CN116148187A - Photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement - Google Patents
Photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement Download PDFInfo
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
- G01N21/03—Cuvette constructions
- G01N21/0303—Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
- G01N2021/1704—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
- G01N2021/396—Type of laser source
- G01N2021/399—Diode laser
Abstract
The invention relates to an optical acoustic spectrum gas detection system based on open differential resonant cavity optical path enhancement, which comprises: the system comprises a tunable laser light source module, a first optical range-extending module, an open differential T-shaped photoacoustic resonant cavity, a second optical range-extending module and a photoacoustic signal acquisition and central processing module, wherein the tunable laser light source module is used for generating incident light modulated by a main path wavelength; the first optical range-extending module is arranged on the light path of the tunable laser source module and is arranged on one side of the open differential T-shaped photoacoustic resonant cavity; the second optical range-extending module is arranged on the other side of the open differential T-shaped photoacoustic resonant cavity; the photoacoustic signal acquisition and central processing module is connected with the open differential T-shaped photoacoustic resonant cavity. In the detection system, the open differential T-shaped photoacoustic resonant cavity realizes multiple multiplexing of light energy, resonance enhancement and differential denoising, so that the detection system has the advantages of no need of sampling, small loss, high Q value, firm structure, long-distance operation, safe use and the like.
Description
Technical Field
The invention belongs to the technical field of trace gas optical nondestructive detection, and particularly relates to an optical acoustic spectrum gas detection system based on open differential resonant cavity optical path enhancement.
Background
The nondestructive on-line detection of trace gas has important research value and application significance in the fields of atmosphere monitoring, industrial safety, medical diagnosis and the like. Industrial production activities have caused great damage to the natural environment, most typically the formation of the greenhouse effect, CO 2 And CH (CH) 4 The method is a main greenhouse gas, and monitoring the component change of the greenhouse gas in the atmosphere can be used for researching climate change; in addition, monitoring the emission concentration of pollutant gases such as nitrogen oxides, sulfides, carbon monoxide and the like is also a powerful means of protecting the atmospheric environment. The detection of toxic and harmful gases mainly aims at industrial waste gas emission and industrial process leakage, such as hydrogen sulfide, hydrogen chloride, hydrogen cyanide and the like, and the content of the gases is extremely low, but once leakage occurs, the consequences are not considered. The monitoring of volatile organic compounds has attracted long attention, and VOCs have hundreds of volatile organic compounds, wherein a considerable part of the volatile organic compounds are harmful to human health or to ecological environment, and the characteristic of sample injection in the traditional chromatographic method determines that the detection time is long, so that continuous online monitoring is impossible. In order to improve the atmospheric environment, scientific monitoring and accurate assessment of the emission of various areas and industries in China are required, and the emission reduction effect is achieved.
The traditional gas detection method mainly adopts a chemical method, needs sample sampling and processing, is easy to be interfered by other gases, and can not meet the requirements of on-site measurement in parameters such as measurement sensitivity, measurement range, response time and the like. At present, the photoacoustic detection technology is widely used for trace gas detection due to the advantages of high sensitivity, high detection speed and the like.
To improve the detection sensitivity, the existing photoacoustic detection apparatus often adopts a multi-channel cell to increase the absorption optical path, for example, a White cell and a Herriott Chi Laiti generation single-channel cell, but these multi-channel cells are usually large in size, difficult to calibrate the optical path, and unfavorable for miniaturization. In addition, the existing closed photoacoustic cell needs to sample gas, control the flow of the gas to be measured, has complicated inflation and purification steps, needs additional devices, has high cost and is inconvenient for practical operation.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a photoacoustic spectrometry gas detection system based on optical path enhancement of an open differential resonant cavity. The technical problems to be solved by the invention are realized by the following technical scheme:
the embodiment of the invention provides a photoacoustic spectrometry gas detection system based on open differential resonant cavity optical path enhancement, which comprises the following components: the device comprises a tunable laser light source module, a first optical range-extending module, an open differential T-shaped photoacoustic resonant cavity, a second optical range-extending module and a photoacoustic signal acquisition and central processing module, wherein,
the tunable laser light source module is used for generating incident light modulated by main path wavelength;
the first optical range-extending module is arranged on the optical path of the tunable laser source module and on one side of the open differential T-shaped photoacoustic resonant cavity, and is used for enabling the incident light to enter the open differential T-shaped photoacoustic resonant cavity at a certain longitudinal deflection angle and generating first reflected light for multiple times;
the second optical range-extending module is arranged on the other side of the open differential T-shaped photoacoustic resonant cavity and is used for generating second reflected light for a plurality of times;
the open differential T-shaped photoacoustic resonant cavity is used for carrying out resonance enhancement and differential amplification on photoacoustic signals generated by absorbing the incident light, the first reflected light and the second reflected light by the gas to be detected entering the cavity, so as to obtain output photoacoustic signals;
the photoacoustic signal acquisition and central processing module is connected with the open differential T-shaped photoacoustic resonant cavity and is used for receiving the output photoacoustic signal and processing the output photoacoustic signal so as to realize qualitative and quantitative detection of the gas to be detected.
