CN110274891B - System for measuring water vapor temperature-changing absorption spectrum and using method thereof - Google Patents
System for measuring water vapor temperature-changing absorption spectrum and using method thereof Download PDFInfo
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Abstract
The invention provides a system for measuring water vapor variable-temperature absorption spectrum and a using method thereof, wherein the system comprises a difference frequency light source module, a difference frequency light source frequency monitoring and calibrating module, a data acquisition and processing module, a three-optical-path temperature control multi-pass cell device and a gas distribution module; the differential frequency light generated by the differential frequency light source module is guided into the three-optical-path temperature control multi-pass cell device, the laser is injected into the acquisition and processing module of the absorption information guide-in data generated by the sample cell, the gas distribution module is specifically a mixing container and used for mixing water vapor and dry air in a fixed proportion, the acquisition and processing module of the data comprises a computer with an integrated multispectral fitting program, and the novel BaGa light source device is adopted4Se7The crystal is used as a frequency conversion device to generate 3-11 mu m mid-infrared difference frequency light, is used together with a three-optical-path temperature-controllable absorption cell, is combined with a multispectral fitting program, can provide systematic and accurate basic experimental data for atmospheric detection and laser atmospheric transmission research, and can also provide effective criteria for improvement of a water molecule spectral parameter theoretical calculation model CRB.
Description
Technical Field
The invention belongs to the technical field of forming dies, and particularly relates to a system for measuring a water vapor temperature-variable absorption spectrum and a using method thereof.
Background
Water vapor is an important component of the earth's atmosphere and has a broad absorption spectrum. The measurement of the water vapor temperature-changing absorption spectrum can obtain basic spectral parameters such as strong absorption line, pressure broadening coefficient, temperature dependence coefficient and the like of the water molecule absorption spectrum line, and the basic parameters have very important significance for researching the change of earth climate and weather and laser atmospheric transmission. Generally, the specific method for measuring the temperature-variable absorption spectrum of water vapor is as follows: introducing a water vapor gas sample into a sample cell, accurately controlling the pressure and the temperature of the sample in the sample cell, and then allowing a laser beam to pass through a light through hole in the sample cell to obtain an absorption signal of the sample; the pressure and the temperature of the sample in the sample cell are tuned and accurately controlled to obtain a plurality of groups of water vapor absorption signals under pressure and temperature points, and then the spectrum parameters of the measured target gas are obtained by fitting the spectrums through a linear fitting program. At present, two methods for measuring the temperature-variable absorption spectrum of water vapor molecules at home and abroad are mainly used: one is based on experimental measurement research of a Fourier transform spectrometer and a low-temperature sample cell; the other is a measurement method based on a tunable semiconductor laser and a low-temperature sample cell. The method based on the Fourier transform spectrometer can realize the measurement of the broad-band and high-frequency standard water vapor absorption spectrum.
However, the instrument function of a general fourier spectrometer is large and prone to change over time, which not only limits its resolution but also introduces errors in measuring the moisture absorption spectrum. The measurement method based on the tunable semiconductor laser can obtain the water vapor absorption spectrum with high resolution and high frequency standard, but the tuning range of the water vapor absorption spectrum is limited generally, and the measurement of a wide waveband range cannot be realized; in addition, when the water vapor absorption spectrum is measured at present, the pressure measurement error caused by water molecule adsorbability is difficult to overcome, and then the water vapor spectrum inversion error is easily caused.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a system for measuring a temperature-variable absorption spectrum of water vapor and a method for using the same, so as to solve the problems that the general fourier spectrometer proposed in the background art has a large instrument function and is easy to change along with the change of time, which not only limits the resolution ratio of the general fourier spectrometer and introduces errors when measuring the water vapor absorption spectrum, but also can obtain the water vapor absorption spectrum of a high resolution and high frequency standard based on the measurement method of the tunable semiconductor laser, but the tuning range of the general fourier spectrometer is limited, and the measurement of a wide band range cannot be realized.
