CN112710628B - Ultrasensitive SF6 gas decomposition component detection method based on broadband dual-comb spectroscopy - Google Patents

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

Ultrasensitive SF6 gas decomposition component detection method based on broadband dual-comb spectroscopy

technical field

The invention belongs to the technical field of gas detection, and specifically refers to an ultrasensitive SF ₆ gas decomposition component detection system and method based on broadband dual-comb spectroscopy.

Background technique

SF ₆ (sulfur hexafluoride) gas-insulated equipment such as GIS (totally enclosed gas combined electrical equipment), open switches, and transformers have been widely used in power systems due to their small footprint and high reliability. Since all components are enclosed in metal shells, early failures are more difficult to find than conventional equipment. Even if the equipment is disassembled for maintenance, due to the complex process of the equipment, the maintenance work is difficult and time-consuming, so the loss caused by the failure is also greater. Monitoring the internal status of GIS and other equipment to avoid accidents has always been a research hotspot of scientific research institutions at home and abroad. By detecting the decomposition products of SF ₆ gas in GIS equipment, the fault diagnosis and status evaluation of the internal insulation of the equipment are carried out. It has the characteristics of strong anti-interference ability and high sensitivity, and is widely used in the on-site detection and analysis of equipment. In the actual GIS equipment, SF ₆ gas contains trace impurities such as air, water and mineral oil, and these impurities participate in the reaction to generate stable decomposition products, such as SO ₂ , SOF ₂ , H ₂ S, HF, etc. Therefore, detecting the volume fraction of SF ₆ gas decomposition products is of great help in discovering latent faults and fault location of equipment.

The current gas detection methods mainly include: contact technology (such as: semiconductor sensor, contact combustion sensor, electrochemical sensor) and non-contact technology (such as: Fourier transform infrared spectroscopy, spectral absorption method). However, the current gas detection scheme has the following problems:

1) The contact detection technology targets a single type of gas, and the gas types that can be monitored are very limited. It cannot comprehensively detect SF ₆ decomposition products, thereby introducing a single data error, resulting in misjudgment; and this type of technology has fixed-point detection or requires on-site inspection. Operation and other disadvantages; especially for dangerous gases, there are problems of short service life, easy to be corroded, and online real-time monitoring cannot be achieved.

2) The non-contact optical detection scheme mainly includes the following technologies.

a) Frequency-modulation-based tunable semiconductor laser absorption spectroscopy (i.e., TDLAS). The absorption spectrum is obtained by tuning the wavelength (or frequency) of the laser and detecting the transmitted light intensity through the absorption cell point by point. Combined with a long optical path gas cell, it has high measurement sensitivity, high precision, and high resolution, but the measurement speed is extremely slow, the types of detected gases are limited, and the cost is high.

b) Differential Absorption Spectroscopy (ie DOAS). The differential absorption of light by a sample is used to measure the concentration of a substance. Its advantage is that multiple trace gases can be measured at the same time, but the disadvantage is that the technology is limited to gas molecules with narrow absorption lines in the measured band, and its monitoring system will also be affected by water vapor in the environment.

c) Photoacoustic spectroscopy (PAS). A photoacoustic spectroscopy detection system generally includes a light source, an optical modulator, a photoacoustic cell, a microphone, a demodulator, and an audio amplifier. Its working process is to use the light modulator to periodically modulate the intensity of the light source radiation. The modulated light then enters the photoacoustic cell, where it interacts with gas molecules. After absorbing the light energy, the molecules to be tested are excited to a high energy state, and yearn to radiate heat energy to generate sound waves with modulated frequencies. At this time, the microphone receives sound waves. The method can detect the concentration of the gas with obvious absorption in the emission spectrum range of the infrared light source, and the selection of the spectrum range can be realized by a filter. The disadvantage of this method is that due to the low coherence and stability of the infrared light source, the detection accuracy is low, the resolution is low, and the repeatability is poor. In addition, it is difficult to realize simultaneous measurement of multi-component gas absorption peaks, which is also a drawback of this method.

