WO2017153765A1 - Détecteur photo-acoustique - Google Patents

Détecteur photo-acoustique Download PDF

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Publication number
WO2017153765A1
WO2017153765A1 PCT/GB2017/050639 GB2017050639W WO2017153765A1 WO 2017153765 A1 WO2017153765 A1 WO 2017153765A1 GB 2017050639 W GB2017050639 W GB 2017050639W WO 2017153765 A1 WO2017153765 A1 WO 2017153765A1
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Prior art keywords
sensor
laser
cavity
acoustic
modulating
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English (en)
Inventor
David Stothard
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Fraunhofer UK Research Ltd
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Fraunhofer UK Research Ltd
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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
    • 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
    • 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
    • G01N21/39—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
    • 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

Definitions

  • the present invention relates to a detector for detecting fluid (e.g. gas or liquid).
  • fluid e.g. gas or liquid
  • the present invention relates to a gas detector.
  • the detector may be operable to detect very low levels of gas leaking from the surface of the earth or fugitive from a man-made object such as a processing plant.
  • the gas may be ethane.
  • ultra-high sensitivity detection technologies have been developed. These can be categorised as falling into three general technologies: analytical (gas chromatography, spectrometry, etc.); electro- and bio-chemical; and laser optical absorption. Whilst delivering the most sensitive and robust measurements, analytical devices do not offer real-time measurements and are large, laboratory-based instruments that cannot be readily deployed in the field. Electro- and bio-chemical sensors offer reasonable sensitivity (ppm), are compact and consume very little energy making them very well suited to small, remotely-operated instruments. However, they do not exhibit the required sensitivity for the current application and their very slow response time (many minutes), hysteresis and sensitivity to humidity also render them unsuitable in many scenarios. In contrast, optical absorption sensors offer significantly faster detection times ( ⁇ 1 sec), are highly target-molecule specific, can be compact, and can potentially offer sensitivities down to sub-ppt concentration levels.
  • All forms of laser absorption sensor are dependent upon the principle that incident electromagnetic radiation of the correct frequency resonates with a particular electronic (in the case of visible and near-IR) or rotational / vibrational (for infrared) transition or mode of the molecule of interest, and in so doing is absorbed.
  • the resonant nature of this interaction means that only light in a narrow bandwidth around the correct frequency contributes to this process, requiring spectrally pure radiation to be used.
  • the peak absorption wavelength lies in the so-called spectral fingerprint region at 6-12 ⁇ . For maximum optical absorption this requires the use of a laser which operates at this wavelength.
  • Photo-acoustic spectroscopy is a form of laser absorption spectroscopy. It works on the principle that absorption of laser light causes localised heating. If the incident light is modulated (in amplitude or frequency), the absorption is modulated and a periodic pressure wave (i.e. a sound wave) is produced at the modulation frequency which can then be detected with a microphone.
  • the sound wave can be substantially enhanced by conducting this process within an absorption cell which is acoustically resonant at the modulation frequency, so the sound wave bounces back and forth within the cell acquiring more intensity on each pass.
  • the microphone can be placed at an anti-nodal point in the acoustic wave so as to maximise the detection of this enhanced signal.
  • Quartz-enhanced photo-acoustic spectroscopy is a refinement of classical photo-acoustic spectroscopy. Quartz-enhanced photo-acoustic spectroscopy uses a quartz tuning fork, which is a sharply resonant detection element, to detect the pressure or sound wave.
  • FIG 1 shows a schematic diagram of a standard quartz-enhanced photo-acoustic system.
  • An excitation beam from a laser source is focused down in between two vertical prongs of a quartz tuning fork.
  • the incident radiation is frequency or amplitude modulated at the resonant frequency of the quartz tuning fork.
  • a very small thermally induced expansion caused by optical absorption within the gas causes a local pressure wave, as shown in Figure 2.
  • This induces a symmetric bending mode of the quartz tuning fork.
  • the amplitude of this mode is increased over time by the very high Q of the quartz tuning fork.
  • the signal obtained from the quartz tuning fork can be enhanced further by placing it within a micro-resonator tube of organ-pipe (i.e.
  • quartz-enhanced photo-acoustic spectroscopy is that it is immune from background acoustic noise. Also, quartz-enhanced photo- acoustic spectroscopy lends itself to compact detection topologies.
  • absolute sensitivity is related to the strength of the optical absorption feature exhibited by the molecule of interest, its concentration and, critically, the power of the excitation laser used.
  • quartz- enhanced photo-acoustic spectroscopy devices have been demonstrated on complex molecules whose peak absorption wavelength occurs in the deeper-infrared.
  • Figure 4 shows an example of a photoacoustic sensor used for the detection of such complex molecules.
  • the long wavelengths at which these molecules absorb mean that commonly used, shorter wavelength lasers cannot be used, and so well-established deeper-IR sources, such as quantum-cascade lasers, are used as the excitation source.
