CN112097953B - High-frequency two-color coherent anti-Stokes Raman spectrum temperature measuring device and method - Google Patents
High-frequency two-color coherent anti-Stokes Raman spectrum temperature measuring device and method Download PDFInfo
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Abstract
The invention relates to a high-frequency two-color coherent anti-Stokes Raman spectrum temperature measuring device and a method, wherein the device comprises: the high-frequency laser is used for generating 1064nm laser with the repetition frequency of 100kHz and outputting 355nm laser and 532nm laser after the 1064nm laser is subjected to frequency tripling and frequency doubling respectively, wherein the 532nm laser is used as pump light/probe light; a seed laser module for generating two seed lasers around 855 nm; the optical parametric oscillator is used for converting 355nm laser input by the high-frequency laser and 855nm laser input by the seed laser into 607nm laser serving as Stokes light; the coherent anti-Stokes Raman signal generation module is used for mixing 532nm pump light and the Stokes laser light near 607nm at the position of the detected gas molecules through a lens to generate a coherent anti-Stokes Raman signal; and the imaging spectrometer is used for imaging the input coherent anti-Stokes Raman signal and calculating the spectral data of the image to obtain the temperature of the detected gas.
Description
Technical Field
The invention belongs to the field of photoelectric temperature measurement, and particularly relates to a high-frequency two-color coherent anti-Stokes Raman spectrum temperature measurement device and method.
Background
The combustion diagnosis is to perform experimental measurement on the combustion process and analyze the result to obtain the relevant information of the fuel, the combustion products and the combustion flow field. The diagnosis of the combustion flow field involves a wide range of knowledge, such as the knowledge in the aspects of physical optics, physical chemistry, statistical thermodynamics, laser spectroscopy, instrument analysis, data processing and the like, the measured object comprises important parameters of the flow field, such as speed, temperature, density and the like, and the flow field has the characteristics of high-temperature flame radiation and condensation two-phase complex flow, thereby providing high requirements for the diagnosis and measurement technology. In the past, the combustion diagnosis technology adopts a sensor for measuring pressure, a pitot tube or a hot wire anemometer for measuring speed, a thermocouple for measuring temperature and the like, the classical methods are used at present according to the old, but the classical methods cannot meet the modern requirements for measuring and displaying a complex flow field, belong to contact measurement and have the problem of influencing the measurement result by the interference of the flow field. With the advent of laser technology, laser is used as a photon beam with good monochromaticity and directivity, high brightness and large energy, a powerful tool is provided for non-contact measurement, the non-contact measurement can obtain flow field information while reducing or avoiding pneumatic, thermal or chemical disturbance by utilizing the knowledge of spectroscopy, and the non-contact measurement has necessary time and spatial resolution and displays great superiority. At present, a plurality of laser-based non-contact measurement methods exist, and a coherent anti-stokes raman spectroscopy (CARS) is one of them, which is a nonlinear four-wave mixing technology, three-beam laser interaction generates a laser-like coherent output signal containing required spectral information, i.e. a molecular raman coherence (such as rotation or rotational vibration) is established between two molecular states by pump light and stokes light beams, and then the coherence is detected by probe light beams, so that coherent anti-stokes raman signal light is generated. The spectrum can be used for measuring the temperature and the relative species concentration, the temperature can be inferred through the boltzmann equilibrium distribution depending on the temperature, the intensity of the coherent anti-stokes Raman signal is proportional to the square of the concentration of the detected molecule, and the substance concentration measurement can also be carried out.
Coherent anti-stokes raman spectroscopy has found widespread use in many fields, and many experiments are performed in condensed phases, such as biological and medical lipid studies, because high density samples of the condensed phase produce strong coherent anti-stokes raman signals. The technology has important significance in the measurement of the gas phase state, and has the advantages of high spatial resolution and accurate spectral measurement. The method for measuring the temperature of the nitrogen by vibration rotation spectrum is considered as a 'gold standard' for measuring the temperature of a combustion field, has great significance for relevant combustion processes and applications, and is the target of the experiment. The traditional coherent anti-Stokes Raman spectrum technology has low frequency, has interference of non-resonant background, limits the technical precision, and has appeared at present a picosecond-level and femtosecond-level high-frequency coherent anti-Stokes Raman spectrum technology and a mixed femtosecond/picosecond-level coherent anti-Stokes Raman spectrum technology combining the advantages of the two technologies. And, on the basis of this method, the conventional spot measurement method is extended to one-dimensional and two-dimensional temperature and concentration measurement.
