CN115479921B - Method and device for optimizing detection light wavelength in time domain Brillouin scattering experiment - Google Patents

Abstract

The present invention discloses a method and device for optimizing the wavelength of a detection light in a time-domain Brillouin scattering experiment. The method uses the conclusion that the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated when the wavelength of the detection light changes, and uses this to perform a computer simulation experiment to optimize the wavelength of the detection light. The present invention optimizes the wavelength of the detection light in the time-domain Brillouin scattering experiment, and can obtain a better effect of detection and analysis using the time-domain Brillouin scattering experiment.

Description

Method and device for optimizing detection light wavelength in time-domain Brillouin scattering experiment

Technical Field

The present application relates to the field of detection and analysis technology, and in particular to a method and device for optimizing the wavelength of detection light in a time-domain Brillouin scattering experiment.

Background Art

Time-domain Brillouin scattering (TDBS) is a highly sensitive detection and analysis technology. Its principle is to use a pump pulse to stimulate the movement of atoms or molecules in the sample, and then use a probe pulse with adjustable time difference to detect the change of atomic or molecular movement in the sample at a certain moment, that is, the detection of phonons. The experimentally measured manifestation is the change of reflectivity on the surface of the sample. Depending on the material, the wavelength and power of the probe light and the pump light, the measured reflectivity change will also change. The change is generally composed of a curve caused by electronic fluctuations and a damped oscillation. The damped oscillation is the core of the research, which contains three important parameters: the amplitude of the oscillation, the frequency of the oscillation, and the attenuation coefficient of the oscillation.

TDBS technology has the advantages of being non-destructive, contactless, and highly sensitive, and can usually detect reflectivity changes of the order of 10 ^-5 . Using TDBS technology, time domain signals can be converted into frequency domain signals for measuring the sound velocity of the sample (when the refractive index is known); by tracking the amplitude attenuation of the signal, the dissipation rate of the sample sound wave energy can be calculated; nanoscale particles, biological samples and other structures can be non-invasively imaged; at the same time, TDBS technology can also play a role in the study of inter-band transitions of electrons.

Phonons are divided into optical and acoustic branches. The acoustic branch has the following characteristics: 1. The oscillation frequency varies with the wavelength of the detection light, that is, the Brillouin frequency. Where λ _pr is the wavelength of the probe light, n _pr is the refractive index of the sample at the probe wavelength, and v is the speed of sound of the sample; 2. The oscillation frequency of acoustic phonons is usually only in the sub-GHz range, which is much smaller than the THz range of optical phonons; 3. Coherent acoustic phonon oscillations can usually be observed within a time range of 100ps, while the observable range of optical phonons is much smaller. For example, in the TDBS experiment of Ge, the acoustic branch (CAP) is usually measured. The TDBS experimental method can detect the CAP in most samples. In the experiment, Ge is only displayed as a common semiconductor system. Since the wavelength of light used in the experiment is usually in the visible light range, millimeter-scale Ge materials can be regarded as bulk materials.

In TDBS experiments, in order to extract effective information from experimental data more efficiently and accurately, it is usually hoped that the amplitude of the oscillation signal is large enough and that enough signals can be observed. At the same time, due to the limited resolution of the optoelectronic devices in the experiment, the smaller the frequency of the oscillation, the more difficult it is to analyze. Therefore, it is very important to find a method that can meet these three requirements at the same time.

Summary of the invention

In view of the above problems, the present invention provides a method and device for optimizing the wavelength of detection light in time-domain Brillouin scattering experiments. The method and device use the conclusion that the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated when the wavelength of the detection light changes, and thus a computer simulation experiment is performed to optimize the wavelength of the detection light.

In a first aspect of the present invention, a method for optimizing the wavelength of a detection light in a time-domain Brillouin scattering experiment comprises:

Based on the formula for the change of reflectivity in the time-domain Brillouin scattering experiment, it is concluded that when the wavelength of the probe light changes, the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated;

The optimal detection wavelength is found through simulation experiments, including:

For a material system, simulation is performed according to the parameters of the material system:

In consideration of the duration of oscillation, a parameter τ = 1/(α _pu × v) is used to quantify the duration of oscillation, and it is concluded that different detection wavelengths will cause the parameter τ to change, where α _pu is the absorption coefficient of the pump light and v is the sound velocity of the medium;

Considering the oscillation amplitude, find the detection wavelength when the amplitude is maximum;

Considering the oscillation frequency, we found that the oscillation frequency decreases as the detection wavelength increases;

The amplitude A ₀ , frequency f and oscillation duration τ of the oscillation signal are multiplied and plotted, and the optimal detection wavelength is found through the plot.