  • the optical field emitted by the quantum cascade laser is focussed down into the photoacoustic cell, which in the case of Figure 4 comprises a quartz-enhanced spectrophone.
  • the quantum cascade laser is tuned to the wavelength corresponding with the absorption feature exhibited by the molecule of interest, and is modulated in amplitude or frequency in order to stimulate a periodic acoustic pressure wave resonant within the tube located in the photoacoustic cell.
  • the sensitivity of such systems is limited by the low power exhibited by quantum cascade lasers.
  • FIG. 5 Various attempts to address the problem with low power quantum cascade lasers have been proposed.
  • a low power single- frequency quantum-cascade laser is placed within a high-finesse Fabry-Perot cavity that is held on resonance. This can enhance the power by a factor of -500.
  • a quartz enhanced photoacoustic sensor is placed within the enhancement cavity in order to take advantage of the enhanced circulating field. Whilst an improvement in sensitivity of over two orders of magnitude is observed, the system is very complex. Also, the enhancement cavity must remain on resonance with the incident optical field from the quantum-cascade laser, and so the system is sensitive to the effects of mechanical vibration. Summary of the Invention
  • a fluid sensor comprising: a solid state laser that has a solid state gain material in a laser cavity, means for modulating light in the cavity of the solid state laser to induce an acoustic or pressure wave caused by absorption of the resonant wave, and means, for example a microphone, located in the beam path of the light for detecting the acoustic or pressure wave.
  • the solid state laser may be a semiconductor laser.
  • the very high circulating fields found there can be accessed. Therefore, even though only low levels of optical power may be output coupled from the laser under normal circumstances, the very high field in the laser cavity can serve as the excitation source for a photoacoustic sensor.
  • a photoacoustic cell By placing a photoacoustic cell within the cavity of a high finesse solid state laser, such as a semiconductor excitation laser, operating in the spectral region of interest, the very high circulating fields found there can be accessed. Therefore, even though only low levels of optical power may be output coupled from the laser under normal circumstances, the very high field in the laser cavity can serve as the excitation source for a photoacoustic sensor.
  • This provides a simple and compact sensor solution that can provide high levels of sensitivity.
  • this means the sensor of the invention can be made portable.
  • semiconductor lasers can exhibit a broad gain-bandwidth, and so are tunable. This allows many different molecules, exhibiting absorption at different wavelengths to be detected with a single device.
  • the device can operate with a very narrow optical line width, and this, along with its very broad tunability and high power circulating field, confers very high sensitivity (due to high circulating power), flexibility in choice of target molecular species (because of the broad tunability) and target specificity (because of the narrow optical line width of the resonating field). This is very useful in applications such as pollution monitoring, where many different polluting substances exhibit optical absorption lines in close proximity.
  • the broad tunability allows more of the unique spectral profile to be acquired.
  • the laser may be operable to emit light with a wavelength in any of the following ranges: UV, IR and THz.
  • the laser cavity may be a linear cavity.
  • the linear cavity may be adapted to provide a standing wave.
  • the laser cavity may be a ring cavity.
  • the ring wave cavity may be adapted to provide a travelling wave.
  • only a single optical cavity is provided. Only a single wavelength of light may be resonant in the single cavity at any given time (although that wavelength may be variable).
  • the sensor may include a photo-acoustic cell, the microphone being located in the photo-acoustic cell.
  • the microphone may comprise a tuning fork, for example a quartz tuning fork.
  • the means for modulating may comprise a modulator, for example an optical element such as an etalon or grating for modulating the light.
  • the means for modulating may be operable to vary a characteristic of the primary pump power source or the optical cavity thereby to cause modulation.
  • the means for modulating may be operable to vary the current used to drive the semiconductor laser.
  • the means for modulating may be operable to vary the length of the optical cavity.
  • the means for modulating light may be operable to modulate the resonant light at a frequency tuned to the resonant frequency of the tuning fork or the acoustic cell.
  • the means for modulating light may modulate the frequency or intensity of the light.
  • the means for modulating light may be operable to modulate the current applied to the semiconductor laser, thereby to cause modulation of light in the laser cavity.
  • the wavelength of the resonant light is selected to match an absorption characteristic of a molecule or fluid of interest. For example, for TATP (an explosive compound) detection applications, the resonant wavelength may be in the region of 9.2 ⁇ or 10.5 ⁇ for sulphur hexafluoride.
  • the sensor may comprise an acoustic amplifier, for example a microresonator tube, for enhancing the acoustic or pressure wave.
  • a tuning fork the amplifier may be located either side of the two forks of the tuning fork.
  • the tuning fork may be located immediately adjacent to a small opening in the side of the resonator tube.
  • the laser cavity is adapted to substantially prevent output coupling of light.
  • light power levels within the cavity are optimised.
  • the laser may be tunable. Additionally or alternatively, the laser may be operable in a continuous wave or pulsed mode.
