CN108469426A - One kind is coaxially without angle pumping detecting method and system - Google Patents

Abstract

The invention discloses a pump detection method and system in which the pump light and the detection light are coaxial and have no included angle, which is used for the detection of optical nonlinearity. Light, the beam with weak light intensity is the probe light, the pump light is focused on the nonlinear sample to be tested after a time delay, so that the nonlinear sample in the ground state produces nonlinear absorption; the probe light is converged by the lens after passing through a concentric baffle On the nonlinear sample to be tested, the outgoing pump light is blocked by the second concentric baffle, and all the probe light enters the detector after passing through the second baffle; the baffle in front of the lens and the baffle behind the lens in the detection light path The distance to the lens conforms to the lens imaging law, and the radius of the front baffle of the lens is larger than the radius of the pump light mirror, and the radius of the rear baffle can completely block the pump light and allow all the detection light to pass through; no polarizer and filter are required The light sheet can realize the coaxial measurement of the transient optical nonlinear absorption dynamics of the material with the pump light and the probe light.

Description

A coaxial angle-free pump detection method and system

technical field

The invention relates to a device for studying the nonlinear optical physical mechanism of materials and measuring its optical physical parameters, and belongs 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. It is very important to understand the optical nonlinear mechanism of materials and how to accurately determine the important physical parameters of materials for how to apply materials. Z-scan method (Mansoor Sheik-Bahae, Ali A.Said, Tai-Hui Wei, David J.Hagan, E.W.Van Stryland. "Sensitive measurement of optical nonlinearities using asingle beam", IEEE J.Quantum Elect, 26, 760-769 (1990 )) is currently the most commonly used method for measuring the optical nonlinearity of materials with a single beam. This method is proposed on the basis of the beam distortion measurement method. Linear absorption and refraction. But this method is difficult to accurately determine the optical nonlinear mechanism of the material and the corresponding important optical physical parameters of the material.

On the basis of Z-scan, in 1994, J.Wang et al proposed the time-resolved Z-scan technology (J.Wang, M.Sheik-Bahae, A.A.Said, D.J.Hagan, and E.W.Van Stryland, "Time-resolved Z -scanmeasurements of optical nonlinearities”, J.Opt.Soc.Am.B, 11, 1009-1017, 1994). This method determines the optical nonlinear mechanism of the material and the important optical physical parameters of each energy level by analyzing the phase and intensity changes of the probe light at different moments when the sample is emitted. However, this method is cumbersome when measuring the characteristics of the nonlinear refraction of the sample over time, and the error is relatively large. The specific performance is: (1) the time characteristics of the nonlinear absorption of the sample must be measured first, and then the samples are separated It is placed in two positions for the measurement of nonlinear refraction time characteristics, and finally the influence of nonlinear absorption must be removed. (2) The measurement of nonlinear absorption and nonlinear refraction time characteristics cannot be performed at the same time, because the spatial distribution and energy of the laser light are different at different times, which will cause large measurement errors. In addition, although this method adopts the coaxial pump detection method, the coaxial pump detection method of this method uses polarizers or optical filters, and the corresponding polarizers or optical filters need to be replaced for different wavelengths of laser light. This method and this method have very high requirements on the parameters of the polarizer or filter, otherwise the error of the experimental result is very large. If a polarizer is used, the angle between the pump light and the probe light can only be 90°. If optical filters are used, the laser wavelengths of the two optical paths cannot be the same, and only non-degenerate pump detection can be used, and degenerate pump detection cannot be realized.

There is also a phase object pump-probe technique that can simultaneously measure transient nonlinear absorption and nonlinear refraction (Junyi Yang, Yinglin Song, Yuxiao Wang, Changwei Li, Xiao Jin, and Min Shui, “Time-resolved pump-probe technology with phase object for measurements of optical nonlinearities”, Optics Express 17, 7110–7116 (2009)), is to add a phase object at the position of the front focal plane of the lens of the detection optical path on the basis of the original traditional pump detection system, but In this method, there is a certain angle between the pump light and the probe light, and the pump light and the probe light cannot be coaxial.