Optical frequency comb (referred to as "optical comb") is a broadband laser light source with good coherence and stable time-frequency characteristics. Optical comb-based spectral detection technology can realize simultaneous, high-precision, and high-resolution measurement of hundreds of molecular absorption peaks. However, due to the wide spectrum and energy dispersion of the optical comb, the detection sensitivity of this method is low, and it cannot be compared with the above-mentioned several traditional gas detection technologies.

Spectral detection technology has important application value in troubleshooting and early warning of power equipment. However, due to the complex components and different contents of the characteristic gases of electrical equipment faults, strict requirements are placed on the characteristics of gas detection technology such as gas identification or resolution (selectivity), sensitivity, accuracy, and detectable gas types.

The existing non-contact gas detection technology more or less has the problems of low spectral precision and accuracy, limited detection sensitivity, difficult quantitative analysis and limited information collection. The above problems largely restrict the accuracy of current gas detection and the real-time and reliability of power transmission and transformation equipment evaluation.

Contents of the invention

The purpose of the present invention is to propose an optical comb source as the excitation source, improve the time-frequency stability and coherence of the excitation light, and then improve the accuracy and repeatability of the measurement; through the multi-longitudinal mode beat frequency effect of the dual optical comb, Realize the frequency modulation of multiple molecular absorption peaks, generate photoacoustic audio signals corresponding to the absorption peaks, and be detected by the microphone at the same time; increase the interaction between molecules and light by confining the laser and molecules in the hollow fiber The ultra-sensitive SF ₆ gas decomposition component detection system and method based on broadband dual-comb spectroscopy to increase the molecular absorption intensity and improve the detection sensitivity of photoacoustic signals.

To achieve the above object, the technical solution adopted in the present invention is:

A kind of ultrasensitive _SF6 gas decomposition component detection system based on broadband double optical comb spectrum, described system comprises:

1) Optical comb light source: There are two optical comb light sources, and the carrier envelope phase zero frequency and repetition frequency of the optical comb light source are respectively: f ₀₁ and f _r1 , and f ₀₂ and f _r2 ; each optical comb has It consists of n frequency teeth; the frequency of the nth comb tooth is f ₀ +nf _r . The frequency difference f _b =|(f ₀₂ +nf _r2 )-(f ₀₁ +nf _r1 )| of the nth tooth of the two optical combs is the beat frequency signal of the nth tooth of the two optical combs. By tuning the laser parameters f ₀ and f _r , the beat frequency signal f _b can be in the audio frequency domain (20Hz-20kHz), and the output lights of two broadband optical comb lasers are spatially overlapped by the beam combiner to form a double optical comb laser beam.

2) Beam combiner: used to couple the output lights of two optical combs into spatially coincident beams.

3) Enhanced enhanced gas sample cell: used for ultra-sensitive gas photoacoustic spectroscopy detection, enhanced gas sample cell, the gas sample cell includes an air inlet, an air outlet, a light window, and a section wound on the micro A hollow-core fiber on the sounder and a coupling lens that couples the laser light into the fiber. Hollow-core optical fiber refers to the optical transmission medium that makes the optical fiber hollow to form a cylindrical space, and is coupled into the hollow-core optical fiber through the lens; the hollow-core optical fiber contains gas molecules to be measured.

4) Microphone: used to receive audio signals.

5) Audio amplifier: used to amplify weak signals.

6) Data acquisition card: used to record audio signals.

Utilize above-mentioned ultrasensitive _SF6 gas decomposition component detection system based on broadband dual-comb spectrum, the present invention also provides

A kind of ultrasensitive _SF6 gas decomposition component detection method based on broadband double optical comb spectrum, described detection method comprises the steps:

Step 1: The output light of two broadband optical comb lasers is spatially overlapped by a beam combiner to form a double optical comb laser beam; here the spectrum of the optical comb needs to cover multiple molecular absorption peaks;

