WO2020238386A1 - 一种痕量气体的探测方法及探测装置 - Google Patents

一种痕量气体的探测方法及探测装置 Download PDF

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WO2020238386A1
WO2020238386A1 PCT/CN2020/082019 CN2020082019W WO2020238386A1 WO 2020238386 A1 WO2020238386 A1 WO 2020238386A1 CN 2020082019 W CN2020082019 W CN 2020082019W WO 2020238386 A1 WO2020238386 A1 WO 2020238386A1
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resonant cavity
gas
measured
detection
trace gas
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PCT/CN2020/082019
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French (fr)
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胡水明
王进
孙羽
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中国科学技术大学
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Priority to US17/614,763 priority Critical patent/US12031903B2/en
Priority to EP20813712.5A priority patent/EP3978906A4/en
Publication of WO2020238386A1 publication Critical patent/WO2020238386A1/zh

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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
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
    • G—PHYSICS
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    • 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
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    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • 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
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    • 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
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    • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
    • G01N2021/3166—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths using separate detectors and filters
    • 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
    • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
    • G01N2021/317—Special constructive features
    • 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
    • G01N2021/3185—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry typically monochromatic or band-limited
    • G01N2021/3188—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry typically monochromatic or band-limited band-limited
    • 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
    • G01N2021/391—Intracavity sample
    • 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
    • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/061—Sources
    • G01N2201/06113—Coherent sources; lasers
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    • G01N2201/063—Illuminating optical parts
    • G01N2201/0636—Reflectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/069—Supply of sources
    • G01N2201/0691—Modulated (not pulsed supply)

Definitions

  • This application relates to the field of optical detection technology, and more specifically, to a detection method and detection device for trace gases.
  • Molecular Absorption Spectrometry (Molecular Absorption Spectrometry) technology is a technology for measuring the concentration of target gas molecules. Specifically, it measures the absorption line of a target gas molecule component in the gas to be measured to obtain the absorption rate of the target gas molecule. Using the corresponding relationship between the absorption rate and the concentration of the target gas to be measured, the concentration of the target gas to be measured in the gas to be measured is obtained.
  • the commonly used molecular absorption spectroscopy technology is to measure the absorption rate of a certain absorption line of the target gas molecule (isotope), which satisfies the Beer-Lambert relationship.
  • the database HITRAN discloses the absorption line parameters of dozens of major atmospheric molecules and their isotopes.
  • it is usually necessary to scan the wavelength.
  • a complete envelope of an isolated spectral line of the target gas molecule is obtained. The method eliminates the influence of the linear function to obtain the concentration of the target gas.
  • the Doppler broadening (full width at half maximum) of molecular near-infrared transitions can reach the level of hundreds of MHz. Due to the presence of other molecules (or isotopes) in the background gas, if the target gas The content of molecules (isotopes) is low or the absorption line is weak (that is, when the target gas is a trace gas), the line is easily covered by the absorption of other background gases, and the absorption signal of the target line will be submerged in the background Unable to extract, resulting in measurement failure.
  • the method of measuring the molecular saturation absorption spectrum of trace gas is usually adopted, and it is expected to take advantage of the narrower molecular saturation absorption spectrum line width and not being affected by the absorption of the gas background gas to achieve trace amounts in the gas to be measured.
  • Gas concentration measurement but in practical applications, it is found that conventional continuous wave lasers cannot achieve gas molecular transition saturation under normal temperature conditions, so the purpose of using conventional continuous wave lasers to measure trace gases can not be achieved under normal temperature conditions.
  • this application provides a trace gas detection method and detection system, so as to use the cavity of the trace gas or isotope to be detected to enhance the molecular saturation absorption spectrum without Doppler effect under normal temperature conditions.
  • a trace gas detection method and detection system so as to use the cavity of the trace gas or isotope to be detected to enhance the molecular saturation absorption spectrum without Doppler effect under normal temperature conditions.
  • a method for detecting trace gas including:
  • the probe light enters the interior of the resonant cavity from one end of the extension direction of the resonant cavity, and exits from the other end of the extension direction of the resonant cavity to obtain the trace to be measured Detection light of gas information;
  • the cavity of the resonant cavity has a degree of freedom of expansion and contraction in the extension direction of the resonant cavity, so that the longitudinal mode frequency of the resonant cavity matches the frequency of the incident detection light;
  • the molecular saturated absorption spectrum of the trace gas to be measured is obtained, and the molecular saturated absorption spectrum of the trace gas is calculated to calculate the content of the gas to be measured. State the concentration of the trace gas to be measured.
  • it includes: a laser generating device, a resonant cavity, a photodetection device, a feedback control device, and a scanning control device; wherein,
  • the inside of the cavity of the resonant cavity is used to fill the gas to be measured, and the gas to be measured includes the trace gas to be measured;
  • the cavity of the resonant cavity has a degree of freedom of expansion and contraction in the extension direction of the resonant cavity;
  • the laser generating device is used to provide probe light of different frequencies under the control of the feedback control device, and the probe light enters the interior of the resonant cavity from one end of the extension direction of the resonant cavity and passes from The other end of the extending direction of the resonant cavity is emitted to obtain the detection light carrying information of the trace gas to be measured;
  • the photoelectric detection device is used to convert the detection light carrying the trace gas information to be detected into detection information in the form of electrical signals
  • the scanning control device is used to record the detection information in the form of electrical signals, and is used to control the laser generating device to adjust the frequency of the emitted detection light in a stepwise manner;
  • the feedback control device is used to control the frequency of the probe light emitted by the laser generating device to match the longitudinal mode frequency of the resonant cavity.
  • the resonant cavity includes:
  • a housing the housing having an incident end and an exit end that are arranged oppositely;
  • a first reflector located inside the housing and close to the incident end, and the first reflector has an anti-reflection coating on the side facing the incident end;
  • a second reflector located inside the housing and close to the side of the exit end, and the reflective surfaces of the first reflector and the second reflector are opposed to each other;
  • the adjacent first mirror and/or second mirror move, so that the cavity of the resonant cavity has a degree of freedom of expansion and contraction in the extension direction of the resonant cavity.
  • the feedback control device includes: a radio frequency signal source, a phase detection device and a PID amplification device; wherein,
  • the radio frequency signal source is used to generate a sinusoidal radio frequency signal
  • the phase detection device is used to convert the detection information in the form of an electrical signal into an error signal according to the sinusoidal radio frequency signal;
  • the PID amplifying device is used to convert the error signal into a feedback lock signal so that the frequency of the probe light emitted by the laser generating device matches the longitudinal mode frequency of the resonant cavity.
  • the laser generating device includes: a laser, a frequency modulation device and a coupling lens;
  • the laser is used to generate laser light
  • the frequency modulation device is configured to modulate the laser light generated by the laser according to the feedback locking information to obtain a probe light whose frequency matches the longitudinal mode frequency of the resonant cavity;
  • the coupling lens is used for coupling the probe light to enter the resonant cavity.
  • the frequency modulation device is an electro-optical modulator.
  • the scanning control device includes: an information storage device and a frequency scanning device; wherein,
  • the information storage device is used to record the detection information in the form of the electrical signal
  • the frequency scanning device is used to generate a control electric signal and transmit it to the laser.
