CN112710628B - Ultrasensitive SF based on broadband double-optical comb spectrum 6 Method for detecting gas decomposition component - Google Patents
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Abstract
The invention provides an ultrasensitive SF based on broadband double-optical comb spectrum 6 The gas decomposition component detecting system includes two optical combs, beam combiner, reinforced gas sample cell, lens, hollow fiber, microphone, audio amplifier and data collecting card. The invention discloses an ultrasensitive SF based on broadband double optical comb spectrum 6 According to the method for detecting the gas decomposition components, the characteristic of wide spectrum coverage of the optical comb is utilized, and simultaneous measurement of a plurality of molecular absorption peaks can be realized by a modulation mode of beat frequency of the double optical comb, so that the dilemma of point-by-point sweep spectrum measurement of the traditional photoacoustic spectrum is solved; the photoacoustic effect and the hollow optical fiber are combined, so that the effective optical path and the action cross section of the interaction of light and molecules are increased, and the problem of low sensitivity of the traditional spectrum detection technology is solved; the technology is applied to SF 6 The detection of the gas decomposition components can effectively improve the detection capability of the power equipment fault gas detection device on complex multicomponent gas.
Description
Technical Field
The invention belongs to the technical field of gas detection, and particularly relates to an ultrasensitive SF (sulfur hexafluoride) based on broadband double-optical comb spectrum 6 A system and method for detecting gas decomposition components.
Background
SF (gas insulated switchgear) such as GIS (fully enclosed gas combined electrical apparatus), open switch, transformer and the like 6 The (sulfur hexafluoride) gas insulation equipment is widely applied to the power system due to small occupied area and high reliability. Because all the components are enclosed in the metal shell, early faults are more difficult to find than conventional equipment, and even if disassembly and overhaul are performed, the equipment process is complex, the overhaul work is difficult and time-consuming, so that the loss caused by the faults is also larger. The internal states of the devices such as GIS and the like are monitored, and the occurrence of accidents is always a hot spot for research of domestic and foreign scientific research institutions. By detecting SF in GIS equipment 6 The gas decomposition products are used for carrying out fault diagnosis and state evaluation on the internal insulation of the equipment, have the characteristics of strong anti-interference capability, high sensitivity and the like, and are widely used for on-site detection and analysis of the equipment. In an actual GIS device, SF 6 The gas contains trace amounts of air, moisture and mineral oil impurities which participate in the reaction to form stable decomposition products, such as SO 2 、SOF 2 、H 2 S, HF, etc. Thus, by detecting SF 6 The gas decomposition product volume fraction is a great aid in the discovery of equipment latent faults and fault localization.
The current gas detection means mainly comprise: contact technology (e.g., semiconductor sensors, contact combustion sensors, electrochemical sensors) and non-contact technology (e.g., fourier transform infrared spectroscopy, spectral absorption). However, the current gas detection schemes have the following problems:
1) The contact detection technology aims at single gas type, the type of the gas which can be monitored is very limited, and SF can not be detected 6 The decomposed product is comprehensively detected, so that a single data error is introduced, and misjudgment is caused; and the technology has the defects of fixed-point detection or manual field operation and the like; especially, aiming at dangerous gas, the problems of short service life and easy corrosion exist, and online real-time monitoring cannot be realized.
2) The non-contact optical detection scheme mainly comprises the following technologies.
a) Tunable semiconductor laser absorption spectroscopy (i.e., TDLAS) based on frequency modulation. By tuning the wavelength (or frequency) of the laser, the transmitted light intensity through the absorption cell is detected point by point to obtain the absorption spectrum. The combination of the long-optical-path gas cell has high measurement sensitivity, high precision and high resolution, but the measurement speed is extremely slow, the detected gas type is limited, and the cost is high.
b) Differential absorption spectroscopy (i.e., DOAS). The differential absorption of light by the sample is used to achieve a concentration measurement of the substance. The method has the advantages that various trace gases can be measured simultaneously, but the method is limited to gas molecules with narrow absorption lines in the measured wave band, and a monitoring system of the method is also influenced by water vapor in the environment.
c) Photoacoustic spectroscopy (PAS). Photoacoustic spectrometry detection systems generally include light sources, light modulators, photoacoustic cells, microphones, demodulators, and audio amplifiers. The working process is that the light modulator is used for periodically modulating the intensity of the light source radiation. The modulated light then enters the photoacoustic cell and interacts with the gas molecules. After absorbing light energy, the molecules to be tested are excited to a high energy state and radiate heat energy to the front to generate sound waves with modulated frequency. At this time, the microphone receives sound waves. The method can detect the concentration of the gas which is obviously absorbed in the emission spectrum range of the infrared light source, and the selection of the spectrum range can be realized through a filter. The method has the defects of low detection precision, low resolution and poor repeatability due to low coherence and stability of the infrared light source. Furthermore, simultaneous measurement of the absorption peaks of the multicomponent gas is difficult to achieve, which is also a disadvantage of this method.