Baxter et al, "OPO CARS: coherent anti-Stokes Raman spectroscopy using tunable optical parametric oscillators" describes a two-color OPO-CARS method using two seed lasers injected into an optical parametric oscillator to thereby generate a two-color coherent anti-Stokes Raman signal, which is dispersed by a grating spectrometer and captured by a camera to obtain two coherent anti-Stokes Raman spectra, whose relative intensities are used to measure temperature. However, the two-color coherent anti-stokes raman spectroscopy method based on the optical parametric oscillator has the problems that the laser frequency is low, the high repetition rate is difficult to realize, the measurement time resolution and the spatial resolution are low, two raman spectrums are obtained by two-color lasers, and the temperature measurement precision is low.
Bohlin and Kliewer have proposed Two-dimensional coherent anti-Stokes Raman spectroscopy methods in Communication with Two-dimensional gas-phase coherent anti-Stokes Raman spectroscopy (2D-CARS) and multiplex spectroscopy in a single laser shot (Communication with Two-dimensional gas-phase coherent anti-Stokes Raman spectroscopy (2D-CARS) Simultaneous planar imaging and multiple spectroscopy). The method adopts a mixed femtosecond/picosecond coherent anti-Stokes Raman spectrum technology to detect nitrogen N2And oxygen O2The pumping/Stokes light is focused into a slice through the cylindrical lens, the detection light is collimated and is intersected with the pumping/Stokes light to generate a coherent two-dimensional coherent anti-Stokes Raman signal, and the signal is imaged into a camera after being diffracted by the grating to obtain a two-dimensional spectral image. This hybrid femtosecond/picosecond coherent anti-stokes raman spectroscopy method uses a high repetition rate laser to generate laser light,the time resolution and the spatial resolution are also improved, but at least two lasers are required to be used simultaneously to generate femtosecond laser and picosecond laser respectively, the system structure is complex, the lasers are used as broadband, the continuous rotation vibration Raman spectrum of the target gas is measured, the generated non-resonance background interference is strong, and the efficiency is low.
Disclosure of Invention
The invention aims to provide a high-frequency two-color coherent anti-Stokes Raman spectrum temperature measuring device and a method thereof, so as to overcome the problems of the two methods.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
according to an aspect of the present invention, there is provided a high-frequency two-color coherent anti-stokes raman spectroscopy temperature measurement apparatus, comprising:
the high-frequency laser is used for generating 1064nm laser with the repetition frequency of 100kHz and outputting 355nm laser and 532nm laser after the 1064nm laser is subjected to frequency tripling and frequency doubling respectively, wherein the 532nm laser is used as pump light/probe light;
a seed laser module for generating two seed lasers around 855 nm;
the optical parametric oscillator is used for converting 355nm laser input by the high-frequency laser and 855nm laser input by the seed laser into 607nm laser serving as Stokes light;
the coherent anti-Stokes Raman signal generation module is used for mixing 532nm pump light and the Stokes laser light near 607nm at the position of the detected gas molecules through a lens to generate a coherent anti-Stokes Raman signal;
and the imaging spectrometer is used for imaging the input coherent anti-Stokes Raman signal and calculating the spectral data of the image to obtain the temperature of the detected gas.
In the preferred embodiment, the high frequency laser is a Nd: YAG laser.
In a preferred embodiment, the seed laser module comprises two semiconductor lasers and an optoelectronic isolator, the two semiconductor lasers are used for generating two semiconductor lasers near 855nm, and the two seed lasers near 855nm are output after being processed by the optoelectronic isolator.
In a preferred embodiment, the seed laser module further comprises two mirror plates, arranged between the semiconductor laser and the opto-isolator, for reflecting two 855 nm-close semiconductor lasers towards the opto-isolator,
in a preferred embodiment, the seed laser output by the optoelectronic isolator is reflected by a lens to enter the optical parametric oscillator and 355nm laser to generate stokes light near 607nm, the lens is used for reflecting 820-.
In the preferred embodiment, the optical parametric oscillator comprises a BBO crystal, and a front lens and two rear lenses which are positioned at two sides of the BBO crystal, wherein the front lens is positioned between the BBO crystal and the high-frequency laser and is used for transmitting light of 355nm and reflecting light of 600-640nm and 820-860 nm; the rear lens close to the BBO crystal in the two rear lenses is used for transmitting the light of 355nm and reflecting the light of 600-640nm and 820-860nm by 20 percent, and the other rear lens is used for reflecting the light of 355nm and transmitting the light of 600-640nm and 820-860 nm.