  • the solid state laser may be a semiconductor laser, such as a quantum cascade laser or an interband cascade laser.
  • Figure 1 is a schematic diagram of a quartz-enhanced photo-acoustic system
  • FIG. 2 is an expanded schematic view of a typical quartz tuning fork for use in the system of Figure 1 ;
  • Figure 3(a) is an expanded schematic view of a quartz tuning fork in which an acoustic micro-resonator is included to enhance the acoustic signal
  • Figure 3(b) is a photograph of an actual system showing its highly compact form
  • Figure 4 is a schematic representation of a prior art photo acoustic spectroscopy system that uses a quantum-cascade laser as an excitation source
  • Figure 5 is a schematic representation of a prior art photo acoustic spectroscopy system that uses a quantum-cascade laser, in which sensitivity is enhanced using an external optical cavity held on resonance;
  • Figure 6 is a schematic representation of a photo acoustic spectroscopy system, where the photo acoustic apparatus is located within the cavity of a quantum cascade laser;
  • Figure 7 is a schematic representation of the system of Figure 6 with the addition of a reference cell
  • Figure 8 is a schematic representation of a system similar to that of Figure 6, but implemented in a ring-cavity geometry.
  • Figure 6 shows a laser that has a laser gain material in a single optical cavity.
  • the laser gain material is adapted to emit substantially a single wavelength of light. Light emitted by the laser gain material is resonant in the single cavity. Within the cavity, a quartz-enhanced photo-acoustic spectroscopy cell is located.
  • the laser gain material may be, for example, a quantum-cascade laser gain material.
  • the laser can be operated in a continuous wave (CW) mode or a pulsed mode.
  • the quantum-cascade laser has a quantum-cascade gain material within a laser cavity. The quantum-cascade gain material exhibits optical gain when electrically pumped.
  • the laser cavity is defined by an end mirror M1 and the highly reflective facet M2 of the gain material.
  • the end mirror M1 could be replaced by, for example, a littrow grating for line narrowing and control.
  • a photo- acoustic spectroscopy cell is provided between the quantum-cascade laser gain material and the end mirror M1 .
  • this is a quartz- enhanced photoacoustic spectroscopy cell.
  • This has a gas chamber for sampling gas, and a quartz tuning fork with a micro-resonator tube located inside the chamber.
  • the length of the acoustic tube is chosen such that its resonance coincides with that of the quartz element.
  • the chamber has a gas inlet and a gas outlet to allow gas samples to be circulated through the chamber passively or actively for example via a micro pump (not shown). Windows are provided on opposing sides of the chamber to allow the light circulating in the cavity to pass through the chamber.
  • optional suitably placed anti-reflection coated lenses can be provided within the cavity to collimate and refocus the circulating beam down onto the acoustically resonant tube within which the acoustic sensor is located.
  • the gas to be measured flows through the cell and the quantum-cascade laser is modulated at the acoustic resonance of the quartz enhanced photoacoustic sensor module.
  • the quantum-cascade laser can be modulated in either amplitude or optical frequency and the means by which this can be brought about could, for example, be through electrical variation of the quantum-cascade laser pump current, variation of the Littrow-grating (if used) angle; reciprocating the position of the end mirror M1 , or modulation of some other intra-cavity frequency-selective element such as an etalon (not shown in Figure 6).
  • the modulated light will be absorbed, cause a thermal expansion and will build up an acoustic wave whose amplitude is proportional to the concentration of the target molecule. This will induce an electrical signal in the quartz tuning fork or microphone, which can subsequently be measured and processed as per Figure 1 .
  • the quantum-cascade laser cavity is designed such that optical round-trip loss is minimised, in order to maximise finesse and therefore circulating field power. No output coupling for the circulating mode is provided. It should be noted that this is contrary to standard practice where some output coupling is used to enable some of the circulating mode to leak usefully out of the cavity.
  • the detection element is located within the cavity of the excitation laser, it is advantageous to keep as much circulating field locked within the cavity in order to obtain high circulating powers, and hence highly sensitive measurements. This could lead to excitation powers in the >1W range. Furthermore, because the field oscillates in both directions, it is absorbed by the gas twice on each round trip, giving an effective excitation power of twice this value. As already described, absorption of the modulated circulating wave causes localised heating, which in turn causes a pressure or sound wave that is amplified and can be detected by the quartz tuning fork. This allows very sensitive quartz-enhanced photo-acoustic spectroscopy.
  • a tunable quantum-cascade laser could be used to allow for the acquisition of spectra over a large spectral range. This is important when detecting molecules whose features are broad and spread out over the fingerprint range.
  • a Littrow grating is used as the cavity end mirror. The angle of the Littrow grating is slowly varied to set the measurement wavelength, and the amplitude of the quantum- cascade laser is modulated at the acoustic resonance of the photoacoustic sensor module in order to induce the acoustic wave. The spectrum is then acquired as the angle of the grating is changed and the laser tunes across its gain bandwidth.