In order to solve the technical problems, the invention adopts the technical scheme that: a system for measuring the temperature-varying absorption spectrum of water vapor comprises a difference frequency light source module, a difference frequency light source frequency monitoring and calibrating module, a data acquisition and processing module, a three-optical-path temperature-control multi-pass cell device and a gas distribution module;
the laser emitted by the YAG laser irradiates to a two-color beam combiner after passing through an optical isolator and a quarter wave plate, the laser emitted by the titanium sapphire laser is divided into three beams of laser after passing through two beam splitters, and the two beams of laser respectively irradiate to the inside of the difference frequency light source frequency monitoring and calibrating module for monitoring and calibrating;
the frequency monitoring and calibration module of the difference frequency light source comprises a wavelength meter, an etalon and an electro-optic modulator, wherein one laser beam of three laser beams which are divided by laser emitted by the titanium sapphire laser after passing through two beam splitters is monitored by the wavelength meter, information is transmitted to the data acquisition and processing module, the other laser beam sequentially passes through the etalon and the electro-optic modulator, a first-order second-order sideband generated by electro-optic modulation is combined with an etalon signal by the electro-optic modulator, the purpose of calibrating the laser emitted by the titanium sapphire laser is achieved, and meanwhile calibrated laser information is transmitted to the data acquisition and processing module;
the rest laser beam irradiates to a two-color beam combining mirror to be combined with the laser beam emitted by the Nd-YAG laser, and the combined beam light passes through a first converging lens to be in BaGa4Se7The nonlinear optical effect generated in the nonlinear optical crystal generates difference frequency light, and the difference frequency light is guided into the three-optical-path temperature-control multi-pass pool device 4 after passing through the second converging lens and the germanium sheet;
the three-optical-path temperature-control multi-pass cell device is internally provided with three sample cells, absorption signals generated by leading laser into the sample cells are transmitted to a data acquisition and processing module, wherein the sample cells are placed in a vacuum heat insulation cavity, the vacuum heat insulation cavity is also provided with a cooling mechanism, and the effect of blocking the sample cells from carrying out heat convection and heat conduction with the outside is achieved through the vacuum heat insulation cavity;
the gas distribution module is specifically a mixing container and is used for mixing water vapor and dry air in a fixed proportion, the mixing container is provided with a cooling mechanism and is used for pre-cooling mixed gas obtained by mixing the water vapor and the dry air, and after the mixed gas is pre-cooled to the temperature required by an experiment, the mixed gas is controlled to pass through a sample cell connected in series with the mixing container according to the set flow rate through a mass flow controller and a pressure controller which are arranged on the mixing container;
the data acquisition and processing module comprises a computer and three photoelectric detectors, wherein an integrated multispectral fitting program is compiled based on Labview software, laser of three sample pools of the three-optical-path temperature-control multi-pass pool device respectively passes through the photoelectric detectors, laser absorption information is transmitted into the computer, signals generated in the difference frequency light source frequency monitoring and calibrating module are collected, the frequency of the laser absorption information detected by the photoelectric detectors and transmitted into the computer is calibrated, the measured water vapor laser absorption information is processed through the multispectral fitting program, water vapor experimental spectral data when different linear models are fitted are obtained, a water vapor spectral parameter of a corresponding experimental waveband is calculated through a CRB theoretical model, a theoretical calculation result is compared with the experimental data, and the CRB theoretical model is optimized.
Preferably, cooling body specifically is spiral copper pipe and the dewar bottle with the copper pipe intercommunication, spiral copper pipe is provided with two sets ofly, winds respectively around sample cell outer wall and mixing vessel outer wall, the inside liquid nitrogen vapour that is equipped with constant pressure of dewar bottle, and controls through the high accuracy valve for control liquid nitrogen vapour constant voltage accomplishes the cooling action in independently flowing into the spiral copper pipe of sample cell outer wall or mixing vessel outer wall.
Preferably, the volume of the mixing container is 1 cubic meter, and the inside of the mixing container is provided with a moisture-proof adsorption stirrer and a pt100 type temperature sensor.