In order to overcome some shortcomings of the above-mentioned technologies, the present invention provides a coaxial pumping detection method capable of measuring transient absorption optical nonlinear dynamics of materials without polarizers and filters.

Contents of the invention

The purpose of the present invention is to solve the problem that the delay line structure of the mobile platform is complex and easy to introduce system errors in the traditional pump detection; to provide a pump detection method in which the pump light and the detection light are coaxial and have no angle, which is used for optical nonlinearity Material detection; use the coaxial pump light and probe light to more accurately determine the optical nonlinear mechanism of the material and accurately measure important nonlinear optical parameters of the material at the same time.

A coaxial non-included angle pump detection method, the laser beam is divided into two beams, the beam with strong light intensity is the pump light, and the beam with weak light intensity is the probe light; the pump light is used after passing through the time delay component The mirror group couples the pump light into the optical path with the same optical axis as the probe light, and uses a converging lens to focus the pump light onto the nonlinear sample to be measured, so that the nonlinear sample to be measured in the ground state produces nonlinear absorption; The converging lens also converges the probe light onto the nonlinear sample to be tested; the detector is used to receive the probe light emitted from the nonlinear sample, and the spot image collected by the detector is processed to analyze the nonlinearity of the sample to be tested. Absorption time characteristic curve. The reflective mirror group is a reflective mirror assembly composed of multiple reflective mirrors for deflecting light to a specific direction for propagation. Preferably: the sample to be tested is removed, and the detector is used to collect the light spot image after removing the sample to be tested. By analyzing the light spots collected by the detector after the sample is removed, the systematic error introduced by the test environment can be eliminated through the differential method, and the test accuracy can be further improved.

The time delay component is composed of two reflecting mirrors and a reflecting prism, the direction of the pumping light is changed by the reflecting mirror, the distance between the reflecting prism and the reflecting mirror is adjusted, and the traveling distance of the pumping light is changed, that is, Realize the adjustment of the delay time. The time delay component may also be a time delay mirror or a time delay window.

The moving range of the reflective prism is 0 to 22.5 cm, and the time delay range is -200 ps to 1.3 ns.

A first concentric baffle and a second concentric baffle are arranged on both sides of the converging lens, and the distance from the first concentric baffle and the second concentric baffle to the converging lens conforms to the lens imaging law, wherein the first concentric baffle It is used to block part of the probe light so that the pump light coupled to the common optical axis with the probe light is focused by the converging lens onto the nonlinear sample to be measured, and the second concentric baffle is used to block the pump light emitted from the nonlinear sample Pu light, the edge detection light not blocked by the first concentric baffle passes through the nonlinear sample to be measured and is received by the detector.

The diameter of the first concentric baffle is larger than the section diameter of the pumping light, and the diameter of the second concentric baffle is larger than the section diameter of the pumping light at its position.

The specific measurement steps using the above method are:

(1) Put the sample to be tested, and use the detector to collect the energy of the detected light at different delay times;

(2) Process the detection light energy curves obtained above with different delay times to obtain the required optical nonlinear parameters of the detection material.

In the above-mentioned technical solution, the processing in the step (2) includes, making a normalized curve of the normalized transmission energy with the delay time, and fitting the curve of the normalized transmission energy with the delay time to obtain Magnitude and lifetime of optical parameters related to nonlinear absorption.

The probe light and the pump light are focused on the sample to be measured, and the angle (α) between the two optical axes is zero.

A coaxial angle-free pump detection system according to the above method, including a laser, a beam splitter, a time delay component, a mirror group, a converging lens, and a detector; it is characterized in that: the laser beam emitted by the laser is incident on the beam splitter The detector is divided into pump light and probe light; the pump light passes through the time delay component and is coupled into the optical path with the common optical axis of the probe light by the mirror group; the converging lens focuses the pump light onto the nonlinear sample to be measured, The non-linear sample to be measured in the ground state produces non-linear absorption; the converging lens also converges the detection light to the non-linear sample to be measured; the detector receives the detection light emitted from the non-linear sample.