Step 2: The double-comb laser is injected into the enhanced gas sample cell, and coupled into the hollow fiber through the lens; the hollow fiber contains the gas molecules to be measured; When within the range, the molecule will absorb the optical comb photons of this frequency, and enter into a high excited state of the vibration energy level, the vibration frequency is equal to the frequency of the excitation light, namely (f ₀₂ +nf _r2 ) and (f ₀₁ +nf _r1 ); A beat frequency signal is generated between two vibration states of different frequencies, that is, f _b = |(f ₀₂ +nf _r2 )-(f ₀₁ +nf _r1 )|; under the photoacoustic effect, the vibration of molecules is converted into audio frequency signal, 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, that is, the beat frequency 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 discrete Fourier transform of the waveform; because of different absorption peaks, the absorption Different frequencies produce different beat signals, so it can be distinguished by measuring the frequency of the beat signal, so as to realize the simultaneous measurement of the absorption peaks of multiple gas molecules; at the same time, since the laser and molecules are bound in the hollow fiber , increasing the interaction distance and absorption cross-section between light and molecules, and improving the detection sensitivity, so as to realize the ultra-sensitive spectral detection of the decomposition products of multi-component sulfur hexafluoride electrical equipment.

The invention uses a wide-band dual-comb light source to measure the photoacoustic spectrum, which increases the problem of simultaneous measurement of multiple absorption peaks in the photoacoustic spectrum measurement, improves the resolution ability of complex multi-component power equipment fault gas detection, and solves the traditional technology. Sensitivity and poor selectivity; by combining hollow-core optical fiber with photoacoustic spectroscopy and optical comb spectroscopy, the spectral width and detection sensitivity of the spectrum are increased. Compared with the traditional gas spectroscopic analysis method, the present invention has the advantages of high sensitivity, high resolution, simultaneous detection of multiple absorption peaks, etc., and can realize efficient and accurate analysis of the spectral lines of the characteristic gases of power grid fault equipment.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the schematic diagram of dual optical comb beat frequency among the present invention;

Fig. 3 is the content structure diagram of enhanced gas pool in the present invention;

Fig. 4 is a schematic structural diagram of an embodiment of the present invention.

In the figure, 1, 2—optical comb laser source, 3—polarization controller, 4—beam combiner, 5—half-wave plate, 6—enhanced gas sample cell, 7—lens, 8—hollow fiber, 9—micro Speaker, 10—filter, 11—audio amplifier, 12—data acquisition card.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

A kind of ultra-sensitive SF gas decomposition component detection system (Fig. 1) based on broadband _double optical comb spectrum, said system comprises:

1) Optical comb light source: There are two optical comb light sources, and the carrier envelope phase zero frequency and repetition frequency of the optical comb light source are respectively: f ₀₁ and f _r1 , and f ₀₂ and f _r2 ; each optical comb has It consists of n frequency teeth; the frequency of the nth comb tooth is f ₀ +nf _r (Figure 2). The frequency difference f _b =|(f ₀₂ +nf _r2 )-(f ₀₁ +nf _r1 )| of the nth tooth of the two optical combs is the beat frequency signal of the nth tooth of the two optical combs. By tuning the laser parameters f ₀ and f _r , the beat frequency signal f _b can be in the audio frequency domain (20Hz-20kHz).

2) Beam combiner: used to couple the output lights of two optical combs into spatially coincident beams.

3) Enhanced enhanced gas sample cell: for ultra-sensitive gas photoacoustic spectroscopy detection, enhanced gas sample cell (Figure 3), the gas sample cell includes an air inlet, an air outlet, and a light-through window, A section of hollow fiber wrapped around the microphone and a coupling lens that couples the laser light into the fiber. Hollow-core optical fiber refers to the optical transmission medium in which the optical fiber is made hollow to form a cylindrical space.

4) Microphone: used to receive audio signals.

5) Audio amplifier: used to amplify weak signals.

6) Data acquisition card: used to record audio signals.