  • the scanning control device is further configured to obtain the molecular saturation absorption spectrum of the trace gas to be measured according to the recorded detection information in the form of the electrical signal, and to obtain the molecular saturation absorption spectrum of the trace gas according to the molecular saturation absorption of the trace gas. Spectrum, calculate the concentration of the trace gas to be measured in the gas to be measured.
  • the photoelectric detection device includes: a lens matching module and a photodetection module; wherein,
  • the lens matching module is used to match the spatial pattern of the internal light field of the photodetection device
  • the photoelectric detection module is used to convert the detection light carrying the trace gas information to be detected into detection information in the form of electrical signals.
  • the embodiments of the present application provide a trace gas detection method and detection system, wherein the trace gas detection method fills the gas to be measured in a resonant cavity, and uses a resonant cavity one On the one hand, it enhances the laser power of the probe light incident into the resonant cavity to increase the saturation parameter of the molecular transition of the trace gas to be measured; on the other hand, it enhances the effective absorption range of the trace gas to be measured, thereby improving the weak absorption of the trace gas to be measured
  • the detection sensitivity is high, and the molecular saturation absorption spectrum of the trace gas to be detected is obtained, so that under normal temperature conditions, the detection light provided by a conventional laser can be used to detect the concentration of the trace gas.
  • the molecular saturation absorption spectrum of the trace gas to be measured is effectively separated from the absorption spectrum of the background gas molecules in the gas to be measured, thereby eliminating the interference of the background gas. Realize the detection of trace gas to be measured. Since the saturated absorption spectrum frequencies of different isotopes of molecules are obviously different, the method for detecting trace gases provided in the embodiments of the present application is also particularly effective for detecting molecules of specific isotopes.
  • FIG. 1 is a schematic flow chart of a method for detecting trace gases according to an embodiment of the application
  • FIG. 2 is a schematic structural diagram of a resonant cavity provided by an embodiment of the application.
  • FIG. 3 is a schematic structural diagram of a trace gas detection system provided by an embodiment of the application.
  • Figure 4 shows the relationship between the partial pressure of the trace gas ( 12 C 16 O) in the gas to be measured and the area of its R(19) transition Lamb depression obtained by simulation;
  • the commonly used laser absorption spectroscopy technology is to measure the absorption rate of a certain absorption line of the target gas molecule (isotope), which satisfies the Beer-Lambert relationship:
  • T v represents the transmittance of the laser through the L optical path in the medium
  • k v is the absorption rate, which is the concentration of the target gas molecule X gas , the absorption line intensity S(T) and the line type under the pressure P function Function, and the linear function satisfies Among them, v represents frequency.
  • the absorption rate k v can be expressed as:
  • HITRAN discloses the absorption line parameters of dozens of major atmospheric molecules and their isotopes (including the center of the spectrum, S(T), etc.).
  • S(T) the center of the spectrum
  • a complete envelope of an isolated spectral line of the target gas molecule is obtained. Way to eliminate The influence of the linear function to obtain the concentration of the target gas.
  • the Doppler broadening (full width at half maximum) of molecular near-infrared transitions can reach the level of hundreds of MHz. Due to the presence of other molecules (or isotopes) in the background gas, if the target gas The content of molecules (isotopes) is low or the absorption line is weak, the line is easily covered by the absorption of other background gases, and the absorption signal of the target line will be submerged in the background and cannot be extracted, which will lead to measurement failure.
  • Molecular saturation absorption spectroscopy is when a beam of narrow linewidth excitation light excites some molecules to the upper state, so that the number of molecules living in the lower state decreases. At this time, the absorption signal measured by the probe light decreases. If the excitation light and the detection light have the same frequency and opposite directions, at this time, because both of them only interact with molecules with zero lateral velocity at the same time, an absorption pit with no Doppler broadening and a narrow line width will be obtained, which is called Lamb depression. Since the molecular saturation absorption spectrum linewidth is generally about three orders of magnitude narrower than the Doppler broadening, it will not be affected by the absorption of other background gases, which can greatly improve the selectivity of detection.
  • the depth ⁇ of the molecular saturation absorption peak (Lamb recess) can be expressed by the following formula:
  • P i is the partial pressure of the gas to be measured
  • ⁇ m P is the molecular absorption coefficient measured without considering the saturation effects
  • S is the saturation parameter can be obtained by the following formula:
  • I s is the saturation power
  • I s0 is the saturation power of the test gas at zero pressure limit
  • ⁇ P is the pressure broadening coefficient
  • ⁇ T is the widening of the transit time
  • P is the total pressure of the sample gas.
  • ⁇ FWHM is the full width at half maximum of the Lamb recess. According to the measured area of the Lamb depression, the concentration of the gas to be measured can be calculated.
  • a trace gas detection method including:
  • the probe light enters the interior of the resonant cavity from one end of the extension direction of the resonant cavity, and exits from the other end of the extension direction of the resonant cavity to obtain the trace to be measured Detection light of gas information;
  • the cavity of the resonant cavity has a degree of freedom of expansion and contraction in the extension direction of the resonant cavity, so that the longitudinal mode frequency of the resonant cavity matches the frequency of the incident detection light;
  • the molecular saturated absorption spectrum of the trace gas to be measured is obtained, and the molecular saturated absorption spectrum of the trace gas is calculated to calculate the content of the gas to be measured. State the concentration of the trace gas to be measured.
  • the trace gas detection method fills the gas to be measured in a resonant cavity, and on the one hand, the resonant cavity is used to increase the laser power of the probe light incident into the resonant cavity and increase the saturation parameter of the molecular transition of the trace gas to be measured; On the one hand, the effective absorption range of the trace gas to be measured is enhanced, thereby improving the detection sensitivity of the weak absorption of the trace gas to be measured, and obtaining the molecular saturation absorption spectrum of the trace gas to be measured, so as to realize the use of conventional lasers under normal temperature conditions.
  • the detection light can achieve the purpose of detecting the concentration of trace gas.
  • the molecular saturation absorption spectrum of the trace gas to be measured is effectively separated from the absorption spectrum of the background gas molecules in the gas to be measured, thereby eliminating the interference of the background gas. Realize the detection of trace gas to be measured. Since the saturated absorption spectrum frequencies of different isotopes of molecules are obviously different, the method for detecting trace gases provided in the embodiments of the present application is also particularly effective for detecting molecules of specific isotopes.
  • the embodiment of the present application provides a method for detecting trace gas, as shown in FIG. 1, including:
  • S101 Provide a resonant cavity, and fill the cavity of the resonant cavity with a gas to be measured, and the gas to be measured includes trace gas to be measured;
  • S102 Provide probe light of different frequencies, the probe light enters the interior of the resonant cavity from one end of the resonant cavity in the extending direction, and exits from the other end of the resonant cavity in the extending direction to obtain a portable test Trace gas information detection light;
  • the cavity of the resonant cavity has a degree of freedom of expansion and contraction in the extension direction of the resonant cavity, so that the longitudinal mode frequency of the resonant cavity matches the frequency of the incident detection light;
  • S103 Obtain the molecular saturated absorption spectrum of the trace gas to be detected according to the probe light carrying information of the trace gas to be detected at different frequencies, and calculate the gas to be detected based on the molecular saturated absorption spectrum of the trace gas The concentration of the trace gas to be measured as described in.