In the technical solution of the present invention, after the nonlinear sample is excited by the pump light, the particles in the ground state jump to the excited state, and the change of the particle population distribution leads to nonlinear absorption and nonlinear refraction response to the incident light; The population number is constantly changing with time, so the impact on the probe light at different times is different. The particle population in the sample at this time can be known from the phase and intensity changes of the sample probe beam. Through By analyzing the probe light at different times, the nonlinear absorption and nonlinear refraction time characteristic curves of the sample can be measured simultaneously, so that the absorption cross-section, lifetime and refractive index volume of each energy level can be determined. The measurement system provided by the method of the present invention greatly reduces the requirements on the optical path, and the pump light and the probe light can pass through the sample to be tested coaxially, greatly increasing the overlapping area of the pump light and the probe light; the sample does not need to be moved during the measurement process .

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

1. The measurement is very convenient, there is no movement of the sample, and the theoretical model is simple.

2. In this method, the pump light and the probe light can coaxially measure the transient optical nonlinear absorption dynamics of materials without polarizers and filters.

3. Although there is no angle between the pump light and the probe light in this method, they can be separated after passing through the sample, so it is very convenient to use the detector to receive the signal. And through the method, any combination of polarization directions of pump light and probe light can be realized very conveniently, and any wavelength combination can be realized at the same time, that is, degenerate and non-degenerate pump-probe technologies are covered.

5. The measurement method of the present invention can be widely used in research fields such as nonlinear optical measurement, nonlinear photonic 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 ensure more accurate test results and greatly eliminate the interference of uncertain factors; in addition, the method has simple requirements on the quality of the laser and the optical path, and the test speed is fast.

Description of drawings

Accompanying drawing 1 is the working principle diagram of the coaxial pump detection method with no included angle;

Accompanying drawing 2 is the change diagram of normalized transmittance with delay time;

Among them: 1. Incident laser beam; 2. Beam splitter; 3. Probe optical path; 4. Pump optical path; 5. Reflector; 6. Reflective prism; 7. Reflector; 8. Reflector; 9. Reflector; 10. Convex lens; 11. Convex lens; 12. First baffle; 13. Mirror; 14. Convex lens; 15. Sample to be tested; 16. Aperture diaphragm; 17. Second baffle; detector.

Detailed ways

In order to illustrate the invention more clearly, the following will be further described in conjunction with the accompanying drawings and embodiments

Embodiment one:

As shown in Figure 1, a coaxial pumping detection method with no included angle is based on the detection optical path 3 and the pumping optical path 4. The pumping optical path is composed of a reflector, a rectangular prism, and a convex lens. The reflective prism can be translated back and forth. To change the delay time of the pump light; the detection light path is composed of a mirror, a baffle, a convex lens, a small hole, and a detector; the pump light path and the detection light path are simultaneously focused on the sample to be tested.

Use the beam splitter 2 to divide the laser pulse 1 into the detection optical path 3 and the pump optical path 4, the detection optical path 3 passes through the mirror 9 to change the direction, after the lens 10 and the convex lens 11 expand the beam, it is blocked by the baffle 12 coaxial with the beam. After light, the edge light beam passes through the pump light reflector 13, then passes through the convex lens 14, and then focuses on the sample 15 to be tested. After passing through the small hole 16 and the baffle 17, it is converged by the convex lens 18 and then detected by the detector 19; the pump light path 4 Through the delay platform formed by reflector 5, reflector 6 and reflector 7, the propagation direction is changed by reflector 8 and reflector 13, and then focused on the sample 15 to be tested through convex lens 14, and completely blocked by baffle plate 17 after passing through the sample. The pump light causes the particles in the ground state of the sample 15 to be tested to be excited and transition to the excited state, and the change of the population distribution of the particles affects the absorption of the detection optical path 3, and because the population of the particles changes with time, the forward and backward translation The reflective prism 6 can have different influences on the detection optical path 3 at different times and be received by the detector 19 .