In one embodiment of the invention, the tunable laser light source module comprises a tunable laser diode light source and a signal generator, wherein,
the tunable laser diode light source is used for generating incident laser;
the signal generator is connected with the tunable laser diode light source and is used for carrying out wavelength modulation on the incident laser by utilizing current of superposition of sine waves and triangular waves so as to generate the incident light for exciting the gas to be detected.
In one embodiment of the present invention, the first optical range module comprises a plane mirror and a collimating mirror, wherein,
the collimating mirror is embedded in the plane mirror and is arranged on the light path of the tuning laser light source module;
the collimating mirror is used for enabling the incident light to enter the open differential T-shaped photoacoustic resonant cavity at a certain longitudinal deflection angle, and the plane mirror is used for generating first reflected light for multiple times.
In one embodiment of the invention, the second optical range extender module includes a concave mirror for generating the second reflected light a plurality of times.
In one embodiment of the invention, the plane mirror adopts BK7 glass, the half aperture is 2.9-3.1mm, and the thickness is 1.9-2.1mm;
the collimating lens adopts BK7 glass, the half aperture is 0.05-0.25mm, and the deflection angle is 27-31 degrees of x-axis deflection;
the collimating mirror is positioned at a position 1.9-2.1mm above the y axis of the center of the plane mirror;
the concave mirror adopts BK7 glass, the half aperture is 2.9-3.1mm, the thickness is 1.9-2.1mm, and the curvature radius is 49.9-50.1mm;
the distance between the concave mirror and the plane mirror is 21.9-22.1mm.
In one embodiment of the invention, the open differential T-photoacoustic resonator comprises a first buffer chamber, a second buffer chamber, an absorber chamber, a first resonant chamber and a second resonant chamber, wherein,
the first buffer cavity is positioned at one end part of the absorption cavity, the second buffer cavity is positioned at the other end part of the absorption cavity, the side surfaces of the first buffer cavity and the second buffer cavity are of an open structure, and the first buffer cavity and the second buffer cavity are distributed in a bilateral symmetry manner;
the first resonant cavity and the second resonant cavity are vertically and symmetrically arranged above the absorption cavity, form a differential double-resonance T-shaped structure with the absorption cavity, and are connected with the photoacoustic signal acquisition and central processing module;
the first buffer cavity and the second buffer cavity are used for enabling the gas to be tested to enter the absorption cavity and changing the resonance condition of the acoustic boundary;
the absorption cavity is used for enabling the gas to be detected to absorb the incident light, the first reflected light and the second reflected light so as to generate the photoacoustic signal;
the first resonant cavity and the second resonant cavity are used for forming standing wave acoustic signals with the same amplitude and opposite phases, so that the photoacoustic signals are subjected to resonance enhancement and differential amplification, and the output photoacoustic signals are obtained.
In one embodiment of the present invention, the first buffer chamber, the second buffer chamber, the absorption chamber, the first resonant chamber and the second resonant chamber all adopt a cylindrical structure.
In one embodiment of the invention, the diameters of the first buffer chamber and the second buffer chamber are larger than the diameters of the absorption chamber, the first resonance chamber and the second resonance chamber.
In one embodiment of the invention, the diameter of the first and second resonant cavities is smaller than the diameter of the absorption cavity.