An optical frequency comb (optical comb for short) is a broadband laser light source with good coherence and stable time-frequency characteristics. The spectrum detection technology based on the optical comb can realize simultaneous, high-precision and high-resolution measurement of hundreds of molecular absorption peaks. However, the optical comb has a wide spectrum and energy dispersion, so that the detection sensitivity of the method is low and cannot be compared with the conventional gas detection technologies.
The spectrum detection technology has important application value in aspects of power equipment fault detection, early warning and the like. However, since the components and contents of the gas are complex and different in the fault characteristic of the electrical equipment, stringent requirements are put on the characteristics of the gas identification or resolving power (selectivity), sensitivity, accuracy, and detectable gas species of the gas detection technology.
The existing non-contact gas detection technology has the problems of low spectral precision and accuracy, limited detection sensitivity, difficult quantitative analysis and limited information acquisition content. The problems limit the accuracy of the current gas detection and the real-time performance and reliability of the power transmission and transformation equipment evaluation to a great extent.
Disclosure of Invention
The invention aims to provide a method for improving the time-frequency stability and coherence of excitation light by adopting an optical comb source as an excitation source, so as to improve the measurement precision and repeatability; the frequency modulation of a plurality of molecular absorption peaks is realized through the multi-longitudinal mode beat frequency effect of the double optical comb, and a photoacoustic audio signal corresponding to the absorption peaks is generated and detected by a microphone at the same time; by means of binding laser and molecules in the hollow optical fiber, the interaction section of the molecules and light is increased, the absorption intensity of the molecules is improved, and the detection sensitivity of photoacoustic signals is improved 6 A system and method for detecting gas decomposition components.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
ultrasensitive SF based on broadband double-optical comb spectrum 6 A gas decomposition component detection system, the system comprising:
1) Optical comb light source: the number of the optical comb light sources is two, and the carrier envelope phase zero frequency and the repetition frequency of the optical comb light sources are respectively: f (f) 01 And f r1 And f 02 And f r2 The method comprises the steps of carrying out a first treatment on the surface of the Each optical comb is composed of n frequency teeth; wherein the frequency of the nth comb teeth is f 0 +nf r . Frequency difference f of nth comb teeth of two optical combs b ＝|(f 02 +nf r2 )-(f 01 +nf r1 ) And I, then the beat frequency signals of the nth comb teeth of the two optical combs. By tuning the laser parameters, i.e. f 0 And f r The beat signal f can be made b In the audio frequency domain (20 Hz-20 kHz), the output light of the two broadband optical comb lasers is overlapped through the beam combiner to form a double optical comb laser beam.
2) A beam combiner: for coupling the output light of the two optical combs into spatially coincident light beams.
3) Enhancement type gas sample pool: the gas sample cell comprises an air inlet, an air outlet, a light-passing window, a section of hollow optical fiber wound on a microphone and a coupling lens for coupling laser into the optical fiber. The hollow optical fiber is an optical transmission medium which is hollow and forms a cylindrical space and is coupled into the hollow optical fiber through a lens; the hollow optical fiber contains gas molecules to be measured.
4) A microphone: for receiving an audio signal.
5) An audio amplifier: for amplifying weak signals.
6) A data acquisition card: for recording audio signals.
