CN111650127A - High-resolution photoacoustic spectroscopy gas detection system and method based on optical frequency comb frequency calibration - Google Patents
High-resolution photoacoustic spectroscopy gas detection system and method based on optical frequency comb frequency calibration Download PDFInfo
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Abstract
The invention discloses a high-resolution photoacoustic spectrometry gas detection system based on frequency calibration of an optical frequency comb, which comprises an infrared optical comb, an infrared tunable continuous laser, a first beam splitter, a second beam combiner, an infrared photoelectric detector, a frequency spectrograph, a chopper, a photoacoustic cell and a microphone, wherein the infrared optical comb is used for carrying out frequency calibration on photoacoustic spectrometry, and frequency information of photoacoustic spectrometry is increased, so that the resolution capability of detecting fault gas of complex multi-component power equipment is improved, and the problems of cross sensitivity and poor selectivity of the traditional technology are solved; by using a broadband frequency-modulated infrared continuous laser as a light source, the measurement spectrum width of photoacoustic spectroscopy and the detectable gas species can be increased.
Description
Technical Field
The invention relates to the technical field of gas detection, in particular to a high-resolution photoacoustic spectroscopy gas detection system and method based on optical frequency comb frequency calibration.
Background
The ultra-sensitive detection technology for the decomposition products of sulfur hexafluoride electrical equipment is an important means for troubleshooting potential faults of electrical equipment (such as transformers, circuit breakers, gas insulated metal enclosed switchgear, mutual inductors, capacitors and the like) and ensuring the operation safety of the equipment. The decomposition product of sulfur hexafluoride electrical equipment refers to H generated after chemical reaction of sulfur hexafluoride SF6 gas or solid insulating material in the electrical equipment2S、HF、SO2、CF4、CO、CO2、C3F8、 SO2F2、SOF2And the like. Because the components of the fault characteristic gas of the electrical equipment are complex and have different contents, strict requirements are put forward on the characteristics of gas identification or distinguishing capability (selectivity), sensitivity and accuracy of a gas detection technology, detectable gas types and the like.
Currently, the commonly used gas detection means include the following.
1) An electrochemical method. The technology utilizes the electrochemical reaction of the gas to be measured to convert the concentration change of the gas to be measured into a sensing measuring device with potential or current change. Gas detectable objectMainly comprises H2S、HF、SO2、CF4And CO. The method has high sensitivity, but needs to be in direct contact with the gas to be detected, is easy to corrode, and is easy to limit the dynamic range of the types of the detectable gases and the detectable concentration.
2) Gas detection tube method. Gas to be detected is introduced into a transparent tube filled with a chemical reagent, and the color of the reagent is changed through chemical reaction, so that the information such as the concentration of the gas is determined. The detectable gas object mainly comprises H2S、HF、SO2、CF4And CO. The method is convenient to use, but cannot realize accurate quantitative analysis, has limited measurement sensitivity and precision, and cannot distinguish mixed complex gas samples.
3) A gas chromatograph. And analyzing and detecting different components in the mixed gas by utilizing a chromatographic principle. The detectable gas object mainly comprises H2S、SO2、CF4、CO、CO2、C3F8、 SO2F2、SOF2. The method has high detection sensitivity, can detect all kinds, but needs a complex gas sample preparation process, and is time-consuming in detection, namely, poor in timeliness.
4) Gas spectroscopy. Based on Lambert beer's law, the qualitative and quantitative analysis of the species and concentration of different gases can be carried out by using the absorption line intensity of gas molecules. The method can detect various gas types, and can realize simultaneous non-contact detection. At present, the following gas absorption spectrum detection technologies are mainly used.
a) Tunable semiconductor laser absorption spectroscopy (i.e., TDLAS) based on frequency modulation. The absorption spectrum is obtained by tuning the wavelength (or frequency) of the laser and detecting the transmitted light intensity transmitted through the absorption cell point by point. The gas cell with long optical path is combined, the measurement sensitivity is high, the precision is high, the resolution is high, but the measurement speed is extremely slow, the detection gas type is limited, and the cost is high.
b) Differential absorption spectroscopy (i.e., DOAS). The substance concentration measurement is achieved by using the differential absorption of light by the sample. Its advantages are simultaneous measurement of multiple trace gases, but its technique is limited to the gas molecules with narrow absorption lines in the measured band, and its monitoring system is affected by the moisture in the environment.
