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

Abstract

The invention discloses a method for measuring the nonlinear refraction of a material with a single pulse. A phase object is added in the detection optical path. Under the action of a single pulse, the nonlinear transmittance of a small hole in the far field can be measured to determine the nonlinear refraction of the material. Linear index of refraction. The measurement system working according to the method of the invention has the advantages of simple optical path, simple data processing, single pulse measurement, no need to move the sample, simultaneous measurement of the magnitude and sign of nonlinear refraction, accurate measurement results, and greatly reduced measurement cost.

Description

A single-pulse method for measuring nonlinear refraction of materials

technical field

The invention relates to a method for measuring optical nonlinear refraction of materials, belonging to the fields of nonlinear photonic materials and nonlinear optical information processing.

Background technique

With the rapid development of technologies in the fields of optical communication and optical information processing, the research on nonlinear optical materials is becoming increasingly important. The realization of functions such as optical logic, optical memory, optical transistor, optical switch and phase complex conjugation mainly depends on the research progress of nonlinear optical materials.

Optical nonlinear measurement technology is one of the key technologies for studying nonlinear optical materials. Commonly used measurement methods include Z-scan, 4f system coherent imaging technology, Mach-Zehnder interferometry, four-wave mixing, third harmonic nonlinear interferometry, ellipsometry, phase object Z-scan, etc. Among them, the Z-scan method (MansoorSheik-Bahae, Ali A.Said, Tai-Hui Wei, David J.Hagan, E.W.Van Stryland. "Sensitive measurement of optical nonlinearities using a single beam", IEEEJ.Quantum Elect, 26, 760-769 (1990)) has a simple optical path and high sensitivity, and is currently the most commonly used method for measuring the optical nonlinearity of materials with a single beam. However, in this measurement method, the sample needs to be moved in the direction of laser propagation, and the laser needs to be excited multiple times, which is not suitable for thin films and easily damaged materials. Phase object Z-scan (Junyi Yang and Yinglin Song, "Direct observation of the transient thermal lensing effect using the PO Z-scan" Vol.34, No.2, Doc.ID 100701) is based on traditional Z-scan, It is realized by adding a phase object at the position of the front focal plane of the lens. Compared with the traditional Z-scan, the result of the nonlinear refraction of the measured material is changed from the peak-valley characteristic curve of the traditional Z-scan to a single-peak or single-valley characteristic curve. However, like traditional Z-scanning, this measurement method also requires the movement of the sample in the direction of laser propagation, requires multiple excitations of the laser, and is easy to damage the material.

4f phase coherent imaging system (G.Boudebs and S.Cherukulappurath, "Nonlinear optical measurements using a 4f coherent imaging system with phase object", Phys.Rev.A, 69, 053813 (2004)) is a measurement material proposed in recent years New method for nonlinear refraction. The use of 4f phase coherent imaging technology to measure nonlinear refraction has the advantages of simple optical path, high sensitivity, single pulse measurement, no need for sample movement, and low requirements for light source energy stability. However, this method requires complex processing of the collected images, and the detector needs to use a CCD, and the requirements for the CCD are relatively high, which increases the cost of the measurement.

Contents of the invention

The purpose of the present invention is to provide a method for measuring the nonlinearity of materials with a single pulse, which can simply and accurately measure the nonlinear refractive index of materials by using only one beam of single pulses, and reduce the cost of measurement.

In order to achieve the above object, the technical solution adopted by the present invention is: a method for measuring the nonlinear refraction of materials with a single pulse, which divides the pulsed laser beam into two beams, one beam is the monitoring light, which is recorded by the detector; the other beam is the detection beam. The light is focused on the sample to be tested through the lens, and the probe light is irradiated on the sample to be tested after passing through a phase object. The pulsed light emitted from the sample to be tested passes through a small aperture diaphragm whose center coincides with the optical axis Two detectors record that the phase object is a ring structure, the phase difference between the ring part and the inner hole is between π/4～3π/4, and the inner hole diameter is 0.1～0.3 times the radius of the beam waist of the incident spot, and the measurement The steps are,

(1) Put the sample to be tested at a position away from the focal point, use the detector to collect the pulsed light energy after passing through the aperture, and calculate the ratio of the energy passing through the small hole to the monitored light energy;

(2) Put the sample to be tested on the focal plane of the lens, use the detector to collect the pulsed light energy after passing through the aperture, and calculate the ratio of the energy passing through the small hole to the monitored light energy;

(3) Process the two ratios obtained above to obtain the desired optical nonlinear refraction index of the detection material.