  • trace gas refers to gas components with extremely low component content (ppm level or lower) in a gas sample at a certain pressure.
  • ppm level or lower gas components with extremely low component content
  • carbon dioxide or methane in the atmosphere and its isotope gases can be considered as Trace gas.
  • the resonant cavity includes a housing, a first mirror 22 and a second mirror 23 disposed in the housing 21. And at least one piezoelectric device (not shown in FIG. 2); wherein, the housing 21 includes an incident end and an emission end that are oppositely arranged, the first mirror 22 and the second mirror 23 are respectively arranged near the incident end and the emission end, and The reflecting surfaces of the first reflecting mirror 22 and the second reflecting mirror 23 are opposite; the first reflecting mirror 22 located near the incident end may be attached with an anti-reflection coating to increase the transmittance of the incident detection light.
  • the trace gas detection method fills the gas to be measured in a resonant cavity, and the resonant cavity is used to increase the laser power of the detection light incident into the resonant cavity and increase the molecular transition of the trace gas to be measured.
  • the resonant cavity is used to increase the laser power of the detection light incident into the resonant cavity and increase the molecular transition of the trace gas to be measured.
  • it enhances the effective absorption range of the trace gas to be measured, thereby improving the detection sensitivity of the weak absorption of the trace gas to be measured, and obtains the molecular saturation absorption spectrum of the trace gas to be measured, so as to achieve under normal temperature conditions
  • the detection light provided by the conventional laser can be used to detect the concentration of trace gas.
  • the molecular saturation absorption spectrum of the trace gas to be measured is effectively separated from the absorption spectrum of the background gas molecules in the gas to be measured, thereby eliminating the interference of the background gas. Realize the detection of trace gas to be measured. Since the saturated absorption spectrum frequencies of different isotopes of molecules are obviously different, the method for detecting trace gases provided in the embodiments of the present application is also particularly effective for detecting molecules of specific isotopes.
  • the trace gas detection system includes: a laser generating device 10, a resonant cavity 20, Photoelectric detection device 30, feedback control device 40 and scanning control device 50; among them,
  • the inside of the cavity of the resonant cavity 20 is used to fill the gas to be measured, and the gas to be measured includes the trace gas to be measured; the cavity of the resonant cavity 20 has freedom of expansion and contraction in the extension direction of the resonant cavity 20 degree;
  • the laser generating device 10 is used to provide probe light of different frequencies under the control of the feedback control device 40, and the probe light enters the interior of the resonant cavity 20 from one end of the extension direction of the resonant cavity 20 , And emitted from the other end of the resonant cavity 20 in the extending direction to obtain the detection light carrying information of the trace gas to be measured;
  • the photoelectric detection device 30 is used to convert the detection light carrying the trace gas information to be detected into detection information in the form of electrical signals;
  • the scanning control device 50 is used to record the detection information in the form of electrical signals, and is used to control the laser generating device 10 to adjust the frequency of the emitted detection light in a stepwise manner;
  • the feedback control device 40 is used to control the frequency of the probe light emitted by the laser generator 10 to match the longitudinal mode frequency of the resonant cavity 20.
  • the scanning control device 50 can only use It is sufficient to control the laser generating device 10 to adjust the frequency of the emitted detection light in a stepwise manner.
  • the feedback control The device 40 adjusts the longitudinal mode frequency of the resonant cavity 20 and/or the frequency of the probe light emitted by the laser generator 10 in real time, so that the frequency of the probe light emitted by the laser generator 10 is equal to that of the resonant cavity 20 Longitudinal mode frequency matching.
  • the purpose of the scanning control device 50 controlling the laser generating device 10 to adjust the frequency of the emitted detection light in a step-by-step manner is to enable the scanning control device 50 to record the detection light carried by different frequencies.
  • the detection information in the form of electrical signals corresponding to the trace gas information can be used to obtain the molecular saturation absorption spectrum of the trace gas to be measured based on the detection information in the form of the recorded electrical signal, and according to the molecular saturation of the trace gas
  • the absorption spectrum is used to calculate the concentration of the trace gas to be measured in the gas to be measured.
  • the scan control device 50 is further configured to obtain the molecular saturation absorption spectrum of the trace gas to be measured according to the recorded detection information in the form of the electrical signal, And according to the molecular saturation absorption spectrum of the trace gas, the concentration of the trace gas to be measured in the gas to be measured is calculated.
  • the resonant cavity 20 includes:
  • a housing 21, the housing 21 has an incident end and an exit end that are arranged oppositely;
  • the second reflecting mirror 23 is located inside the housing 21 and is close to the side of the exit end, and the reflecting surfaces of the first reflecting mirror 22 and the second reflecting mirror 23 are arranged opposite to each other;
  • the first mirror 22 and/or the second mirror 23 adjacent to the device move, so that the cavity of the resonant cavity 20 has a degree of freedom of expansion and contraction in the extension direction of the resonant cavity 20.
  • the cavity of the resonant cavity 20 is formed between the first reflector 22 and the second reflector 23, so that the detection laser can be cavity enhanced in the cavity.
  • the anti-reflection coating on the side of the first reflector 22 facing the incident end is used to increase the transmittance of the probe light incident on the first reflector 22 and improve the light energy utilization rate of the probe light.
  • the feedback control device 40 includes: a radio frequency signal source, a phase detection device and a PID (proportional-integral-derivative) amplification device; wherein,
  • the radio frequency signal source is used to generate a sinusoidal radio frequency signal
  • the phase detection device is used to convert the detection information in the form of an electrical signal into an error signal according to the sinusoidal radio frequency signal;
  • the PID amplifying device is used to convert the error signal into a feedback lock signal so that the frequency of the probe light emitted by the laser generator 10 matches the longitudinal mode frequency of the resonant cavity 20.
  • the radio frequency signal source in the feedback control device 40 is used to provide the working reference signal of the phase detection device, the phase detection device converts the detection information in the form of an electrical signal into an error signal, and the PID amplifying device
  • the error signal is converted into a feedback locking signal and transmitted to the piezoelectric device, so that the piezoelectric device adjusts the resonant cavity 20 in the extending direction of the resonant cavity 20 according to the feedback locking signal.
  • the length of the cavity is adjusted to adjust the longitudinal mode frequency of the resonant cavity 20 to match the frequency of the probe light emitted by the laser generator 10.
  • the scanning control device 50 only needs to control the laser generating device 10 to adjust the frequency of the emitted detection light in a stepwise manner, and the feedback control device 40 adjusts the cavity of the resonant cavity 20
  • the length method makes the longitudinal mode frequency of the resonant cavity 20 match the frequency of the probe light emitted by the laser generator 10.
  • the frequency variation range of the detection light of the laser generating device 10 controlled by the scanning control device 50 may be on the order of megahertz or hundreds of megahertz. This application does not limit the specific value of the change step length of the detection light and the specific frequency change range of the detection light, and it depends on the actual situation.
