Coaxial degenerate and non-degenerate ultrafast carrier dynamics material measurement system and method

Abstract

The invention discloses a material measurement system and method for coaxial degenerate and non-degenerate ultrafast carrier dynamics. The system is compatible with coaxial degenerate and non-degenerate pumping detection light paths; the resonance process of the material at a single wavelength and the interaction process of different energy levels are observed, and the detection sensitivity and selectivity are improved. According to the system, a microscope objective is adopted for imaging, the position of a to-be-detected sample is adjusted through a three-dimensional high-precision electric displacement table, and the surface appearance and light spots of the micron-sized sample can be monitored in real time; the system adopts a photoelectric detector to synchronously test transmission and reflection signals of a sample, and solves the problem that the dynamic process of ultrafast carriers of materials of different types and different thicknesses in a microcell is difficult to completely and accurately measure. The ultrafast carrier dynamic process measurement technology is optimized; and the application range of the ultrafast carrier dynamic process measurement technology is expanded. The system realizes automatic control, and has the technical characteristics of rapidness, sensitivity and high integration level.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and in particular to a material measurement system and method for coaxial degenerate and non-degenerate ultrafast carrier dynamics. Background Art

[0002] Pump-probe techniques play a vital role in nonlinear optics, especially in the fields of lasers, sensors, and spectroscopy. In laser technology, pump-probe methods are widely used to study ultrafast dynamics, such as relaxation processes in semiconductor lasers and absorption processes in laser gain media. This is essential for optimizing laser performance, improving beam quality, and developing high-speed pulsed lasers. In sensor applications, pump-probe techniques are used to characterize nanoscale materials, such as two-dimensional materials (such as graphene and MoS2) and metamaterials, where nonlinear responses to light can reveal unique material properties. It is particularly valuable for the development of highly sensitive optical sensors that can detect small changes in the environment, making it suitable for biochemical sensing and environmental monitoring. In addition, in the field of spectroscopy, such as charge carrier dynamics in photovoltaic materials and photochemical reactions in biomolecules. This makes it possible to capture real-time changes in material properties, thereby promoting progress in areas such as solar energy harvesting, photodynamic therapy, and the development of new photonic devices.

[0003] Patent document CN108667426A discloses a carrier dynamics process measurement device. By changing the relative polarization direction of the pump light and the excitation light, the time-resolved current under different polarization configurations can be obtained, thereby obtaining the anisotropy parameters of the photovoltaic device. Patent document CN116087156A discloses a high signal-to-noise ratio degenerate pump-detection device. By introducing technical means such as beam splitters and beam expanders, the pump light and the detection light are separated to the greatest extent in space, thereby improving the test signal-to-noise ratio.

[0004] However, factors such as wavelength, power threshold, sample characteristics and material thickness need to be carefully considered in the detection process in different fields. Traditional pump-probe methods often find it difficult to meet these requirements at the same time and show limitations when dealing with the nonlinear characteristics of complex samples. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a system and method for coaxial degenerate and non-degenerate measurement of ultrafast carrier dynamics processes of materials, so as to realize the observation of the resonance process and the interaction process of different energy levels of the material at a single wavelength, improve the detection sensitivity and selectivity, realize the synchronous measurement of the transmission and reflection signals of the carrier dynamics process of the material, and realize the real-time imaging of the sample and the light spot at the same time, so as to solve the problem that it is difficult to fully and accurately measure the carrier dynamics process of materials with different thicknesses in micro-areas.

[0006] The technical solution of the present invention is as follows:

[0007] A material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics, characterized by:

[0008] Femtosecond pulse laser, used to generate ultrashort pulse laser;

[0009] A first polarizer and a first plane beam splitter are sequentially arranged on the same optical axis along the output beam direction of the femtosecond pulse laser; wherein the first plane beam splitter divides the ultrashort pulse laser into transmitted light and reflected light, i.e., pump light and detection light;

[0010] At least a first optical parametric oscillator, a first variable neutral density filter, an optical chopper and an adjustable hollow roof prism reflector are arranged in the transmission direction of the pump light, wherein the first optical parametric oscillator is used to adjust the wavelength of the pump light, the first variable neutral density filter is used to adjust the energy of the pump light, the optical chopper is used to modulate the pump light to generate an optical signal of a specific frequency, and the adjustable hollow roof prism reflector is used to adjust the path and delay of the pump light;

[0011] At least a second optical parametric oscillator, a second variable neutral density filter, a second bandpass filter and a wide-band half-wave plate are arranged in the transmission direction of the detection light, wherein the second optical parametric oscillator is used to adjust the wavelength of the detection light, the second variable neutral density filter is used to adjust the energy of the detection light, the second bandpass filter is used to select the wavelength of the detection light, and the wide-band half-wave plate is used to adjust the polarization angle of the detection light;

[0012] The pump light and the detection light are combined into a main light path through a multi-band dichroic mirror or a second plane beam splitter;

[0013] A fifth reflector, a third pinhole diaphragm, a third plane beam splitter, a fourth plane beam splitter, a fifth plane beam splitter, a microscopic focusing objective lens, a sample to be measured, a microscopic collecting objective lens, a third band-pass filter, a fourth pinhole diaphragm, a second polarizer and a first photodetector are sequentially arranged along the transmission direction of the main light path and the same optical axis; wherein a fourth band-pass filter, a third polarizer and a second photodetector are sequentially arranged on the reflected light side of the third plane beam splitter; a white light source is also arranged on the reflected light side of the fourth plane beam splitter; and a microscopic imaging camera is also arranged on the reflected light side of the fifth plane beam splitter;