c) Photoacoustic spectroscopy (PAS). The gas sample is injected by using an infrared wide-spectrum light source, sample molecules are excited to a high-energy state after absorbing light energy, and the generated heat energy is released in a sound wave mode of specific frequency and is received by a microphone. The method can be used for detecting the concentration of the gas which is obviously absorbed in the infrared light source emission spectrum range, and the selection of the spectrum range can be realized through the filter plate. However, the PAS technology does not precisely calibrate the frequency of the excitation light, and therefore lacks the optical frequency measurement characteristic, so that the difficulty in detecting and distinguishing the gas with a relatively close absorption spectrum line is high, that is, the problem of cross sensitivity is not solved, and the selectivity is poor, so that the gas concentration is difficult to be precisely measured.
In summary, compared with other methods, the gas spectrum measurement method has the advantages of non-contact, no need of gas preparation, safety of detection mode and the like, but has problems in the aspects of gas resolution, sensitivity, waveband selectivity and the like. Particularly, the photoacoustic spectrum PAS technology with high detection sensitivity has no background noise interference, and the intensity of the ultrasonic signal can directly reflect the amount of light energy absorbed by a substance, so that the influence of light reflection and scattering is not easily caused, but the defects caused by a wide-spectrum infrared light source, such as low quantitative analysis accuracy caused by the failure to realize the frequency calibration of exciting light, poor resolution capability of mixed gas and other technical bottlenecks, need to be effectively avoided.
Disclosure of Invention
Aiming at the problems, the invention provides a high-resolution photoacoustic spectroscopy gas detection system and method based on optical frequency comb frequency calibration.
In order to realize the purpose, the invention designs a high-resolution photoacoustic spectroscopy gas detection system based on frequency calibration of an optical frequency comb, which comprises an infrared optical comb, an infrared tunable continuous laser, a first beam splitter, a second beam combiner, an infrared photoelectric detector, a frequency spectrograph, a chopper, a photoacoustic cell and a microphone, wherein the output end of the infrared optical comb is connected with the input optical path of the second beam combiner, the output end of the infrared tunable continuous laser is connected with the input optical path of the first beam splitter, the first output end of the first beam splitter is connected with the input optical path of the second beam combiner, the output end of the second beam combiner is connected with the input optical path of the infrared photoelectric detector, the output end of the infrared photoelectric detector is connected with the electrical signal input end of the frequency spectrum analyzer, the output end of the first beam splitter is opposite to the light source entrance port of the photoacoustic cell, the chopper is arranged between the output end of the first beam splitter and the light source entrance port of the photoacoustic cell, the chopper is used for periodically modulating the intensity of the optical signal output by the first beam splitter, the gas to be detected is filled in the photoacoustic cell, the optical signal output by the first beam splitter is subjected to intensity modulation by the chopper and then is emitted into the gas to be detected in the photoacoustic cell, and the microphone is used for detecting the acoustic wave signal generated after the gas to be detected absorbs the optical energy.
A high-resolution photoacoustic spectrometry gas detection method based on optical frequency comb frequency calibration comprises the following steps:
step 1: the output frequency f of the infrared tunable continuous lasercwThe infrared continuous laser signal is output by the infrared comb, the infrared continuous laser signal is input to the second beam combiner through the first beam splitter, and a beat frequency signal f is obtained by beating the infrared continuous laser signal and the infrared comb signal in the second beam combinerb；
Step 2: the infrared photoelectric detector converts the beat frequency signal fbCapturing and recording the data in a spectrum analyzer;
and step 3: the spectrum analyzer utilizes infrared continuous laser signal and beat frequency signal fbAnd the frequency f to be measured in the infrared continuous laser signal is calibrated by an optical combcwCarrying out measurement;
and 4, step 4: the output frequency of the infrared tunable continuous laser is fcwAfter intensity modulation is carried out on the infrared continuous laser signal by the chopper, the infrared continuous laser signal is injected into the gas to be detected in the photoacoustic cell, and a microphone is used for detecting a sound wave signal generated after the gas to be detected absorbs optical energy and converting the sound wave signal into a sound wave signal;
and 5: the acoustic wave electric signal is amplified by a phase-locked amplifier, collected by a data acquisition card and acquired by using an acoustic-optical spectrum detection method to obtain an acoustic-optical spectrum intensity signal of the gas to be detected;
step 6: and (2) adjusting the wavelength or frequency of the infrared laser output by the infrared tunable continuous laser by adopting a continuous laser frequency sweeping method, realizing wavelength or frequency scanning in a broadband spectrum range, and simultaneously, measuring the frequency of the tuned continuous laser in real time by using the optical comb calibration method in the steps 1-3 to obtain a broadband photoacoustic spectrogram with the frequency corresponding to the photoacoustic signal amplitude one by one, thereby realizing the spectrum detection of the decomposition product of the multi-component sulfur hexafluoride electrical equipment.
