Material measurement system and method for coaxial degenerate and non-degenerate ultrafast carrier dynamics

Abstract

A kind of material measuring system and method of coaxial degenerate and non-degenerate type ultrafast carrier dynamics, the system is compatible with coaxial degenerate and non-degenerate type pumping probe light path;Resonance process and different energy level interaction process of material at single wavelength are observed, and detection sensitivity and selectivity are improved.The system uses microscopic objective imaging and utilizes three-dimensional high-precision electric displacement table to adjust the position of sample to be measured, and can realize real-time monitoring of the surface morphology of micron-sized sample and light spot;The system uses photoelectric detector to synchronously test sample transmission and reflection signals, solves the problem that it is difficult to completely and accurately measure the ultrafast carrier dynamics process of micro-area different types and different thickness materials.Optimize ultrafast carrier dynamics process measurement technology and expand its applicable range.The application realizes automatic control, with the technical characteristics of quick, sensitive and high integration.

Description

Technical Field

[0001] This 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 Technology

[0002] Pump-probe techniques play a crucial role in nonlinear optics, particularly in 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 (e.g., graphene and MoS2) and metamaterials, where nonlinear responses to light can reveal unique material properties. This is particularly valuable for developing highly sensitive optical sensors capable of detecting minute changes in the environment, making them suitable for biochemical sensing and environmental monitoring. Furthermore, in spectroscopy, pump-probe techniques are used for applications such as charge carrier dynamics in photovoltaic materials and photochemical reactions in biomolecules. This enables the capture of real-time changes in material properties, driving advancements in areas such as solar energy harvesting, photodynamic therapy, and the development of novel 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, time-resolved currents 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-probe device. By introducing techniques such as beam splitters and beam expanders, the pump light and probe light are separated to the greatest extent in space, improving the test signal-to-noise ratio.

[0004] However, in the detection process of different fields, factors such as wavelength, power threshold, sample characteristics and material thickness need to be carefully considered. Traditional pump detection methods often cannot meet these requirements at the same time and show limitations when dealing with the nonlinear characteristics of complex samples. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a system and method for measuring ultrafast carrier dynamics processes in materials using coaxial degenerate and non-degenerate methods. This system enables the observation of resonance processes and interactions between different energy levels in materials at a single wavelength, improves detection sensitivity and selectivity, achieves simultaneous measurement of transmitted and reflected signals of carrier dynamics processes in materials, and simultaneously enables real-time imaging of the sample and light spot. This solves the problem of difficulty in completely and accurately measuring carrier dynamics processes in materials of different thicknesses within a micro-region.

[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 comprising:

[0008] Femtosecond pulsed lasers are used to generate ultrashort pulsed lasers.

[0009] A first polarizer and a first planar beam splitter are sequentially arranged along the optical axis of the output beam direction of the femtosecond pulse laser; wherein, the first planar beam splitter splits the ultrashort pulse laser into transmitted light and reflected light, namely pump light and probe 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 provided in the transmission direction of the pump light. 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 wideband half-wave plate are provided in the transmission direction of the probe light. The second optical parametric oscillator is used to adjust the wavelength of the probe light, the second variable neutral density filter is used to adjust the energy of the probe light, the second bandpass filter is used to select the wavelength of the probe light, and the wideband half-wave plate is used to adjust the polarization angle of the probe light.

[0012] The pump light and the probe light are combined into the main optical path by a multi-band dichroic mirror or a second plane beam splitter.

[0013] Along the transmission direction of the main optical path, a fifth reflecting mirror, a third pinhole aperture, a third plane beam splitter, a fourth plane beam splitter, a fifth plane beam splitter, a microscope focusing objective, a sample to be tested, a microscope collecting objective, a third bandpass filter, a fourth pinhole aperture, a second polarizer, and a first photodetector are arranged sequentially along the optical axis. On the reflected light side of the third plane beam splitter, a fourth bandpass filter, a third polarizer, and a second photodetector are also arranged sequentially. A white light source is also arranged on the reflected light side of the fourth plane beam splitter. A microscope 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 lock-in amplifier. The adjustable hollow roof prism reflector is electrically connected to the first electric displacement stage for placing the adjustable hollow roof prism reflector. The electric displacement stage, the lock-in amplifier, the microscope imaging camera, and the second electric displacement stage for placing the sample to be tested are electrically connected to the computer.

