulappurath; " Nonlinearoptical measurements using a 4f coherent imaging system with phase object "; Phys.Rev.A; 69,053813 (2004)) be a kind of new method of measuring nonlinear refraction coefficient of materials that proposes in recent years.Utilize the nonlinear refraction of 4f phase coherent imaging commercial measurement to have that light path is simple, highly sensitive, single-pulse measurement, need not sample move, to energy of light source stability requirement advantages of higher not.But this method need compare complex processing to the image of gathering, and detector need adopt CCD, and to the requirement of CCD than higher, increased the cost of measuring.

Summary of the invention

The purpose of this invention is to provide a kind of method for measuring nonlinearity of material based on monopulse, only utilize a branch of monopulse, simply and exactly measure the nonlinear refraction coefficient of material, and reduce the cost of measuring.

For achieving the above object, the technical scheme that the present invention adopts is: a kind of method of single-pulse measurement nonlinear refraction coefficient of materials, pulse laser beam is divided into two bundles, and a branch of for monitoring light, by the detector record; Another bundle is for surveying light, and to testing sample, said detection light shines on the testing sample after through a phase object through lens focus; From the testing sample the pulsed light of outgoing through the small-bore diaphragm of a center and optical axis coincidence after by the second detector record; Said phase object is a loop configuration, and the phase differential at this ring part and endoporus place is between π/4～3 π/4, and the endoporus aperture is 0.1～0.3 times of launching spot waist radius; Measuring process does

(1) puts testing sample in position, collect through the pulsed light energy behind the diaphragm, and calculate through the ratio of aperture energy with the monitoring luminous energy with detector away from focus;

(2) put testing sample in the focal plane position of lens, collect through the pulsed light energy behind the diaphragm, and calculate through the ratio of aperture energy with the monitoring luminous energy with detector;

(3) two ratios of above-mentioned acquisition are handled, obtained the optical nonlinear refraction coefficient of required test material.

In the technique scheme, the said detector and second detector can adopt luminous energy.

In the technique scheme; Processing in the said step (3) comprises; The ratio that draws in ratio that draws in the step (2) and the step (1) is divided by, obtains the normalized non-linear transmitance of sample, normalized non-linear see through carried out theoretical fitting and obtained the nonlinear refraction coefficient.

Wherein, said phase object is arranged in and surveys before the light path lens.Calculate for convenient, optimized technical scheme is that said phase object is arranged on the front focal plane of surveying the light path lens.

In the technique scheme, the phase differential when said phase object ring part and endoporus place is a pi/2, and when interior hole size was approximately 0.1 times of launching spot waist radius, the measuring accuracy of system reached the highest.Its size and phase delay can be regulated according to actual conditions.

Further technical scheme, the radius of the small-bore diaphragm before said second detector equals the radius of the far field construction hot spot of phase object.

In the technical scheme of the present invention, after nonlinear sample received the effect of pulsed light, the refractive index of material changed, and produced nonlinear phase shift, and the light intensity of laser is strong more, and nonlinear phase shift is big more.Like this, locate the phase object that sample just is equivalent to a variation in the focal plane.According to the phase contrast principle, in the far field, the variation of nonlinear phase shift just shows as light field oscillation amplitude change in the phase object diffraction pattern, thereby will cause the variation of the transmitance of aperture.In addition, oscillation amplitude change is relevant with the refraction symbol of material nonlinearity.If nonlinear refraction is self-focusing, the normalized transmitance of aperture is just greater than 1, otherwise, just less than 1.So, in focal plane position, need not mobile example, under the effect of a monopulse,, just can obtain the nonlinear refraction coefficient of sample and the nonlinear refraction symbol of material through measuring the normalized non-linear transmitance of aperture.

The inventive method has realized the measurement to the nonlinear refraction coefficient with a kind of new way, compares with other nonlinear optics measuring techniques, has the following advantages:

1. the present invention adopts single-pulse measurement, and sample need not to move;

2. measurement of the present invention is very convenient, and theoretical model is simple, can adopt luminous energy as detector, need not adopt expensive ccd detector, thereby has reduced the measurement cost;

3. the present invention measures highly sensitively, and not only can measure nonlinear size but also can measure symbol;

4. measuring method of the present invention; Can be widely used in nonlinear optics measurement, research fields such as non-linear photon material, nonlinear optics information processing and photonics device; Especially key links such as the test of nonlinear optical functional material and modification are utilized the inventive method, can reduce greatly and measure cost (need not mobile platform and CCD); And can guarantee that test parameter is comprehensive, test result is accurate; This method requires simply light path in addition, and test speed is quick.

Description of drawings

Accompanying drawing 1 is the phase object synoptic diagram in the embodiment of the invention one;

Accompanying drawing 2 is the fundamental diagrams that contain phase object single-pulse measurement nonlinear refraction coefficient method in the embodiment of the invention one.