A system for measuring the temperature-variable absorption spectrum of water vapor and a using method thereof comprise the following steps:
s1, adjusting the air temperature of the air path part of the three-optical-path temperature-control multi-pass cell device to the temperature required by the experiment according to the temperature required by the experiment, then filling the sample cell with water vapor with partial pressure required by the experiment for environment presetting until the pressure is stable, configuring and generating mixed gas of the water vapor and dry air in a certain proportion in a mixing container of the gas distribution module, pre-cooling, and controlling the mixed gas to pass through the sample cells connected in series according to the set flow through a mass flow controller and a pressure controller after the mixed gas is pre-cooled to the temperature required by the experiment;
s2, generating mid-infrared difference frequency light by using a difference frequency light source module, simultaneously monitoring and calibrating laser emitted by the titanium gem laser by using the difference frequency light source frequency monitoring and calibrating module, transmitting information to a data acquisition and processing module, and simultaneously guiding the generated mid-infrared difference frequency light into three sample cells of a three-optical-path temperature-control multi-pass cell device filled with flowing mixed gas;
s3, the middle and outside difference frequency light with absorption information derived from the sample pool enters a data acquisition system for acquisition processing, and then the computer with a multispectral fitting program is used for processing to obtain the spectral parameters of the water vapor molecular absorption spectral line position, the pressure broadening coefficient and the temperature dependence coefficient and analyzing the information of the change relation of the absorption line shape along with the temperature.
Compared with the prior art, the invention has the following advantages:
1. the invention adopts novel BaGa4Se7The crystal is used as a frequency conversion device to generate 3-11 mu m mid-infrared difference frequency light, is used together with a three-optical-path temperature-controllable absorption cell, is combined with a multispectral fitting program, and solves the problem of spectral measurement caused by water molecule viscosity by presetting the required water vapor concentration in the absorption cell and measuring the water vapor in a flowing state; the high-fineness etalon and the electro-optical modulator are used together, so that the problem that a difference frequency light source with a high-frequency standard is obtained under the condition of not losing idle optical power is solved, a novel method for measuring the water vapor absorption spectrum under the condition of variable temperature is provided, systematic and accurate basic experimental data can be provided for the research of atmospheric detection and laser atmospheric transmission, and a linear model of water molecular absorption under the actual atmospheric condition can be perfected。
2. The invention can improve the frequency calibration precision of the pumping light source emitted by the titanium gem laser, and then can implant the high-frequency standard into the difference frequency output light by utilizing the frequency relation among the pumping light, the signal light and the idle light, thereby completing the calibration of the difference frequency light frequency on the premise of not losing the power of the high-frequency standard, and having important significance for obtaining the water vapor absorption spectrum with high frequency precision.
Drawings
FIG. 1 is a general principle framework of the present invention;
FIG. 2 is a schematic diagram of the difference frequency light generation process of the present invention;
FIG. 3 shows BaGa in the present invention4Se7A non-linear optical crystal object diagram;
FIG. 4 shows BaGa in the present invention4Se7An optical crystal transmittance map;
fig. 5 is a diagram of etalon to electro-optic modulator signal correspondence of the present invention, where the different numbers represent different sidebands.