In one embodiment of the invention, the photoacoustic signal acquiring and central processing module comprises an acoustic wave detecting and acquiring module, a lock-in amplifier and a signal processor, wherein,
the sound wave detection and acquisition module is connected with the open differential T-shaped photoacoustic resonant cavity and is used for converting the output photoacoustic signal into an electric signal;
the phase-locked amplifier is connected with the tunable laser light source module and the sound wave detection and acquisition module and is used for processing the electric signals to adjust second harmonic signals with the same resonance frequency as the open differential T-shaped photoacoustic resonant cavity so as to obtain processed electric signals;
the signal processor is connected with the phase-locked amplifier and is used for storing and analyzing the processed electric signals so as to realize qualitative and quantitative detection of the gas to be detected.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the gas detection system, the first optical range-extending module and the second optical range-extending module are respectively arranged on two sides of the open differential T-shaped photoacoustic resonant cavity and used for generating reflected light for multiple times, so that the light propagation direction can be changed, the length of a light path can be increased, the gas detection sensitivity can be improved, and the miniaturization of the detection system can be realized.
2. The gas detection system adopts the structure of the open type photoacoustic resonant cavity, an optical lens is not needed as a window, optical power loss is greatly reduced, a gas sampling and airflow control device is not needed, a complex procedure of inflating/purifying a traditional closed type sensor is avoided, instrument cost and operation difficulty are reduced, and long-time high-precision online detection of trace gas is facilitated.
3. In the gas detection system, the end parts of the first buffer cavity and the second buffer cavity adopt an open structure, on one hand, the buffer cavities do not need to be provided with optical windows made of materials such as calcium fluoride, zinc selenide and the like, so that the optical power loss is greatly reduced; on the other hand, the side surface of the closed type photoacoustic cell does not have an acoustic wall boundary, the absorption optical path is enhanced by matching with the reflecting mirror, an optical window background signal is not generated, the problem that the existing closed type photoacoustic cell generates coherent noise due to interaction of an optical window and a modulated laser beam is avoided, acoustic boundary conditions are changed, and the sensitivity and accuracy of gas detection are improved.
4. In the gas detection system, the opposite-phase photoacoustic signals generated by the first resonant cavity and the second resonant cavity are subjected to differential processing, so that the same-phase background noise can be eliminated, the different-phase photoacoustic signals can be amplified by 2 times, and the sensitivity and the accuracy of gas detection are improved.
5. In the detection system, the open differential T-shaped photoacoustic resonant cavity realizes the multiple multiplexing of light energy, resonance enhancement and differential denoising, so that the detection system has the advantages of no need of sampling, small loss, high Q value, firm structure, long-distance operation, safe use and the like.
Drawings
Fig. 1 is a schematic structural diagram of a photoacoustic spectrometry gas detection system based on open differential resonant cavity optical path enhancement according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of another photoacoustic spectroscopy gas detection system based on open differential resonator optical path enhancement according to an embodiment of the present invention;
FIG. 3 is a schematic view of an optimized combination of concave mirrors and planar mirrors and a ray trace according to an embodiment of the present invention;
FIGS. 4 a-4 b are schematic illustrations of irradiance of reflected light from the inner surface of a concave mirror and a flat mirror according to embodiments of the present invention;
fig. 5 is a schematic structural diagram of an amplification type differential T-type photoacoustic resonator according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but embodiments of the present invention are not limited thereto.
Example 1
Referring to fig. 1, fig. 1 is a schematic structural diagram of a photoacoustic spectrometry gas detection system based on open differential resonator optical path enhancement according to an embodiment of the present invention. The gas detection system comprises a tunable laser light source module 1, a first optical range-extending module 2, an open differential T-shaped photoacoustic resonant cavity 3, a second optical range-extending module 4 and a photoacoustic signal acquisition and central processing module 5. Wherein the tunable laser light source module 1 is used for generating main-path wavelength modulated incident light. The first optical extended-range module 2 is connected with the tunable laser light source module 1 and is arranged on one side of the open differential T-shaped photoacoustic resonant cavity 3, and is used for enabling incident light to enter the open differential T-shaped photoacoustic resonant cavity 3 at a certain longitudinal deflection angle and generating first reflected light for multiple times. The second optical range-extending module 4 is disposed on the other side of the open differential T-type photoacoustic resonator 3 and is used for generating second reflected light multiple times. The open differential T-shaped photoacoustic resonant cavity 3 is used for carrying out resonance enhancement and differential amplification on a photoacoustic signal generated by the first reflected light and the second reflected light absorbed by the gas to be detected entering the cavity, so as to obtain an output photoacoustic signal. The photoacoustic signal acquisition and central processing module 5 is connected with the open differential T-shaped photoacoustic resonant cavity 3 and is used for receiving and processing output photoacoustic signals so as to realize qualitative and quantitative detection of the gas to be detected.