  • the laser generating device 10 includes: a laser, a frequency modulation device and a coupling lens;
  • the laser is used to generate laser light
  • the frequency modulation device is configured to modulate the laser light generated by the laser according to the feedback locking information to obtain the probe light whose frequency matches the longitudinal mode frequency of the resonant cavity 20;
  • the coupling lens is used to couple the probe light to enter the resonant cavity 20.
  • the laser may be a conventional laser type such as a semiconductor laser, a fiber laser or a solid laser. This application does not limit this, and it depends on the actual situation.
  • the frequency modulation device is an electro-optical modulator.
  • the scanning control device 50 includes: an information storage device and a frequency scanning device; wherein,
  • the information storage device is used to record the detection information in the form of the electrical signal
  • the frequency scanning device is used to generate a control electric signal and transmit it to the laser.
  • the scanning control device 50 controls the frequency of the laser light generated by the laser to change in a certain step through the generated control electrical signal.
  • the photodetection device 30 includes: a lens matching module and a photodetection module; wherein,
  • the lens matching module is used to match the spatial pattern of the internal light field of the photodetection device 30;
  • the photoelectric detection module is used to convert the detection light carrying the trace gas information to be detected into detection information in the form of electrical signals.
  • the trace gas to be measured is 12 C 16 O gas molecules
  • the purpose is to measure the molecular saturation absorption spectrum of the infrared vibrational transition of the 12 C 16 O gas molecules, and obtain 12 C according to the area of the peak.
  • the laser is an external cavity semiconductor laser
  • the output laser light is modulated by an electro-optic modulator and coupled by a coupling lens and then enters the resonant cavity 20
  • the cavity 20 is filled with a gas to be measured, the gas to be measured Contains 12 C 16 O gas, the total pressure of the gas to be measured is P, which is measured by a pressure gauge connected to the resonant cavity 20
  • the resonant cavity 20 is provided with a first mirror 22 and a second mirror 23, the first mirror The reflectivity of the second mirror 22 and the second mirror 23 is 99.995%.
  • the first mirror 22 and the second mirror 23 constitute an optical resonant cavity 20.
  • the back of the first mirror 22 or the second mirror 23 is connected to a piezoelectric
  • the device can drive the lens to move slightly in the direction of the optical path (the direction in which the cavity 20 extends).
  • the detection light emitted from the resonant cavity 20 carrying information of the trace gas to be measured is converted into detection information in the form of electrical signals by the photodetection device 30.
  • the detection signals in the form of electrical signals are filtered and amplified and divided into two signals, one signal It is sent to the feedback control device 40 and is demodulated by the feedback control device 40 to generate a feedback lock signal, so that the longitudinal mode frequency of the resonant cavity 20 matches the frequency of the probe light emitted by the laser generator 10;