Description of reference numerals:
1-difference frequency light source module; 2-difference frequency light source frequency monitoring and calibration module; 3-a data acquisition and processing module; 4-three light path temperature control multi-pass pool device; and 5-an air distribution module.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the present invention provides a technical solution: a system for measuring the temperature-varying absorption spectrum of water vapor comprises a difference frequency light source module 1, a difference frequency light source frequency monitoring and calibrating module 2, a data acquisition and processing module 3, a three-optical-path temperature-control multi-pass cell device 4 and a gas distribution module 5;
wherein the difference frequencyThe light source module 1 comprises an Nd-YAG laser and a titanium sapphire laser, laser emitted by the Nd-YAG laser irradiates to a two-color beam combining mirror after passing through an optical isolator and a quarter wave plate, the laser emitted by the titanium sapphire laser is divided into three beams of laser after passing through two beam splitting mirrors, one beam of laser irradiates to the two-color beam combining mirror and is combined with laser emitted by the Nd-YAG laser, and the combined beam passes through a first converging lens and is in a BaGa beam4Se7The generation of the nonlinear optical effect in the nonlinear optical crystal produces a difference-frequency light, wherein its frequency can be continuously tuned by continuously tuning the resonant cavity of the titanium-sapphire laser, as shown in fig. 2, the difference frequency is essentially the process of generating a new radiation light wave in the nonlinear optical crystal, i.e. the input frequencies are respectively ωpAnd ωsThe seed light source of (1) interacting in the nonlinear crystal to generate a frequency of ωi＝ωp–ωsThe new radiation of (2) is characterized in that in the process of generating the difference frequency, the behavior of the three-wave light vector is determined by a coupled wave differential equation, wherein the magnitude relation of the three-wave frequency is omegap>ωs>ωiAnd are respectively called pump light, signal light and idle light, in order to perform nonlinear optical frequency conversion efficiently, the signal light, the pump light and the idle light are required to satisfy the following two conditions in the nonlinear crystal:
conservation of energy; the signal light, the idle light and the pumping light wavelength are required to satisfy the relation:
conservation of momentum; the wave vectors of the three light waves are required to meet:
that is, the phase matching condition, if the wave vector directions of the three light waves participating in the interaction are the same (collinear), there are:
ωsns+ωini＝ωpnp (3)
the above formula is the phase matching condition of three-wave interaction under the collinear condition. There are two main types of phase matching: when the polarization directions of the signal light source and the difference frequency light source are consistent, the phase matching is called as I-type phase matching; if the two phases are different, II-type phase matching is performed;
the difference frequency light passes through a first convergent lens and BaGa4Se7The nonlinear optical crystal, the second converging lens and the germanium sheet are led into a three-optical-path temperature-control multi-pass cell device 4, as shown in fig. 3 and 4, BaGa is adopted4Se7As a nonlinear frequency conversion crystal, the crystal has the advantages of large light transmission range, high transmittance and the like, and is suitable for generating 3-11 mu m mid-infrared difference frequency laser.
In addition, the strong absorption spectral line of iodine in a 532nm waveband is taken as reference frequency, so that active iodine absorption frequency stabilization of the Nd-YAG laser is realized, frequency drift of the Nd-YAG laser is reduced, line width narrowing of difference frequency light is finally realized, and spectral resolution of a difference frequency light source is improved;
the two remaining laser beams respectively irradiate the inside of the difference frequency light source frequency monitoring and calibrating module 2 for monitoring and calibrating, the difference frequency light source frequency monitoring and calibrating module 2 comprises a wavelength meter, an etalon and an electro-optical modulator, one laser beam of three laser beams divided by laser beams emitted by the titanium sapphire laser after passing through two beam splitters is monitored by the wavelength meter, information is transmitted to the data acquisition and processing module 3, the other laser beam sequentially passes through the etalon and the electro-optical modulator, a first-order and second-order sideband generated by electro-optical modulation is combined with an etalon signal by the electro-optical modulator, the purpose of calibrating the laser emitted by the titanium sapphire laser is achieved, and meanwhile calibrated laser information is transmitted to the data acquisition and processing module 3;
in the difference frequency technology, the relationship between the wavelength of the signal light and the idle light and the wavelength of the pumping light emitted by the titanium sapphire laser satisfies the formula (1), and after the frequency of the signal light is stabilized, the wavelength lambda of the signal light can be considered to besIs constant, in which case the wavelength lambda of the pump light can be calibrated firstpThen, the wavelength λ of the difference frequency light is calculated according to the formula (1)iFurther completing the frequency calibration of the obtained absorption spectrum;
as shown in the figure, in the present invention, the electro-optical modulator is used with the etalon to complete the frequency calibration of the difference frequency light source, specifically: the part of the pump light which is divided by about 4 percent is incident to the electro-optical modulator, a first-order second-order sideband generated by the electro-optical modulation is combined with an etalon signal, namely, a transmission peak is inserted between transmission peaks of the etalon, the free spectral range FSR of the etalon is reduced, the frequency calibration precision is improved, the purpose of calibrating the pump light is achieved, and if the free spectral range FSR of the etalon is 1.5GHz, the fineness is 200, and the sideband distance of the electro-optical modulator is 312.3MHz, the frequency lambda of the calibrated pump light ispThe precision of the signal light is within 3MHz, and the frequency of the signal light after frequency stabilization is assumed to be vsAnd the frequency v of the difference frequency light can be obtained according to the difference frequency principlei＝νp-νsTheoretically, the error of the difference frequency light after calibration cannot exceed 3MHz, so that the calibration of the absorption spectrum frequency of water molecules is completed under the condition of not losing the power of the difference frequency light.