Ultrasensitive SF based on broadband double optical comb spectrum 6 The invention also provides a gas decomposition component detection system
Ultrasensitive SF based on broadband double-optical comb spectrum 6 A method for detecting a gas-decomposed component, the method comprising the steps of:
step 1: the output light of the two broadband optical comb lasers are overlapped through the beam combiner to form a double optical comb laser beam; the spectrum of the optical comb needs to cover a plurality of molecular absorption peaks;
step 2: the double-light comb laser light enters the enhanced gas sample cell and is coupled into the hollow optical fiber through the lens; the hollow optical fiber contains gas molecules to be detected; when the nth comb tooth frequency of the two optical combs is in the range of the absorption peak frequency spectrum of the gas molecules, the molecules will absorb the optical comb photons of the frequency and enter into the high excitation state of the vibration energy level, and the vibration frequency is equal to the excitation light frequency, namely (f respectively 02 +nf r2 ) And (f) 01 +nf r1 ) The method comprises the steps of carrying out a first treatment on the surface of the Generating a beat signal between two different frequency vibromens, i.e. f b ＝|(f 02 +nf r2 )-(f 01 +nf r1 ) I (I); under the effect of the photoacoustic effect, the vibration of the molecules is converted into an audio signal with the frequency f b ；
Step 3: the optical fiber is wound around the microphone, and the microphone can effectively receive the audio signal caused by molecular vibration, namely beat signal f b ；
Step 4: the audio signal is amplified after passing through the amplifier, and then recorded by the data acquisition card; the recorded signal is a time domain waveform; the frequency of the beat frequency signal can be obtained after the waveform is subjected to discrete Fourier transform; because of different absorption peaks and absorption frequencies, the generated beat frequency signals are different, and therefore, the beat frequency signals can be distinguished by measuring the beat frequency signals, and the simultaneous measurement of a plurality of gas molecular absorption peaks is realized; meanwhile, as the laser and the molecules are bound in the hollow optical fiber, the interaction distance and the absorption section of the light and the molecules are increased, and the detection sensitivity is improved, so that the ultrasensitive spectrum detection of the decomposition products of the multicomponent sulfur hexafluoride electrical equipment is realized.
According to the invention, the broadband double-light comb light source is used for measuring the photoacoustic spectrum, so that the difficulty in simultaneous measurement of multiple absorption peaks in photoacoustic spectrum measurement is increased, the resolving power for detecting fault gas of complex multi-component power equipment is improved, and the problems of cross sensitivity and poor selectivity in the traditional technology are solved; by adopting a method of combining the hollow optical fiber with the photoacoustic spectrum and the optical comb spectrum, the spectrum width and the detection sensitivity of the spectrum are increased. Compared with the traditional gas spectrum analysis method, the method has the advantages of high sensitivity, high resolution, simultaneous detection of a plurality of absorption peaks and the like, and can realize efficient and accurate analysis of the spectral line of the characteristic gas of the power grid fault equipment.
Drawings
FIG. 1 is a schematic diagram of the structure of the present invention;
FIG. 2 is a schematic diagram of the beat frequency of the dual optical comb of the present invention;
FIG. 3 is a diagram of the content structure of an enhanced gas cell in accordance with the present invention;
fig. 4 is a schematic structural diagram of an embodiment of the present invention.
In the figure, a 1, 2-optical comb laser source, a 3-polarization controller, a 4-beam combiner, a 5-half-wave plate, a 6-enhanced gas sample cell, a 7-lens, an 8-hollow optical fiber, a 9-microphone, a 10-filter, an 11-audio amplifier and a 12-data acquisition card.
Detailed Description
The invention is described in further detail below with reference to the attached drawings and specific examples:
ultrasensitive SF based on broadband double-optical comb spectrum 6 A gas decomposition component detection system (fig. 1), the system comprising:
1) Optical comb light source: the number of the optical comb light sources is two, and the carrier envelope phase zero frequency and the repetition frequency of the optical comb light sources are respectively: f (f) 01 And f r1 And f 02 And f r2 The method comprises the steps of carrying out a first treatment on the surface of the Each optical comb is composed of n frequency teeth; wherein the frequency of the nth comb teeth is f 0 +nf r (FIG. 2). Frequency difference f of nth comb teeth of two optical combs b ＝|(f 02 +nf r2 )-(f 01 +nf r1 ) And I, then the beat frequency signals of the nth comb teeth of the two optical combs. By tuning the laser parameters, i.e. f 0 And f r The beat signal f can be made b In the audio frequency domain (20 Hz-20 kHz).
2) A beam combiner: for coupling the output light of the two optical combs into spatially coincident light beams.
3) Enhancement type gas sample pool: the gas sample cell is used for ultrasensitive gas photoacoustic spectrum detection and comprises an air inlet, an air outlet, a light passing window, a section of hollow optical fiber wound on a microphone and a coupling lens for coupling laser into the optical fiber (figure 3). Hollow fiber refers to an optical transmission medium in which an optical fiber is hollow to form a cylindrical space.
4) A microphone: for receiving an audio signal.
5) An audio amplifier: for amplifying weak signals.