  • the signal is sent to the scanning control device 50 for recording, and the scanning control device 50 controls the laser generator to perform step-wise frequency scanning.
  • Figure 4 shows the trace gas ( 12 C 16 O) The relationship between the partial pressure and the area of its R(19) transition Lamb depression.
  • the abscissa is the Partial Pressure of 12 C 16 O gas
  • the unit is Pascal (Pa)
  • the ordinate is Lamb.
  • the embodiments of the present application provide a trace gas detection method and detection system, wherein the trace gas detection method fills the gas to be measured in a resonant cavity, and uses the resonant cavity to enhance the incident
  • the laser power of the detection light into the resonant cavity improves the saturation parameter of the molecular transition of the trace gas to be measured; on the other hand, it enhances the effective absorption range of the trace gas to be measured, thereby improving the detection sensitivity of the weak absorption of the trace gas to be measured ,
  • the molecular saturation absorption spectrum of the trace gas to be measured is effectively separated from the absorption spectrum of the background gas molecules in the gas to be measured, thereby eliminating the interference of the background gas. Realize the detection of trace gas to be measured. Since the saturated absorption spectrum frequencies of different isotopes of molecules are obviously different, the method for detecting trace gases provided in the embodiments of the present application is also particularly effective for detecting molecules of specific isotopes.

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Abstract

一种痕量气体的探测方法及探测系统，探测方法包括：提供谐振腔（20），谐振腔（20）的腔体内部充填待测气体（S101）；提供不同频率的探测光线，所述探测光线从谐振腔（20）的延伸方向的一端入射到谐振腔（20）内部，并从谐振腔（20）的延伸方向的另一端出射，以获得携带待测痕量气体信息的探测光线，谐振腔（20）的腔体在延伸方向上具有伸缩自由度，以使谐振腔（20）的纵模频率与入射的探测光线的频率匹配（S102）；根据不同频率的携带待测痕量气体信息的探测光线，获取所述待测痕量气体的分子饱和吸收光谱，计算待测痕量气体的浓度（S103）。探测系统包括：激光发生装置（10）、谐振腔（20）、光电探测装置（30）、反馈控制装置（40）和扫描控制装置（50）。在常温条件下，利用常规激光器提供的探测光线实现对痕量气体的浓度的探测。

Description

一种痕量气体的探测方法及探测装置
本申请要求于2019年5月29日提交中国专利局、申请号为201910456370.9、发明名称为“一种痕量气体的探测方法及探测装置”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及光学探测技术领域，更具体地说，涉及一种痕量气体的探测方法及探测装置。
背景技术
分子吸收光谱(Molecular Absorption Spectrometry)技术是一种测量被测目标气体分子浓度的技术，具体为：对待测气体中某一目标气体分子组分的吸收线进行测量，获取目标气体分子的吸收率，利用吸收率和被测目标气体分子浓度的对应关系，获得被测目标气体在待测气体中的浓度。
目前常用的分子吸收光谱技术是测量目标气体分子(同位素)某条吸收谱线的吸收率，它满足Beer-Lambert关系式。数据库HITRAN公开了数十种主要大气分子及其同位素的吸收线参数。测量时，为了避免受到激光功率漂移、光学介质透射率起伏等效应的影响，通常需要扫描波长，通过记录一定波段范围的激光光谱，得到目标气体分子一条孤立谱线的完整包络，通过积分的方式消除线型函数的影响，从而得到目标气体的浓度。
然而，在常温或者高温条件下，即使在低压下，分子近红外跃迁的多普勒展宽(半高全宽)也达到数百MHz水平，由于背景气体中其它分子(或同位素)的存在，如果目标气体分子(同位素)的含量较低或者吸收谱线较弱(即目标气体为痕量气体时)，该谱线很容易被其它背景气体的吸收所覆盖，目标谱线的吸收信号会淹没在背景中无法提取，从而导致测量失效。
因此，现有技术中通常采用测量痕量气体的分子饱和吸收光谱的方式，期 望利用分子饱和吸收光谱线宽较窄，不会受到气体背景气体吸收的影响的优势，实现待测气体中痕量气体的浓度测量，但在实际应用中发现，采用常规的连续波激光器无法实现在常温条件下使气体分子跃迁饱和，因此无法在常温条件下实现利用常规连续波激光器测量痕量气体的目的。
发明内容
为解决上述技术问题，本申请提供了一种痕量气体的探测方法及探测系统，以实现在常温条件下，利用待测痕量气体或同位素的腔增强无多普勒效应的分子饱和吸收光谱，对待测痕量气体或同位素的浓度探测的目的。
为实现上述技术目的，本申请实施例提供了如下技术方案：
一种痕量气体的探测方法，包括：
提供谐振腔，并在所述谐振腔的腔体内部充填待测气体，所述待测气体中包括待测痕量气体；
提供不同频率的探测光线，所述探测光线从所述谐振腔的延伸方向的一端入射到所述谐振腔内部，并从所述谐振腔的延伸方向的另一端出射，以获得携带待测痕量气体信息的探测光线；所述谐振腔的腔体在所述谐振腔的延伸方向上具有伸缩自由度，以使所述谐振腔的纵模频率与入射的探测光线的频率匹配；
根据不同频率的携带待测痕量气体信息的探测光线，获取所述待测痕量气体的分子饱和吸收光谱，并根据所述痕量气体的分子饱和吸收光谱，计算所述待测气体中所述待测痕量气体的浓度。
可选的，包括：激光发生装置、谐振腔、光电探测装置、反馈控制装置和扫描控制装置；其中，
所述谐振腔的腔体内部用于充填待测气体，所述待测气体中包括待测痕量气体；所述谐振腔的腔体在所述谐振腔的延伸方向上具有伸缩自由度；
所述激光发生装置，用于在所述反馈控制装置的控制下，提供不同频率的探测光线，所述探测光线从所述谐振腔的延伸方向的一端入射到所述谐振腔内部，并从所述谐振腔的延伸方向的另一端出射，以获得携带待测痕量气体信息 的探测光线；
所述光电探测装置，用于将携带待测痕量气体信息的探测光线转换为电信号形式的探测信息；
所述扫描控制装置，用于记录所述电信号形式的探测信息，和用于控制所述激光发生装置以步进的方式调整出射的探测光线的频率；