The three-optical-path temperature-control multi-pass cell device 4 is internally provided with three sample cells, absorption signals generated by leading laser into the sample cells are transmitted to a data acquisition and processing module 3, wherein the sample cells are placed in a vacuum heat insulation cavity, the vacuum heat insulation cavity is also provided with a cooling mechanism, the cooling mechanism is specifically a spiral copper tube and a Dewar flask communicated with the copper tube, the spiral copper tube is provided with two groups of spiral copper tubes which are respectively wound on the outer wall of the sample cells and the outer wall of a mixing container, liquid nitrogen vapor with constant pressure is filled in the Dewar flask and is controlled by a high-precision valve and is used for controlling the liquid nitrogen vapor to independently flow into the spiral copper tube on the outer wall of the sample cells or the outer wall of the mixing container to finish cooling, in order to obtain stable sample cell temperature, the liquid nitrogen vapor pressure in the Dewar flask needs to be kept constant, and the vapor pressure in the Dewar flask keeps liquid nitrogen cooling gas constantly flow into, therefore, the cold energy transferred to the wall of the sample cell makes the temperature of the sample cell reduced and the heat dissipated by the sample cell balanced, and the purpose of controlling the temperature of the sample cell is further achieved. According to the previous experimental result, the method can control the temperature of the sample to be measured within 0.5 ℃.
The two spherical reflectors of the sample cell and the wall of the glass cell are both made of high-conductivity oxygen-free copper with excellent thermal conductivity and are matched with the spiral copper pipe of the cooling mechanism to cool the mixed gas, so that the reflectors and the cell wall obtain good temperature uniformity, and the change of a light path caused by the deformation of a reflecting surface due to nonuniform temperature of the reflectors can be avoided; on the other hand, the temperature uniformity of the sample to be detected in the pool is facilitated.
The base of the sample cell is made of indium steel, so that the distance between the two spherical reflectors is prevented from changing when the temperature changes; in order to keep the temperature stability of the sample absorption cell, three sample cells can be placed into a vacuum heat insulation cavity to be the core part of the three-optical-path temperature-controllable multi-pass absorption cell device;
the gas distribution module 5 is specifically a mixing container, the volume of the mixing container is 1 cubic meter, a waterproof steam adsorption stirrer and a pt100 type temperature sensor are arranged in the mixing container and used for mixing water steam and dry air in a fixed proportion, the mixing container is provided with a cooling mechanism and used for pre-cooling mixed gas obtained by mixing the water steam and the dry air, and after the mixed gas is pre-cooled to the temperature required by an experiment, the mixed gas is controlled to pass through a sample cell connected in series with the mixing container according to a set flow rate through a mass flow controller and a pressure controller which are arranged on the mixing container;
the data acquisition and processing module 3 comprises a computer and three photodetectors which are based on Labview software and compile integrated multispectral fitting programs, laser of three sample pools of the three-optical-path temperature control multi-pass pool device 4 respectively passes through the photodetectors, information is transmitted into the computer, signals generated in the difference frequency light source frequency monitoring and calibrating module 2 are collected, the data acquisition is completed on line in real time by adopting the Labview software and compiling the integrated programs, different modules can be arranged in a split mode by adopting a tab mode, the program operation is convenient and orderly, and then the acquired data are processed by the multispectral fitting program, and the program can simultaneously fit absorption spectra acquired under multiple groups of different experimental conditions and comprises various linear models such as Gaussian, Lorentzian, Voigt, Galatry, Rautian, SDVP and the like. And analyzing and comparing fitting results of different linear models, inducing the characteristic that water molecule absorption changes along with temperature, and trying to optimize the linear model of the water molecule absorption spectral line under the atmospheric condition. And calculating the water vapor spectrum parameters of the corresponding experimental wave bands by adopting a CRB theoretical model, comparing the theoretical calculation result with the experimental data, and adjusting parameters such as intermolecular potential energy, convergence and the like in the CRB model so as to optimize the CRB theoretical model.