In the above technical solution, the detector and the second detector may use light energy meters.

In the above technical solution, the processing in step (3) includes dividing the ratio obtained in step (2) by the ratio obtained in step (1) to obtain the normalized nonlinear transmittance of the sample , and theoretically fit the normalized nonlinear transmission to obtain the nonlinear refraction coefficient.

Wherein, the phase object is located before the lens in the detection optical path. For the convenience of calculation, the preferred technical solution is that the phase object is located on the front focal plane of the lens in the detection optical path.

In the above technical solution, when the phase difference between the annular portion of the phase object and the inner hole is π/2, and the size of the inner hole is about 0.1 times the beam waist radius of the incident spot, the measurement accuracy of the system reaches the highest. Its size and phase delay can be adjusted according to actual conditions.

In a further technical solution, the radius of the small aperture stop in front of the second detector is equal to the radius of the far-field diffraction spot of the phase object.

In the technical solution of the present invention, after the nonlinear sample is subjected to the action of pulsed light, the refractive index of the material changes, resulting in a nonlinear phase shift. The stronger the laser light intensity, the greater the nonlinear phase shift. In this way, the sample acts as a varying phase object at the focal plane. According to the principle of phase contrast, in the far field, the change of nonlinear phase shift is manifested as the change of the amplitude of the light field in the diffraction spot of the phase object, which will cause the change of the transmittance of the small hole. In addition, the change in amplitude is related to the sign of refraction of the material nonlinearity. If the nonlinear refraction is self-focusing, the normalized transmittance of the pinhole is greater than 1, otherwise, it is less than 1. Therefore, at the focal plane position, without moving the sample, under the action of a single pulse, the nonlinear refractive index of the sample and the nonlinear refractive sign of the material can be obtained by measuring the normalized nonlinear transmittance of the pinhole.

The method of the present invention realizes the measurement of the nonlinear refractive index with a brand-new idea, and has the following advantages compared with other nonlinear optical measurement techniques:

1. The present invention adopts single pulse measurement, and the sample does not need to be moved;

2. The measurement of the present invention is very convenient, the theoretical model is simple, and the light energy meter can be used as the detector, and the high-cost CCD detector is not needed, thereby reducing the measurement cost;

3. The invention has high measurement sensitivity, and can measure both the magnitude of the nonlinearity and the sign;

4. The measurement method of the present invention can be widely used in research fields such as nonlinear optical measurement, nonlinear photonics materials, nonlinear optical information processing and photonic devices, especially the testing and modification of nonlinear optical functional materials and other key links, using the method of the present invention can greatly reduce the measurement cost (no need for a mobile platform and a CCD), and can ensure that the test parameters are comprehensive and the test results are accurate; in addition, the method has simple requirements on the optical path and fast test speed.

Description of drawings

Accompanying drawing 1 is a schematic diagram of a phase object in Embodiment 1 of the present invention;

Accompanying drawing 2 is the working principle diagram of the single-pulse measuring nonlinear refraction index method of the phase-containing object in the first embodiment of the present invention.

Among them: 1. Laser pulse; 2. Beam splitter; 3. Detector; 4. Phase object; 5. Convex lens; 6. Sample to be tested; 7. Small hole; 8. Second detector.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Embodiment 1: See accompanying drawing 2, a kind of device that contains phase object single-pulse measurement the nonlinear parameter of functional material, optical route beam splitter 2, phase object 4, convex lens 5, pinhole 7, detector 3 and The second detector 8 is composed; the laser pulse 1 is focused on the sample 6 to be tested.