A further technical solution of the present invention is: the method further comprises performing multiple simulation experiments to verify the found optimal detection wavelength.

A further technical solution of the present invention is: the specific change formula of the reflectivity in the time-domain Brillouin scattering experiment is:

in, i represents an imaginary number, k = 2π/λ _pr represents the detection light wave number, λ _pr represents the detection light wavelength, represents the derivative of the dielectric constant of the medium with respect to the photon energy, v represents the sound velocity of the medium; a _cv represents the relative deformation potential coupling constant, n _pr represents the complex refractive index of the medium for the probe light, α _pu represents the absorption coefficient of the pump light, R _pu represents the reflectivity of the medium for the pump light, F represents the pump light flux, ρ represents the density of the medium, t represents the time, c is the speed of light, represents the reduced Planck constant; ω _pu represents the angular frequency of the pump light.

A further technical solution of the present invention is: the parameters of the material system include the derivative of the dielectric constant of the medium with respect to photon energy, the sound velocity of the medium, the relative deformation potential coupling constant, the absorption coefficient of the pump light, the reflectivity of the medium to the pump light, the density of the medium, and the complex refractive index of the medium to the detection light.

A further technical solution of the present invention is: when the material system is Ge, the preferred detection wavelength range of the time-domain Brillouin scattering experiment is 600-820nm.

A second aspect of the present invention provides a device for optimally detecting light wavelength in a time-domain Brillouin scattering experiment, comprising:

The detection light wavelength relationship confirmation module is used to obtain the conclusion that the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated when the detection light wavelength changes based on the reflectivity change formula in the time-domain Brillouin scattering experiment;

The simulation experiment module is used to find the optimal detection wavelength through simulation experiments, including:

For a material system, simulation is performed according to the parameters of the material system:

In consideration of the duration of oscillation, a parameter τ = 1/(α _pu × v) is used to quantify the duration of oscillation, and it is concluded that different detection wavelengths will cause the parameter τ to change, where α _pu is the absorption coefficient of the pump light and v is the sound velocity of the medium;

Considering the oscillation amplitude, find the detection wavelength when the amplitude is maximum;

Considering the oscillation frequency, we found that the oscillation frequency decreases as the detection wavelength increases;

The amplitude A ₀ , frequency f and oscillation duration τ of the oscillation signal are multiplied and plotted, and the optimal detection wavelength is found through the plot.

The present invention provides a method and device for optimizing the wavelength of a detection light in a time-domain Brillouin scattering experiment. The method and device utilize the conclusion that the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated when the wavelength of the detection light changes, and thus a computer simulation experiment is performed to optimize the wavelength of the detection light. The present invention optimizes the wavelength of the detection light in the time-domain Brillouin scattering experiment, and can obtain a better effect of detection and analysis using the time-domain Brillouin scattering experiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a ) is a diagram showing the TDBS simulation results in an embodiment of the present invention when the pump wavelength is 800 nm, the pump light flux is 0.3 mJ/cm ² , and the probe light wavelengths are 539 nm, 652 nm, and 1127 nm respectively;

FIG1( b ) is a plot obtained by extracting the damped oscillation amplitude in an embodiment of the present invention, wherein the detected photon energy is in the range of 1-4 eV;

FIG1( c ) is a simulation result diagram of the time range in which an oscillation signal can be observed and the frequency of the oscillation signal in an embodiment of the present invention;

FIG. 1( d ) is a diagram showing the variation of the product of the amplitude, frequency and observation range of the oscillation signal with the detection wavelength in an embodiment of the present invention;

FIG. 2( a ) is a diagram showing the TDBS experimental results in another embodiment of the present invention, with a pump wavelength of 800 nm, a pump light flux of 0.3 mJ/cm ² , and detection photon energies of 625, 730, 870, and 920 nm;

FIG2( b ) is a diagram showing the variation of the product of the amplitude, frequency and observation range of the oscillation signal with the detection wavelength in another embodiment of the present invention;

FIG. 3 is a schematic diagram of the structure of a device for optimally detecting light wavelength in a time-domain Brillouin scattering experiment according to an embodiment of the present invention.