In a preferred embodiment, the pump/probe and stokes light are each turned 90 degrees by a respective mirror before entering the lens.
According to another aspect of the invention, a high-frequency two-color coherent anti-stokes Raman spectrum temperature measurement method is also provided, and the method comprises the following steps:
generating a spectral image by the high-frequency bicolor coherent anti-stokes Raman spectral temperature measuring device;
mapping the spectral image to a grid with a proper size, wherein each node represents a space position, and calculating the spectral signal intensity of each node through integration;
selecting an intensity threshold, and removing low-intensity noise data from each spectrum;
establishing a model of coherent anti-Stokes Raman spectrum signal intensity and temperature;
fitting according to a least square method to minimize residual errors between the experimental value and the theoretical value of each node, and extracting a corresponding best-fit temperature value;
and performing the previous step on each node of the image grid to generate a temperature distribution schematic diagram.
In a preferred embodiment, the specific process of modeling the coherent anti-stokes raman spectrum signal intensity and temperature is as follows:
calculating the Raman transition line width according to a modified index gap Model (MEG), wherein the expression is as follows:
in the formula, gammaf，iIs the transition line width from the initial state i to the final state f; p is gas pressure in atm; alpha is an adjustable parameter, in cm-1atm-1(ii) a T is temperature in K, where T0295K; n is a species-dependent unitless constant that accounts for the temperature dependence of rotational energy transfer; m, delta and beta are scaling parameters which can be adjusted without a unit; k is a radical ofBBoltzmann constant; a is another species-related constant; eiAnd EfThe energies of the transition initial energy level and the final energy level, respectively;
a third order nonlinear response, also known as a molecular response, is then calculated, expressed as:
in the formula, the molecule responds to RCARS(t) is the summation of Raman active transitions from the initial state m to the final state n,
is a reduced Planck constant, I is an imaginary unit, Im，n、ΔEm，n、Γm，nRespectively raman transition intensity, transition frequency and transition line width;
the molecular response is combined with the detection optical electric field to obtain the corresponding third-order polarization, namely the spectrum signal on the time domain, and the expression is as follows:
in the formula (I), the compound is shown in the specification,
for third order polarization response, Epr(t- τ) is the linear chirp in the probe beam, RCARS(t) is the molecular response;
obtaining a frequency domain signal of third-order polarization response, namely a spectrum signal on a frequency domain through Fourier transform, wherein the signal intensity on the frequency domain is the square of the absolute value of a frequency domain signal value;
in the imaging spectrometer, the signals pass through a grating and a reflector to separate images corresponding to different wavelengths, and the relationship between the intensity of the corresponding spectral signals and the temperature can be obtained according to the wavelength of the bicolor coherent anti-Stokes Raman spectral signals.
The invention combines the advantages of two schemes of a bicolor coherent anti-Stokes Raman spectrum method and a two-dimensional mixed femtosecond/picosecond coherent anti-Stokes Raman spectrum method based on an optical parametric oscillator, uses a high-frequency laser to generate incident laser with the repetition frequency of 100kHz, improves the time resolution and the spatial resolution, uses the Optical Parametric Oscillator (OPO) to convert the wavelength and injects bicolor seed laser, so that the structure of an experimental device is more compact and efficient, the Stokes radiation measured by the experiment is concentrated in two independent channels, the non-resonance background interference is inhibited, and the temperature measurement and the two-dimensional imaging can be efficiently and rapidly realized.
Drawings
FIG. 1 is a schematic diagram of a high-frequency two-color coherent anti-Stokes Raman spectrum temperature measurement experimental device.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings in order to more clearly understand the objects, features and advantages of the present invention. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the present invention, but are merely intended to illustrate the spirit of the technical solution of the present invention.