[0015] By using a microscopic focusing objective lens for imaging and a second electric displacement stage to adjust the position of the sample under test, real-time monitoring of the surface morphology and light spot of micron-sized samples can be achieved. The transmission and reflection signals of the sample are tested simultaneously using a first photodetector and a second photodetector to obtain the ultrafast carrier dynamics of materials of different types and thicknesses in the micro-region.

[0016] Furthermore, along the direction of the transmitted light of the first planar beam splitter, i.e. the direction of the pump light, a first reflecting mirror, a second reflecting mirror, a first optical parametric oscillator, a first pinhole aperture, a first bandpass filter, a first variable neutral density filter, an optical chopper, a second pinhole aperture, an adjustable hollow roof prism reflecting mirror, and a third reflecting mirror are arranged sequentially along the optical axis.

[0017] Along the direction of the reflected light from the first planar beam splitter, i.e. the direction of the probe light, a second optical parametric oscillator, a second variable neutral density filter, a second bandpass filter, a fourth reflector, and a broadband half-wave plate are sequentially arranged.

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

[0019] Furthermore, the first variable neutral density filter, the second variable neutral density filter, the broadband half-wave plate, the first polarizer, the second polarizer, the third polarizer, the first bandpass filter, the second bandpass filter, the third bandpass filter, and the fourth bandpass filter are perpendicular to the laser propagation direction, and their rotation axes are parallel to the laser optical axis.

[0020] Furthermore, the sample to be tested is perpendicular to the laser propagation direction and is placed on a second electric displacement stage, which 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 mounted on the first electric displacement stage, which is electrically connected to the computer.

[0022] Furthermore, the first, second, third, fourth, and fifth reflectors, the first, second, third, fourth, and fifth plane beam splitters, the multi-band dichroic mirror, the adjustable hollow roof prism reflector, and the laser optical axis all have an angle of 45°.

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

[0024] The optical path adjustment includes the following steps:

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

[0026] Adjust the centers of the first pinhole aperture, 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 fifth plane beam splitter, the first reflecting mirror, the second reflecting mirror, the third reflecting mirror, the fourth reflecting mirror, the fifth reflecting mirror, the first bandpass filter, the second bandpass filter, the third bandpass filter, the fourth bandpass filter, the microscope focusing objective, the microscope collecting objective, the first photodetector, and the second photodetector to be at the same height and coincide with the center of the main optical path;

[0027] Adjust the first and second reflecting mirrors so that the laser passes through the center of the first and second pinhole apertures at the same height;

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

[0029] The reflected light from the first planar beam splitter is denoted as the probe light; the transmitted light from the first planar beam splitter is denoted as the pump light.

[0030] The energy of the pump light and the probe light are adjusted by the first variable neutral density filter and the second variable neutral density filter, respectively.

[0031] The position of the micro-area sample is determined by a microscopic imaging camera, and the second and fourth reflective mirrors are adjusted to ensure that the pump light and probe light coincide with the upper position of the sample to be tested.

[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 pump light direction passing through the first band-pass filter, the first electric displacement stage includes an initial position Z0, a termination position Z of the first electric displacement stage, and a minimum displacement ΔZ for 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 number 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 rear 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 at 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 at different time delay differences τ between the pump light and the probe light r(τ) ;

[0041] where, L is the depth of focus of the microscopic focusing objective lens, λ is the wavelength of the probe light, f is the focal length of the microscope focusing objective, and D is the radius of the laser beam incident on the surface of the microscope focusing objective.

[0042] Transmission and reflection non-degenerate measurements, the steps include:

[0043] Based on the transmittance and reflectance spectra of the sample to be tested, adjust the first optical parametric oscillator and the second optical parametric oscillator to ensure that their output wavelengths are different;

[0044] Set the polarization angle θ of the first polarizer, adjust the polarization angles of the second and third polarizers to be the same and parallel to the polarization angle of the first polarizer, and rotate the optical axis of the wide-band half-wave plate to ensure that the polarization angle of the probe light is parallel to the polarization angle of the second and third polarizers.