The invention has the beneficial effects that:
according to the invention, the infrared optical comb is used for carrying out frequency calibration on the photoacoustic spectrum, and the frequency information measured by the photoacoustic spectrum is increased, so that the resolution capability of detecting the fault gas of the complex multi-component power equipment is improved, and the problems of cross sensitivity and poor selectivity of the traditional technology are solved; by using a broadband frequency-modulated infrared continuous laser as a light source, the measurement spectrum width of photoacoustic spectroscopy and the detectable gas species can be increased. Meanwhile, the photoacoustic spectroscopy technology is adopted, compared with the traditional spectroscopy, the photoacoustic spectroscopy technology has high sensitivity and short detection time, and can realize the rapid and hypersensitive measurement of the center frequency and the line width of the spectral line of the characteristic gas of the power grid fault equipment and the real-time analysis of the concentration, the type and the content of the gas.
Drawings
FIG. 1 is a schematic structural view of the present invention;
fig. 2 is a schematic diagram of frequency scaling of an optical comb in the present invention.
The system comprises an infrared optical comb 1, an infrared tunable continuous laser 2, a first beam splitter 3, a second beam combiner 4, an infrared photoelectric detector 5, a frequency spectrograph 6, a chopper 7, a photoacoustic cell 8, a microphone 9, a phase-locked amplifier 10 and a data acquisition card 11.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
the high-resolution photoacoustic spectrometry gas detection system based on optical frequency comb frequency calibration as shown in fig. 1 comprises an infrared optical comb 1, an infrared tunable continuous laser 2, a first beam splitter 3, a second beam combiner 4, an infrared photodetector 5, a spectrometer 6, a chopper 7, a photoacoustic cell 8 and a microphone 9, wherein the output end of the infrared optical comb 1 is connected with the input optical path of the second beam combiner 4, the output end of the infrared tunable continuous laser 2 is connected with the input optical path of the first beam splitter 3, the first output end of the first beam splitter 3 is connected with the input optical path of the second beam combiner 4, the output end of the second beam combiner 4 is connected with the input optical path of the infrared photodetector 5, the second beam combiner 4 is used for spatially combining the infrared optical comb signal output by the infrared optical comb 1 and the infrared continuous laser signal output by the infrared tunable continuous laser 2, the space coincidence is a necessary condition for realizing optical beat frequency of the two, the first beam splitter 3 is used for splitting the infrared tunable continuous laser 2 into two paths, one path is subjected to beat frequency detection with an infrared comb signal, the other path directly enters the photoacoustic cell 8 and is used for gas detection, the output end of the infrared photoelectric detector 5 is linked with the electric signal input end of the spectrum analyzer 6, the output end of the first beam splitter 3 is opposite to the light source entrance port of the photoacoustic cell 8, the chopper 7 is arranged between the output end of the first beam splitter 3 and the light source entrance port of the photoacoustic cell 8, the chopper 7 is used for periodically modulating the intensity of the optical signal output by the first beam splitter 3, the gas to be detected is filled in the photoacoustic cell 8, the optical signal output by the first beam splitter 3 is subjected to intensity modulation by the chopper 7 and then enters the gas to be detected in the photoacoustic cell 8, and the sound wave signal generated after the gas to be detected absorbs the light energy is detected by the microphone 9.