[0014] The optical chopper is electrically connected to the chopper frequency controller, the first photodetector, the second photodetector, and the chopper frequency controller are electrically connected to the phase-locked amplifier respectively, the adjustable hollow roof prism reflector is electrically connected to the first electric displacement stage for placing the adjustable hollow roof prism reflector, and the electric displacement stage, the phase-locked amplifier, the microscopic imaging camera, and the second electric displacement stage for placing the sample to be tested are electrically connected to the computer;

[0015] The microscopic focusing objective is used for imaging and the second electric translation stage is used to adjust the position of the sample to be tested, so as to realize real-time monitoring of the surface morphology and light spot of the micron-sized sample. The first photodetector and the second photodetector are used to synchronously test the transmission and reflection signals of the sample to obtain the ultrafast carrier dynamics process of materials of different types and thicknesses in the micro-area.

[0016] Further, a first reflector, a second reflector, a first optical parametric oscillator, a first pinhole diaphragm, a first bandpass filter, a first variable neutral density filter, an optical chopper, a second pinhole diaphragm, an adjustable hollow roof prism reflector and a third reflector are sequentially arranged along the transmitted light direction of the first plane beam splitter, that is, the same optical axis as the pump light direction;

[0017] A second optical parametric oscillator, a second variable neutral density filter, a second bandpass filter, a fourth reflector and a wide-band half-wave plate are sequentially arranged along the reflected light direction of the first plane beam splitter, that is, the detection light direction;

[0018] The reflected light and the transmitted light along the first plane beam splitter are combined into a beam at a multi-band dichroic mirror or a second plane beam splitter;

[0019] Furthermore, the first variable neutral density filter, the second variable neutral density filter, the wide-band half-wave plate, the first polarizer, the second polarizer, the third polarizer, the first band-pass filter, the second band-pass filter, the third band-pass filter, and the fourth band-pass filter are perpendicular to the laser propagation direction, and the rotation axis is parallel to the laser optical axis.

[0020] Furthermore, the sample to be tested is perpendicular to the laser propagation direction and is arranged on a second electric translation stage, and the second electric translation stage is electrically connected to the computer.

[0021] Furthermore, the multi-band dichroic mirror, the second plane beam splitter and the adjustable hollow roof prism reflector are arranged on a first electric translation stage, and the first electric translation stage is electrically connected to the computer.

[0022] Furthermore, the angle between the first reflector, the second reflector, the third reflector, the fourth reflector, the fifth reflector, the first plane beam splitter, the second plane beam splitter, the third plane beam splitter, the fourth plane beam splitter, the fifth plane beam splitter, the multi-band dichroic mirror, and the adjustable hollow roof prism reflector and the laser optical axis is 45°.

[0023] The present invention also provides a material measurement method for coaxial degenerate and non-degenerate ultrafast carrier dynamics, which is characterized in that it includes the steps of optical path adjustment, reflection degenerate measurement, reflection non-degenerate measurement, transmission degenerate measurement, transmission non-degenerate measurement and data processing;

[0024] The optical path adjustment comprises the steps of:

[0025] Turn on the femtosecond pulse laser, and select the laser wavelength, repetition frequency and initial energy according to measurement requirements;

[0026] Adjust the first pinhole aperture, the center of the second pinhole aperture, the third pinhole aperture, the fourth pinhole aperture, the first plane beam splitter, the second plane beam splitter, the third plane beam splitter, the fourth plane beam splitter, the first reflector of the fifth plane beam splitter, the second reflector, the third reflector, the fourth reflector, the fifth reflector, the first band-pass filter, the second band-pass filter, the third band-pass filter, the fourth band-pass filter, the microscopic focusing objective lens, the microscopic collecting objective lens, the first photodetector, and the second photodetector so that their centers are at the same height and coincide with the center of the main optical path;

[0027] Adjust the first reflector and the second reflector so that the laser passes through the centers of the first pinhole diaphragm and the second pinhole diaphragm at the same height;

[0028] Adjust the multi-band dichroic mirror and the fifth reflector to make the laser pass through the center of the third and fourth pinhole apertures of equal height, ensure that the focus of the microscopic focusing objective lens and the microscopic collecting objective lens coincide; ensure that the white light source and the microscopic imaging camera are perpendicular to the propagation direction of the main light path;

[0029] The reflected light of the first plane beam splitter is referred to as the detection light; the transmitted light of the first plane beam splitter is referred to as the pump light;

[0030] Adjusting the energy of the pump light and the detection light respectively through a first variable neutral density filter and a second variable neutral density filter;

[0031] Determine the position of the micro-area sample by a microscopic imaging camera, and adjust the second reflector and the fourth reflector to ensure that the pump light and the detection light coincide with the upper position of the sample to be measured;