Specifically, the first optical range-extending module 2 and the second optical range-extending module 4 together form an optical range-extending combination, which is used for generating reflected light for multiple times, increasing the absorption optical path, and increasing the acoustic signal generated by the absorption light intensity of the gas to be measured along with the increase of the optical path.
The gas detection system of this embodiment is used for producing the reflected light many times through setting up first optics increase journey module and second optics increase journey module respectively in open differential T type optoacoustic resonant cavity's both sides, can change the direction of light propagation, increases the length of light path to improve gas detection sensitivity, be favorable to realizing detecting system's miniaturization.
Specifically, the open differential T-type photoacoustic resonator 3 has a ventilation window to allow a gas to be measured to enter the cavity, and then irradiates the gas to be measured in the cavity with a light beam including incident light, first reflected light, and second reflected light to generate a photoacoustic signal, and performs resonance enhancement and differential amplification on the photoacoustic signal to obtain an output photoacoustic signal.
The gas detection system of the embodiment adopts the structure of the open type photoacoustic resonant cavity, an optical lens is not needed as a window, optical power loss is greatly reduced, meanwhile, a gas sampling and airflow control device is not needed, the complex procedure of inflating/purifying a traditional closed type sensor is avoided, the instrument cost and the operation difficulty are reduced, and the long-time high-precision online detection of trace gas is more facilitated.
Specifically, the signal processing module 5 is configured to convert the output photoacoustic signal into an electrical signal, and process the electrical signal to complete detection of the gas to be detected.
Referring to fig. 2, fig. 2 is a schematic structural diagram of another photoacoustic spectroscopy gas detection system based on open differential resonator optical path enhancement according to an embodiment of the present invention. In a specific embodiment, the tunable laser light source module 1 comprises a tunable laser diode light source 11 and a signal generator 12. Wherein a tunable laser diode light source 11 is used for generating an incident laser light. The signal generator 12 is connected to the tunable laser diode light source 11 for wavelength modulating the incident laser light with a current of sine wave and triangular wave superimposed to generate incident light that excites the gas to be measured.
Specifically, the tunable laser diode light source 11 is mainly used for providing a laser with an adjustable wavelength, and the wavelength of the laser can be adjusted according to the main absorption peak of the gas to be measured, that is, the wavelength of the laser needs to correspond to the main absorption peak of the gas to be measured. The signal generator 12 modulates the laser wavelength generated by the tunable laser diode light source 11 at a certain frequency, the modulation frequency is half of the eigenmode frequency of the open differential T-type photoacoustic resonator, and the incident light which can be directly incident into the open differential T-type photoacoustic resonator 3 can be obtained after the modulation is completed.
Referring to fig. 3 and fig. 4 a-fig. 4b, fig. 3 is a schematic view of an optimized combination structure of a concave mirror and a plane mirror and a ray tracing diagram of a mirror provided by an embodiment of the present invention, fig. 4 a-fig. 4b are schematic views of irradiance of reflected light on an inner surface of the concave mirror and an inner surface of the plane mirror provided by an embodiment of the present invention, a light spot of fig. 4a is a irradiance map of reflected light on the surface of the concave mirror, a light spot of fig. 4b is an irradiation intention of reflected light on the inner surface of the plane mirror, and a number of light spots of irradiance in fig. 4a and 4b indicates a number of reflections of incident laser between the two mirrors. In a specific embodiment, the first optical range module 2 includes a plane mirror 21 and a collimator mirror 22. The collimating mirror 22 is embedded in the plane mirror 21 and is arranged on the optical path of the tunable laser source module 1, and is connected with the tunable laser source module 1 through an optical fiber; the collimator lens 22 is used for making incident light enter the open differential T-type photoacoustic resonator 3 at a certain longitudinal deflection angle, and the plane mirror 21 is used for generating first reflected light multiple times. The second optical add-on module 4 comprises a concave mirror 41, the concave mirror 41 being adapted to generate a second reflected light a plurality of times.
Specifically, the plane mirror may be a gold-plated plane mirror, and the concave mirror may be a gold-plated concave mirror. The plane mirror, the collimating mirror and the concave mirror are combined together to form a reflecting mirror combination for generating reflected light for a plurality of times. The collimator lens 22 is used to make incident light enter the open differential T-type photoacoustic resonator 3 at a longitudinal deflection angle that is the same as the deflection angle of the collimator lens 22. By optimizing the diameters of the concave mirror and the plane mirror, the focal length of the concave mirror and the deflection angle of the collimator, the light beam can realize multiple reflection on the plane mirror and the concave mirror as shown in fig. 3, so that the absorption optical path is enhanced, and the multiple reflection only occurs in the open differential T-shaped photoacoustic resonant cavity, namely the buffer cavity and the absorption cavity, so that the side wall absorption can be effectively inhibited and the influence of coherent noise can be eliminated.