Fig. 1 is a schematic diagram of a high-frequency two-color coherent anti-stokes raman spectrum temperature measurement experimental apparatus, which includes five modules, namely a high-frequency laser 1, a seed laser module 2, an optical parametric oscillator 3, a coherent anti-stokes raman signal generation module 4, and an imaging spectrometer 5. The high-frequency laser 1 is used for generating 1064nm laser with a repetition frequency of 100kHz and outputting 355nm laser and 532nm laser after the 1064nm laser is subjected to frequency tripling and frequency doubling respectively, wherein the 532nm laser is used as pump light/probe light (pump/probe); the seed laser module 2 is used to generate two seed lasers around 855nm, typically 857.3nm and 858.5nm in the preferred embodiment; the optical parametric oscillator 3 is used for converting 355nm laser light input by the high-frequency laser and 855nm laser light input by the seed laser into 607nm laser light which is used as stokes light (stokes); the coherent anti-stokes raman signal generation module 4 is used for mixing 532nm pump light and stokes laser light near 607nm at a probe gas molecule 42 (in the embodiment, nitrogen is used) through a lens 41 to generate a coherent anti-stokes raman signal (CARS); the imaging spectrometer 5 is used for imaging the input coherent anti-stokes raman signal and calculating the temperature of the detected gas by the spectral data of the image. Each block will be described below.
In a specific embodiment, the high frequency laser 1 is a Nd: YAG laser for generating 1064nm laser with a repetition frequency of 100kHz, and the 1064nm laser outputs 355nm laser light and 532nm laser light after frequency tripling and frequency doubling, respectively. Wherein, 532nm laser is used as pump light/detecting light after passing through a half-wave plate 6.
The seed laser module 2 includes two semiconductor lasers 21, 22, two reflection mirrors 23, 24, and one photo isolator 25, the two semiconductor lasers 21, 22 are used to generate two semiconductor lasers near 855nm, the two reflection mirrors 23, 24 are used to reflect the two semiconductor lasers near 855nm (turn 90 degrees, i.e., change from the horizontal direction to the vertical direction) so that the two seed lasers are collinear, and input to the photo isolator 25, and the photo isolator 25 outputs the two seed lasers near 855 nm. It should be understood that the directions herein refer to the page directions of the drawing, not the actual physical space directions.
In the present embodiment, the seed laser output from the optoelectronic isolator 25 is reflected by a lens 7 into the optical parametric oscillator 3 and 355nm laser to generate stokes light (stokes) near 607 nm. The lens 7 can reflect 820-860nm p-direction polarized light and transmit 600-640nm p-direction polarized light, so that seed laser light near 855nm can be reflected by the lens 7 to turn 90 degrees (change from the vertical direction to the horizontal direction) to enter the optical parametric oscillator 3, and stokes light near 607nm generated by stokes light can enter the coherent anti-stokes raman signal generation module 4 through the lens 7. By designing the lens 7, the whole device structure is more compact.
The optical parametric oscillator 3 comprises BBO crystals 32 and 33, and a front lens 31 and two rear lenses 34 and 35 which are positioned at two sides of the BBO crystals, wherein the front lens 31 is positioned between the BBO crystals 32 and the high-frequency laser 1, can transmit 355nm light and reflect 600-640nm light and 820-860nm light; the back lens 34 near the BBO crystal 33 of the two back lenses can transmit the light of 355nm and reflect the light of 600-640 and 820-860nm by 20% and the other back lens 35 can reflect the light of 355nm and transmit the light of 600-640 and 820-860 nm. Therefore, 355nm light emitted by the high-frequency laser 1 can enter the BBO crystals 32 and 33 through the front mirror 31 and be reflected back by the rear mirror 35, and seed laser light near 855nm can enter the BBO crystals 32 and 33 through the two rear mirrors 34 and 35, the 355nm light and the 855nm light in the BBO crystals 32 and 33 are subjected to wavelength conversion to obtain 607nm light, and the front mirror 31 reflects the light with the wavelength of 600-640nm and 820-860nm, so the 607nm light is transmitted and output as Stokes light through the rear mirrors 34 and 35.
In the present embodiment, the pump/probe light (pump/probe) and stokes light (stokes) are turned by 90 degrees by the respective mirrors 8 and 9 before entering the lens 41 (convex lens) of the coherent anti-stokes raman signal generating module 4. This is advantageous in that the horizontal direction of the entire apparatus is prevented from being too long, so that the apparatus is compact.
The coherent anti-stokes raman signal generating module 4 comprises a lens 41 (convex lens), probe gas molecules 42 and a lens 43 (convex lens), the lens 41 (convex lens) is used to focus parallel pump/probe and stokes light on the probe gas molecules 42 to generate a coherent anti-stokes raman signal, and the lens 43 is used for collimation (i.e. outputting a parallel coherent anti-stokes raman signal). Simultaneously, the pump/probe and stokes lights are collected in the beam dump 51.