Wherein: 1, laser pulse; 2, beam splitter; 3, detector; 4, phase object; 5, convex lens; 6, testing sample; 7, aperture; 8, second detector.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is further described:

Embodiment one: shown in accompanying drawing 2, and a kind of device that contains the nonlinear parameter of phase object single-pulse measurement functional material, optical routing beam splitter 2, phase object 4, convex lens 5, aperture 7, the detector 3 and second detector 8 are formed; Laser pulse 1 focuses on the testing sample 6.

Utilize beam splitter 2 to be divided into two-beam to laser pulse 1, the energy of monitoring light is received by detector 3, and a branch of in addition light transmission phase object 4 backs are focused on the testing sample 6 by convex lens 5, and the light beam after the transmission is received by detector 8 behind aperture 7.

In the present embodiment, laser beam is Nd:YAG laser instrument (Ekspla, PL2143B) the later 532nm laser of frequency multiplication, pulsewidth 21ps.Model for two detectors of (Rjp-765 energy probe) be connected energy meter (Rj-7620 ENERGY RATIOMETER, Laserprobe) on.Testing sample is carbon disulphide (CS ₂).

Concrete detection step is: (1) is placed on the position near convex lens 5 with testing sample 6; Utilize second detector 8 to measure the energy that sees through aperture 7; Utilize detector 3 to measure the energy of monitoring light simultaneously; The energy that second detector 8 is measured obtains an energy ratio divided by the energy of detector 3.(2) sample 6 is placed on the position of the focal plane of lens 5; Utilize second detector 8 to measure the energy that sees through aperture 7; Utilize detector 3 to measure the energy of monitoring light simultaneously, the energy that second detector 8 is measured obtains an energy ratio divided by the energy of detector 3.(3) with the ratio in the step (2) divided by the ratio in the step (1), obtain sample and see through the normalized non-linear transmitance of aperture.(4), draw the nonlinear refraction coefficient of sample according to the non-linear transmitance that obtains in the step (3).

For CS ₂The experiment of nonlinear measurement and Theoretical Calculation detailed process are following:

Suppose that incident beam is the basic mode Gauss light, its field intensity expression formula is:

$E(r,t)=E_0\exp (-\frac{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}{{{\mathrm{\&omega;}}_e}^2})\exp (-\frac{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}{{2\mathrm{\&tau;}}^2})---\left(1\right)$

In the formula, E ₀Be the maximum field strength value of pulse laser, r is the radius of light beam, ω _eBe the waist radius of incident beam, τ is the time of pulsed light 1/e half-breadth.

The transmitance of phase object is:

(r＜Lp) or t (r)=1 (r＞Lp) (2)

In the formula,

is the phase delay of phase object.

The field strength distribution on surface is behind the phase object:

E ₀₁(r，t)＝E(r，t)t(r) (3)

The light field that propagates into sample surfaces can obtain through Fourier-bessel transform,

$E_{02}({\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1,t)=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;f}}{\&Integral;}_0^{\&infin;}r{E}_{01}(r,t)J_0\left({2\mathrm{\&pi;rr}}_1\right)\mathrm{dr}---\left(4\right)$

In the formula, f is the focal length of lens, J ₀Be zero Bessel function.

In sample, consider to become slowly the situation that amplitude is approximate and thin sample is approximate, the phase change of pulse laser communication satisfaction in sample

$\frac{\mathrm{d\&Delta;\&phi;}}{\mathrm{dz}\&prime;}=\mathrm{k\&Delta;n}---\left(5\right)$

Δ n is a variations in refractive index, the light path that z ' laser is propagated in sample.At CS ₂In,

Δn＝n ₂I (6)

In the formula, n ₂Nonlinear refraction coefficient for sample; I=|E ₀₂| ²For acting on the light intensity on the sample.

Then the light field on surface does behind the sample

E ₀₃＝E ₀₂exp(iΔφ) (7a)

When not considering that sample is non-linear, then the light field on surface does behind the sample

E′ ₀₃＝E ₀₂ (7b)

The light field that propagates into aperture from the back surface of sample can obtain through the fresnel diffraction formula:

$E_{04}({\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_2,t)=\frac{2\mathrm{\&pi;}}{\mathrm{i\&lambda;d}}\exp \left(\frac{\mathrm{i\&pi;}{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}^2}{\mathrm{\&lambda;d}}\right){\&Integral;}_0^{+\&infin;}{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1{\mathrm{dr}}_1{E}_{03}({\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1,t)\exp \left(\frac{\mathrm{i\&pi;}{{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1}^2}{\mathrm{\&lambda;d}}\right)J_0\left(\frac{2\mathrm{\&pi;}{r}_2{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1}{\mathrm{\&lambda;d}}\right)---\left(8a\right)$

