CN201072406Y - Pump detecting device based on 4f phase coherent imaging - Google Patents

Abstract

The utility model discloses a pump detection device based on 4f phase incoherent imaging, which is characterized in that the utility model essentially consists of an optical laser, a beam splitter, a detection light path and a pump light path. The beam splitter splits laser pulse sent from the optical laser into the detection light path and the pump light path. The detection light path comprises a beam expanding system, a 4f system and a record system; samples to be detected are positioned on the focal plane of the 4f system. The pump light path comprises a steering element and a delayed light path. The output of the pump light path focuses on the samples to be detected. The included angle (Beta) of the detection light path and the pump light path on the samples to be detected is between 1.5 degrees and 10 degrees. The device of the utility model does not have rigorous requirement for precision of light paths; absorption pump detection and refraction pump detection are finished simultaneously; during the whole detection process, the samples does not need to move; monopulse measurement reduces chemical cumulative effect and has simple measurement process and low sensitiveness to the random fluctuation of laser beans; measurement result is precise and measurement speed is fast.

Description

Pump-detection device based on 4f phase coherent imaging

technical field

The utility model relates to a measuring device for measuring nonlinear photonics materials, in particular to a device for studying nonlinear absorption and refraction characteristics with respect to time, and belongs to the field of nonlinear photonics materials and nonlinear optical information processing.

Background technique

With the rapid development of technologies in the fields of optical communication and optical information processing, 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. At present, the commonly used methods for measuring nonlinear optical parameters include Z-scan, 4f-based phase coherent imaging measurement, four-wave mixing, third-harmonic nonlinear interferometry, and ellipsometry. Except for the Z-scan and 4f phase-coherent imaging methods, other measurement methods require two or more laser beams, which complicates the optical path of the measurement device, and this type of measurement device cannot simultaneously measure nonlinear refraction and absorption.

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 a single beam", IEEE J. Quantum Elect, 26, 760-769 (1990)) is currently the most commonly used method for measuring optical nonlinearity with a single beam. When measuring, the sample is placed on a mobile platform, and the pulsed light output by the laser is focused on the sample by a lens, and then divided into two paths by a beam splitter. One path is used to detect nonlinear absorption, and the other path is used to detect nonlinear refraction through a small hole. During the measurement process, the sample must be moved to measure the nonlinear response under different light intensities. The device for realizing the above method has a simple optical path, and can simultaneously measure nonlinear absorption and refraction. However, this method has high requirements on the spatial distribution and energy stability of the laser. During the measurement process, the sample needs to move in the direction of laser propagation; in addition, due to the need for multiple excitations of the laser, it is easy to cause changes in material properties and even damage. Additional experiments are needed to judge reliability.

The method of measuring the third-order nonlinear refractive index of materials based on 4f phase coherent imaging was proposed by Georges Boudebs et al. in 1996 (G.Boudebs, M.Chis, and J.P.Bourdin, "Third-order susceptibility measurements by nonlinear image processing", J.Opt.Soc.Am.B, 13, 1450-1456 (1996)), after several improvements, it evolved into measuring the nonlinearity of materials by adding a phase diaphragm on the incident surface of the 4f system. This method is inspired by Zernike's spatial filtering experiment, which can convert the phase change into the amplitude change of light. Like the Z-scan method, it also belongs to beam distortion measurement. When measuring, place the nonlinear sample on the spectrum plane of a 4f system, then let the laser pass through the 4f system, use the CCD to record the spatial change of the light field distribution, and then cooperate with the numerical simulation to obtain the nonlinear refractive index of the material. However, 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 the nonlinear absorption and nonlinear refraction response to the incident light; during this process, the particle population The number is constantly changing with time, so the impact on the detection light at different times is different. In the above measurement method based on 4f phase coherent imaging, the neglect of the time item will lead to relatively large deviations in the results.

Contents of the invention

The purpose of this utility model is to provide a pumping-probe measuring device based on 4f system, which can analyze the nonlinear parameters of the detected material from the perspective of space and time.