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-765energy probe) are connected to the energy meter (Rj-7620ENERGYRATIOMETER, Laserprobe). The sample to be tested is copper sulfonated peptide cyanide (CuPcTs), which has a weak linear absorption at 532nm and is optically nonlinear in an excited state.

The specific detection steps are: (1) Place the detector 19 at the position of the sample 15 to measure the energy of the pump light. (2) Put the sample 15 on, translate the reflective prism 6 back and forth, and continuously record the energy of the probe light with different delay times. (3) Make a curve of the normalization of the normalized transmission energy of the opening with the delay time.

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

Considering the slowly varying amplitude approximation and the thin sample approximation, the propagation of the probe light in the sample satisfies

Δn is the change in refractive index, Δα is the change in absorption coefficient, and z' is the optical path of the laser in the sample. In CuPcTs solution samples,

Δα＝σ ₀ N ₀ +σ ₁ N ₁ (3)

Δn=Δη ₁ N ₁ (4)

In the formula, N ₀ and N ₁ are the particle population numbers of the ground state and the first excited state, respectively; σ ₀ , σ ₁ are the absorption cross sections of the ground state and the first excited state, respectively; Δη ₁ is the refraction volume and The difference in the ground state refractive volume.

Because the probe light is many times weaker than the pump light in the pump-probe experiment, it can be considered that the particle distribution data on the excited state is generated by the pump light

N ₀₀ is the initial particle population number of the ground state.

The light intensity change after the pump light passes through each layer of the sample is:

Figure 2 is the pump-probe absorption curve of CuPcTs solution. Initially, the absorption of the solution increases rapidly with time, which is mainly due to the absorption of the first excited state, indicating that the absorption cross section σ ₁ of the first excited state is larger than the absorption cross section σ ₀ of the ground state. When the pump pulse light passes through the sample, the transmittance of the probe light does not recover, and remains unchanged for a period of low and constant transmittance. This is mainly because the energy level lifetime of the first excited state is very long, the population of particles remains unchanged, and the absorption cross section σ ₁ of the first excited state is larger than that of the ground state σ ₀ . By fitting the absorption-pump-probe curve in Fig. 2, the absorption cross section of the first excited state can be obtained as σ ₁ =89.5×10 ^-22 m ² .

The invention provides a pump detection method in which the pump light and the detection light are coaxial and have no included angle, and the material is used for the detection of optical nonlinearity. Using the coaxiality of the pump light and the probe light can more accurately determine the optical nonlinear mechanism of the material and simultaneously accurately measure the important nonlinear optical parameters of the material. The laser beam is divided into two beams, the strong beam is the pump light, and the weak beam is the probe light. The pump light is focused on the sample to be tested after a time delay, so that the nonlinear sample in the ground state produces nonlinear absorption. ; The probe light is converged by the lens to the sample to be tested after passing through a concentric baffle, the outgoing pump light is blocked by the second concentric baffle, and all the probe light enters the detector D after passing through the second baffle. The distance between the baffle in front of the lens and the baffle behind the lens in the detection light path to the lens conforms to the law of lens imaging. In addition, the radius of the baffle in front of the lens is greater than the radius of the reflector of the pump light, and the radius of the rear baffle can completely block the pump light and allow all the probe light to pass through. The method is very convenient for measurement, there is no sample movement, and the theoretical model is simple. The method can realize the coaxial measurement of the transient optical nonlinear absorption dynamics of the material by the pump light and the probe light without the polarizer and the filter. And through the method, it is very convenient to realize any combination of the polarization directions of the pump light and the probe light, and simultaneously realize any combination of the wavelengths of the pump light and the probe light.