DETAILED DESCRIPTION

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

It should be mentioned before discussing the exemplary embodiments in more detail that some exemplary embodiments are described as processes or methods depicted as flow charts. Although the flow charts describe the steps as sequential processes, many of the steps therein can be implemented in parallel, concurrently or simultaneously. In addition, the order of the steps can be rearranged. The process can be terminated when its operation is completed, but can also have additional steps not included in the accompanying drawings. The process can correspond to a method, function, procedure, subroutine, subprogram, etc.

The embodiment of the present invention provides the following embodiments for a method and device for optimizing the wavelength of detection light in a time-domain Brillouin scattering experiment:

Embodiment 1 based on the present invention

A method for optimizing the wavelength of a detection light in a time-domain Brillouin scattering experiment according to Embodiment 1 of the present invention comprises:

Based on the formula for the change of reflectivity in the time-domain Brillouin scattering experiment, it is concluded that when the wavelength of the probe light changes, the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated;

Specifically, the damped oscillation signal in the TDBS experiment is affected by multiple dimensions, such as the detection wavelength, the change of the complex refractive index of the material with the wavelength of the incident light, the derivative of the dielectric constant of the material with the energy of the incident photon, etc. The change of reflectivity can be expressed as:

in, i represents an imaginary number, k = 2π/λ _pr represents the detection light wave number, λ _pr represents the detection light wavelength, represents the derivative of the dielectric constant of the medium with respect to the photon energy, v represents the sound velocity of the medium; a _cv represents the relative deformation potential coupling constant, n _pr represents the complex refractive index of the medium for the probe light, α _pu represents the absorption coefficient of the pump light, R _pu represents the reflectivity of the medium for the pump light, F represents the pump light flux, ρ represents the density of the medium, t represents the time, c is the speed of light, represents the reduced Planck constant; ω _pu represents the angular frequency of the pump light. It can be seen from the formula that when the wavelength of the detection light changes, the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated, so the optimal detection wavelength can be found through computer simulation.

The optimal detection wavelength is found through simulation experiments, including:

For a material system, simulation is performed according to the parameters of the material system:

In consideration of the duration of oscillation, a parameter τ = 1/(α _pu × v) is used to quantify the duration of oscillation, and it is concluded that different detection wavelengths will cause the parameter τ to change, where α _pu is the absorption coefficient of the pump light and v is the sound velocity of the medium;

Considering the oscillation amplitude, find the detection wavelength when the amplitude is maximum;

Considering the oscillation frequency, we found that the oscillation frequency decreases as the detection wavelength increases;

The amplitude A ₀ , frequency f and oscillation duration τ of the oscillation signal are multiplied and plotted, and the optimal detection wavelength is found through the plot.

Preferably, for a new material system, it is only necessary to find out the derivative of the dielectric constant of the medium with respect to the photon energy, the sound velocity of the medium, the relative deformation potential coupling constant, the absorption coefficient of the pump light, the reflectivity of the medium to the pump light, the density of the medium, the complex refractive index of the medium to the detection light and other parameters to perform simulation.

In a specific embodiment, see Figure 1, which is a simulation result given that the medium is a bulk Ge material, the pump light wavelength and flux are 800nm and 0.3mJ/cm2 respectively. In the range of incident light wavelength greater than 300nm, the absorption coefficient of Ge to incident light shows a downward trend, so the larger the detection light wavelength, the longer the detection distance, which is manifested in the time domain as a longer duration of oscillation. A parameter τ=1/(α _pu ×v) is used to quantify the duration of the oscillation. As shown in Figure 1(c), the time range of the oscillation signal τ=1/(α _pu ×v) and the frequency of the oscillation signal can be observed. When the detection wavelength is less than 550nm, the value of τ is only at the level of 1ps. At this time, it is difficult to observe a complete oscillation. Figure 1(a) also confirms this point. Figure 1(a) shows the TDBS simulation results when the pump wavelength is 800nm, the pump light flux is 0.3mJ/ ^cm2 , and the detection light wavelengths are 539nm, 652nm and 1127nm respectively. The expression is a damped oscillation of the reflectivity change with time delay. It is difficult to observe a complete oscillation in the curve corresponding to the detection wavelength of 539nm; as the detection wavelength increases to 1127nm, oscillation can still be observed within the range of 200ps. Therefore, the change of τ caused by different detection wavelengths is a key factor to be considered in the experiment.