[0032] Set the parameters of the first electric displacement stage, including starting from the center position of the first band-pass filter, i.e., the coordinate zero point (Z = 0), the first electric displacement stage moves along the direction of the pump light passing through the first band-pass filter, the first electric displacement stage includes the initial position Z0, the termination position Z of the first electric displacement stage, and the minimum displacement ΔZ of each movement of the first electric displacement stage, and 0 < Z0 < Z < 300 mm, where, Z i = Z0 + i * ΔZ, i = 0, 1, 2,..., [(Z - Z0) / ΔZ], i is the displacement times of the first electric displacement stage, Z i is the distance between the position after each movement of the first electric displacement stage and the center position of the first band-pass filter. When the first electric displacement stage is at the coordinate zero point, the optical path difference between the pump light and the probe light is denoted as Z Δ , ensure that for every 1 mm movement of the first electric displacement stage, there is a 6.66 ps time delay difference between the pump light and the probe light, i.e., τ = (Z0 + i * ΔZ - Z Δ ) * 6.66;

[0033] Set the frequency f of the chopper frequency controller to ensure that the optical signal with frequency f in the photodetector is demodulated and amplified by the lock-in amplifier and then input into the computer;

[0034] Transmission-reflection degenerate measurement, the steps include:

[0035] According to the transmission-reflection spectrum of the sample to be measured, adjust the first optical parametric oscillator and the second optical parametric oscillator to ensure that their output wavelengths are the same;

[0036] Set the polarization angle θ of the first polarizer, adjust the polarization angles of the second polarizer and the third polarizer to be the same and orthogonal to the polarization angle of the first polarizer, and rotate the optical axis direction of the broadband half-wave plate to ensure that the polarization angle of the probe light is parallel to the polarization angles of the second polarizer and the third polarizer;

[0037] Adjust the position of the second plane beam splitter and replace the multi-band dichroic mirror;

[0038] According to the thickness d of the sample to be measured, adjust the front and back positions of the sample to be measured along the optical path direction to ensure that the probe light is focused on the surface of the sample to be measured:

[0039] When d < L, the first photodetector collects the transmission signal E of the sample to be measured under different time delay differences τ between the pump light and the probe light t(τ) ;

[0040] When d > L, the second photodetector collects the reflection signal E of the sample to be measured under different time delay differences τ between the pump light and the probe light r(τ) ;

[0041] where, L is the focal depth of the microscopic focusing objective lens, λ is the wavelength of the detection light, f is the focal length of the micro-focusing objective lens, and D is the spot radius of the laser beam incident on the surface of the micro-focusing objective lens;

[0042] Transflective non-degenerate measurement, the steps include:

[0043] According to the transmission and reflection spectra of the sample to be tested, adjusting the first optical parametric oscillator and the second optical parametric oscillator to ensure that their output wavelengths are different;

[0044] Setting the polarization angle θ of the first polarizer, adjusting the polarization angles of the second polarizer and the third polarizer to be the same and parallel to the polarization angle of the first polarizer, rotating the optical axis direction of the wide-band half-wave plate, and ensuring that the polarization angle of the detection light is parallel to the polarization angles of the second polarizer and the third polarizer;

[0045] adjusting the position of the multi-band dichroic mirror and replacing the second plane beam splitter;

[0046] According to the relationship between the thickness of the sample to be measured and the focal depth of the microscope objective lens, the first photodetector and the second photodetector are used to collect the transflection signal E respectively. t(τ) 、E r(τ) ;

[0047] The data processing steps include:

[0048] Adjust the first electric translation stage back to the initial position Z0, and when the delay difference τ between the pump light and the detection light is 0, it is recorded as the zero position Z τ =0;

[0049] Calculate the detection light signal intensity I, the formula is as follows:

[0050]

[0051] Where w0 is the spot radius of the detection light, σ is the pulse width of the detection light, and E is the transmission and reflection energy corresponding to the intensity of the detection light signal.

[0052] Calculate the differential transmittance curve and the differential reflectance curve, the formula is as follows:

[0053]

[0054]

[0055] In the formula, I r (τ) is the reflected light intensity of the sample to be tested under the time delay difference of τ, I r (0) is the reflected light intensity of the sample to be tested at the zero position, I t (τ) is the transmitted light intensity of the sample to be tested under the time delay difference of τ, I t(0) is the transmitted light intensity of the sample to be tested at the zero position, ΔR is the differential reflectivity of the sample to be tested, R is the linear reflectivity of the sample to be tested, ΔT is the differential transmittance of the sample to be tested, and T is the linear transmittance of the sample to be tested. The carrier dynamics process curve of the sample to be tested is obtained using the e-exponential model:

[0056]

[0057] Where τ1 and A1 are the time constant and intensity of the fast process, τ2 and A2 are the time constant and intensity of the slow process, erfc is the error function related to the laser pulse width, σ is the laser pulse width, and τ is the delay difference between the pump light and the detection light.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] 1) Compatible with coaxial degenerate and non-degenerate pump-probe optical paths; realize the observation of the resonance process of the material at a single wavelength and the interaction process of different energy levels, and improve the detection sensitivity and selectivity;

[0060] 2) The system adopts a microscopic imaging system and uses a three-dimensional high-precision electric translation stage to adjust the position of the sample to be tested, which can realize real-time monitoring of the surface morphology and light spot of micron-sized samples;

[0061] 3) The system uses photodetectors to synchronously test the sample transmission and reflection signals, solving the problem of difficulty in completely and accurately measuring the carrier dynamics process of materials of different thicknesses in micro-areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 Schematic diagram of the structure of a material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics according to an embodiment of the present invention.