In order to achieve the above object, the technical solution adopted by the utility model is: a pump detection device based on 4f phase coherent imaging, which is mainly composed of a laser, a beam splitter, a detection optical path and a pump optical path, and the beam splitter combines the laser The emitted laser pulse is split into a detection optical path and a pump optical path. The detection optical path includes a beam expander system, a 4f system and a recording system. The sample to be measured is located on the focal plane of the 4f system. The pump optical path includes a steering element and an extension The optical path and the output of the pumping optical path are focused on the sample to be tested, the probe light and the pump light are kept spatially overlapping at the sample to be tested, and the angle (β) between the two light beams is in the range of 1.5° to 10°.

In the above, the beam splitter divides the light from the laser into two beams, the strong one is the pump light, and the weak one is the probe light. Usually, the beam splitter uses a low-transmittance high-reflection lens, and the transmittance and reflection The rate ratio is: 1:10～1:100. The pump light is focused on the sample to be tested through the time delay system, causing the sample to be tested to produce optical nonlinear effects; the probe light passes through the 4f system to measure the optical nonlinear effect caused by the pump light, and then is received by the recording system. The optical nonlinear parameters of the sample to be tested can be determined according to the condition of the probe light.

In the above technical solution, the beam expander system is composed of a first lens, a second lens and a phase diaphragm arranged in sequence along the detection optical path direction, the first lens is a short-focus lens, the second lens is a telephoto lens, and the first lens The back focus of the second lens coincides with the front focus of the second lens, so that the outgoing probe light forms a Gaussian beam that has been collimated and expanded, and then the edge of the spot is filtered through the phase diaphragm to obtain a uniform spot in the center. The first lens The focal length is less than or equal to 10 centimeters, and the focal length of the second lens is greater than or equal to 40 centimeters.

The recording system consists of an attenuator and a CCD camera. Wherein, the attenuation factor of the attenuator is greater than or equal to 100, and the dynamic range of the CCD camera is greater than or equal to 12.

In the above technical solution, the delayed optical path of the pump light is a right-angle prism installed on the micro-motion platform, the direction of the pump light is changed by the reflector, and it is incident into the right-angle prism, and then exits after being totally reflected by the right-angle prism. After being turned by another mirror, it is focused on the sample to be tested by a convex lens.

The movement range of the rectangular prism is 0 to 31 cm, and the time delay range is -350 ps to 1.7 ns.

In the above technical solution, the pump light is irradiated on the sample to be tested to cause a nonlinear response, that is, the physical properties change, and the physical change is measured by the probe light, and the light intensity distribution of the probe light is received by the CCD, which can be analyzed in different regions. In addition, by moving the rectangular prism up and down to change the time delay between the pump light and the probe light, the characteristics of the sample under different time delay conditions can also be analyzed.

Due to the application of the above-mentioned technical solution, the utility model has the advantages compared with the prior art:

1. Since the utility model adopts single-pulse measurement, there is no sample movement, low sensitivity to random fluctuations of the laser beam, accurate measurement, fast speed, etc. Due to its single-pulse measurement characteristics, it can be used to measure the dynamic process of the nonlinear refractive index of materials changing with exposure time.

2. The optical path of this device is simple, and the requirements for the optical path are not high, as long as the pump light and the probe light can be spaced to overlap at the focal point, there is no requirement whether the pump light and the probe light are coaxial. In this device, the pump light and probe light are automatically separated after passing through the sample, which is applicable to degenerate and non-degenerate light of any polarization state. However, the pump-detection method based on the Z-scan method has the coaxiality of the pump light and the probe light. When the beam passes through the sample, the separation of the beam must be considered, especially when the wavelengths of the pump light and the probe light are close or equal. Even more troublesome.

3. Since the sample does not need to move during the measurement process of this device, compared with the pump detection method based on the Z-scan method, the sample needs to be placed in three different positions (focus, peak position and valley position once each) , it can be seen that the device of the utility model is simple to use and convenient to measure.