所述反馈控制装置，用于控制所述激光发生装置出射的探测光线的频率与所述谐振腔的纵模频率匹配。
可选的，所述谐振腔包括：
外壳，所述外壳具有相对设置的入射端和出射端；
位于所述外壳内部，靠近所述入射端一侧的第一反射镜，所述第一反射镜朝向所述入射端一侧具有增透膜；
位于所述外壳内部，靠近所述出射端一侧的第二反射镜，所述第一反射镜和第二反射镜的反射面相对设置；
与所述第一反射镜相邻设置和/或与所述第二反射镜相邻设置的压电装置；所述压电装置用于根据接收的控制电信号，推动与所述压电装置相邻的第一反射镜和/或第二反射镜移动，以使所述谐振腔的腔体在所述谐振腔的延伸方向上具有伸缩自由度。
可选的，所述反馈控制装置包括：射频信号源、检相装置和PID放大装置；其中，
所述射频信号源，用于产生正弦射频信号；
所述检相装置，用于根据所述正弦射频信号，将电信号形式的探测信息转换为误差信号；
所述PID放大装置，用于将所述误差信号，转换为反馈锁定信号，以使所述激光发生装置出射的探测光线的频率与所述谐振腔的纵模频率匹配。
可选的，所述激光发生装置包括：激光器、频率调制装置和耦合透镜；
所述激光器，用于产生激光；
所述频率调制装置，用于根据所述反馈锁定信息，对所述激光器产生的激光进行调制，以获得频率与所述谐振腔的纵模频率匹配的探测光线；
所述耦合透镜，用于对所述探测光线进行耦合后向所述谐振腔入射。
可选的，所述频率调制装置为电光调制器。
可选的，所述扫描控制装置包括：信息存储装置和频率扫描装置；其中，
所述信息存储装置，用于记录所述电信号形式的探测信息；
所述频率扫描装置，用于产生控制电信号，并向所述激光器传输。
可选的，所述扫描控制装置还用于，根据记录的所述电信号形式的探测信息，获取所述待测痕量气体的分子饱和吸收光谱，并根据所述痕量气体的分子饱和吸收光谱，计算所述待测气体中所述待测痕量气体的浓度。
可选的，所述光电探测装置包括：透镜匹配模块和光电探测模块；其中，
所述透镜匹配模块，用于匹配所述光电探测装置内部光场的空间模式；
所述光电探测模块，用于将携带待测痕量气体信息的探测光线转换为电信号形式的探测信息。
从上述技术方案可以看出，本申请实施例提供了一种痕量气体的探测方法及探测系统，其中，所述痕量气体的探测方法将待测气体充填于谐振腔中，利用谐振腔一方面增强入射到谐振腔中的探测光线的激光功率，提升待测痕量气体分子跃迁的饱和参数；另一方面增强待测痕量气体的有效吸收程，从而提高对待测痕量气体的微弱吸收的检测灵敏度，获得待测痕量气体的分子饱和吸收光谱，以实现在常温条件下，利用常规的激光器提供的探测光线即可实现对痕量气体的浓度进行探测的目的。
另外，由于分子饱和吸收光谱的消多普勒展宽特性，使得获得的待测痕量气体的分子饱和吸收光谱和待测气体中的背景气体分子的吸收光谱有效分开，从而消除背景气体的干扰，实现对待测痕量气体的探测。由于分子不同同位素的饱和吸收光谱频率明显不同，本申请实施例提供的痕量气体的探测方法对于探测特定同位素的分子也特别有效。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的实施例，对于本领域普通技术人员来讲，在不付出创 造性劳动的前提下，还可以根据提供的附图获得其他的附图。
图1为本申请的一个实施例提供的一种痕量气体的探测方法的流程示意图；
图2为本申请的一个实施例提供的一种谐振腔的结构示意图；
图3为本申请的一个实施例提供的一种痕量气体的探测系统的结构示意图；
图4为模拟得到的待测气体中的待测痕量气体( 12C 16O)分压和其R(19)跃迁兰姆凹陷面积的关系；
图5为测得的腔增强的分子V＝3-0、R(19)跃迁的分子饱和吸收光谱。
具体实施方式
正如背景技术所述，目前常用的激光吸收光谱技术是测量目标气体分子(同位素)某条吸收谱线的吸收率，它满足Beer-Lambert关系式：
T v＝I v/I 0＝exp(-k vL)；
其中，T v表示激光在介质中经过L光程的透射率，k v为吸收率，它是压力P下，被测目标气体分子的浓度X gas、吸收谱线强度S(T)和线型函数
Figure PCTCN2020082019-appb-000001
的函数，且线性函数满足
Figure PCTCN2020082019-appb-000002
其中，v表示频率。吸收率k v可以表示为：
Figure PCTCN2020082019-appb-000003
其中，
Figure PCTCN2020082019-appb-000004
为线型函数，由高斯型的多普勒加宽线形和洛仑兹型的压力加宽线形卷积得到，且线型函数满足
Figure PCTCN2020082019-appb-000005
数据库HITRAN公开了数十种主要大气分子及其同位素的吸收线参数(包括谱线中心、S(T)等)。测量时，为了避免受到激光功率漂移、光学介质透射率起伏等效应的影响，通常需要扫描波长，通过记录一定波段范围的激光光谱，得到目标气体分子一条孤立谱线的完整包络，通过积分的方式消除
Figure PCTCN2020082019-appb-000006
线型函数的影响，从而得到目标气体的浓度。
然而，在常温或者高温条件下，即使在低压下，分子近红外跃迁的多普勒展宽(半高全宽)也达到数百MHz水平，由于背景气体中其它分子(或同位素)的存在，如果目标气体分子(同位素)的含量较低或者吸收谱线较弱，该谱线很容易被其它背景气体的吸收所覆盖，目标谱线的吸收信号会淹没在背景中无 法提取，从而导致测量失效。
分子饱和吸收光谱是当一束窄线宽激发光将部分分子激发到上态，使得布居在下态的分子数减少，这时探测光所测得的吸收信号减小。如果激发光和探测光频率相同、方向相反，这时候由于二者同时仅仅和横向速度为零的分子相作用，这时将得到无多普勒展宽、线宽大为压窄的吸收凹陷，被称为兰姆凹陷。由于分子饱和吸收光谱线宽一般比多普勒展宽窄约三个量级，因此不会受到其它背景气体吸收的影响，可以大大提高探测的选择性。
分子饱和吸收峰(兰姆凹陷)的深度△α可以由下面公式表示：
Figure PCTCN2020082019-appb-000007
其中，P i为待测气体分压，α mP为待测分子在不考虑饱和效应下的吸收系数，S为饱和参数，可以由下面公式计算得到：
Figure PCTCN2020082019-appb-000008
其中，I s为饱和功率，I s0为待测气体在零压力极限下的饱和功率，Γ P为压力加宽系数，压力加宽系数用于描述分子饱和吸收光谱的线宽与气体压力的关系，Γ T为渡越时间加宽，P为样品气体总压。而兰姆凹陷的面积可以由以下公式得到：
Figure PCTCN2020082019-appb-000009
其中Γ FWHM为兰姆凹陷的半高全宽。根据所测得到兰姆凹陷的面积，可以计算得到待测气体的浓度。
然而，利用分子饱和吸收光谱来探测痕量分子，还存在很多困难。首先是分子的近红外振转跃迁矩很小，在常温条件下，分子的渡越加宽(约数百kHz)远大于自然加宽(亚Hz甚至更小)，使得需要很高的激光功率(kW/cm2以上)才可能使得跃迁饱和。在气体检测中常用的连续波半导体激光器无法达到所需的要求。同时，饱和吸收受到压力加宽的影响比较明显，为得到具有足够对比度的饱和吸收光谱，一般需要在低压(10Pa或更低)下测量，这对测量灵敏度 提出了更高的要求。
有鉴于此，本申请实施例提供了一种痕量气体的探测方法，包括：
提供谐振腔，并在所述谐振腔的腔体内部充填待测气体，所述待测气体中包括待测痕量气体；
提供不同频率的探测光线，所述探测光线从所述谐振腔的延伸方向的一端入射到所述谐振腔内部，并从所述谐振腔的延伸方向的另一端出射，以获得携带待测痕量气体信息的探测光线；所述谐振腔的腔体在所述谐振腔的延伸方向上具有伸缩自由度，以使所述谐振腔的纵模频率与入射的探测光线的频率匹配；
根据不同频率的携带待测痕量气体信息的探测光线，获取所述待测痕量气体的分子饱和吸收光谱，并根据所述痕量气体的分子饱和吸收光谱，计算所述待测气体中所述待测痕量气体的浓度。
所述痕量气体的探测方法将待测气体充填于谐振腔中，利用谐振腔一方面增强入射到谐振腔中的探测光线的激光功率，提升待测痕量气体分子跃迁的饱和参数；另一方面增强待测痕量气体的有效吸收程，从而提高对待测痕量气体的微弱吸收的检测灵敏度，获得待测痕量气体的分子饱和吸收光谱，以实现在常温条件下，利用常规的激光器提供的探测光线即可实现对痕量气体的浓度进行探测的目的。