[0063] In the figure:

[0064] Femtosecond pulse laser 10;

[0065] A first polarizing plate 20;

[0066] A first plane beam splitter 30, a first optical parametric oscillator 31, a second variable neutral density filter 32, a fourth reflector 33, a second bandpass filter 34, and a wide-band half-wave plate 35;

[0067] A first reflector 40;

[0068] A second reflecting mirror 50, a first optical parametric oscillator 501, a first pinhole diaphragm 502, a first bandpass filter 503, a first variable neutral density filter 504, an optical chopper 505, a second pinhole diaphragm 506, an adjustable hollow roof prism reflecting mirror 507, a first electric translation stage 508, and a third reflecting mirror 509;

[0069] A multi-band dichroic mirror 60 and a second plane beam splitter 61;

[0070] a fifth reflecting mirror 70;

[0071] A third aperture stop 80;

[0072] A third plane beam splitter 90, a fourth bandpass filter 91, a third polarizer 92, and a second photodetector 93;

[0073] A fourth plane beam splitter 100 and a white light source 101;

[0074] A fifth plane beam splitter 110 and a microscopic imaging camera 111;

[0075] Microscopic focusing objective lens 120;

[0076] A sample to be tested 130 and a second electric translation stage 131;

[0077] Microscopic collection objective 140;

[0078] A third bandpass filter 150;

[0079] A fourth aperture stop 160;

[0080] A second polarizer 170;

[0081] A first photodetector 180;

[0082] Lock-in amplifier 190;

[0083] Chopper frequency controller 200;

[0084] Computer 210. DETAILED DESCRIPTION

[0085] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0086] See also Figure 1 , Figure 1The structural schematic diagram of the material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics of the present invention, as shown in the figure, includes a femtosecond pulse laser 10, a first polarizer 20 and a first plane beam splitter 30 are sequentially arranged along the output light beam direction of the femtosecond pulse laser; a first reflector 40, a second reflector 50, a first optical parametric oscillator 501, a first pinhole aperture 502, a first bandpass filter 503, a first variable neutral density filter 504, an optical chopper 505, a second pinhole aperture 506, a first bandpass filter 507, a first variable neutral density filter 508, a first optical chopper 509, a second optical chopper 510, a second optical chopper 511, a first optical chopper 512, a second optical chopper 513, a second optical chopper 514, a first optical chopper 515, a second optical chopper 516, a first optical chopper 517, a first optical chopper 518, a first optical chopper 519, a first optical chopper 520, a first optical chopper 521, a first optical chopper 522, a first optical chopper 523, a first optical chopper 524, a first optical chopper 525, a first optical chopper 526, a first optical chopper 527, a first optical chopper 528, a first optical chopper 529, a first optical chopper 530, a first optical chopper 531, a first optical chopper 532, a first optical chopper 533, a first optical chopper 534, a first optical chopper 535, a first optical chopper 536, a first optical chopper 537, a first optical chopper 538, a first optical chopper 539, a first optical chopper 540, a first optical c Aperture 506, adjustable hollow roof prism reflector 507, third reflector 509; along the direction of the reflected light of the first plane beam splitter 30, the first plane beam splitter 30, the first optical parametric oscillator 31, the second variable neutral density filter 32, the fourth reflector 33, the second bandpass filter 34, and the wide-band half-wave plate 35 are sequentially arranged; the reflected light along the first plane beam splitter 30 and the transmitted light are combined in the multi-band dichroic mirror 60 or the second plane beam splitter 61; the fifth reflector 70, the third aperture 509, and the third aperture 509 are sequentially arranged along the reflection direction of the multi-band dichroic mirror 60. Aperture 80, third plane beam splitter 90, fourth plane beam splitter 100, fifth plane beam splitter 110, microscopic focusing objective 120, sample to be measured 131, microscopic collecting objective 140, third band-pass filter 150, fourth pinhole aperture 160, second polarizer 170 and first photodetector 180; fourth band-pass filter 91, third polarizer 92 and second photodetector 93 are arranged along the other side direction of the reflected light of the third plane beam splitter 90; white light source 101 is arranged along the other side direction of the reflected light of the fourth plane beam splitter 100; A microscopic imaging camera 111 is arranged along the other side direction of the reflected light of the fifth plane beam splitter 110; the optical chopper 505 is electrically connected to the chopper frequency controller 200; the first photodetector 180, the second photodetector 93, and the chopper frequency controller 200 are electrically connected to the phase-locked amplifier 190 respectively; the adjustable hollow roof prism reflector 507 is electrically connected to the first electric translation stage 508; the electric translation stage 508, the phase-locked amplifier 190, the microscopic imaging camera 111, the second electric translation stage 131 are electrically connected to the computer 210.

[0087] The first variable neutral density filter 504, the second variable neutral density filter 31, the wide-band half-wave plate 34, the first polarizer 20, the second polarizer 170, the third polarizer 92, the first band-pass filter 503, the second band-pass filter 32, the third band-pass filter 150, and the fourth band-pass filter 91 are perpendicular to the laser propagation direction, and the rotation axis is parallel to the laser optical axis.