Description of drawings

Accompanying drawing 1 is the schematic diagram of the optical path structure of the phase coherent imaging pump detection device in the first embodiment of the utility model;

Accompanying drawing 2 is the change diagram of transmittance with delay time in embodiment one;

Accompanying drawing 3 is the graph of the change of ΔT with the delay time in the first embodiment.

Among them: 1. Incident laser beam; 2. Beam splitter; 3. Probe optical path; 4. Pump optical path; 5. Right-angle prism; 6. Reflector; 7. Reflector; 8. Convex lens; 9. Reflector; 10 1, the first lens; 11, the second lens; 12, the phase diaphragm; 13, the convex lens; 14, the sample to be tested 15, the convex lens; 16, the attenuator; 17, the CCD camera.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the utility model is further described:

Embodiment 1: Referring to the accompanying drawing 1, a pump detection device based on 4f phase coherent imaging is characterized in that it is mainly composed of a laser, a beam splitter, a detection optical path and a pump optical path, and the beam splitter combines The laser pulse emitted by the laser is split into a detection optical path and a pumping optical path. The detection optical path includes a beam expander system, a 4f system and a recording system. The sample to be measured is located on the focal plane of the 4f system. The pumping optical path includes a steering element and a Delaying the optical path, the output of the pumping optical path is focused on the sample to be tested, and the included angle (β) between the probe light and the pumping light at the sample to be tested is within the range of 1.5° to 10°.

The incident laser beam 1 from the laser is divided into two paths by a beam splitter 2 , the strong one is the pumping light path 4 , and the weak one is the detection light path 3 . The pump light path is composed of a reflector 6, a rectangular prism 5, a reflector 7, and a convex lens 8, wherein the reflectors 6 and 7 are respectively on the upper left and upper right of the rectangular prism 5, and the rectangular prism 5 can move up and down, and can be installed on the The movement of the rectangular prism in the up and down direction is realized on the movable support; the detection optical path is composed of a reflector 9, a first lens 10, a second lens 11, a phase diaphragm 12, a convex lens 13, a sample to be tested 14, and a convex lens 15 from left to right. Attenuator 16, CCD camera 18 composition.

The beam splitter 2 adopts a low-transmittance reflective mirror, the ratio of transmittance to reflectance is 1:10-1:100, and the pumping light and the incident light are vertically linearly polarized light.

The reflector 6 changes the direction of the pumping light by 90°, and it is vertically incident on the hypotenuse of the rectangular prism 5. On the test sample 14, the rectangular prism can move up and down to change the traveling distance of the pumping light. The moving distance depends on the actual situation. Usually, the movable range is 0 to 31 cm.

The reflector 9 changes the direction of travel of the probe light by 90°, and the first lens 10 and the second lens 11 carry out beam expansion and collimation of the light, requiring the rear focal point of the lens 10 and the front focal point of the lens 11 to coincide between them, and the lens The focal length of lens 10 is less than 10 cm, and the focal length of lens 11 is greater than 40 cm.

The optical density value of the CCD camera 17 and the attenuation multiple of the attenuator 16 are generally greater than 100 and the optical density value is generally greater than 12 according to the actual needs and the intensity of the actual outgoing probe light.

During use, the laser pulse 1 is divided into a detection optical path 3 and a pump optical path 4 by using a beam splitter 2, and the detection optical path 3 passes through a reflector 9, lenses 10, 11, a diaphragm 12, and a lens 13 is irradiated onto the sample 14 to be measured, and the Then pass through the lens 15 and the attenuator 16 to be received by the CCD 17; the pump light path 4 passes through the reflector 6, the rectangular prism 5, the reflector 7, and the lens 8 to irradiate the sample 14 to be tested. Block the pump light path 4, take away the sample 14 to be tested, and collect a "sample-free image" with a CCD camera. Block the pumping light 4, put the sample 14 to be tested, and collect a "linear image" with a CCD camera. Release the pump light, adjust the rectangular prism 5 up and down, continuously collect the probe light images with different delay times, and perform two processes on each image with different delay times: 1. Integrate the image to obtain the energy of the transmitted pulse at this delay time; 2. , find the difference between the average intensity inside the phase object (PO) in the center of each image and the average intensity outside the PO, and define the ratio of this difference to the average intensity of the linear image as ΔT. The normalized transmission energy and the variation curve of ΔT with delay time were drawn respectively. The change curve of normalized transmission energy with delay time is only related to nonlinear absorption, while the change curve of ΔT with delay time is related to both nonlinear absorption and nonlinear refraction.