[0045] Adjust the position of the multi-band dichroic mirror and replace the second planar beam splitter;

[0046] Based on the relationship between the thickness of the sample to be tested and the depth of focus of the microscope objective, transmitted and reflected signals E are collected in the first and second photodetectors, respectively. t(τ) E r(τ) ;

[0047] Data processing steps include:

[0048] Adjust the first electric displacement stage back to its initial position Z0, and when the delay difference τ between the pump light and the probe light is 0, record this as the zero point position Z. τ＝0 ;

[0049] The intensity I of the probe light signal is calculated using the following formula:

[0050]

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

[0052] The formulas for calculating the differential transmittance curve and the differential reflectance curve are as follows:

[0053]

[0054] In the formula, I r (τ) represents the intensity of reflected light from the sample under a time delay of τ, I r (0) represents the intensity of reflected light from the sample at the zero point position, I t (τ) represents the transmitted light intensity of the sample under a time delay of τ, I t(0) represents the transmitted light intensity of the sample at the zero point position, ΔR represents the differential reflectance of the sample, R represents the linear reflectance of the sample, ΔT represents the differential transmittance of the sample, and T represents the linear transmittance of the sample. The carrier dynamics process curve of the sample is obtained using the e-exponential model:

[0055]

[0056] In the formula, τ1 and A1 are the time constants and intensities of the fast process, τ2 and A2 are the time constants and intensities 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 probe light.

[0057] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0058] 1) Compatible with coaxial degenerate and non-degenerate pumped detection optical paths; enabling the observation of resonance processes and interaction processes of different energy levels in materials at a single wavelength, improving detection sensitivity and selectivity;

[0059] 2) This system uses a microscopic imaging system and a three-dimensional high-precision electric displacement 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.

[0060] 3) The system uses a photodetector to simultaneously 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 with different thicknesses in a micro-region. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of the material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics according to an embodiment of the present invention.

[0062] In the picture:

[0063] Femtosecond pulsed laser 10;

[0064] First polarizer 20;

[0065] First planar beam splitter 30, second optical parametric oscillator 31, second variable neutral density filter 32, fourth reflector 33, second bandpass filter 34, and broadband half-wave plate 35;

[0066] First reflecting mirror 40;

[0067] Second reflector 50, first optical parametric oscillator 501, first pinhole aperture 502, first bandpass filter 503, first variable neutral density filter 504, optical chopper 505, second pinhole aperture 506, adjustable hollow roof prism reflector 507, first motorized displacement stage 508, third reflector 509.

[0068] Multi-band dichroic mirror 60, second plane beam splitter 61;

[0069] Fifth reflecting mirror 70;

[0070] The third small aperture is 80°.

[0071] Third plane beam splitter 90, fourth bandpass filter 91, third polarizer 92, second photodetector 93;

[0072] Fourth plane beam splitter 100, white light source 101;

[0073] Fifth plane beam splitter 110, microscopic imaging camera 111;

[0074] Microscope focusing objective 120;

[0075] Sample to be tested 130, second electric displacement stage 131;

[0076] Microscope collecting objective 140;

[0077] The third bandpass filter is 150;

[0078] The fourth aperture stop is 160°.

[0079] Second polarizer 170;

[0080] First photodetector 180;

[0081] Lock-in amplifier 190;

[0082] Chopper frequency controller 200;

[0083] Computer 210. Detailed Implementation

[0084] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0085] Please see Figure 1 , Figure 1The figure shows a schematic diagram of the material measurement system for coaxial degenerate and non-degenerate ultrafast carrier dynamics of the present invention. It includes a femtosecond pulsed laser 10, a first polarizer 20 and a first planar beam splitter 30 arranged sequentially along the output beam direction of the femtosecond pulsed laser; and a first reflecting mirror 40, a second reflecting mirror 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, and a second pinhole aperture arranged sequentially along the transmission beam direction of the first planar beam splitter 30. Aperture 506, adjustable hollow roof prism reflector 507, and third reflector 509; along the reflected light direction of the first planar beam splitter 30, the first planar beam splitter 30, the second optical parametric oscillator 31, the second variable neutral density filter 32, the fourth reflector 33, the second bandpass filter 34, and the broadband half-wave plate 35 are arranged sequentially; the reflected light and transmitted light along the first planar beam splitter 30 are combined at the multi-band dichroic mirror 60 or the second planar beam splitter 61; along the reflection direction of the multi-band dichroic mirror 60, the fifth reflector 70 and the third pinhole are arranged sequentially. The system includes an aperture 80, a third plane beam splitter 90, a fourth plane beam splitter 100, a fifth plane beam splitter 110, a microscopic focusing objective 120, a sample to be tested 131, a microscopic collecting objective 140, a third bandpass filter 150, a fourth pinhole aperture 160, a second polarizer 170, and a first photodetector 180; a fourth bandpass filter 91, a third polarizer 92, and a second photodetector 93 are arranged along the other side of the reflected light from the third plane beam splitter 90; a white light source 101 is arranged along the other side of the reflected light from the fourth plane beam splitter 100. A microscopic imaging camera 111 is arranged along the other side of the reflected light from 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 lock-in amplifier 190 respectively; the adjustable hollow roof prism reflector 507 is electrically connected to the first electric displacement stage 508; the electric displacement stage 508, the lock-in amplifier 190, the microscopic imaging camera 111, and the second electric displacement stage 131 are electrically connected to the computer 210.