S1, adjusting the air temperature of the air path part of the three-optical-path temperature-control multi-pass cell device 4 to the temperature required by the experiment according to the temperature required by the experiment, then filling partial-pressure water vapor required by the experiment into the sample cell for environment presetting until the pressure is stable, then configuring mixed gas of the generated uniform water vapor and dry air in a certain proportion in the mixing container of the gas distribution module 5, pre-cooling, and controlling the mixed gas to pass through the sample cells connected in series according to the set flow rate through a mass flow controller and a pressure controller after the mixed gas is pre-cooled to the temperature required by the experiment;
s2, generating mid-infrared difference frequency light by using the difference frequency light source module 1, simultaneously monitoring and calibrating laser emitted by the titanium gem laser by the difference frequency light source frequency monitoring and calibrating module 2, transmitting information to the data acquisition and processing module 3, and simultaneously guiding the generated mid-infrared difference frequency light into three sample cells of the three-optical-path temperature-control multi-pass cell device 4 filled with flowing mixed gas;
s3, the middle and outside difference frequency light with absorption information derived from the sample pool enters a data acquisition system for acquisition processing, and then the computer with a multispectral fitting program is used for processing to obtain the spectral parameters of the water vapor molecular absorption spectral line position, the pressure broadening coefficient and the temperature dependence coefficient and analyzing the information of the change relation of the absorption line shape along with the temperature.
The invention is based on BaGa4Se7The nonlinear optical crystal is characterized in that a set of difference frequency light source with a mid-infrared wavelength of 3-11 mu m, a narrow line width and a high frequency standard is established, and the absorption spectrum characteristic of water vapor molecules under a temperature change condition is researched, so that accurate spectrum number is provided for actual atmospheric engineering applicationAccording to the method, the change rule of the water vapor absorption line shape along with the temperature is discussed, and an effective criterion is provided for the improvement of a CRB theoretical model.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (5)
1. A system for measuring the temperature-variable absorption spectrum of water vapor is characterized in that: the device comprises a difference frequency light source module (1), a difference frequency light source frequency monitoring and calibrating module (2), a data acquisition and processing module (3), a three-optical-path temperature control multi-pass cell device (4) and a gas distribution module (5);
the laser emitted by the YAG laser irradiates to a two-color beam combiner after passing through an optical isolator and a quarter wave plate, the laser emitted by the titanium sapphire laser is divided into three beams of laser after passing through two beam splitters, and the two beams of laser respectively irradiate to the inside of the difference frequency light source frequency monitoring and calibrating module (2) for monitoring and calibrating;
the frequency difference light source frequency monitoring and calibrating module (2) comprises a wavelength meter, an etalon and an electro-optic modulator, wherein laser emitted by the titanium sapphire laser passes through two beam splitters and then is divided into three laser beams, one laser beam is monitored by the wavelength meter, information is transmitted to the data acquisition and processing module (3), the other laser beam sequentially passes through the etalon and the electro-optic modulator, a first-order second-order sideband generated by electro-optic modulation is combined with an etalon signal by the electro-optic modulator, the purpose of calibrating the laser emitted by the titanium sapphire laser is achieved, and meanwhile calibrated laser information is transmitted to the data acquisition and processing module (3);
the rest laser beam irradiates to a two-color beam combining mirror to be combined with the laser beam emitted by the Nd-YAG laser, and the combined light passes through a first converging lens to be in BaGa4Se7Nonlinear optical effect occurs in the nonlinear optical crystal to generate difference frequency light, and the difference frequency light is guided into the three-optical-path temperature-control multi-pass pool device (4) after passing through the second converging lens and the germanium sheet;
the three-optical-path temperature-control multi-pass cell device (4) is internally provided with three sample cells, absorption signals generated by leading laser into the sample cells are transmitted to a data acquisition and processing module (3), wherein the sample cells are placed in a vacuum heat insulation cavity, the outer wall of each sample cell is also provided with a cooling mechanism, and the effect of blocking the sample cells from carrying out heat convection and heat conduction with the outside is achieved through the vacuum heat insulation cavity;