In one embodiment, the flat mirror 21 is BK7 glass with a half-aperture of 2.9-3.1mm and a thickness of 1.9-2.1mm. The collimating lens 22 adopts BK7 glass, the half aperture is 0.05-0.25mm, and the deflection angle is 27-31 degrees of x-axis deflection. The collimator lens 22 is located 1.9-2.1mm above the center y-axis of the plane mirror 21. The concave mirror 41 is made of BK7 glass, has a half aperture of 2.9-3.1mm, a thickness of 1.9-2.1mm, and a radius of curvature of 49.9-50.1mm. The distance between the concave mirror 41 and the plane mirror 21 is 21.9-22.1mm.
Preferably, the diameter of the concave mirror and the plane mirror, the focal length of the concave mirror, the deflection angle of the collimating mirror, the interval distance of the reflecting mirrors and other parameter combinations are optimized through a genetic algorithm, and after optimization, the plane mirror 21 adopts BK7 glass, the half aperture is 3mm, and the thickness is 2mm; the collimating lens 22 adopts BK7 glass, the half aperture is 0.15mm, and the deflection angle is 29 degrees of x-axis deflection; the collimating mirror 22 is positioned 2mm above the y axis of the center of the plane mirror 21; the concave mirror 41 is made of BK7 glass, has a half aperture of 3mm, a thickness of 2mm and a radius of curvature of 50mm; the distance between the concave mirror 41 and the plane mirror 21 is 22mm. Under the combination of the parameters, the detection system reaches the maximum optical path increment, 31 reflections are achieved on the plane mirror, and the enhancement effect of 32 reflections is achieved on the concave mirror, as shown in fig. 4 a-4 b, and the multiple light spots in fig. 4a and 4b represent that light is reflected between the plane mirror and the concave mirror for multiple times.
It should be noted that the first optical range-extending module 2 and the second optical range-extending module 4 are not limited to the above-mentioned structure, and may be any other type of reflecting mirror combination, for example, the first optical range-extending module 2 may be any one of a right angle prism and a roof prism, and the second optical range-extending module 4 may be any other one of a right angle prism and a roof prism.
Referring to fig. 5, fig. 5 is a schematic structural diagram of an amplification type differential T-type photoacoustic resonator according to an embodiment of the present invention. In a specific embodiment, the open differential T-shaped photoacoustic resonator 3 is a dual-resonant differential T-shaped photoacoustic resonator, including a first buffer chamber 31, a second buffer chamber 32, an absorber chamber 33, a first resonant chamber 34, and a second resonant chamber 35. The first buffer chamber 31 is located at one end of the absorption chamber 33, the second buffer chamber 32 is located at the other end of the absorption chamber 33, the sides of the first buffer chamber 31 and the second buffer chamber 32 are all in an open structure, and the first buffer chamber 31 and the second buffer chamber 32 are distributed symmetrically. The first resonant cavity 34 and the second resonant cavity 35 are vertically and symmetrically arranged above the absorption cavity 33, form a differential double-resonance T-shaped structure with the absorption cavity 33, and are connected with the photoacoustic signal acquisition and central processing module 5. The first buffer chamber 31 and the second buffer chamber 32 are used to let the gas to be measured into the absorption chamber 33 and change the resonance condition of the acoustic boundary; the absorption cavity 33 is used for enabling the gas to be measured to absorb the incident light, the first reflected light and the second reflected light to generate a photoacoustic signal; the first resonant cavity 34 and the second resonant cavity 35 are used for forming standing wave acoustic signals with the same amplitude and opposite phases, so that the photoacoustic signals are subjected to resonance enhancement and differential amplification, and output photoacoustic signals are obtained.
Specifically, the first buffer chamber 31 and the second buffer chamber 32 are disposed at two ends of the absorption chamber 33, the sides of the first buffer chamber 31 and the second buffer chamber 32 adopt an open structure, no optical lens is used as an incident window, and ventilation windows are disposed at two ends and are communicated with the external air environment, so that the air to be measured enters the resonant cavity; and the first buffer chamber 31 and the second buffer chamber 32 are symmetrically distributed left and right. The first buffer chamber 31 and the second buffer chamber 32 are used to change the resonance condition of the acoustic boundary.