[0086] The first variable neutral density filter 504, the second variable neutral density filter 32, the broadband half-wave plate 34, the first polarizer 20, the second polarizer 170, the third polarizer 92, the first bandpass filter 503, the second bandpass filter 34, the third bandpass filter 150, and the fourth bandpass filter 91 are perpendicular to the laser propagation direction, and their rotation axes are parallel to the laser optical axis.

[0087] The sample to be tested 130 is perpendicular to the laser propagation direction and is placed on the second electric displacement stage 131, which is electrically connected to the computer 210.

[0088] The multi-band dichroic mirror 60, the second plane beam splitter 61, and the adjustable hollow roof prism reflector 507 are mounted on the first electric displacement stage 508, which is electrically connected to the computer 210.

[0089] 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 all have an angle of 45° with the laser optical axis.

[0090] A method for measuring ultrafast carrier dynamics in materials using coaxial degenerate and non-degenerate methods includes a main optical path step, a reflection degenerate measurement step, a reflection non-degenerate measurement step, a transmission degenerate measurement step, a transmission non-degenerate measurement step, and data processing.

[0091] The main optical path adjustment steps include:

[0092] Turn on the femtosecond pulse laser 10, and select the laser wavelength, repetition frequency, and initial energy according to the measurement requirements;

[0093] Adjust the centers of the first pinhole aperture 502, the second pinhole aperture 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 reflecting mirror 40, the second reflecting mirror 50, the third reflecting mirror 509, the fourth reflecting mirror 33, the fifth reflecting mirror 70, the first bandpass filter 503, the second bandpass filter 34, the third bandpass filter 150, the fourth bandpass filter 91, the microscope focusing objective 120, the microscope collecting objective 140, the first photodetector 180, and the second photodetector 93 to be at the same height and coincide with the center of the main optical path;

[0094] Adjust the first reflector 40 and the second reflector 50 so that the laser passes through the center of the first pinhole aperture 502 and the second pinhole aperture 506 at the same height;

[0095] Adjust the multi-band dichroic mirror 60 and the fifth reflecting mirror 70 so that the laser passes through the center of the third pinhole aperture 80 and the fourth pinhole aperture 160 at the same height; ensure that the focus of the microscope focusing objective 120 and the microscope collecting objective 140 coincides; and ensure that the white light source 101 and the microscope imaging camera 111 are perpendicular to the main optical path propagation direction.

[0096] 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;

[0097] Determine the position of the micro-region sample 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 overlapped and focused on the sample to be measured 130;

[0098] 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 number 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;

[0099] Set the frequency of the chopper frequency controller 200 to f, and ensure that the optical signals with the f frequency 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;

[0100] The transmission-reflection degenerate measurement steps include:

[0101] 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;

[0102] 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 of the wide-band half-wave plate 35 to ensure that the polarization angle of the probe light is parallel to the polarization angle of the second polarizer 170 and the third polarizer 92, adjust the position of the second planar beam splitter 61 and replace the multi-band dichroic mirror 60.

[0103] Adjust the position of the sample 130 along the optical path according to its thickness to ensure that the probe light is focused on the surface of the sample 130; when the thickness of the sample 130 is less than the depth of focal length of the microscope focusing objective 120. When, λ is the wavelength of the probe light, f is the focal length of the microscopic focusing objective 120, and D is the radius of the laser beam incident on the surface of the microscopic focusing objective 120; the first photodetector 180 collects the transmission signal of the sample 130 under different time delays of the pump light and the probe light and records it as E respectively. t(τ) When the thickness of the sample to be tested 130 is greater than the depth of focal length of the microscope focusing objective 120, At that time, the second photodetector 93 collects the reflected signals of the sample under different time delay differences between the pump light and the probe light, and records them as E respectively. r(τ) .