Another important factor to consider is the amplitude of the oscillation. Therefore, the wavelengths in the range of 310-1240nm were simulated and the corresponding amplitudes were extracted to plot the curve in Figure 1(b). Figure 1(b) extracts the amplitude A0 of the damped oscillation, where the detection photon energy is in the range of 1-4eV. It is noted that the maximum amplitude is at 620nm, and the amplitude decreases rapidly as the wavelength increases or decreases. This is because the maximum amplitude at 620nm The contribution to the amplitude is the largest, and as the wavelength increases or decreases, The contribution has dropped sharply.

In addition, the frequency of oscillation also has a certain influence on the extraction of experimental data. As shown in Figure 1(c), within the detection wavelength range of 310-1240nm, the frequency of oscillation generally shows a downward trend with the increase of wavelength. In the TDBS experiment, due to the influence of noise and the accuracy of optoelectronic devices, the larger the oscillation frequency, the more oscillations can be observed at the same time scale, which is beneficial for analyzing the signal. Therefore, the amplitude A0, frequency f and oscillation duration τ of the oscillation signal are multiplied and displayed in the form of Figure 1(d). Figure 1(d) shows that the product of the amplitude A0, frequency f and observation range τ of the oscillation signal changes with the detection wavelength, reflecting the contribution of the three important indicators to the experimental results. The gray box part is the optimal wavelength selection range recommended for the TDBS experiment. As can be seen from the figure, although there are higher values after 1100nm, the amplitude of the oscillation is too small and is not taken into consideration. The wavelength range covered by the grayscale area, whether it is the oscillation amplitude, frequency, or duration, meets the requirements of the experimental results. Therefore, it can be considered that in the Ge TDBS experiment, the optimal detection wavelength selection range is 600-820nm.

Preferably, the method further comprises performing multiple simulation experiments to verify the found preferred detection wavelength.

Specifically, see Figure 2. Figure 2(a) is a TDBS experimental result diagram under the same medium and pumping conditions. The curve consists of background thermal signals and damped oscillations. Figure 2(a) is a TDBS experimental result diagram with a pump wavelength of 800nm, a pump light flux of 0.3mJ/ ^cm2 , and detection photon energies of 625, 730, 870, and 920nm. By subtracting the background signal, the damped oscillation form can be extracted. After processing the experimental data, the three parameters mentioned above are extracted and multiplied to draw a curve as shown in Figure 2(b). Figure 2(b) is similar to Figure 1(d). The vertical axis consists of the product of the three parameters extracted from the experimental data, and the horizontal axis is the corresponding detection wavelength. It has the same trend as Figure 1(d), proving that the simulation has guiding significance for the experiment.

Embodiment 2 based on the present invention

The device 300 for preferentially detecting the wavelength of light in a time-domain Brillouin scattering experiment provided in Example 2 of the present invention can execute the method for preferentially detecting the wavelength of light in a time-domain Brillouin scattering experiment provided in any embodiment of the present invention, and has functional modules and beneficial effects corresponding to the execution method. The system can be implemented by software and/or hardware (integrated circuit) and can generally be integrated into a server or terminal device.

FIG3 is a schematic diagram of the structure of a device 300 for preferentially detecting light wavelengths in a time-domain Brillouin scattering experiment in Embodiment 2 of the present invention. Referring to FIG3 , the device 300 for preferentially detecting light wavelengths in a time-domain Brillouin scattering experiment in the embodiment of the present invention may specifically include:

The detection light wavelength relationship confirmation module 310 is used to obtain the conclusion that the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated when the detection light wavelength changes based on the reflectivity change formula in the time-domain Brillouin scattering experiment;

The simulation experiment module 320 is used to find the optimal detection wavelength through simulation experiments, specifically including:

For a material system, simulation is performed according to the parameters of the material system:

In consideration of the duration of oscillation, a parameter τ = 1/(α _pu × v) is used to quantify the duration of oscillation, and it is concluded that different detection wavelengths will cause the parameter τ to change, where α _pu is the absorption coefficient of the pump light and v is the sound velocity of the medium;

Considering the oscillation amplitude, find the detection wavelength when the amplitude is maximum;

Considering the oscillation frequency, we found that the oscillation frequency decreases as the detection wavelength increases;

The amplitude A ₀ , frequency f and oscillation duration τ of the oscillation signal are multiplied and plotted, and the optimal detection wavelength is found through the plot.