6) A data acquisition card: for recording audio signals.
The ultra-sensitive SF based on broadband double optical comb spectrum of the present invention as shown in FIG. 4 6 The gas decomposition component detection system comprises optical comb laser sources 1 and 2, a polarization controller 3, a beam combiner 4, a half-wave plate 5, an enhanced gas sample cell 6, a lens 7, a hollow fiber 8 and a microphone 9, and filtersA wave device 10, an audio amplifier 11, and a data acquisition card 12. The output light of the optical combs 1 and 2 is spatially combined by a beam combiner 4, wherein one path of optical comb light passes through a polarization controller to adjust the polarization state, so that the polarization of the two paths of optical combs is the same. Spatial coincidence and polarization control are the necessary conditions to achieve both optical beat frequencies. After beam combination, the laser passes through a half-wave plate, and the polarization state of the laser is optimized, so that the laser can enter the hollow optical fiber 8 with optimal coupling efficiency after passing through the lens 7. The double optical comb beam interacts with the gas molecules to be measured in the optical fiber, is absorbed, generates an acoustic wave signal by the photoacoustic effect, and is received by the microphone 9. The output audio signal of the microphone 9 is amplified by an audio amplifier 11 after the background and high-frequency noise are filtered by a filter 10, and finally, the data is recorded and processed by a data acquisition card 12.
In the above technical scheme, the gas to be measured is introduced into the enhanced gas sample cell 6 through the gas inlet. In measurement, the gas inlet and outlet of the enhanced gas sample tank are closed, and the gas in the tank enters the hollow optical fiber through a diffusion process. And after the measurement is finished, vacuumizing the gas tank through the gas outlet, and discharging the gas of the original residual sample.
In the above technical solution, the microphone 9 is used to measure the acoustic signal generated by molecules absorbing the double-light comb light, and the signal frequency is equal to the beat frequency signal f between the absorbed double-light comb teeth b . Different absorption peaks generate different audio frequencies, and can be used for distinguishing the absorption peaks, so that the identification of gas types is realized.
In the above technical solution, after the electric signal is amplified by the amplifier 11, the electric signal is collected by the data collecting card 12, and the photoacoustic spectrum intensity signal of the gas to be detected is obtained by using the fourier transform method, and the signal and the concentration of the gas are in a proportional relationship, so that the signal can be used for identifying the concentration of the gas and the type of the gas.
Ultrasensitive SF based on broadband double optical comb spectrum 6 The detection method of the embodiment of the gas decomposition component detection system comprises the following steps:
step 1: the output light of the two broadband optical comb lasers 1 and 2 are overlapped in space through the beam combiner 4 to form a double optical comb laser beam;
step 2: the double-light comb laser light enters the enhanced gas sample cell 6 and is coupled into the hollow optical fiber 8 through the lens 7; the hollow optical fiber contains gas molecules to be detected, and under the action of photoacoustic effect, the vibration of the molecules is converted into audio signals, and the signal frequency is f b ；
Step 3: the optical fiber is wound around the microphone, and the microphone can effectively receive the audio signal caused by molecular vibration, namely beat signal f b ；
Step 4: the audio signal is amplified after passing through the amplifier, and then recorded by the data acquisition card; the recorded signal is a time domain waveform; the frequency of the beat frequency signal can be obtained after the waveform is subjected to discrete Fourier transform; because of different absorption peaks and absorption frequencies, the generated beat frequency signals are different, and therefore, the beat frequency signals can be distinguished by measuring the beat frequency signals, and the simultaneous measurement of a plurality of gas molecular absorption peaks is realized; meanwhile, as the laser and the molecules are bound in the hollow optical fiber, the interaction distance and the absorption section of the light and the molecules are increased, and the detection sensitivity is improved, so that the ultrasensitive spectrum detection of the decomposition products of the multicomponent sulfur hexafluoride electrical equipment is realized.
In the above technical solution, as shown in fig. 2, the optical comb refers to a broadband coherent laser light source, the spectrum of which is in a range of 1-12 μm, and the spectrum of which is in comb-tooth distribution, i.e. the spectrum is composed of N equally spaced frequency teeth or comb teeth, N is any integer, and typically N is 10 3 ～10 6 Wherein each frequency tooth corresponds to a beam of single longitudinal mode laser, and the frequency of the first comb tooth of the optical comb is f 0 The frequency spacing of the adjacent comb teeth is f r The absolute frequency of the nth comb tooth is expressed as: f (f) n ＝f 0 +nf r Wherein 0 is<n<N。
In the above technical solution, the double optical combs refer to carrier envelope phase zero frequency (i.e. the frequency of the first comb tooth) and repetition frequency respectively as follows: f (f) 01 And f r1 F 02 And f r2 Is a comb of the optical fiber bundle.