The absorption cavity 33 is located in the middle of the lower part of the open photoacoustic resonator, absorbs incident light and produces a photoacoustic effect, and may act as a cavity for multiple reflections of light.
The first resonant cavity 34 and the second resonant cavity 35 are located above the absorption cavity 33, are distributed symmetrically left and right, and form a T-shaped structure with the absorption cavity 33. The first resonant cavity 34 and the second resonant cavity 35 are used for generating standing wave photoacoustic signals with equal amplitude and opposite phases, and outputting the photoacoustic signals after resonance enhancement and differential amplification.
Specifically, the gas detection system with the open differential T-shaped photoacoustic resonant cavity 3 is placed in the atmosphere of the gas to be detected, and the gas to be detected can enter the photoacoustic resonant cavity through the ventilation windows at the two ends of the absorption cavity, so that the inside of the open differential T-shaped photoacoustic resonant cavity 3 is filled with the atmosphere. The incident light enters the absorption cavity 33 of the photoacoustic resonant cavity at a certain longitudinal deflection angle and is reflected in the absorption cavity 33, the first buffer cavity 31 and the second buffer cavity 32 for multiple times, so that the gas to be tested periodically absorbs light and relaxes, photoacoustic signals are generated, the size of the photoacoustic signals is in linear relation with the concentration of the gas to be tested, and the intensity of the light absorbed by the gas in the open type T-shaped photoacoustic resonant cavity 33 is increased along with the increase of the optical path, so that acoustic signal enhancement is generated. Further, the double resonant cavities perform resonance increase and differential amplification on the photoacoustic signals generated by the absorption cavities, and then the processed photoacoustic signals are output to the signal processing module to demodulate second harmonic signals.
According to the embodiment, the open differential T-shaped photoacoustic resonant cavity is adopted, on one hand, due to the fact that the open buffer cavity is added, the structure of the open resonant photoacoustic cell is formed, an optical window made of materials such as calcium fluoride and zinc selenide is not needed to be placed, and optical power loss is greatly reduced; on the other hand, the side surface of the buffer cavity is not provided with an acoustic wall boundary, the absorption optical path enhancement is realized by matching with the reflector combination, an optical window background signal can not be generated, an optical lens is not needed to be used as a window, the problem that the existing closed type photoacoustic cell generates coherent noise due to interaction of the optical window and a modulated laser beam is avoided, acoustic boundary conditions are changed, external noise is isolated, and the sensitivity and accuracy of gas detection are improved.
In the embodiment, the double resonant cavities are adopted to generate the photoacoustic signals with the same amplitude and opposite phases, the in-phase environmental noise after differential processing is eliminated, the opposite-phase photoacoustic signals of the target gas are amplified by 2 times, the sensitivity and the accuracy of gas detection are improved, and the detection signal-to-noise ratio is improved.
The embodiment adopts the open differential T-shaped photoacoustic resonant cavity as the resonant photoacoustic cell to realize light energy multiplexing, resonance enhancement and differential denoising, so that the detection system has the advantages of no need of sampling, small loss, high Q value, firm structure, long-distance operation, safe use and the like.
In one embodiment, the first buffer chamber 31, the second buffer chamber 32, the absorption chamber 33, the first resonant chamber 34, and the second resonant chamber 35 each have a cylindrical structure. The diameters of the first buffer chamber 31 and the second buffer chamber 32 are larger than the diameters of the absorption chamber 33, the first resonance chamber 34, and the second resonance chamber 35. The diameter of the first and second resonant cavities 34, 35 is smaller than the diameter of the absorption cavity 33.
In a specific embodiment, the photoacoustic signal acquisition and central processing module 5 is disposed on top of the open differential T-shaped photoacoustic resonant cavity 3, and includes an acoustic wave detection and acquisition module 51, a lock-in amplifier 52, and a signal processor 53. The acoustic wave detection and acquisition module 51 is connected to the open differential T-type photoacoustic resonant cavity 3, specifically, connected to the top of the first resonant cavity 34 and the second resonant cavity 35, and is used for converting the output photoacoustic signal into an electrical signal. The lock-in amplifier 52 is connected to the tunable laser light source module 1 and the acoustic wave detection and acquisition module 51, and is configured to process the electrical signal to adjust a second harmonic signal having the same resonant frequency as the open differential T-type photoacoustic resonator 3, so as to obtain a processed electrical signal. Specifically, the lock-in amplifier 52 is connected to the signal generator 12 and the acoustic wave detecting and collecting module 51, and the signal generator 12 is used for providing a reference signal. The signal processor 53 is connected to the lock-in amplifier 52, and is used for storing and analyzing the processed electric signals to realize qualitative and quantitative detection of the gas to be detected.