[0104] Transmission-reflection non-degenerate measurement steps include:

[0105] Based on the transmittance and reflectance spectra of the sample to be tested, the first optical parametric oscillator 501 and the second optical parametric oscillator 31 are adjusted to ensure that their output wavelengths are different.

[0106] Adjust the polarization angle of the first polarizer 20 to θ, and 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 of the wide-band half-wave plate 35 to ensure that the polarization angle of the probe light is parallel to the polarization angle of the second polarizer 170 and the third polarizer 92, adjust the position of the multi-band dichroic mirror 60 and replace the second planar beam splitter 61.

[0107] Based on the relationship between the thickness of the sample 130 and the depth of focus of the microscope objective, transmitted and reflected signals are collected at the first photodetector 180 and the second photodetector 93, respectively. Energy calibration is performed on the first photodetector 180 and the second photodetector 93 to give the transmitted and reflected energy E under the measured signal value. t(τ) E r(τ) .

[0108] Data processing steps include:

[0109] After the measurement is completed, the first electric displacement stage 508 returns to its initial position Z0; wherein, during the process of adjusting the position of the first electric displacement stage 508 by the computer 210, the position where the delay difference between the pump light and the probe light is zero (τ=0) is recorded as the zero point position Z. τ＝0 ;

[0110] The experimental data were processed accordingly to obtain the carrier dynamics process curve of the sample under test. Using the formula...

[0111]

[0112] By substituting E t(τ) E r(τ) Calculate the intensity of the probe light signal, where w0 is the radius of the probe light spot, σ is the pulse width of the probe light, and E is the transmission and reflection energy corresponding to the intensity of the probe light signal.

[0113] Through formula

[0114]

[0115] The differential transmittance and differential reflectance curves were calculated separately, and the differential transmittance curves were fitted using the e-exponential model to obtain the composite time constant of the material.

[0116]

[0117] Where u(τ) is the step function,

[0118]

[0119] τ1 and A1 are the time constants and intensities of the fast process, and τ2 and A2 are the time constants and intensities 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. To correct the signal, a Gaussian distribution of the pump light and probe light needs to be introduced, the expression of which is:

[0120]

[0121] Where σ is the laser pulse width and v0 is the center wavelength. Introducing pump light f(τ) and probe light g(τ), and then performing an e-exponential model convolution on the difference curve, we have:

[0122]

[0123] Where erfc is the error function related to the laser pulse width; g0′(τ) is the carrier dynamics process of the sample under test.

[0124] This embodiment combines multi-wavelength laser sources and microscopic imaging to observe the resonance process and interaction process of different energy levels of materials at a single wavelength, thereby improving detection sensitivity and selectivity; enabling real-time monitoring of the surface morphology and light spot of micron-sized samples; and accurately measuring the ultrafast carrier dynamics processes of different types and thicknesses of materials in micro-regions.

[0125] Experiments have shown that the system of this invention employs automated control and features rapid, sensitive, and highly integrated technical characteristics. The system is compatible with coaxial degenerate and non-degenerate pump-probe optical paths; it enables observation of the resonance process and interaction processes of different energy levels in materials at a single wavelength, improving detection sensitivity and selectivity. The system utilizes a microscopic imaging system and a three-dimensional high-precision electric displacement stage to adjust the position of the sample under test, enabling real-time monitoring of the surface morphology and light spot of micron-sized samples. The system uses a photodetector to simultaneously test the transmission and reflection signals of the sample, solving the problem of difficulty in completely and accurately measuring the carrier dynamics processes of materials with different thicknesses in micro-regions, optimizing ultrafast carrier dynamics measurement technology and expanding its applicability.