[0088] The sample 130 to be tested is perpendicular to the laser propagation direction and is disposed on a second electric translation stage 131 . The second electric translation stage 131 is electrically connected to the computer 210 .

[0089] The multi-band dichroic mirror 60 , the second plane beam splitter 61 and the adjustable hollow roof prism reflector 507 are arranged on a first electric translation stage 508 , and the first electric translation stage 508 is electrically connected 210 to the computer.

[0090] The angle between the first reflector 40, the second reflector 50, the third reflector 509, the fourth reflector 33, the fifth reflector 70, the first plane beam splitter 30, the second plane beam splitter 61, the third plane beam splitter 90, the fourth plane beam splitter 100, the fifth plane beam splitter 110, the multi-band dichroic mirror 60, and the adjustable hollow roof prism reflector 507 and the laser optical axis is 45°.

[0091] A method for coaxial degenerate and non-degenerate measurement of ultrafast carrier dynamics of a material, comprising a main light path step, a reflection degenerate measurement step, a reflection non-degenerate measurement, a transmission degenerate measurement, a transmission non-degenerate measurement step, and data processing;

[0092] The main optical path adjustment steps include:

[0093] Turn on the femtosecond pulse laser 10, and select the laser wavelength, repetition frequency and initial energy according to measurement requirements;

[0094] Adjust the centers of the first pinhole aperture 502, the second pinhole aperture center 506, the third pinhole aperture 80, the fourth pinhole aperture 160, the first plane beam splitter 30, the second plane beam splitter 61, the third plane beam splitter 90, the fourth plane beam splitter 100, the fifth plane beam splitter 110, the first reflector 40, the second reflector 50, the third reflector 509, the fourth reflector 33, the fifth reflector 70, the first band-pass filter 503, the second band-pass filter 34, the third band-pass filter 150, the fourth band-pass filter 91, the microscopic focusing objective lens 120, the microscopic collecting objective lens 140, the first photodetector 180, and the second photodetector 93 to be equal in height and coincide with the center of the main optical path;

[0095] Adjust the first reflector 40 and the second reflector 50 so that the laser passes through the centers of the first pinhole aperture 502 and the second pinhole aperture 506 of equal height;

[0096] Adjust the multi-band dichroic mirror 60 and the fifth reflecting mirror 70 to make the laser pass through the center of the third pinhole aperture 80 and the fourth pinhole aperture 160 of equal height; ensure that the focal points of the microscopic focusing objective lens 120 and the microscopic collecting objective lens 140 coincide with each other; ensure that the white light source 101 and the microscopic imaging camera 111 are perpendicular to the propagation direction of the main light path.

[0097] Denote the reflected light of the first planar beam splitter 30 as the probe light, and the transmitted light of the first planar beam splitter 30 as the pump light; adjust the energies of the pump light and the probe light respectively through the first variable neutral density filter 504 and the second variable neutral density filter 32;

[0098] Determine the micro-region sample position through the microscopic imaging camera 111, and adjust the second mirror 50 and the fourth mirror 33 to ensure that the pump light and the probe light are coincidentally focused on the sample to be measured 130;

[0099] Set the parameters of the first electric displacement stage 508, including taking the center position of the first band-pass filter 503 as the starting point, i.e., the coordinate zero point (Z = 0), the first electric displacement stage 508 moves along the direction of the pump light passing through the first band-pass filter 503, the first electric displacement stage 508 includes the initial position Z0, the termination position Z of the first electric displacement stage 508, and the minimum displacement ΔZ of each movement of the first electric displacement stage 508, and 0 < Z0 < Z < 300 mm, where, Z i = Z0 + i * ΔZ, i = 0, 1, 2, …, [(Z - Z0) / ΔZ], i is the displacement times of the first electric displacement stage 508, Z i is the distance between the center position of the first band-pass filter 503 after each movement of the first electric displacement stage 508. When the first electric displacement stage 508 is at the coordinate zero point, the optical path difference between the pump light and the probe light is denoted as Z Δ . Ensure that there is a 6.66 ps time delay difference between the pump light and the probe light for every 1 mm movement of the first electric displacement stage 508, i.e., τ = (Z0 + i * ΔZ - Z Δ ) * 6.66;

[0100] Set the frequency of the chopper frequency controller 200 to f, and ensure that the optical signals with the frequency f in the first photodetector 180 and the second photodetector 93 are demodulated and amplified by the lock-in amplifier 190 and then input into the computer 210;

[0101] The transmission-reflection degenerate measurement steps include:

[0102] According to the transmission-reflection spectrum of the sample to be measured, adjust the first optical parametric oscillator 501 and the second optical parametric oscillator 31 to ensure that the output wavelengths of the probe light and the pump light are the same;

[0103] Adjust the polarization angle of the first polarizer 20 to θ, adjust the polarization angles of the second polarizer 170 and the third polarizer 92 to be the same and orthogonal to the polarization angle of the first polarizer 20, rotate the optical axis direction of the wide-band half-wave plate 35 to ensure that the polarization angle of the detection light is parallel to the polarization angles of the second polarizer 170 and the third polarizer 92, adjust the position of the second plane beam splitter 61 and replace the multi-band dichroic mirror 60.