Parts not described in detail in this technical solution belong to the well-known technology of those skilled in the art.

Claims (10)

1. A coaxial angle-free pump detection method, which divides the laser beam into two beams, wherein the beam with strong light intensity is the pump light, and the beam with weak light intensity is the probe light; the pump light passes through the time delay component Finally, the mirror group is used to couple the pump light into the optical path with the same optical axis as the probe light, and the converging lens is used to focus the pump light onto the nonlinear sample to be measured, so that the nonlinear sample to be measured in the ground state produces nonlinear absorption The converging lens will also focus the probe light onto the non-linear sample to be tested; use the detector to receive the probe light emitted from the nonlinear sample, perform data processing on the spot image collected by the detector, and analyze the sample to be tested Nonlinear absorption time characteristic curve. 2 . The coaxial angle-free pump detection method according to claim 1 , wherein the sample to be tested is removed, and the detector is used to collect a spot image after removing the sample to be tested. 3 . 3. The coaxial angle-free pump detection method according to claim 1, characterized in that: the time delay component is composed of two reflectors and a reflector prism, and the reflector changes the pump light Direction, adjusting the distance between the reflecting prism and the reflecting mirror, and changing the traveling distance of the pump light can realize the adjustment of the delay time. 4. The coaxial angle-free pump detection method according to claim 3, characterized in that: the moving range of the reflecting prism is 0 to 22.5 cm, and the time delay range is -200 ps to 1.3 ns. 5. The coaxial angle-free pump detection method according to any one of claims 1 to 4, characterized in that a first concentric baffle and a second concentric baffle are arranged on both sides of the converging lens, the first The distance between the concentric baffle and the second concentric baffle to the converging lens conforms to the lens imaging law, wherein the first concentric baffle is used to block part of the probe light so that the pump light coupled to the common optical axis with the probe light is captured by the The converging lens is focused on the nonlinear sample to be measured, and the second concentric baffle is used to block the pump light emitted from the nonlinear sample, and the edge probe light not blocked by the first concentric baffle passes through the nonlinear sample to be measured and is The detector receives. 6. The coaxial angle-free pump detection method according to claim 5, the diameter of the first concentric baffle is larger than the cross-sectional diameter of the pump light, and the diameter of the second concentric baffle is larger than the pump light at the position section diameter. 7. A coaxial non-included angle pump detection system, including a laser, a beam splitter, a time delay component, a mirror group, a converging lens, and a detector; it is characterized in that: the laser beam emitted by the laser is incident on the beam splitter and is It is divided into pump light and probe light; after the pump light passes through the time delay component, it is coupled into the optical path with the common optical axis of the probe light by the mirror group; the converging lens focuses the pump light on the nonlinear sample to be measured, so that The nonlinear sample to be measured in the ground state produces nonlinear absorption; the converging lens also converges the detection light onto the nonlinear sample to be measured; the detector receives the detection light emitted from the nonlinear sample. 8. The coaxial angle-free pumping detection system according to claim 7, wherein the time delay component is composed of two reflection mirrors and a reflection prism. 9. The coaxial angle-free pumping detection system according to claim 7 or 8, a first concentric baffle and a second concentric baffle are arranged on both sides of the converging lens, and the first concentric baffle and the second The distance from the concentric baffle to the converging lens conforms to the lens imaging law, wherein the first concentric baffle is used to block part of the detection light so that the pump light coupled to the common optical axis with the detection light is focused by the converging lens to the On the nonlinear sample, and the second concentric baffle is used to block the pump light emitted from the nonlinear sample, and the edge detection light not blocked by the first concentric baffle passes through the nonlinear sample to be measured and is received by the detector. 10. The coaxial non-included angle pump detection system according to claim 9, the diameter of the first concentric baffle is larger than the cross-sectional diameter of the pump light, and the diameter of the second concentric baffle is larger than the pump light at the position section diameter.