As shown in Figure 4, the ultrasensitive _SF6 gas decomposition component detection system based on broadband double optical comb spectrum of the present invention comprises optical comb laser source 1 and 2, polarization controller 3, beam combiner 4, half-wave plate 5 , Enhanced gas sample cell 6, lens 7, hollow fiber 8 and microphone 9, filter 10, audio amplifier 11-, data acquisition card 12. The output lights of the optical combs 1 and 2 are spatially combined by the beam combiner 4, wherein one optical comb light passes through a polarization controller to adjust the polarization state so that the two optical combs have the same polarization. Spatial coincidence and polarization state control are the necessary conditions to realize the optical beat frequency of both. After beam combining, the laser light passes through a half-wave plate to optimize the polarization state of the laser light so that it can enter the hollow fiber 8 with the best coupling efficiency after passing through the lens 7 . The double-comb light beam interacts with the gas molecules to be measured in the optical fiber, and after being absorbed, an acoustic wave signal is generated through the photoacoustic effect, and is received by the microphone 9 . The output audio signal of the microphone 9 passes through the filter 10 to filter out the background and high-frequency noise, and then is amplified by the audio amplifier 11, and finally the data acquisition card 12 performs data recording and signal processing.

In the above technical solution, the gas to be measured is introduced into the enhanced gas sample cell 6 through the air inlet. During the measurement, the gas inlet and outlet of the enhanced gas sample cell are sealed, and the gas in the cell enters the hollow fiber through the diffusion process. After the measurement is finished, the gas cell is evacuated through the gas outlet to discharge the original residual sample gas.

In the above technical solution, the microphone 9 is used to measure the acoustic wave signal generated by molecules absorbing the light of the double-light comb, and the frequency of the signal is equal to the beat frequency signal f _b between the teeth of the absorbed double-light comb. Different absorption peaks produce different audio frequencies, which can be used to distinguish absorption peaks, thereby realizing the identification of gas types.

In the above technical solution, after the electrical signal is amplified by the amplifier 11, it is collected by the data acquisition card 12, and the photoacoustic spectrum intensity signal of the gas to be measured is obtained by using the Fourier transform method, and the signal is proportional to the concentration of the gas. It can be used to identify the concentration and type of gas.

Utilize above-mentioned ultrasensitive _SF6 gas decomposition component detection system based on broadband dual-comb spectrum, the detection method of the present embodiment, comprises the following steps:

Step 1: The output lights of two broadband optical comb lasers 1 and 2 are spatially overlapped by a beam combiner 4 to form a double optical comb laser beam;

Step 2: The double-comb laser is injected into the enhanced gas sample cell 6, and coupled into the hollow fiber 8 through the lens 7; the hollow fiber contains the gas molecules to be measured, and the vibration of the molecules is converted into an audio signal under the action of the photoacoustic effect , 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, that is, the beat frequency 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 discrete Fourier transform of the waveform; because of different absorption peaks, the absorption Different frequencies produce different beat signals, so it can be distinguished by measuring the frequency of the beat signal, so as to realize the simultaneous measurement of the absorption peaks of multiple gas molecules; at the same time, since the laser and molecules are bound in the hollow fiber , increasing the interaction distance and absorption cross-section between light and molecules, and improving the detection sensitivity, so as to realize the ultra-sensitive spectral detection of the decomposition products of multi-component sulfur hexafluoride electrical equipment.

In the above technical solution, as shown in Figure 2, the optical comb refers to a broadband coherent laser light source, the spectral range is between 1 and 12 μm, and its spectrum presents a comb-like distribution, that is, the spectrum consists of N equally spaced Distributed frequency teeth or comb teeth, N is any integer, usually N is between 10 ³ and 10 ⁶ , where each frequency tooth is equivalent 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 between adjacent comb teeth is f _r , then the absolute frequency of the nth comb tooth is expressed as: f _n =f ₀ +nf _r , where 0<n<N.

In the above technical solution, the dual optical comb refers to an optical comb with a carrier envelope phase of zero frequency (that is, the frequency of the first comb tooth) and a repetition frequency of f ₀₁ and f _r1 and f ₀₂ and f _r2 , respectively.