[0104] According to the thickness of the sample 130 to be tested, the front and rear positions of the sample 130 to be tested are adjusted along the optical path direction to ensure that the detection light is focused on the surface of the sample 130 to be tested; when the thickness of the sample 130 to be tested is less than the focal depth of the micro-focusing objective lens 120 When λ is the wavelength of the detection light, f is the focal length of the micro-focusing objective lens 120, and D is the spot radius of the laser beam incident on the surface of the micro-focusing objective lens 120; the first photodetector 180 collects the transmission signals of the sample to be tested 130 under different time delay differences between the pump light and the detection light and records them as E t(τ) When the thickness of the sample 130 to be tested is greater than the focal depth of the micro-focusing lens 120 When the second photodetector 93 collects the reflected signals of the sample to be tested under different time delays between the pump light and the detection light, they are recorded as E r(τ) .

[0105] The steps of transflective non-degenerate measurement include:

[0106] According to the transmission and reflection spectra of the sample to be tested, adjusting the first optical parametric oscillator 501 and the second optical parametric oscillator 31 to ensure that their output wavelengths are different;

[0107] Adjust the polarization angle of the first polarizer 20 to θ, adjust the polarization angles of the second polarizer 170 and the third polarizer 92 to be the same and parallel to the polarization angle of the first polarizer 20; rotate the optical axis direction of the wide-band half-wave plate 35 to ensure that the polarization angle of the detection light is parallel to the polarization angles of the second polarizer 170 and the third polarizer 92, adjust the position of the multi-band dichroic mirror 60 and replace the second plane beam splitter 61.

[0108] According to the relationship between the thickness of the sample 130 to be tested and the focal depth of the microscope objective lens, the first photodetector 180 and the second photodetector 93 are used to collect the transflection signal, and the energy of the first photodetector 180 and the second photodetector 93 is calibrated to give the transflection energy E under the measured signal value. t(τ) 、E r(τ) .

[0109] Data processing steps include:

[0110] After the measurement is completed, the first electric translation stage 508 returns to the initial position Z0; during the process of adjusting the position of the first electric translation stage 508 by the computer 210, the position where the delay difference between the pump light and the detection light is zero (τ=0) is recorded as the zero point position Z τ =0;

[0111] The experimental data are processed accordingly to obtain the carrier dynamics curve of the sample to be tested.

[0112]

[0113] By bringing in E t(τ) 、E r(τ) , calculate the intensity of the detection light signal, where w0 is the detection light spot radius, σ is the detection light pulse width, and E is the transmission and reflection energy corresponding to the detection light signal intensity.

[0114] By formula

[0115]

[0116]

[0117] Calculate the differential transmittance and differential reflectance curves respectively, fit the differential rate curve using the e-exponential model, and obtain the composite time constant of the material

[0118]

[0119] Where u(τ) is a step function,

[0120]

[0121] τ1 and A1 are the time constant and intensity of the fast process, and τ2 and A2 are the time constant and intensity of the slow process. Considering that both the pump light and the probe light have a certain pulse width, the dispersion in the pump-probe system will cause pulse broadening. In order to correct the signal, it is necessary to introduce the Gaussian distribution of the pump light and the probe light, and the expression is:

[0122]

[0123] Where σ is the laser pulse width and v0 is the central wavelength. Introducing pump light f(τ) and probe light g(τ) and then performing e-exponential model convolution on the difference curve, we get:

[0124]

[0125] Wherein erfc is an error function related to the laser pulse width; g0′(τ) is the carrier dynamics process of the sample to be tested.

[0126] This embodiment combines multi-wavelength laser sources, microscopic imaging and other means to achieve observation of the resonance process of the material at a single wavelength and the interaction process of different energy levels, thereby improving detection sensitivity and selectivity; achieving real-time monitoring of the surface morphology and light spot of micron-sized samples; and accurately measuring the ultrafast carrier dynamics process of materials of different types and thicknesses in micro-areas.

[0127] Experiments have shown that the system of the present invention adopts automatic control and has the technical characteristics of being fast, sensitive and highly integrated; the system is compatible with coaxial degenerate and non-degenerate pump-detection optical paths; it realizes the observation of the resonance process of the material at a single wavelength and the interaction process of different energy levels, and improves the detection sensitivity and selectivity; the system adopts a microscopic imaging system and uses a three-dimensional high-precision electric translation stage to adjust the position of the sample to be tested, and can realize real-time monitoring of the surface morphology and light spot of micron-sized samples; the system uses a photoelectric detector to synchronously test the transmission and reflection signals of the sample, which solves the problem of difficulty in completely and accurately measuring the carrier dynamics process of materials of different thicknesses in micro-areas, optimizes the ultrafast carrier dynamics process measurement technology and expands its scope of application.