In the technical proposal, when two optical combs are usedWhen the nth comb tooth frequency is in the range of the absorption peak spectrum of the gas molecules, the molecules absorb the optical comb photons of the frequency and enter a high excitation state of a vibration level, and the vibration frequency is equal to the excitation light frequency, namely (f) 02 +nf r2 ) And (f) 01 +nf r1 ) The method comprises the steps of carrying out a first treatment on the surface of the Generating a beat signal between two different frequency vibromens, i.e. f b ＝|(f 02 +nf r2 )-(f 01 +nf r1 ) | a. The invention relates to a method for producing a fibre-reinforced plastic composite. The stimulated molecule induces the periodic variation of the refractive index of the medium, and the periodic frequency is f b . This change in refractive index will result in a frequency f b Through the gas and hollow fiber optics, to the microphone 9. Because the optical comb source has broadband spectral characteristics, a plurality of molecular absorption peaks can be excited at one time to generate acoustic wave signals with different frequencies. The sound wave frequency and the absorption peak or the absorption spectral line are in one-to-one correspondence, so that the microphone 9 can detect the audio signals at the same time, thereby achieving the purpose of measuring a plurality of absorption peaks.
In the above technical scheme, the hollow optical fiber 8 has the function of binding the light beam and the molecules in a narrow physical space, increasing the interaction section, simultaneously, the optical fiber can increase the interaction length of the light and the molecules, avoiding the limitation of the physical space of the sample cell on the effective optical path, and finally achieving the purpose of improving the detection sensitivity.
In the above technical solution, the decomposition product of sulfur hexafluoride electrical equipment refers to an electrical equipment failure characteristic gas with infrared absorption characteristic, such as H 2 S、HF、SO 2 、CO、CO 2 。
Example 1:
taking as an example the measurement of the absorption peak group around 1.28 μm for Hydrogen Fluoride (HF) gas molecules.
As shown in FIG. 4, two optical comb light sources with center wavelengths around 1.28 μm were used. One of which passes through a polarization controller to adjust the polarization state. The two optical combs are spatially overlapped after passing through a 50:50 beam combiner 4. Repetition frequency (i.e. comb tooth spacing) f of two optical combs r1 ＝10MHz，f r2 =10mhz+1hz, carrier envelope phase zero frequency f 0 Are all set to 0 (usually using a regulated optical comb pumpOptical power).
After passing through the half wave plate 5, the double-optical comb beam enters an enhanced gas sample cell 6 filled with HF gas. The light beam is coupled into the hollow fiber through a lens having a numerical aperture na=0.5. The hollow fiber has a pore diameter of 10 μm and a length of 10m. The optical fiber is wound around the microphone 9. The photo acoustic signals induced by the optical comb are captured by a microphone 9 attached to the cell wall and converted into electric signals, and the electric signals are sent to a data acquisition card for acquisition processing after noise suppression and amplification. The acquisition signals are time domain signals, and frequency characteristics of sound waves are obtained through Fourier time-frequency transformation, so that spectrum information corresponding to the HF is obtained. For example, if the nth comb tooth of two optical combs is absorbed by HF molecules, a frequency f is generated b Is a signal of (a). Beat frequency signal f between nth comb teeth b ＝n·|f r2 -f r1 |。f r2 -f r1 =1hz is a known quantity, f b Is a measurement of microphone 9. Thus, the value of n can be calculated. Therefore, the frequency corresponding to the absorption line is nf r2 Nf (nf) r1 The intensity is in direct proportion to the amplitude of the sound wave audio signal.
In conclusion, the invention provides the ultrasensitive SF based on the broadband double-optical comb spectrum 6 The gas decomposition component detection system and method can realize simultaneous measurement of multiple molecular absorption peaks, and are dominant in sensitivity and selectivity, can obtain absorption spectrum information of molecules which are single or a plurality of relatively close distances and are difficult to distinguish, and simultaneously solves the problem of cross sensitivity among the gas absorption peaks. The system can realize high-sensitivity and quick-response characteristic gas (such as SF) in the aspect of power grid safety maintenance 6 Gas and its decomposition products) spectral line parameters. The method can be used for sensitively and accurately measuring the concentration, content, type and other important information of the gas, and provides a path for the safety of power grid operation and the detection of fault characteristic gas.