When not considering that sample is non-linear, then light field does

${E^{\&prime;}}_{04}({\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_2,t)=\frac{2\mathrm{\&pi;}}{\mathrm{i\&lambda;d}}\exp \left(\frac{\mathrm{i\&pi;}{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}^2}{\mathrm{\&lambda;d}}\right){\&Integral;}_0^{+\&infin;}{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1{\mathrm{dr}}_1{E^{\&prime;}}_{03}({\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1,t)\exp \left(\frac{\mathrm{i\&pi;}{{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1}^2}{\mathrm{\&lambda;d}}\right)J_0\left(\frac{2\mathrm{\&pi;}{r}_2{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout>}}_1}{\mathrm{\&lambda;d}}\right)---\left(8b\right)$

In the formula, d is the distance of far field aperture to focus.

The light intensity at aperture place is carried out the integration of room and time, can obtain seeing through the energy of aperture.With this energy with compare at the energy of not considering to obtain under the nonlinear situation of sample that sees through aperture, just obtain seeing through the normalized nonlinear transmitance of aperture:

$T=\frac{{\&Integral;}_{-\&infin;}^{+\&infin;}{\&Integral;}_0^{r_a}2\mathrm{\&pi;}{r}_2{\left(E_{04}\right)}^2{\mathrm{<figure-callout\; id="2"\; label="dr"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">dr</figure-callout>}}_2\mathrm{dt}}{{\&Integral;}_{-\&infin;}^{+\&infin;}{\&Integral;}_0^{r_a}2\mathrm{\&pi;}{r}_2{\left({E^{\&prime;}}_{04}\right)}^2{\mathrm{<figure-callout\; id="2"\; label="dr"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">dr</figure-callout>}}_2\mathrm{dt}}---\left(9\right)$

Normalized nonlinear transmitance to aperture is carried out match, just can obtain the nonlinear refraction coefficient of sample.

In embodiment one; Projectile energy is 0.22 μ J; The radius of phase object is 0.5mm; Phase delay is 2.8mm for the waist radius of incident beam before phase object, and the far field aperture is 1.6m to the distance of focus, and the radius of aperture is 2mm.It is 1.4481 that experiment records the normalized non-linear transmitance of aperture, changes sample nonlinear refraction coefficient n ₂, make the non-linear transmitance of Theoretical Calculation and matching that experiment records to get CS ₂The nonlinear refraction coefficient be n ₂=3.3 * 10 ^-18m ²/ W, consistent with value on the bibliographical information.

Claims (6)

1. the method for a single-pulse measurement nonlinear refraction coefficient of materials is divided into two bundles with pulse laser beam, and is a branch of for monitoring light, by the detector record; Another bundle is for surveying light;, to testing sample, it is characterized in that through lens focus: said detection light shines on the testing sample after through a phase object, from the testing sample the pulsed light of outgoing through the small-bore diaphragm of a center and optical axis coincidence after by the second detector record; Said phase object is a loop configuration; The phase differential at this ring part and endoporus place is between π/4～3 π/4, and the endoporus aperture is 0.1～0.3 times of launching spot waist radius, and the said detector and second detector adopt luminous energy; Measuring process does

(1) puts testing sample in position, collect through the pulsed light energy behind the diaphragm, and calculate through the ratio of aperture energy with the monitoring luminous energy with detector away from focus; Said position away from focus is near the lens place along optical axis;

(2) put testing sample in the focal plane position of lens, collect through the pulsed light energy behind the diaphragm, and calculate through the ratio of aperture energy with the monitoring luminous energy with detector;

(3) two ratios of above-mentioned acquisition are handled, obtained the optical nonlinear refraction coefficient of required test material.

2. the method for single-pulse measurement nonlinear refraction coefficient of materials according to claim 1; It is characterized in that: the processing in the said step (3) comprises; The ratio that draws in ratio that draws in the step (2) and the step (1) is divided by; Obtain the normalized non-linear transmitance of sample, normalized non-linear see through carried out theoretical fitting and obtained the nonlinear refraction coefficient.

3. the method for single-pulse measurement nonlinear refraction coefficient of materials according to claim 1 is characterized in that: said phase object is arranged in to be surveyed before the light path lens.

4. the method for single-pulse measurement nonlinear refraction coefficient of materials according to claim 3 is characterized in that: said phase object is arranged on the front focal plane of surveying the light path lens.

5. the method for single-pulse measurement nonlinear refraction coefficient of materials according to claim 1 is characterized in that: the phase differential at said phase object ring part and endoporus place is a pi/2.

6. the method for single-pulse measurement nonlinear refraction coefficient of materials according to claim 1 is characterized in that: the radius of the small-bore diaphragm before said second detector equals the radius of the far field construction hot spot of phase object.

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