[0128] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics, characterized in that: include: Femtosecond pulse laser, used to generate ultrashort pulse laser; A first polarizer and a first plane beam splitter are sequentially arranged on the same optical axis along the output beam direction of the femtosecond pulse laser; wherein the first plane beam splitter divides the ultrashort pulse laser into transmitted light and reflected light, i.e., pump light and detection light; At least a first optical parametric oscillator, a first variable neutral density filter, an optical chopper and an adjustable hollow roof prism reflector are arranged in the transmission direction of the pump light, wherein the first optical parametric oscillator is used to adjust the wavelength of the pump light, the first variable neutral density filter is used to adjust the energy of the pump light, the optical chopper is used to modulate the pump light to generate an optical signal of a specific frequency, and the adjustable hollow roof prism reflector is used to adjust the path and delay of the pump light; At least a second optical parametric oscillator, a second variable neutral density filter, a second bandpass filter and a wide-band half-wave plate are arranged in the transmission direction of the detection light, wherein the second optical parametric oscillator is used to adjust the wavelength of the detection light, the second variable neutral density filter is used to adjust the energy of the detection light, the second bandpass filter is used to select the wavelength of the detection light, and the wide-band half-wave plate is used to adjust the polarization angle of the detection light; The pump light and the detection light are combined into a main light path through a multi-band dichroic mirror or a second plane beam splitter; A fifth reflector, a third pinhole diaphragm, a third plane beam splitter, a fourth plane beam splitter, a fifth plane beam splitter, a microscopic focusing objective lens, a sample to be measured, a microscopic collecting objective lens, a third band-pass filter, a fourth pinhole diaphragm, a second polarizer and a first photodetector are sequentially arranged along the transmission direction of the main light path and the same optical axis; wherein a fourth band-pass filter, a third polarizer and a second photodetector are sequentially arranged on the reflected light side of the third plane beam splitter; a white light source is also arranged on the reflected light side of the fourth plane beam splitter; and a microscopic imaging camera is also arranged on the reflected light side of the fifth plane beam splitter; The optical chopper is electrically connected to the chopper frequency controller, the first photodetector, the second photodetector, and the chopper frequency controller are electrically connected to the phase-locked amplifier respectively, the adjustable hollow roof prism reflector is electrically connected to the first electric displacement stage for placing the adjustable hollow roof prism reflector, and the electric displacement stage, the phase-locked amplifier, the microscopic imaging camera, and the second electric displacement stage for placing the sample to be tested are electrically connected to the computer; The microscopic focusing objective is used for imaging and the second electric translation stage is used to adjust the position of the sample to be tested, so as to realize real-time monitoring of the surface morphology and light spot of the micron-sized sample. The first photodetector and the second photodetector are used to synchronously test the transmission and reflection signals of the sample to obtain the ultrafast carrier dynamics process of materials of different types and thicknesses in the micro-area.

2. The material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 1, characterized in that: A first reflector, a second reflector, a first optical parametric oscillator, a first pinhole diaphragm, a first bandpass filter, a second variable neutral density filter, an optical chopper, a second pinhole diaphragm, an adjustable hollow roof prism reflector and a third reflector are sequentially arranged along the transmitted light direction of the first plane beam splitter, that is, the same optical axis as the pump light direction; A second optical parametric oscillator, a second variable neutral density filter, a second bandpass filter, a fourth reflector and a wide-band half-wave plate are sequentially arranged along the reflected light direction of the first plane beam splitter, that is, the detection light direction; The reflected light and the transmitted light along the first plane beam splitter are combined into a beam at the multi-band dichroic mirror or the second plane beam splitter.

3. The material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 2, characterized in that: The first variable neutral density filter, the second variable neutral density filter, the wide-band half-wave plate, the first polarizer, the second polarizer, the third polarizer, the first band-pass filter, the second band-pass filter, the third band-pass filter, and the fourth band-pass filter are perpendicular to the laser propagation direction, and the rotation axis is parallel to the laser optical axis.

4. The material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 2, characterized in that The sample to be tested is perpendicular to the laser propagation direction and is arranged on a second electric translation platform, and the second electric translation platform is electrically connected to the computer.

5. The material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 2, characterized in that: The multi-band dichroic mirror, the second plane beam splitter and the adjustable hollow roof prism reflector are arranged on an electric displacement platform, and the electric displacement platform is electrically connected to the computer.

6. The material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 2, characterized in that: The angle between the first reflector, the second reflector, the third reflector, the fourth reflector, the fifth reflector, the first plane beam splitter, the second plane beam splitter, the third plane beam splitter, the fourth plane beam splitter, the fifth plane beam splitter, the multi-band dichroic mirror, and the adjustable hollow roof prism reflector and the laser optical axis is 45°.