In the above technical solution, it further includes a lock-in amplifier 10 and a data acquisition card 11, the signal output end of the microphone 9 is linked to the input end of the lock-in amplifier 10, the output end of the lock-in amplifier 10 is connected to the input end of the data acquisition card 11, the set frequency signal output end of the controller of the chopper 7 is connected to the input end of the data acquisition card 11 (the set frequency of the chopper is also accessed to the data acquisition card 11 as a reference signal, and the set frequency of the chopper, i.e. the frequency of intensity modulation, is equal to the frequency of the acoustic signal detected by the microphone. The sound wave signal is received by a microphone 9 and converted into an electric signal, and the electric signal is sent to a data acquisition card 11 for signal processing after noise suppression and amplification are carried out by a lock-in amplifier 10.
In the above technical solution, the infrared tunable continuous laser 2 is used for outputting the frequency f to be measuredcwThe infrared optical comb 1 is used for outputting an infrared optical comb signal subjected to frequency calibration, and the infrared photoelectric detector 5 is used for beating the infrared continuous laser signal and the infrared optical comb signal to obtain a beat signal fbCaptured and recorded in a spectrum analyzer 6, the spectrum analyzer 6 is used for utilizing infrared continuous laser signals and beat frequency signals fbAnd calibrating the frequency f to be measured in the infrared continuous laser signal by an optical combcwThe measurement is performed.
In the above technical solution, the frequency output by the infrared tunable continuous laser 2 is fcwThe infrared continuous laser signal is subjected to intensity modulation by the chopper 7, then is emitted into the gas to be detected in the photoacoustic cell 8, and a microphone 9 is used for detecting a sound wave signal generated after the gas to be detected absorbs optical energy and converting the sound wave signal into an electric signal.
In the above technical scheme, the electrical signal is amplified by the lock-in amplifier 10, collected by the data acquisition card 11, and the photoacoustic spectrum intensity signal of the gas to be detected is obtained by using a photoacoustic spectrum detection method, and the signal is in direct proportion to the concentration of the gas and can be used for identifying the concentration of the gas and the type of the gas.
A high-resolution photoacoustic spectrometry gas detection method based on optical frequency comb frequency calibration is characterized by comprising the following steps:
step 1: infrared tunable continuous laserThe output of the device 2 is fcwThe infrared optical comb 1 outputs an infrared optical comb signal subjected to frequency calibration, the infrared continuous laser signal is input into the second beam combiner 4 through the first beam splitter 3, and a beat signal f obtained by beating the infrared continuous laser signal and the infrared optical comb signal in the second beam combiner 4 is obtainedb；
Step 2: the infrared photoelectric detector 5 converts the beat frequency signal fbCaptured and recorded in the spectrum analyzer 6;
and step 3: the spectrum analyzer 6 utilizes the infrared continuous laser signal and the beat frequency signal fbAnd calibrating the frequency f to be measured in the infrared continuous laser signal by an optical combcwCarrying out measurement;
and 4, step 4: the frequency of the output of the infrared tunable continuous laser 2 is fcwAfter intensity modulation is carried out on the infrared continuous laser signal by the chopper 7, the infrared continuous laser signal is emitted into gas to be detected in the photoacoustic cell 8, and a microphone 9 is used for detecting a sound wave signal generated after the gas to be detected absorbs optical energy and converting the sound wave signal into a sound wave electric signal;
and 5: the acoustic wave electric signal is amplified by a phase-locked amplifier 10, is collected by a data collecting card 11, and obtains an acoustic-optical spectrum intensity signal of the gas to be detected by using an acoustic-optical spectrum detection method, and molecules have strong absorption cross sections in an infrared band, so that the acoustic-optical effect introduced by infrared light is obvious, the spectral sensitivity is extremely high, and the acoustic-optical spectrum intensity signal can reach the ppb (ppb) level generally;
step 6: and (2) adjusting the wavelength or frequency of the infrared laser output by the infrared tunable continuous laser 2 by adopting a continuous laser frequency sweeping method to realize wavelength or frequency scanning in a broadband spectrum range, and simultaneously, measuring the frequency of the tuned continuous laser in real time by using the optical comb calibration method in the steps 1-3 to obtain broadband photoacoustic spectrograms with the frequencies corresponding to the photoacoustic signal amplitudes one by one, thereby realizing high-resolution spectrum detection of the decomposition product of the multi-component sulfur hexafluoride electrical equipment.