The structure of the imaging spectrometer module 5 is well known and mainly comprises a Beam Dump (Beam Dump) 51, a CCD camera 52, a mirror 53, a cylindrical lens 54 and a grating 55. The beam dump 51 is used to collect pump/probe and stokes light. Coherent anti-stokes raman spectral signals (CARS) are imaged by a cylindrical lens 54 and a grating 55, spatially separated by a lens 53, and the images are captured by a CCD camera 52 to obtain spectral data at different positions.
The procedure for calculating the temperature from the spectral data is as follows:
in the first step, the spectral image captured by the camera is mapped onto a grid of suitable size (e.g. a grid of pixels, one pixel for each grid), each node represents a spatial position, and the spectral signal intensity of each node is calculated by integration.
Second, an intensity threshold is selected, and the low intensity noise data is removed from each spectrum.
And thirdly, establishing a model of the coherent anti-Stokes Raman spectrum signal intensity and temperature. Calculating the Raman transition line width according to a modified index gap Model (MEG), wherein for the measurement of pure nitrogen, the expression is as follows:
in the formula, gammaf，iIs the transition line width from the initial state i to the final state f; p is gas pressure in atm; alpha is an adjustable parameter, in cm-1atm-1(ii) a T is temperature in K, where T0295K; n is a species-dependent unitless constant that accounts for the temperature dependence of rotational energy transfer; m, delta and beta are scaling parameters which can be adjusted without a unit; k is a radical ofBBoltzmann constant; a is another species-related constant; eiAnd EfThe energies of the transition initial energy level and the final energy level, respectively;
a third order nonlinear response, also known as a molecular response, is then calculated, expressed as:
in the formula, the molecule responds to RCARS(t) is the summation of Raman active transitions from the initial state m to the final state n,
is a reduced Planck constant, I is an imaginary unit, Im，n、ΔEm，n、Γm，nRespectively raman transition intensity, transition frequency and transition line width.
The molecular response is combined with the detection optical electric field to obtain the corresponding third-order polarization, namely the spectrum signal on the time domain, and the expression is as follows:
in the formula (I), the compound is shown in the specification,
for third order polarization response, Epr(t- τ) is the linear chirp in the probe beam, RCARS(t) is the molecular response.
Obtaining a frequency domain signal of third-order polarization response, namely a spectrum signal on a frequency domain through Fourier transform, wherein the signal intensity on the frequency domain is the square of the absolute value of a frequency domain signal value;
in the imaging spectrometer, the signals pass through a grating and a reflector to separate images corresponding to different wavelengths, and the relationship between the intensity of the corresponding spectral signals and the temperature can be obtained according to the wavelength of the bicolor coherent anti-Stokes Raman spectral signals.
And fourthly, fitting according to a least square method to minimize residual errors between the experimental value and the theoretical value of each node, and extracting a corresponding optimal fitting temperature value.
And fifthly, performing the previous operation on each node of the image grid to generate a temperature distribution schematic diagram.
While the preferred embodiments of the present invention have been illustrated and described in detail, it should be understood that various changes and modifications of the invention can be effected therein by those skilled in the art after reading the above teachings of the invention. Such equivalents are intended to fall within the scope of the claims appended hereto.
Claims (7)
1. A high-frequency bicolor coherent anti-Stokes Raman spectrum temperature measuring device is characterized by comprising:
the high-frequency laser is used for generating 1064nm laser with the repetition frequency of 100kHz and outputting 355nm laser and 532nm laser after the 1064nm laser is subjected to frequency tripling and frequency doubling respectively, wherein the 532nm laser is used as pump light/probe light;
the seed laser module is used for generating two seed lasers near 855nm, and comprises two semiconductor lasers and a photoelectric isolator, wherein the two semiconductor lasers are used for generating two semiconductor lasers near 855nm, and the two semiconductor lasers near 855nm are processed by the photoelectric isolator and then output two seed lasers near 855 nm;
the optical parametric oscillator is used for converting 355nm laser input by the high-frequency laser and 855nm laser input by the seed laser into 607nm laser serving as Stokes light, and comprises a BBO crystal, a front lens and two rear lenses, wherein the front lens is positioned between the BBO crystal and the high-frequency laser and used for transmitting 355nm light and reflecting 600-doped 640nm light and 820-doped 860nm light; the rear lens close to the BBO crystal in the two rear lenses is used for transmitting the light of 355nm and reflecting the light of 600-640nm and 820-860nm by 20 percent, and the other rear lens is used for reflecting the light of 355nm and transmitting the light of 600-640nm and 820-860 nm;
the coherent anti-Stokes Raman signal generation module is used for mixing 532nm pump light and the Stokes laser light near 607nm at the position of the detected gas molecules through a lens to generate a coherent anti-Stokes Raman signal;
and the imaging spectrometer is used for imaging the input coherent anti-Stokes Raman signal and calculating the spectral data of the image to obtain the temperature of the detected gas.