Experimental and theoretical analysis calculations show that, as shown in Figure 2, the sharp depression at the zero delay position is caused by the two-photon absorption of ZnSe at 532nm, and the two-photon absorption coefficient β=6.5cm/GW is obtained by fitting the position of the lowest valley. From Fig. 3, it is obtained that the lifetime of free carriers is τ _r =2.5ns. Conversely, by refitting the absorption-pump-detection curve, the free carrier absorption cross section can be obtained as σ _α =8.8×10 ^-17 cm ² . Fitting Fig. 3 can obtain the nonlinear refractive index n ₂ =-8.5×10 ^-14 cm ² /W, and the free carrier refraction volume σ _r =-1.3×10 ^-20 cm ³ .

Claims (7)

1. a pump detection device based on 4f phase coherent imaging is characterized in that: it is mainly composed of laser, beam splitter (2), detection optical path (3) and pump optical path (4), and the beam splitter ( 2) splitting the laser pulse emitted by the laser to the detection optical path and the pump optical path, the detection optical path includes a beam expander system, a 4f system and a recording system, the sample to be measured (14) is located on the focal plane of the 4f system, and the pump The pump light path includes a steering element and a delay light path, the output of the pump light path is focused on the sample to be tested, the probe light and the pump light are kept spatially overlapping at the sample to be tested, and the angle (β) between the two light beams is 1.5° to within 10°. 2. The pump detection device based on 4f phase coherent imaging according to claim 1, characterized in that: the beam expander system consists of a first lens (10) and a second lens (11) arranged in sequence along the direction of the detection optical path Constituted with a phase diaphragm (12), the first lens is a short-focus lens, and the second lens is a long-focus lens. The back focus of the first lens coincides with the front focus of the second lens, so that the outgoing probe light forms a collimated and expanded beam Gaussian light, and then filter out the edge part of the light spot through the phase diaphragm to obtain a uniform light spot in the center, the focal length of the first lens is less than or equal to 10 cm, and the focal length of the second lens is greater than or equal to 40 cm. 3. The pump detection device based on 4f phase coherent imaging according to claim 1, characterized in that: the recording system is composed of an attenuator (16) and a CCD camera (17). 4. The pump detection device based on 4f phase coherent imaging according to claim 3, characterized in that: the attenuation factor of the attenuator (16) is greater than or equal to 100, and the dynamic range of the CCD camera (17) is greater than or equal to 100. or equal to 12. 5. The pump detection device based on 4f phase coherent imaging according to claim 1, characterized in that: the optical delay path of the pump light is a rectangular prism (5) installed on the micro-motion platform, and the pump light The direction of the Pu light is changed by the reflector (6), and it is incident into the right-angle prism (5). After being totally reflected by the right-angle prism, it exits. After being diverted by another reflector (7), it is focused by the convex lens (8) to the sample to be tested ( 14) on. 6 . The pump-detection device based on 4f phase coherent imaging according to claim 5 , wherein the movement range of the rectangular prism is 0 to 31 cm, and the time delay range is -350 ps to 1.7 ns. 7. The pump detection device based on 4f phase coherent imaging according to claim 1, characterized in that: the beam splitter (2) adopts a low-transmittance high-reflection sheet, and the ratio of transmittance to reflectance is 1:10～ 1:100.

Images