The detection method of the photoacoustic spectrometry gas detection system based on the open differential resonant cavity optical path enhancement comprises the following steps: the open differential T-shaped photoacoustic resonator 3 is placed in a measurement environment such that the open differential T-shaped photoacoustic resonator 3 is filled with ambient gas. The tunable laser diode light source 11 generates laser light with a wavelength corresponding to the main absorption peak of the trace gas to be measured, and then the signal generator 12 is used for modulating the light intensity of the laser light at a certain frequency, wherein the modulation frequency is half of the eigenmode frequency of the open differential T-shaped photoacoustic resonant cavity 3. The modulated laser is incident into an absorption cavity of the open differential T-shaped photoacoustic resonant cavity 3 at a certain longitudinal deflection angle and is reflected in the absorption cavity for multiple times, so that the gas to be measured periodically absorbs light and relaxes, a photoacoustic signal is generated, and the size of the photoacoustic signal and the concentration of the gas to be measured are in a linear relation. The photoacoustic signal is subjected to resonance amplification and differential processing by the first and second resonant cavities 34 and 35, and then detected and converted into an electrical signal by the acoustic wave detection and acquisition module 51 located at the antinode of the photoacoustic signal. The lock-in amplifier 52 performs a cross-correlation operation and low-pass filtering on the electric signal to filter out an interference signal having a frequency different from that of the photoacoustic signal. The electric signal processed by the lock-in amplifier 52 is transmitted to the signal processor 53, stored by the signal processor 53 and analyzed and processed by the signal processor, thus completing the high-precision on-line detection of trace gas.
The gas detection system based on the open differential T-shaped photoacoustic resonant cavity enhanced by the multiple reflection light does not need an airflow control device, avoids the complex procedure of inflating/purifying the traditional closed sensor, reduces the instrument cost and the operation difficulty, and is more beneficial to long-time high-precision online detection of trace gas.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (10)
1. An open differential resonator optical path enhancement-based photoacoustic spectroscopy gas detection system, comprising: the device comprises a tunable laser light source module (1), a first optical range-extending module (2), an open differential T-shaped photoacoustic resonant cavity (3), a second optical range-extending module (4) and a photoacoustic signal acquisition and central processing module (5), wherein,
the tunable laser light source module (1) is used for generating incident light modulated by main path wavelength;
the first optical range-extending module (2) is arranged on the optical path of the tunable laser light source module (1) and on one side of the open differential T-shaped photoacoustic resonant cavity (3) and is used for enabling the incident light to enter the open differential T-shaped photoacoustic resonant cavity (3) at a certain longitudinal deflection angle and generating first reflected light for multiple times;
the second optical range-extending module (4) is arranged on the other side of the open differential T-shaped photoacoustic resonant cavity (3) and is used for generating second reflected light for multiple times;
the open differential T-shaped photoacoustic resonant cavity (3) is used for carrying out resonance enhancement and differential amplification on photoacoustic signals generated by absorbing the incident light, the first reflected light and the second reflected light by the gas to be detected entering the cavity, so as to obtain output photoacoustic signals;
the photoacoustic signal acquisition and central processing module (5) is connected with the open differential T-shaped photoacoustic resonant cavity (3) and is used for receiving the output photoacoustic signal and processing the output photoacoustic signal so as to realize qualitative and quantitative detection of the gas to be detected.
2. The open differential resonator optical path enhancement based photoacoustic spectroscopy gas detection system of claim 1, wherein the tunable laser light source module (1) comprises a tunable laser diode light source (11) and a signal generator (12), wherein,
the tunable laser diode light source (11) is used for generating incident laser light;
the signal generator (12) is connected with the tunable laser diode light source (11) and is used for carrying out wavelength modulation on the incident laser by utilizing current of superposition of sine waves and triangular waves so as to generate the incident light for exciting the gas to be detected.