  • the speed at which the grating can be moved is dictated by the acoustic resonance Q of the photoacoustic sensor module, the acoustic resonance frequency of the photoacoustic sensor module (and ensuing modulation frequency of the excitation laser) and the signal averaging required.
  • a tunable laser can be useful for applications where many different compounds are present and so spectra need to be acquired at a high resolution and over a wide range.
  • An example of this might be disease diagnosis through examination of exhaled breath. There are as many as 200 compounds and molecules in breath, most of them there in trace ( ⁇ ppb) concentrations. Many early-stage diseases (cancer, certain mental conditions such as schizophrenia) result in enhanced levels of some of these compounds, but only in trace levels, for example ⁇ 1 ppb background, with a change of a couple of ppb. Therefore, «ppb resolution is required to make good measurements. High resolution and high sensitivity spectroscopy over very wide wavelength ranges are therefore required to differentiate between all these compounds.
  • the sensor of the invention is able to deliver this level of sensitivity, whilst being compact and robust.
  • the detection of molecules and compounds whose complexity places their absorption bands at very long wavelengths is particularly relevant as their spectral features are often significantly spread out in wavelength, and large wavelength scans are required in order to fully acquire and identify them.
  • an absorbing medium i.e. the gas or liquid to be detected
  • the round-trip loss experienced by the resonating field and so laser performance.
  • this will lead to a drop in the amount of circulating field produced, once the amount of absorption becomes significant.
  • concentrations which are of primary interest for the present invention
  • the impact upon round-trip loss is negligible and can be ignored. If maximum dynamic range were required, however, then at substantially higher concentrations (many parts per hundred) significant absorption will occur and may begin to significantly impact upon the circulating laser field.
  • the same quartz enhanced photoacoustic sensor signal would be expected for two different target species concentrations - very low concentration (where there is a high optical field inducing an acoustic wave from very few molecules) and very high concentration (where not much field induces the same signal from a large number of molecules).
  • Such an ambiguity could be eliminated through the use of a simple extra- cavity photodetector to monitor the circulating field as the measurement is obtained in order to discern under which one of these conditions the measurement is being performed. This would enable the device to yield maximum dynamic range, from very low (sub-parts per billion) to very high (parts per hundred) concentration.
  • Figure 7 shows the detector of Figure 6 with an optional fluid reference cell.
  • This cell may have a sample of one or more target gaseous or liquid species contained within it.
  • Accurate and automatic tuning of the laser to the peak absorption wavelength can then be achieved by monitoring the absorption of the cell. This detection is achieved by dividing the signal from the reference cell transmission detector by the signal from the circulating field detector.
  • the laser can be coarsely tuned to the spectral region of interest, and then this reference cell absorption signal can be used to fine tune the laser wavelength. It also serves as a safety mechanism to ensure that the wavelength has not drifted, which could lead to false negative detection.
  • FIG. 8 shows another intracavity gas sensor based on a travelling wave 'ring' geometry.
  • This has a laser gain material in a single optical ring cavity.
  • the laser gain material is adapted to emit substantially a single wavelength of light.
  • Light emitted by the laser gain material is resonant in the single ring cavity.
  • a quartz-enhanced photo-acoustic spectroscopy cell is located within the single cavity.
  • the laser gain material may be, for example, a quantum-cascade laser gain material.
  • the ring cavity is defined by four mirrors, M1 , M2, M3 and M4.
  • the device can be operated in the pulsed or the continuous- wave mode. If pulsed, the device can be pulsed at the acoustic-resonant frequency of the photoacoustic sensor module; in a 'tone-burst' mode where a higher frequency pulse train is gated at the acoustic resonance or pulsed continuously and some other means of frequency or amplitude modulation utilised.
  • the system shown in Figure 8 has many optional refinements. For instance, fine frequency control can be brought about by replacing one of the mirrors with a diffraction grating or by utilising an intracavity frequency-selective element such as an etalon or both. For the best performance, the travelling optical wave within the cavity should propagate in only one direction.
  • a generic uni-directional device is shown in Figure 8. This could be based around a faraday-isolator type device, an acousto-optic deflector or even a coupled Fox-Li cavity. As with the embodiment of Figure 6, the optional optical reference cell shown in Figure 7 could be used.
  • the present invention provides a compact, high sensitivity detector with excellent molecular specificity based upon a unique marriage of laser absorption spectroscopy laser light generation technologies.
  • a photo-acoustic spectrophone such as a quartz tuning fork, immersed within the very high optical field found within the cavity of a semiconductor laser, for example a quantum-cascade laser. Quartz- enhanced photo-acoustic spectroscopy detection technology has a proven track record in very low noise, high sensitivity measurements in exceptionally compact and cost effective geometries.
  • the present invention can be used to sense or detect numerous different fluids. Some examples of gases that can be detected are set our below: Pollutant: Absorption Wavelength:

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Abstract

L'invention concerne un capteur de fluide qui comprend un laser à semi-conducteurs comprenant un matériau de gain de laser à semi-conducteurs dans une cavité laser, la lumière émise par le matériau de gain de laser étant résonante dans la cavité laser. Le capteur de fluide comprend en outre des moyens pour moduler la lumière dans la cavité laser pour induire une onde acoustique ou de pression provoquée par l'absorption de l'onde résonante, et des moyens situés dans la cavité laser pour détecter l'onde acoustique ou de pression. Le capteur de fluide peut être utilisé pour détecter un fluide tel qu'un gaz. Le capteur de fluide peut être utilisé pour détecter de très faibles niveaux de gaz s'échappant de la surface de la terre ou s'échappant d'un objet artificiel tel qu'une installation de traitement. Par exemple, le gaz peut être de l'éthane.
PCT/GB2017/050639 2016-03-09 2017-03-09 Détecteur photo-acoustique Ceased WO2017153765A1 (fr)

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GBGB1604075.0A GB201604075D0 (en) 2016-03-09 2016-03-09 Detector
GB1604075.0 2016-03-09

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WO2019122855A1 (fr) * 2017-12-18 2019-06-27 Stratium Limited Système et procédé de détection de produits chimiques gazeux
CN110044824A (zh) * 2019-05-06 2019-07-23 安徽大学 一种基于石英音叉的双光谱气体检测装置及方法
EP3761006A1 (fr) * 2019-07-03 2021-01-06 Nokia Technologies Oy Appareil photo-acoustique et procédés
CN112881299A (zh) * 2021-03-30 2021-06-01 安徽工程大学 基于无源音叉的干涉式全光纤光声光谱系统及其探测方法
CN113267453A (zh) * 2021-03-30 2021-08-17 安徽工程大学 无源音叉共振增强的全光纤三气体探测光声光谱系统及其探测方法
CN113624718A (zh) * 2021-08-13 2021-11-09 哈尔滨工业大学 基于压阻薄膜的光声光谱痕量气体检测装置及方法
US20220205959A1 (en) * 2019-01-16 2022-06-30 Massachusetts Institute Of Technology Acoustic spectrometer
CN116297221A (zh) * 2023-03-17 2023-06-23 哈尔滨工业大学 基于空芯光纤微孔的分布式光声光谱痕量气体检测装置
CN117990612A (zh) * 2023-12-28 2024-05-07 中国电力科学研究院有限公司 一种利用光学反馈的石英增强光声光谱检测方法及系统
CN118730919A (zh) * 2024-07-26 2024-10-01 华中科技大学 半开腔谐振管在轴配置的音叉增强型光声光谱检测系统

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