7. A material measurement method for coaxial degenerate and non-degenerate ultrafast carrier dynamics, characterized in that: It includes the steps of optical path adjustment, reflection type degenerate measurement, reflection type non-degenerate measurement, transmission type degenerate measurement, transmission type non-degenerate measurement and data processing; The optical path adjustment comprises the steps of: Turn on the femtosecond pulse laser, and select the laser wavelength, repetition frequency and initial energy according to measurement requirements; Adjust the first pinhole aperture, the center of the second pinhole aperture, the third pinhole aperture, the fourth pinhole aperture, the first plane beam splitter, the second plane beam splitter, the third plane beam splitter, the fourth plane beam splitter, the first reflector of the fifth plane beam splitter, the second reflector, the third reflector, the fourth reflector, the fifth reflector, the first band-pass filter, the second band-pass filter, the third band-pass filter, the fourth band-pass filter, the microscopic focusing objective lens, the microscopic collecting objective lens, the first photodetector, and the second photodetector so that their centers are at the same height and coincide with the center of the main optical path; Adjust the first reflector and the second reflector so that the laser passes through the centers of the first pinhole diaphragm and the second pinhole diaphragm at the same height; Adjust the multi-band dichroic mirror and the fifth reflector to make the laser pass through the center of the third and fourth pinhole apertures of equal height, ensure that the focus of the microscopic focusing objective lens and the microscopic collecting objective lens coincide; ensure that the white light source and the microscopic imaging camera are perpendicular to the propagation direction of the main light path; The reflected light of the first plane beam splitter is referred to as the detection light; the transmitted light of the first plane beam splitter is referred to as the pump light; Adjusting the energy of the pump light and the detection light respectively through a first variable neutral density filter and a second variable neutral density filter; Determine the position of the micro-area sample by a microscopic imaging camera, and adjust the second reflector and the fourth reflector to ensure that the pump light, the detection light and the upper position of the sample to be measured coincide; Set the parameters of the first electric displacement stage, including taking the center position of the first band-pass filter as the starting point, i.e., the coordinate zero point (Z = 0), the first electric displacement stage moves along the direction of the pump light passing through the first band-pass filter, the first electric displacement stage includes the initial position Z0, the termination position Z of the first electric displacement stage, and the minimum displacement ΔZ of each movement of the first electric displacement stage, and 0 < Z0 < Z < 300 mm, where, Z i = Z0 + i * ΔZ, i = 0, 1, 2,..., [(Z - Z0) / ΔZ], i is the displacement times of the first electric displacement stage, Z i is the distance between the center position of the first band-pass filter after each movement of the first electric displacement stage. When the first electric displacement stage is at the coordinate zero point, the optical path difference between the pump light and the probe light is denoted as Z Δ , ensure that for every 1 mm movement of the first electric displacement stage, there is a 6.66 ps time delay difference between the pump light and the probe light, i.e., τ = (Z0 + i * ΔZ - Z Δ ) * 6.66; Setting the frequency f of the chopper frequency controller to ensure that the optical signal with the frequency f in the photodetector is demodulated and amplified by the lock-in amplifier and then input into the computer; Transflective degenerate measurement, the steps include: According to the transmission and reflection spectra of the sample to be tested, adjusting the first optical parametric oscillator and the second optical parametric oscillator to ensure that their output wavelengths are the same; Set the polarization angle θ of the first polarizer, adjust the polarization angles of the second polarizer and the third polarizer to be the same and orthogonal to the polarization angle of the first polarizer, rotate the optical axis direction of the wide-band half-wave plate, and ensure that the polarization angle of the detection light is parallel to the polarization angles of the second polarizer and the third polarizer; adjusting the position of the second plane beam splitter and replacing the multi-band dichroic mirror; According to the thickness d of the sample to be tested, the front and rear positions of the sample to be tested are adjusted along the optical path direction to ensure that the detection light is focused on the surface of the sample to be tested: When d < L, the first photodetector collects the transmission signal E of the sample to be measured at different time delays τ between the pump light and the probe light. t(τ) ; When d>L, the second photodetector collects the reflection signal E of the sample under test under different delay differences τ between the pump light and the detection light. r(τ) ; Where, L is the focal depth of the micro-focusing objective lens, λ is the wavelength of the detection light, f is the focal length of the micro-focusing objective lens, and D is the spot radius of the laser beam incident on the surface of the micro-focusing objective lens; Transflective non-degenerate measurement, the steps include: According to the transmission and reflection spectra of the sample to be tested, adjusting the first optical parametric oscillator and the second optical parametric oscillator to ensure that their output wavelengths are different; Setting the polarization angle θ of the first polarizer, adjusting the polarization angles of the second polarizer and the third polarizer to be the same and parallel to the polarization angle of the first polarizer, rotating the optical axis direction of the wide-band half-wave plate, and ensuring that the polarization angle of the detection light is parallel to the polarization angles of the second polarizer and the third polarizer; adjusting the position of the multi-band dichroic mirror and replacing the second plane beam splitter; According to the relationship between the thickness of the sample to be tested and the focal depth of the microscope objective lens, the first photodetector and the second photodetector are used to collect the transflection signal E respectively. t(τ) 、E r(τ) ; The data processing steps include: Adjust the first electric translation stage back to the initial position Z0, and when the delay difference τ between the pump light and the detection light is 0, it is recorded as the zero position Z τ＝0 ; Calculate the detection light signal intensity I, the formula is as follows: Where w0 is the spot radius of the detection light, σ is the pulse width of the detection light, and E is the transmission and reflection energy corresponding to the intensity of the detection light signal. Calculate the differential transmittance curve and the differential reflectance curve, the formula is as follows: In the formula, I r (τ) is the reflected light intensity of the sample to be tested under the time delay difference of τ, I r (0) is the reflected light intensity of the sample to be tested at the zero position, I t (τ) is the transmitted light intensity of the sample to be tested under the time delay difference of τ, I t (0) is the transmitted light intensity of the sample to be tested at the zero position, ΔR is the differential reflectivity of the sample to be tested, R is the linear reflectivity of the sample to be tested, ΔT is the differential transmittance of the sample to be tested, and T is the linear transmittance of the sample to be tested. The carrier dynamics process curve of the sample to be tested is obtained using the e-exponential model: Where τ1 and A1 are the time constant and intensity of the fast process, τ2 and A2 are the time constant and intensity of the slow process, erfc is the error function related to the laser pulse width, σ is the laser pulse width, and τ is the delay difference between the pump light and the detection light.

Images