3. The photoacoustic spectroscopy gas detection system of claim 1 based on open differential resonator optical path enhancement, wherein the first optical range-extending module (2) comprises a flat mirror (21) and a collimating mirror (22), wherein,
the collimating mirror (22) is embedded in the plane mirror (21) and is arranged on the light path of the tuning laser light source module (1);
the collimating mirror (22) is used for making the incident light enter the open differential T-shaped photoacoustic resonant cavity (3) at a certain longitudinal deflection angle, and the plane mirror (21) is used for generating first reflected light for a plurality of times.
4. A photoacoustic spectroscopy gas detection system based on open differential resonator optical path enhancement according to claim 3, wherein the second optical range extender module (4) comprises a concave mirror (41), the concave mirror (41) being used to generate the second reflected light multiple times.
5. The photoacoustic spectroscopy gas detection system of claim 4 based on open differential resonator optical path enhancement,
the plane mirror (21) adopts BK7 glass, the half aperture is 2.9-3.1mm, and the thickness is 1.9-2.1mm;
the collimating lens (22) adopts BK7 glass, the half aperture is 0.05-0.25mm, and the deflection angle is 27-31 degrees of x-axis deflection;
the collimating mirror (22) is positioned 1.9-2.1mm above the central y axis of the plane mirror (21);
the concave mirror (41) is made of BK7 glass, the half aperture is 2.9-3.1mm, the thickness is 1.9-2.1mm, and the curvature radius is 49.9-50.1mm;
the distance between the concave mirror (41) and the plane mirror (21) is 21.9-22.1mm.
6. The open differential resonator optical path enhancement based photoacoustic spectroscopy gas detection system of claim 1, wherein the open differential T-shaped photoacoustic resonator (3) comprises a first buffer chamber (31), a second buffer chamber (32), an absorber chamber (33), a first resonant chamber (34) and a second resonant chamber (35), wherein,
the first buffer cavity (31) is positioned at one end part of the absorption cavity (33), the second buffer cavity (32) is positioned at the other end part of the absorption cavity (33), the side surfaces of the first buffer cavity (31) and the second buffer cavity (32) are of an open structure, and the first buffer cavity (31) and the second buffer cavity (32) are distributed in a bilateral symmetry manner;
the first resonant cavity (34) and the second resonant cavity (35) are vertically and symmetrically arranged above the absorption cavity (33), form a differential double-resonance T-shaped structure with the absorption cavity (33), and are connected with the photoacoustic signal acquisition and central processing module (5);
the first buffer chamber (31) and the second buffer chamber (32) are used for enabling the gas to be tested to enter the absorption chamber (33) and changing the resonance condition of an acoustic boundary;
the absorption cavity (33) is used for enabling the gas to be detected to absorb the incident light, the first reflected light and the second reflected light so as to generate the photoacoustic signal;
the first resonant cavity (34) and the second resonant cavity (35) are used for forming standing wave acoustic signals with the same amplitude and opposite phases, so that the photoacoustic signals are subjected to resonance enhancement and differential amplification, and the output photoacoustic signals are obtained.
7. The photoacoustic spectroscopy gas detection system of claim 6, wherein the first buffer chamber (31), the second buffer chamber (32), the absorption chamber (33), the first resonant chamber (34) and the second resonant chamber (35) each have a cylindrical structure.
8. The photoacoustic spectroscopy gas detection system of claim 6, wherein the diameters of the first buffer chamber (31) and the second buffer chamber (32) are greater than the diameters of the absorption chamber (33), the first resonant chamber (34) and the second resonant chamber (35).
9. The photoacoustic spectroscopy gas detection system of claim 6, wherein the first resonant cavity (34) and the second resonant cavity (35) have a diameter that is smaller than the diameter of the absorption cavity (33).
10. The photoacoustic spectrometry gas detection system based on open differential resonator optical path enhancement according to claim 1, wherein the photoacoustic signal acquisition and central processing module (5) comprises an acoustic wave detection and acquisition module (51), a lock-in amplifier (52) and a signal processor (53), wherein,
the sound wave detection and acquisition module (51) is connected with the open differential T-shaped photoacoustic resonant cavity (3) and is used for converting the output photoacoustic signal into an electric signal;
the phase-locked amplifier (52) is connected with the tunable laser light source module (1) and the sound wave detection and acquisition module (51) and is used for processing the electric signals to regulate second harmonic signals with the same resonance frequency as the open differential T-shaped photoacoustic resonant cavity (3) so as to obtain processed electric signals;
the signal processor (53) is connected with the lock-in amplifier (52) and is used for storing and analyzing the processed electric signals so as to realize qualitative and quantitative detection of the gas to be detected.
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