the gas distribution module (5) is specifically a mixing container and is used for configuring water vapor and dry air in a fixed proportion, the mixing container is provided with a cooling mechanism and is used for pre-cooling mixed gas obtained by mixing the water vapor and the dry air, and after the mixed gas is pre-cooled to the temperature required by an experiment, the mixed gas is controlled by a mass flow controller and a pressure controller which are arranged on the mixing container to pass through a three-optical-path temperature-control multi-pass cell device (4) which is connected with the mixing container in series according to the set flow;
the data acquisition and processing module (3) comprises a computer and three photoelectric detectors which are based on an integrated multispectral fitting program compiled by Labview software, laser of three sample pools passing through the three-optical-path temperature-control multi-pass pool device (4) respectively transmits laser absorption information to the interior of the computer through the photoelectric detectors, meanwhile, the signals generated in the difference frequency light source frequency monitoring and calibrating module (2) are collected, the frequency of the laser absorption information detected by the photoelectric detector and transmitted to the computer is calibrated, and processing the measured water vapor laser absorption information through a multispectral fitting program to obtain water vapor experimental spectrum data when different linear models are fitted, calculating water vapor spectrum parameters of corresponding experimental wave bands by adopting a CRB theoretical model, and comparing theoretical calculation results with the experimental data to optimize the CRB theoretical model.
2. The system for measuring the temperature-varying absorption spectrum of water vapor according to claim 1, wherein the cooling mechanism is specifically a spiral copper tube and a dewar flask communicated with the copper tube, the spiral copper tube is provided with two groups which are respectively wound on the outer wall of the sample cell and the outer wall of the mixing container, liquid nitrogen vapor with constant pressure is filled in the dewar flask, and the liquid nitrogen vapor is controlled by a high-precision valve and is used for controlling the liquid nitrogen vapor to independently flow into the spiral copper tube on the outer wall of the sample cell or the outer wall of the mixing container at constant pressure to complete the cooling function.
3. The system for measuring water vapor temperature-changing absorption spectrum according to claim 1, wherein the volume of said mixing container is 1 cubic meter, and said mixing container has a water vapor-proof adsorption stirrer and a pt100 type temperature sensor inside.
4. The system for measuring water vapor temperature-changing absorption spectrum according to claim 1, wherein the base of the sample cell is made of indium steel, and the two spherical mirrors and the glass cell wall are made of oxygen-free copper with high thermal conductivity and high conductivity.
5. The use method of the system for measuring the temperature-varying water vapor absorption spectrum according to any one of claims 1 to 4, comprising the following steps:
s1, adjusting the air temperature of the air path part of the three-optical-path temperature-control multi-pass cell device (4) to the temperature required by the experiment according to the temperature required by the experiment, then filling the water vapor with partial pressure required by the experiment into the sample cell for environment presetting until the pressure is stable, configuring mixed gas of the water vapor and dry air which are generated in a certain proportion in the mixing container of the gas distribution module (5), pre-cooling, and controlling the mixed gas to pass through the sample cells which are connected in series according to the set flow rate through the mass flow controller and the pressure controller after the mixed gas is pre-cooled to the temperature required by the experiment;
s2, generating mid-infrared difference frequency light by using the difference frequency light source module (1), simultaneously monitoring and calibrating laser emitted by the titanium gem laser by using the difference frequency light source frequency monitoring and calibrating module (2), transmitting information to the data acquisition and processing module (3), and simultaneously guiding the generated mid-infrared difference frequency light into three sample cells of a three-optical-path temperature-control multi-pass cell device (4) filled with flowing mixed gas;
s3, the middle and outside difference frequency light with absorption information derived from the sample pool enters a data acquisition system for acquisition processing, and then the computer with a multispectral fitting program is used for processing to obtain the spectral parameters of the water vapor molecular absorption spectral line position, the pressure broadening coefficient and the temperature dependence coefficient and analyzing the information of the change relation of the absorption line shape along with the temperature.
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