A beam splitter 2 is used to split the laser pulse 1 into two beams of light. The energy of the monitoring light is received by the detector 3. The other beam of light passes through the phase object 4 and is focused onto the sample 6 by the convex lens 5. The transmitted beam passes through the The small hole 7 is then received by the detector 8 .

In this embodiment, the laser beam is a 532nm laser after frequency doubling by a Nd:YAG laser (Ekspla, PL2143B), with a pulse width of 21 ps. The two detectors of the model (Rjp-765 energy probe) are connected to the energy meter (Rj-7620 ENERGY RATIOMETER, Laserprobe). The sample to be tested is carbon disulfide (CS ₂ ).

The specific detection steps are: (1) place the sample 6 to be tested at a position close to the convex lens 5, use the second detector 8 to measure the energy passing through the small hole 7, and use the detector 3 to measure the energy of the monitoring light at the same time. The energy measured by the second detector 8 is divided by the energy of the detector 3 to obtain an energy ratio. (2) Sample 6 is placed on the position of the focal plane of lens 5, utilizes second detector 8 to measure the energy that passes through aperture 7, utilizes detector 3 to measure the energy of monitoring light simultaneously, the second detector 8 measures The obtained energy is divided by the energy of the detector 3 to obtain an energy ratio. (3) Divide the ratio in step (2) by the ratio in step (1) to obtain the normalized nonlinear transmittance of the sample through the small hole. (4) According to the nonlinear transmittance obtained in step (3), the nonlinear refractive index of the sample is obtained.

The specific process of the experiment and theoretical calculation for CS ₂ nonlinear measurement is as follows:

Assuming that the incident beam is fundamental mode Gaussian light, the expression of its field strength is:

$\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="t"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">t</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&tau;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, E ₀ is the maximum field intensity value of the pulsed laser, r is the radius of the beam, ω _e is the beam waist radius of the incident beam, and τ is the time of the 1/e half-width of the pulsed light.

The transmittance of the phase object is:

(r＜Lp)或t(r)＝1(r＞Lp)      (2)

(r<Lp) or t(r)=1 (r>Lp) (2)

为相位物体的相位延迟。In the formula,

is the phase delay of the phase object.

The field strength distribution on the rear surface of the phase object is:

E ₀₁ (r,t)=E(r,t)t(r) (3)

The light field propagating to the sample surface can be obtained by Fourier-Bessel transform,

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;\; f</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&infin;</span>}\mathrm{<span\; class="notranslate">\; r</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;rr</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dr</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

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

In the sample, considering the slowly varying amplitude approximation and the thin sample approximation, the phase change of the pulsed laser propagates in the sample to satisfy

$\frac{\mathrm{<span\; class="notranslate">\; d\&Delta;\&phi;</span>}}{\mathrm{<span\; class="notranslate">\; dz</span>}<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k\&Delta;n</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Δn is the change of the refractive index, and the optical path of the z' laser in the sample. In CS ₂ ,

Δn=n ₂ I (6)

In the formula, n ₂ is the nonlinear refractive index of the sample; I=|E ₀₂ | ² is the light intensity acting on the sample.

Then the light field on the rear surface of the sample is

E ₀₃ ＝E ₀₂ exp(iΔφ) (7a)

When the nonlinearity of the sample is not considered, the light field on the rear surface of the sample is

E′ ₀₃ =E ₀₂ (7b)

The light field propagating from the rear surface of the sample to the pinhole can be obtained by the Fresnel diffraction formula:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 04</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; i\&lambda;d</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; i\&pi;</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;d</span>}}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&infin;</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="dr"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">dr</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 03</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; i\&pi;</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;d</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;d</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span>$

When the nonlinearity of the sample is not considered, the light field is

${{\mathrm{<span\; class="notranslate">\; E.</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; 04</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; i\&lambda;d</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; i\&pi;</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;d</span>}}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&infin;</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="dr"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">dr</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; E.</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; 03</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; i\&pi;</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;d</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;d</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span>$

In the formula, d is the distance from the far-field pinhole to the focal point.