In addition to the above two modules, the device 300 may also include other components. However, since these components are irrelevant to the content of the embodiment of the present disclosure, their illustration and description are omitted here.

The specific working process of the device 300 for optimally detecting the wavelength of light in a time-domain Brillouin scattering experiment is described in the above-mentioned method embodiment 1 for optimally detecting the wavelength of light in a time-domain Brillouin scattering experiment, and will not be repeated here.

Based on the above-mentioned methods and devices for optimizing the wavelength of the detection light in the time-domain Brillouin scattering experiment provided by the embodiments, the conclusion that the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated when the wavelength of the detection light changes is used to perform a computer simulation experiment to optimize the wavelength of the detection light. The present invention optimizes the wavelength of the detection light in the time-domain Brillouin scattering experiment, and can obtain a better effect of detection and analysis using the time-domain Brillouin scattering experiment.

Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (6)

1. A method for optimizing the wavelength of detection light in a time-domain Brillouin scattering experiment, comprising: Based on the formula for the change of reflectivity in the time-domain Brillouin scattering experiment, it is concluded that when the wavelength of the probe light changes, the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated; The optimal detection wavelength is found through simulation experiments, including: For a material system, simulation is performed according to the parameters of the material system: To consider the duration of oscillation, a parameter To quantify the duration of the oscillation, we can conclude that different detection wavelengths will cause the parameter τ to change, where is the absorption coefficient of the pump light, is the speed of sound in the medium; Considering the oscillation amplitude, find the detection wavelength when the amplitude is maximum; Considering the oscillation frequency, we found that the oscillation frequency decreases as the detection wavelength increases; The amplitude of the oscillation signal ,frequency and oscillation duration Multiply the three and plot them in a graph, and use the graph to find the optimal detection wavelength. 2. The method for selecting the optimal detection light wavelength in a time-domain Brillouin scattering experiment according to claim 1, characterized in that the method further comprises performing multiple simulation experiments to verify the found optimal detection wavelength. 3. The method for optimizing the detection light wavelength in the time-domain Brillouin scattering experiment according to claim 1, characterized in that the specific change formula of the reflectivity based on the reflectivity change formula in the time-domain Brillouin scattering experiment is: , in, , represents an imaginary number, represents the detected light wave number, represents the wavelength of the detection light, represents the derivative of the dielectric constant of the medium with respect to the photon energy, Indicates the speed of sound in the medium; represents the relative deformation potential coupling constant, represents the complex refractive index of the medium for the probe light, represents the absorption coefficient of the pump light, represents the reflectivity of the medium to the pump light, is the pump light flux, represents the density of the medium, Indicates time, is the speed of light, represents the reduced Planck constant; Indicates the angular frequency of the pump light. 4. The method for optimizing the wavelength of detection light in a time-domain Brillouin scattering experiment according to claim 1 is characterized in that the parameters of the material system include the derivative of the dielectric constant of the medium with respect to photon energy, the sound velocity of the medium, the relative deformation potential coupling constant, the absorption coefficient of the pump light, the reflectivity of the medium to the pump light, the density of the medium, and the complex refractive index of the medium to the detection light. 5. The method for optimally detecting light wavelength in a time-domain Brillouin scattering experiment according to claim 1, characterized in that, when the material system is Ge, the optimal detection wavelength range of the time-domain Brillouin scattering experiment is 600-820 nm. 6. A device for optimally detecting light wavelength in a time-domain Brillouin scattering experiment, characterized in that the device comprises: The detection light wavelength relationship confirmation module is used to obtain the conclusion that the amplitude, frequency and attenuation coefficient of the damped oscillation will be modulated when the detection light wavelength changes based on the reflectivity change formula in the time-domain Brillouin scattering experiment; The simulation experiment module is used to find the optimal detection wavelength through simulation experiments, including: For a material system, simulation is performed according to the parameters of the material system: To consider the duration of oscillation, a parameter To quantify the duration of the oscillation, we can get the parameters that will be caused by different detection wavelengths. The conclusion of the change, is the absorption coefficient of the pump light, is the speed of sound in the medium; Considering the oscillation amplitude, find the detection wavelength when the amplitude is maximum; Considering the oscillation frequency, we found that the oscillation frequency decreases as the detection wavelength increases; The amplitude of the oscillation signal ,frequency and oscillation duration Multiply the three and plot them, and find the optimal detection wavelength through the diagram.