[0126] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A material measurement system of coaxial degenerate and non-degenerate ultrafast carrier dynamics, characterized by, The application relates to a femtosecond pulse laser for generating ultrashort pulse laser. A first polarizer and a first plane beam splitter are arranged along the output beam direction of the femtosecond pulse laser in sequence; the first plane beam splitter divides the ultrashort pulse laser into transmitted light and reflected light, namely pump light and probe light. At least a first optical parametric oscillator, a first variable neutral density filter, an optical chopper and an adjustable hollow ridge prism reflector are arranged in the transmission direction of the pump light; the first optical parametric oscillator is used for adjusting the wavelength of the pump light, the first variable neutral density filter is used for adjusting the energy of the pump light, the optical chopper is used for modulating the pump light to generate an optical signal with a specific frequency, and the adjustable hollow ridge prism reflector is used for adjusting the path and time delay of the pump light. At least a second optical parametric oscillator, a second variable neutral density filter, a second band-pass filter and a wide-band half-wave plate are arranged in the transmission direction of the probe light; the second optical parametric oscillator is used for adjusting the wavelength of the probe light, the second variable neutral density filter is used for adjusting the energy of the probe light, the second band-pass filter is used for selecting the wavelength of the probe light, and the wide-band half-wave plate is used for adjusting the polarization angle of the probe light. The pump light and the probe 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, a sample to be measured, a microscopic collection objective, a third band-pass filter, a fourth pinhole diaphragm, a second polarizer and a first photodetector are arranged in sequence along the transmission direction of the main light path; a fourth band-pass filter, a third polarizer and a second photodetector are further arranged in sequence on the reflected light side of the third plane beam splitter; a white light source is further arranged on the reflected light side of the fourth plane beam splitter; and a microscopic imaging camera is further arranged on the reflected light side of the fifth plane beam splitter. The optical chopper is electrically connected with a chopper frequency controller; the first photodetector and the second photodetector are electrically connected with a lock-in amplifier; the adjustable hollow ridge prism reflector is electrically connected with a first electric displacement table on which the adjustable hollow ridge prism reflector is placed; and the electric displacement table, the lock-in amplifier, the microscopic imaging camera and a second electric displacement table on which the sample to be measured is placed are electrically connected with a computer. The microscopic focusing objective is used for imaging, and the position of the sample to be measured is adjusted by using the second electric displacement table, so that the surface morphology of a micron-level sample and a light spot are monitored in real time; the first photodetector and the second photodetector are used for synchronously testing the transmission and reflection signals of the sample, and the ultrafast carrier dynamics process of different types and different thicknesses of materials in a micro area is obtained. ​ 2. The material measurement system of coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 1, characterized in that, A first mirror, a second mirror, a first optical parametric oscillator, a first pinhole diaphragm, a first band-pass filter, a first variable neutral density filter, an optical chopper, a second pinhole diaphragm, an adjustable hollow ridge prism mirror and a third mirror are arranged along the transmission direction of the first plane mirror, i.e. the direction of the pump light, in sequence. A second optical parametric oscillator, a second variable neutral density filter, a second band-pass filter, a fourth mirror and a wide-band half-wave plate are arranged along the reflection direction of the first plane mirror, i.e. the direction of the probe light, in sequence. The reflected light and the transmitted light of the first plane mirror form a combined beam at the multi-band dichroic mirror or the second plane mirror.

3. The material measurement system of 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 direction of the laser propagation, and the rotation axis is parallel to the laser optical axis.

4. The material measurement system of coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 2, characterized in that The sample to be measured is perpendicular to the direction of the laser propagation and is arranged on a second electrically-driven displacement stage, which is electrically connected to the computer.

5. The material measurement system of coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 2, characterized in that, The multi-band dichroic mirror, the second plane mirror and the adjustable hollow ridge prism mirror are arranged on an electrically-driven displacement stage, which is electrically connected to the computer.

6. The material measurement system of coaxial degenerate and non-degenerate ultrafast carrier dynamics according to claim 2, characterized in that, The first mirror, the second mirror, the third mirror, the fourth mirror, the fifth mirror, the first plane mirror, the second plane mirror, the third plane mirror, the fourth plane mirror, the fifth plane mirror and the multi-band dichroic mirror are all at an angle of 45° with the laser optical axis.