Integrating the light intensity at the small hole in space and time, the energy passing through the small hole can be obtained. Comparing this energy with the energy through the aperture obtained without taking into account the nonlinearity of the sample gives the normalized nonlinear transmission through the aperture:

$\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; \&Integral;</span>}_{<span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&infin;</span>}^{<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&infin;</span>}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 04</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="dr"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">dr</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; dt</span>}}{{<span\; class="notranslate">\; \&Integral;</span>}_{<span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&infin;</span>}^{<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&infin;</span>}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{{\mathrm{<span\; class="notranslate">\; E.</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; 04</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="dr"\; filenames="H200910028325XE00012.png"\; state="\{\{state\}\}">dr</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

By fitting the normalized nonlinear transmittance of the pinhole, the nonlinear refractive index of the sample can be obtained.

In the first embodiment, the incident energy is 0.22μJ, the radius of the phase object is 0.5mm, and the phase delay is The beam waist radius of the incident beam in front of the phase object is 2.8mm, the distance from the far field pinhole to the focus is 1.6m, and the radius of the pinhole is 2mm. The experimentally measured small hole normalized nonlinear transmittance is 1.4481, and the nonlinear refractive index n ₂ of the sample is changed so that the theoretically calculated nonlinear transmittance is consistent with the experimentally measured, and the nonlinearity of CS ₂ can be obtained The refractive index is n ₂ =3.3×10 ^-18 m ² /W, which is consistent with the value reported in the literature.

Claims (6)

1. A method for measuring the nonlinear refraction of materials with a single pulse. The pulsed laser beam is divided into two beams, one beam is the monitoring light, which is recorded by the detector; the other beam is the detection light, which is focused on the sample to be tested through the lens. It is characterized in that: the probe light is irradiated on the sample to be measured after passing through a phase object, and the pulsed light emitted from the sample to be measured is recorded by the second detector after passing through a small aperture diaphragm whose center coincides with the optical axis. The phase object is a ring structure, the phase difference between the ring part and the inner hole is between π/4~3π/4, the inner hole diameter is 0.1~0.3 times the radius of the beam waist of the incident spot, the detector and the second detector The device uses a light energy meter, and the measurement steps are as follows: (1) Put the sample to be tested at a position away from the focal point, use a detector to collect the pulsed light energy after passing through the aperture, and calculate the ratio of the energy passing through the small hole to the monitored light energy; the position away from the focal point is along the The optical axis is close to the lens; (2) Put the sample to be tested on the focal plane of the lens, use the detector to collect the pulsed light energy after passing through the aperture, and calculate the ratio of the energy passing through the small hole to the monitored light energy; (3) Process the two ratios obtained above to obtain the required optical nonlinear refraction index of the detection material. 2. The method for single-pulse measurement of material nonlinear refraction according to claim 1, characterized in that: the processing in the step (3) comprises, the ratio obtained in the step (2) and the step (1) The obtained ratios are divided to obtain the normalized nonlinear transmittance of the sample, and the nonlinear refractive index is obtained by theoretically fitting the normalized nonlinear transmittance. 3 . The method for measuring nonlinear refraction of materials with a single pulse according to claim 1 , wherein the phase object is located before the lens in the detection optical path. 4 . 4. The method for measuring nonlinear refraction of materials with a single pulse according to claim 3, wherein the phase object is located on the front focal plane of the lens in the detection optical path. 5. The method for measuring nonlinear refraction of materials with a single pulse according to claim 1, characterized in that: the phase difference between the annular part of the phase object and the inner hole is π/2. The method for measuring nonlinear refraction of materials with a single pulse according to claim 1, characterized in that: the radius of the small aperture stop in front of the second detector is equal to the radius of the far-field diffraction spot of the phase object.

Images