另外，由于分子饱和吸收光谱的消多普勒展宽特性，使得获得的待测痕量气体的分子饱和吸收光谱和待测气体中的背景气体分子的吸收光谱有效分开，从而消除背景气体的干扰，实现对待测痕量气体的探测。由于分子不同同位素的饱和吸收光谱频率明显不同，本申请实施例提供的痕量气体的探测方法对于探测特定同位素的分子也特别有效。
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本申请实施例提供了一种痕量气体的探测方法，如图1所示，包括：
S101：提供谐振腔，并在所述谐振腔的腔体内部充填待测气体，所述待测气体中包括待测痕量气体；
S102：提供不同频率的探测光线，所述探测光线从所述谐振腔的延伸方向的一端入射到所述谐振腔内部，并从所述谐振腔的延伸方向的另一端出射，以获得携带待测痕量气体信息的探测光线；所述谐振腔的腔体在所述谐振腔的延伸方向上具有伸缩自由度，以使所述谐振腔的纵模频率与入射的探测光线的频率匹配；
S103：根据不同频率的携带待测痕量气体信息的探测光线，获取所述待测痕量气体的分子饱和吸收光谱，并根据所述痕量气体的分子饱和吸收光谱，计算所述待测气体中所述待测痕量气体的浓度。
需要说明的是，痕量气体是指在一定压力的气体样品中组分含量极低(ppm量级或更低)的气体成分，例如大气中的二氧化碳或甲烷及其同位素气体等均可认为是痕量气体。
本申请的一个实施例提供了一种谐振腔的可行结构，参考图2，在本实施例中，所述谐振腔包括外壳、设置于外壳21中的第一反射镜22、第二反射镜23以及至少一个压电装置(图2中未示出)；其中，外壳21包括相对设置的入射端和出射端，第一反射镜22和第二反射镜23分别靠近入射端和出射端设置，且第一反射镜22和第二反射镜23的反射面相对；靠近入射端设置的第一反射镜22朝向入射端一侧可以贴附一个增透膜以增加入射的探测光线的透过率。
在本实施例中，所述痕量气体的探测方法将待测气体充填于谐振腔中，利用谐振腔一方面增强入射到谐振腔中的探测光线的激光功率，提升待测痕量气体分子跃迁的饱和参数；另一方面增强待测痕量气体的有效吸收程，从而提高对待测痕量气体的微弱吸收的检测灵敏度，获得待测痕量气体的分子饱和吸收光谱，以实现在常温条件下，利用常规的激光器提供的探测光线即可实现对痕量气体的浓度进行探测的目的。
另外，由于分子饱和吸收光谱的消多普勒展宽特性，使得获得的待测痕量气体的分子饱和吸收光谱和待测气体中的背景气体分子的吸收光谱有效分开， 从而消除背景气体的干扰，实现对待测痕量气体的探测。由于分子不同同位素的饱和吸收光谱频率明显不同，本申请实施例提供的痕量气体的探测方法对于探测特定同位素的分子也特别有效。
下面本申请实施例提供了一种能够实施痕量气体的探测方法的痕量气体的探测系统，如图3所示，所述痕量气体的探测系统包括：激光发生装置10、谐振腔20、光电探测装置30、反馈控制装置40和扫描控制装置50；其中，
所述谐振腔20的腔体内部用于充填待测气体，所述待测气体中包括待测痕量气体；所述谐振腔20的腔体在所述谐振腔20的延伸方向上具有伸缩自由度；
所述激光发生装置10，用于在所述反馈控制装置40的控制下，提供不同频率的探测光线，所述探测光线从所述谐振腔20的延伸方向的一端入射到所述谐振腔20内部，并从所述谐振腔20的延伸方向的另一端出射，以获得携带待测痕量气体信息的探测光线；
所述光电探测装置30，用于将携带待测痕量气体信息的探测光线转换为电信号形式的探测信息；
所述扫描控制装置50，用于记录所述电信号形式的探测信息，和用于控制所述激光发生装置10以步进的方式调整出射的探测光线的频率；
所述反馈控制装置40，用于控制所述激光发生装置10出射的探测光线的频率与所述谐振腔20的纵模频率匹配。
在本实施例中，由于所述反馈控制装置40可以控制所述激光发生装置10出射的探测光线的频率与所述谐振腔20的纵模频率匹配，因此，所述扫描控制装置50可以仅用于控制所述激光发生装置10以步进的方式调整出射的探测光线的频率即可，当激光发生装置10出射的探测光线的频率在扫描控制装置50的控制下发生变化时，所述反馈控制装置40实时调整所述谐振腔20的纵模频率和/或所述激光发生装置10出射的探测光线的频率，以使所述激光发生装置10出射的探测光线的频率与所述谐振腔20的纵模频率匹配。
另外，所述扫描控制装置50控制所述激光发生装置10以步进的方式调整出射的探测光线的频率的目的，是为了使得所述扫描控制装置50中可以记录 不同频率的探测光线携带的待测痕量气体信息对应的电信号形式的探测信息，以可以根据记录的电信号形式的探测信息，获取所述待测痕量气体的分子饱和吸收光谱，并根据所述痕量气体的分子饱和吸收光谱，计算所述待测气体中所述待测痕量气体的浓度。
即可选的，在本申请的一个实施例中，所述扫描控制装置50还用于，根据记录的所述电信号形式的探测信息，获取所述待测痕量气体的分子饱和吸收光谱，并根据所述痕量气体的分子饱和吸收光谱，计算所述待测气体中所述待测痕量气体的浓度。
参考图2，所述谐振腔20包括：
外壳21，所述外壳21具有相对设置的入射端和出射端；
位于所述外壳21内部，靠近所述入射端一侧的第一反射镜22，所述第一反射镜22朝向所述入射端一侧具有增透膜；
位于所述外壳21内部，靠近所述出射端一侧的第二反射镜23，所述第一反射镜22和第二反射镜23的反射面相对设置；
与所述第一反射镜22相邻设置和/或与所述第二反射镜23相邻设置的压电装置；所述压电装置用于根据接收的控制电信号，推动与所述压电装置相邻的第一反射镜22和/或第二反射镜23移动，以使所述谐振腔20的腔体在所述谐振腔20的延伸方向上具有伸缩自由度。
在本实施例中，所述第一反射镜22和第二反射镜23之间构成了谐振腔20的腔体，以使探测激光可以在腔体中得到腔增强。
位于所述第一反射镜22朝向所述入射端一侧的增透膜用于增加入射到第一反射镜22上的探测光线的透过率，提高探测光线的光能利用率。
可选的，所述反馈控制装置40包括：射频信号源、检相装置和PID(比例-积分-微分)放大装置；其中，
所述射频信号源，用于产生正弦射频信号；
所述检相装置，用于根据所述正弦射频信号，将电信号形式的探测信息转换为误差信号；
所述PID放大装置，用于将所述误差信号，转换为反馈锁定信号，以使所述激光发生装置10出射的探测光线的频率与所述谐振腔20的纵模频率匹配。
在本实施例中，所述反馈控制装置40中的射频信号源用于提供检相装置的工作基准信号，所述检相装置将电信号形式的探测信息转换为误差信号，所述PID放大装置将所述误差信号转换为反馈锁定信号，并传输给所述压电装置，以使所述压电装置根据所述反馈锁定信号，在所述谐振腔20的延伸方向上调整所述谐振腔20的腔体长度，以调节所述谐振腔20的纵模频率，使其与所述激光发生装置10出射的探测光线的频率匹配。
那么相应的，所述扫描控制装置50只需要控制所述激光发生装置10以步进的方式调整出射的探测光线的频率即可，所述反馈控制装置40通过调节所述谐振腔20的腔体长度的方式，使得所述谐振腔20的纵模频率与所述激光发生装置10出射的探测光线的频率匹配。
需要说明的是，所述扫描控制装置50控制所述激光发生装置10的探测光线的频率的变化步长越小，最终计算获得的待测气体的浓度越精确。所述扫描控制装置50控制的所述激光发生装置10的探测光线的频率变化范围可以是兆赫兹量级，也可以是数百兆赫兹量级。本申请对所述探测光线的变化步长的具体取值以及所述探测光线的具体频率变化范围并不做限定，具体视实际情况而定。
可选的，所述激光发生装置10包括：激光器、频率调制装置和耦合透镜；
所述激光器，用于产生激光；
所述频率调制装置，用于根据所述反馈锁定信息，对所述激光器产生的激光进行调制，以获得频率与所述谐振腔20的纵模频率匹配的探测光线；
所述耦合透镜，用于对所述探测光线进行耦合后向所述谐振腔20入射。
所述激光器可以是半导体激光器、光纤激光器或固体激光器等常规的激光器种类。本申请对此并不做限定，具体视实际情况而定。
可选的，所述频率调制装置为电光调制器。
可选的，所述扫描控制装置50包括：信息存储装置和频率扫描装置；其中，
所述信息存储装置，用于记录所述电信号形式的探测信息；
所述频率扫描装置，用于产生控制电信号，并向所述激光器传输。
在本实施中，所述扫描控制装置50通过产生的控制电信号，控制所述激 光器产生的激光的频率以一定的步长变化。