What is not described in detail in this specification is prior art known to those skilled in the art.
Claims (3)
1. The method comprises the following steps ofUltrasensitive SF based on broadband double-optical comb spectrum 6 The gas decomposition component detecting system is characterized in that: the system comprises:
optical comb light source: for the generation of a light source,
the number of the optical comb light sources is two, and the carrier envelope phase zero frequency and the repetition frequency of the optical comb light sources are respectively: f01 and fr1, and f02 and fr2; each optical comb is composed of n frequency teeth; the frequency of the nth comb tooth is f0+ nfr, the frequency difference fb of the nth comb teeth of the two optical combs is = | (f02+ nfr 2) - (f01+ nfr 1) |, then the beat frequency signals of the nth comb teeth of the two optical combs can make the beat frequency signals fb in the audio frequency domain (20 Hz-20 kHz) by tuning the parameters f0 and fr of the laser, and the output light of the two broadband optical comb lasers are overlapped through the beam combiner to form a double optical comb laser beam;
a beam combiner: the optical comb is used for optically coupling the output light of the optical comb into spatially coincident light beams;
enhancement type gas sample pool: is used for the photo-acoustic spectrum detection of ultrasensitive gas,
the enhanced gas sample pool comprises an air inlet, an air outlet, a light-passing window, a section of hollow optical fiber wound on the microphone and a coupling lens for coupling laser into the optical fiber, wherein the hollow optical fiber is a light transmission medium which is formed into a cylindrical space by making the optical fiber hollow, and double-light comb laser light enters the enhanced gas sample pool and is coupled into the hollow optical fiber through the lens; the hollow optical fiber contains gas molecules to be detected;
a microphone: for receiving an audio signal;
an audio amplifier: for amplifying weak signals;
a data acquisition card: for recording audio signals.
2. Ultrasensitive SF based on broadband double optical comb spectra as recited in claim 1 6 The gas decomposition component detecting system is characterized in that: the hollow optical fiber has the functions of binding light beams and molecules in a narrow physical space, increasing the interaction section, increasing the interaction length of the light and the molecules, avoiding the limitation of the physical space of a sample cell on the effective optical path, and finally achieving the purpose of liftingThe purpose of the detection sensitivity is to be improved.
3. Ultrasensitive SF based on broadband double optical comb spectra as claimed in any of claims 1-2 6 The detection method of the gas decomposition component detection system comprises the following steps:
step 1: the output light of the two broadband optical comb lasers are overlapped through the beam combiner to form a double optical comb laser beam; the spectrum of the optical comb needs to cover a plurality of molecular absorption peaks;
step 2: the double-light comb laser light enters the enhanced gas sample cell and is coupled into the hollow optical fiber through the lens; the hollow optical fiber contains gas molecules to be detected; when the nth comb tooth frequency of the two optical combs is in the range of the absorption peak frequency spectrum of the gas molecules, the molecules will absorb the optical comb photons of the frequency and enter into the high excitation state of the vibration energy level, and the vibration frequency is equal to the excitation light frequency, namely (f respectively 02 +nf r2 ) And (f) 01 +nf r1 ) The method comprises the steps of carrying out a first treatment on the surface of the Generating a beat signal between two different frequency vibromens, i.e. f b ＝|(f 02 +nf r2 )-(f 01 +nf r1 ) I (I); under the effect of the photoacoustic effect, the vibration of the molecules is converted into an audio signal with the frequency f b ；
Step 3: the optical fiber is wound around the microphone, and the microphone can effectively receive the audio signal caused by molecular vibration, namely beat signal f b ；
Step 4: the audio signal is amplified after passing through the amplifier, and then recorded by the data acquisition card; the recorded signal is a time domain waveform; the frequency of the beat frequency signal can be obtained after the waveform is subjected to discrete Fourier transform; because of different absorption peaks and absorption frequencies, the generated beat frequency signals are different, and therefore the beat frequency signals are distinguished by measuring the beat frequency signals, and simultaneous measurement of a plurality of gas molecular absorption peaks is realized; meanwhile, as the laser and the molecules are bound in the hollow optical fiber, the interaction distance and the absorption section of the light and the molecules are increased, and the detection sensitivity is improved, so that the ultrasensitive spectrum detection of the decomposition products of the multicomponent sulfur hexafluoride electrical equipment is realized.
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