7. A measurement method based on the material measurement system of the coaxial degenerate and non-degenerate type ultrafast carrier dynamics according to any one of claims 2-6, characterized in that, The method comprises 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: Turning on the femtosecond pulse laser, and selecting the laser wavelength, the repetition frequency and the initial energy according to the measurement requirement; Adjusting the centers of the first pinhole diaphragm, the second pinhole diaphragm, the third pinhole diaphragm, the fourth pinhole diaphragm, the first plane mirror, the second plane mirror, the third plane mirror, the fourth plane mirror, the fifth plane mirror, the first mirror, the second mirror, the third mirror, the fourth mirror, the fifth mirror, 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 collection objective lens, the first photodetector and the second photodetector to be at the same height and to coincide with the center of the main light path; Adjusting the first mirror and the second mirror to make the laser pass through the centers of the first pinhole diaphragm and the second pinhole diaphragm; Adjusting the multi-band dichroic mirror and the fifth mirror to make the laser pass through the centers of the third pinhole diaphragm and the fourth pinhole diaphragm, to ensure that the focal points of the microscopic focusing objective lens and the microscopic collection objective lens coincide, and to ensure that the white light source and the microscopic imaging camera are perpendicular to the direction of the main light path; The reflected light of the first plane mirror is referred to as the probe light, and the transmitted light of the first plane mirror is referred to as the pump light. Adjusting the energy of the pump light and the probe light by the first variable neutral density filter and the second variable neutral density filter respectively; Determining the position of the micro area sample by the microscopic imaging camera, and adjusting the second mirror and the fourth mirror to ensure that the pump light and the probe light coincide with the upper position of the sample to be measured; Set the parameters of the first electric displacement stage, including starting from the center position of the first band-pass filter, that is, the coordinate zero point (Z = 0), the first electric displacement stage moves along the pump light direction passing through the first band-pass filter, the first electric displacement stage includes an initial position Z0, a termination position Z of the first electric displacement stage, and a minimum displacement ΔZ for 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 number of the first electric displacement stage, Z i is the distance between the first electric displacement stage after each movement 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, that is, τ = (Z0 + i * ΔZ - Z Δ ) * 6.66; Setting the frequency f of the chopper frequency controller, so as to ensure that the light signal with the frequency f in the photoelectric detector is demodulated and amplified by the lock-in amplifier and then input into the computer; The transreflective degenerate measurement includes the following steps: Adjusting the first optical parametric oscillator and the second optical parametric oscillator according to the transreflective spectrum of the sample to be measured, so as to ensure that the output wavelengths of the two optical parametric oscillators are the same; 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 orthogonal to the polarization angle of the first polarizer, and rotating the optical axis direction of the wide-band half-wave plate, so as to ensure that the polarization angle of the probe light is parallel to the polarization angles of the second polarizer and the third polarizer; Adjusting the position of the second plane mirror and replacing the multi-band dichroic mirror; Adjusting the positions of the sample to be measured before and after the light path according to the thickness d of the sample to be measured, so as to ensure that the probe light is focused on the surface of the sample to be measured: When d < L, the first photodetector collects the transmission signal E of the sample under test at different delay differences 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 at a different delay difference τ between the pump light and the probe light r(τ) ; wherein L is the depth of focus of the microscope objective, λ is the wavelength of the probe light, f is the focal length of the microscope objective, and D is the spot radius of the laser beam incident on the surface of the microscope objective. The transreflective non-degenerate measurement includes the following steps: Adjusting the first optical parametric oscillator and the second optical parametric oscillator according to the transreflective spectrum of the sample to be measured, so as to ensure that the output wavelengths of the two optical parametric oscillators 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, and rotating the optical axis direction of the wide-band half-wave plate, so as to ensure that the polarization angle of the probe 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 mirror; According to the relationship between the thickness of the sample to be measured and the focal depth of the microscope objective, the transreflected signal E is collected at the first photodetector and the second photodetector, respectively t(τ) , E r(τ) ; The data processing steps include: Adjust the first electric displacement stage back to the initial position Z0, and when the delay difference τ = 0 of the pump light and the probe light, it is recorded as zero position Z τ＝0 ; Calculating the light intensity I of the probe light signal, and the formula is as follows: In the formula, w0 is the spot radius of the probe light, σ is the pulse width of the probe light, and E is the transreflective energy corresponding to the light intensity of the probe light signal; Calculating the differential transmittance curve and the differential reflectance curve, and the formula is as follows: In the formula, I r (τ) is the reflection light intensity of the sample to be tested at τ time delay, I r (0) is the reflection light intensity of the sample to be tested at zero position, I t (τ) is the transmission light intensity of the sample to be tested at τ time delay, I t (0) is the transmission light intensity of the sample to be tested at 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; and the carrier dynamics process curve of the sample to be tested is obtained by using an e exponential model. In the formula, 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 pulse width of the laser, σ is the pulse width of the laser, and τ is the time delay difference between the pump light and the probe light.

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