可选的，所述光电探测装置30包括：透镜匹配模块和光电探测模块；其中，
所述透镜匹配模块，用于匹配所述光电探测装置30内部光场的空间模式；
所述光电探测模块，用于将携带待测痕量气体信息的探测光线转换为电信号形式的探测信息。
下面以具体的实施例说明本申请实施例提供的痕量气体的探测系统的具体实施效果。
在本实施例中，所述待测痕量气体为 12C 16O气体分子，目的是测量 12C 16O气体分子的红外振转跃迁的分子饱和吸收光谱，并根据谱峰的面积获得 12C 16O气体分子的气体分压。
可选的，所述激光器为外腔式半导体激光器，其输出的激光经过一个电光调制器调制以及耦合透镜的耦合后进入谐振腔20；谐振腔20的内部充填待测气体，所述待测气体中包含 12C 16O气体，待测气体的总压力为P，由连接谐振腔20的压力计测得；谐振腔20中设置有第一反射镜22和第二反射镜23，第一反射镜22和第二反射镜23的反射率达99.995％，第一反射镜22和第二反射镜23构成了一个光学谐振腔20，第一反射镜22或第二反射镜23的背面连接一个压电装置，可以带动镜片沿光路方向(谐振腔20延伸方向)作微小的移动。
从谐振腔20中出射的携带待测痕量气体信息的探测光线被光电探测装置30转换为电信号形式的探测信息，电信号形式的探测信号经过滤波放大后，分为两路信号，一路信号被送入反馈控制装置40中，被反馈控制装置40解调后产生反馈锁定信号，以使所述谐振腔20的纵模频率与所述激光发生装置10出射的探测光线的频率匹配；另一路信号送入扫描控制装置50中记录下来，同时扫描控制装置50控制激光产生装置进行步进式的频率扫描。
通过以上的探测激光的扫描过程，即可获得待测痕量气体的分子饱和吸收光谱，参考图4和图5，图4为模拟得到的待测气体中的待测痕量气体( 12C 16O)分压和其R(19)跃迁兰姆凹陷面积的关系，图4中横坐标为 12C 16O气体的气体分压(Partial Pressure)，单位为帕斯卡(Pa)，纵坐标为兰姆凹陷的面积(Area  of Lamb Dip)，单位为10 -9cm -1MHz；图5为测得的腔增强的分子V＝3-0、R(19)跃迁的分子饱和吸收光谱；图5中横坐标为相对频率(Relative Frequency)单位为兆赫兹(MHz)；纵坐标为吸收系数(Absorption Coefficient)，单位为10 -9cm -1。从图4中看出，待测痕量气体( 12C 16O)分压和其R(19)跃迁兰姆凹陷面积在很大范围内都有很好的线性对应关系，适于进行定量测量。拟合图5所示的分子饱和吸收光谱，得到其峰高、峰宽和峰面积，即可确定待测痕量气体( 12C 16O)在待测气体中的分压。
综上所述，本申请实施例提供了一种痕量气体的探测方法及探测系统，其中，所述痕量气体的探测方法将待测气体充填于谐振腔中，利用谐振腔一方面增强入射到谐振腔中的探测光线的激光功率，提升待测痕量气体分子跃迁的饱和参数；另一方面增强待测痕量气体的有效吸收程，从而提高对待测痕量气体的微弱吸收的检测灵敏度，获得待测痕量气体的分子饱和吸收光谱，以实现在常温条件下，利用常规的激光器提供的探测光线即可实现对痕量气体的浓度进行探测的目的。
另外，由于分子饱和吸收光谱的消多普勒展宽特性，使得获得的待测痕量气体的分子饱和吸收光谱和待测气体中的背景气体分子的吸收光谱有效分开，从而消除背景气体的干扰，实现对待测痕量气体的探测。由于分子不同同位素的饱和吸收光谱频率明显不同，本申请实施例提供的痕量气体的探测方法对于探测特定同位素的分子也特别有效。
本说明书中各个实施例采用递进的方式描述，每个实施例重点说明的都是与其他实施例的不同之处，各个实施例之间相同相似部分互相参见即可。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本申请。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本申请的精神或范围的情况下，在其它实施例中实现。因此，本申请将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (9)

  1. 一种痕量气体的探测方法，其特征在于，包括：
    提供谐振腔，并在所述谐振腔的腔体内部充填待测气体，所述待测气体中包括待测痕量气体；
    提供不同频率的探测光线，所述探测光线从所述谐振腔的延伸方向的一端入射到所述谐振腔内部，并从所述谐振腔的延伸方向的另一端出射，以获得携带待测痕量气体信息的探测光线；所述谐振腔的腔体在所述谐振腔的延伸方向上具有伸缩自由度，以使所述谐振腔的纵模频率与入射的探测光线的频率匹配；
    根据不同频率的携带待测痕量气体信息的探测光线，获取所述待测痕量气体的分子饱和吸收光谱，并根据所述痕量气体的分子饱和吸收光谱，计算所述待测气体中所述待测痕量气体的浓度。
  2. 一种痕量气体的探测系统，其特征在于，包括：激光发生装置、谐振腔、光电探测装置、反馈控制装置和扫描控制装置；其中，
    所述谐振腔的腔体内部用于充填待测气体，所述待测气体中包括待测痕量气体；所述谐振腔的腔体在所述谐振腔的延伸方向上具有伸缩自由度；
    所述激光发生装置，用于在所述反馈控制装置的控制下，提供不同频率的探测光线，所述探测光线从所述谐振腔的延伸方向的一端入射到所述谐振腔内部，并从所述谐振腔的延伸方向的另一端出射，以获得携带待测痕量气体信息的探测光线；
    所述光电探测装置，用于将携带待测痕量气体信息的探测光线转换为电信号形式的探测信息；
    所述扫描控制装置，用于记录所述电信号形式的探测信息，和用于控制所述激光发生装置以步进的方式调整出射的探测光线的频率；
    所述反馈控制装置，用于控制所述激光发生装置出射的探测光线的频率与所述谐振腔的纵模频率匹配。
  3. 根据权利要求2所述的系统，其特征在于，所述谐振腔包括：
    外壳，所述外壳具有相对设置的入射端和出射端；
    位于所述外壳内部，靠近所述入射端一侧的第一反射镜，所述第一反射镜 朝向所述入射端一侧具有增透膜；
    位于所述外壳内部，靠近所述出射端一侧的第二反射镜，所述第一反射镜和第二反射镜的反射面相对设置；
    与所述第一反射镜相邻设置和/或与所述第二反射镜相邻设置的压电装置；所述压电装置用于根据接收的控制电信号，推动与所述压电装置相邻的第一反射镜和/或第二反射镜移动，以使所述谐振腔的腔体在所述谐振腔的延伸方向上具有伸缩自由度。
  4. 根据权利要求3所述的系统，其特征在于，所述反馈控制装置包括：射频信号源、检相装置和PID放大装置；其中，
    所述射频信号源，用于产生正弦射频信号；
    所述检相装置，用于根据所述正弦射频信号，将电信号形式的探测信息转换为误差信号；
    所述PID放大装置，用于将所述误差信号，转换为反馈锁定信号，以使所述激光发生装置出射的探测光线的频率与所述谐振腔的纵模频率匹配。
  5. 根据权利要求4所述的系统，其特征在于，所述激光发生装置包括：激光器、频率调制装置和耦合透镜；
    所述激光器，用于产生激光；
    所述频率调制装置，用于根据所述反馈锁定信息，对所述激光器产生的激光进行调制，以获得频率与所述谐振腔的纵模频率匹配的探测光线；
    所述耦合透镜，用于对所述探测光线进行耦合后向所述谐振腔入射。
  6. 根据权利要求5所述的系统，其特征在于，所述频率调制装置为电光调制器。
  7. 根据权利要求3所述的系统，其特征在于，所述扫描控制装置包括：信息存储装置和频率扫描装置；其中，
    所述信息存储装置，用于记录所述电信号形式的探测信息；
    所述频率扫描装置，用于产生控制电信号，并向所述激光器传输。
  8. 根据权利要求2所述的系统，其特征在于，所述扫描控制装置还用于，根据记录的所述电信号形式的探测信息，获取所述待测痕量气体的分子饱和吸收光谱，并根据所述痕量气体的分子饱和吸收光谱，计算所述待测气体中所述 待测痕量气体的浓度。
  9. 根据权利要求2所述的系统，其特征在于，所述光电探测装置包括：透镜匹配模块和光电探测模块；其中，
    所述透镜匹配模块，用于匹配所述光电探测装置内部光场的空间模式；
    所述光电探测模块，用于将携带待测痕量气体信息的探测光线转换为电信号形式的探测信息。
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