2. The high-frequency two-tone coherent anti-stokes Raman spectrum temperature measuring device according to claim 1, wherein the high-frequency laser is a Nd: YAG laser.
3. The high frequency bi-color coherent anti-stokes raman spectroscopy temperature measurement device of claim 2, wherein the seed laser module further comprises two mirror plates disposed between the semiconductor laser and the optoelectronic isolator for reflecting two 855 nm-near semiconductor lasers to the optoelectronic isolator.
4. The device as claimed in claim 2 or 3, wherein the seed laser output by the optoelectronic isolator is reflected by a lens into the optical parametric oscillator and 355nm laser to generate the Stokes light near 607nm, the lens is used for reflecting 820-860nm p-direction polarized light and transmitting 600-640nm p-direction polarized light, and the Stokes light enters the coherent anti-Stokes Raman signal generation module through the lens.
5. The high frequency bi-color coherent anti-stokes raman spectroscopy temperature measurement device of claim 1, wherein the pump/probe and stokes lights are respectively turned by 90 degrees by corresponding mirrors before entering the lens.
6. A high-frequency two-color coherent anti-Stokes Raman spectrum temperature measurement method is characterized by comprising the following steps:
generating a spectral image by a high frequency bi-chromatic coherent anti-stokes raman spectroscopy temperature measuring device according to any one of claims 1 to 5;
mapping the spectral image to a grid with a proper size, wherein each node represents a space position, and calculating the spectral signal intensity of each node through integration;
selecting an intensity threshold, and removing low-intensity noise data from each spectrum;
establishing a model of coherent anti-Stokes Raman spectrum signal intensity and temperature;
fitting according to a least square method to minimize residual errors between the experimental value and the theoretical value of each node, and extracting a corresponding best-fit temperature value;
and performing the previous step on each node of the image grid to generate a temperature distribution schematic diagram.
7. The high-frequency bicolor coherent anti-stokes Raman spectrum temperature measurement method according to claim 6, wherein the specific process of establishing the coherent anti-stokes Raman spectrum signal intensity and temperature model comprises the following steps:
calculating the Raman transition line width according to a modified index gap Model (MEG), wherein the expression is as follows:
in the formula, gammaf，iIs the transition line width from the initial state i to the final state f; p is gas pressure in atm; alpha is an adjustable parameter, in cm-1atm-1(ii) a T is temperature in K, where T0295K; n is a species-dependent unitless constant that accounts for the temperature dependence of rotational energy transfer; m, delta and beta are scaling parameters which can be adjusted without a unit; k is a radical ofBBoltzmann constant; a is another species-related constant; eiAnd EfThe energies of the transition initial energy level and the final energy level, respectively;
a third order nonlinear response, also known as a molecular response, is then calculated, expressed as:
in the formula, the molecule responds to RCARS(t) is the summation of Raman active transitions from initial state m to final state n, h is the reduced Planckian constant, I is the imaginary unit, Im，n、ΔEm，n、Γm，nRespectively raman transition intensity, transition frequency and transition line width;
the molecular response is combined with the detection optical electric field to obtain the corresponding third-order polarization, namely the spectrum signal on the time domain, and the expression is as follows:
in the formula (I), the compound is shown in the specification,
for third order polarization response, Epr(t- τ) is the linear chirp in the probe beam, RCARS(t) is the molecular response;
obtaining a frequency domain signal of third-order polarization response, namely a spectrum signal on a frequency domain through Fourier transform, wherein the signal intensity on the frequency domain is the square of the absolute value of a frequency domain signal value;
in the imaging spectrometer, the signals pass through a grating and a reflector to separate images corresponding to different wavelengths, and the relationship between the intensity of the corresponding spectral signals and the temperature can be obtained according to the wavelength of the bicolor coherent anti-Stokes Raman spectral signals.
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| CN112097953A (en) | 2020-12-18 |
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