In the above technical solution, when the frequency of the nth comb teeth of the two optical combs is within the spectrum range of the absorption peak of gas molecules, the molecules will absorb the optical comb photons of this frequency and enter a high excited state of vibration energy level, the vibration frequency is equal to The excitation light frequencies are respectively (f ₀₂ +nf _r2 ) and (f ₀₁ +nf _r1 ); a beat frequency signal is generated between two vibration states of different frequencies, that is, f _b =|(f ₀₂ +nf _r2 )- (f ₀₁ +nf _r1 )|. The excited molecules induce periodic changes in the refractive index of the medium with a periodic frequency f _b . This change in the refractive index will form a sound wave with frequency f _b , which will be transmitted to the microphone 9 through the gas and the hollow fiber. Due to the broadband spectral characteristics of the optical comb source, multiple molecular absorption peaks can be simultaneously excited at one time to generate acoustic signals of different frequencies. There is a one-to-one correspondence between the sound wave frequency and the absorption peak or absorption line. Therefore, these audio signals can be detected simultaneously by the microphone 9 to achieve the purpose of measuring multiple absorption peaks.

In the above technical solution, the role of the hollow fiber 8 is to confine the light beam and molecules in a narrow physical space and increase the interaction cross-section. Limit, and finally achieve the purpose of improving the detection sensitivity.

In the above technical solution, the decomposition products of sulfur hexafluoride electrical equipment refer to gases characteristic of electrical equipment failure with infrared absorption characteristics, such as H ₂ S, HF, SO ₂ , CO, CO ₂ .

Example 1:

Take the measurement of the absorption peak group of hydrogen fluoride (HF) gas molecules around 1.28 μm as an example.

As shown in Figure 4, two optical comb light sources with a center wavelength around 1.28 μm are used. One of them passes through a polarization controller to adjust the polarization state. The two optical combs overlap in space after passing through the 50:50 beam combiner 4. The repetition frequency of the two optical combs (that is, the spacing between the teeth of the combs) f _r1 = 10MHz, f _r2 = 10MHz+1Hz, and the carrier envelope phase zero frequency f ₀ are all set to 0 (usually by adjusting the pumping power of the optical comb accomplish).

After passing through the half-wave plate 5, the double optical comb beam enters the enhanced gas sample cell 6 filled with HF gas. The beam passes through a lens with a numerical aperture of NA=0.5 and is coupled into a hollow fiber. The hollow fiber has an aperture of 10 μm and a length of 10 m. The optical fiber is wound around the microphone 9. The photoacoustic signal generated by the optical comb is captured by the microphone 9 attached to the pool wall and converted into an electrical signal. After the electrical signal is noise-suppressed and amplified, it is sent to the data acquisition card for acquisition and processing. Among them, the acquisition signal is a time-domain signal, and the frequency characteristics of the sound wave are obtained through Fourier time-frequency transformation, and then the corresponding spectral information of HF is obtained. For example, if the nth teeth of two optical combs are absorbed by HF molecules, a signal with frequency f _b will be generated. The beat frequency signal f _b between the nth comb teeth = n · | f _r2 - f _r1 |. f _r2 −f _r1 =1 Hz is a known quantity, and f _b is a measured value of the microphone 9 . From this, the value of n can be calculated. Therefore, the frequencies corresponding to the absorption spectral lines are nf _r2 and nf _r1 , and the intensity is proportional to the amplitude of the sound wave audio signal.

In summary, a kind of ultra-sensitive SF ₆ gas decomposition component detection system and method based on broadband dual-comb spectroscopy proposed by the present invention can realize the simultaneous measurement of multi-molecular absorption peaks, and it occupies an important position in both sensitivity and selectivity. The advantage is that it can obtain the absorption spectrum information of single or several molecules that are difficult to distinguish at a short distance, and it also solves the problem of cross-sensitivity between the absorption peaks of various gases. In terms of power grid security maintenance, this system can realize the analysis of spectral line parameters of characteristic gases (such as SF ₆ gas and its decomposition products) with high sensitivity and fast response. The method can be used to measure important information such as the concentration, content, and type of gas in a sensitive and accurate manner, and provides a way for power grid operation safety and fault characteristic gas detection.

The content not described in detail in this specification belongs to the 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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