In the above technical solution, as shown in fig. 2, the infrared comb signal is a broadband infrared light source, the spectrum range is 3-12 μm, and the spectrum of the infrared comb signal is representedThe spectrum is composed of N frequency teeth or comb teeth distributed at equal intervals, N is any integer, and N is usually 103～106Wherein 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 f0The frequency spacing of comb teeth adjacent to each other is frThen, the absolute frequency of the nth comb is expressed as: f. ofn＝f0+nfrWherein 0 is<n<N。
The infrared photoelectric detector 5 is used for detecting beat frequency signal fbThe detection mode is that the frequency to be measured is fcwThe infrared continuous laser signal and the infrared optical comb signal are overlapped in space and then transmitted into the infrared photoelectric detector 5, the output signal of the infrared photoelectric detector 5 is transmitted into the spectrum analyzer 6, and the frequency of the beat frequency detection output signal is fb＝|fcw-fn|，fbMeasured by a spectrum analyzer.
In the above technical solution, the infrared optical comb signal after frequency calibration refers to f of the optical combrThe frequency is determined by means of an infrared photodetector 5 and a frequency meter in such a way as to measure the optical comb pulse repetition frequency; f of optical comb0The frequency, i.e. the carrier envelope phase frequency, is measured by the f-2f self-referencing technique, i.e. the comb teeth f with a frequency lower than the center frequency of the optical combn1＝f0+n1·fr，fn1The frequency of the n1 th comb tooth of the optical comb is defined, n1 is a sequence number and is a positive integer, any comb tooth with the frequency lower than the center frequency of the optical comb is subjected to frequency doubling through a nonlinear crystal to generate the frequency of 2fn1＝2f0+2n1·frThen the frequency-doubled light and the comb teeth f of the optical comb which are higher than the center frequency of the optical combn2＝f0+2·n1·frPerforming beat frequency detection, fn2Is the frequency of n2 comb teeth of the optical comb, n2 is an ordinal number and is a positive integer, corresponds to any comb tooth with the frequency higher than the center frequency of the optical comb, and always finds n1 with one comb tooth satisfying n2 equal to 2 times, and obtains the frequency of f'b＝2fn1-fn2＝f0Of the beat signal, f'bIs at a frequency fn1And a frequency offn2The frequency of the beat frequency signal between the comb teeth of the optical comb can be directly measured by a frequency spectrograph, and the frequency of the beat frequency signal is f0Frequency;
at known f0And frThereafter, in order to measure fcwThe number n of comb teeth is determined, and the infrared continuous laser signal is roughly measured in advance by a spectrum analyzer 6 or an optical wavemeter and then by an inequality 0<|fcw-(f0+nfr)|<fr/2 estimating the value of the integer n, using f measured by the spectrum analyzer 6bBy beat frequency detection formula fb＝|fcw-(f0+nfr) I accurately calculate fcwThe precision limit of the high-resolution spectrum analyzer or the optical wavelength meter for measuring the wavelength or the frequency is in the order of 10pm or 1GHz, and the frequency measurement precision can be determined within 1MHz by using an optical comb calibration method, wherein the value is far smaller than the line width and the line spacing (between 0.1 and 1 GHz) of adjacent molecular spectral lines. Therefore, the identification or resolution capability of the measuring means on the molecular spectral lines can be greatly improved.
In the above technical solution, the decomposition product of sulfur hexafluoride electrical equipment refers to a fault characteristic gas of electrical equipment with infrared absorption characteristic, such as H2S、HF、SO2、CO、CO2。
In the above technical solution, in the step 5, the infrared continuous laser signal is modulated by the intensity of the chopper and then irradiated into the photoacoustic cell 8 containing the gas to be detected, the gas molecule absorbs the infrared light with the frequency v and then is excited to generate energy level transition, and the excited molecules return to the ground state through nonradiative transition and convert the absorbed light energy into heat energy, because the incident light is periodically modulated by the chopper, the temperature, i.e., the pressure, also changes periodically, the microphone 9 receives the sound wave signal and converts the sound wave signal into an electrical signal, and the signal is subjected to noise suppression and amplification by the lock-in amplifier 10 and then sent to the data acquisition card 11 for signal processing. With the change of the wavelength of the intermediate infrared continuous light source, the technology can modulate a single absorption peak or a plurality of absorption peaks with relatively close spectral lines of gas molecules to generate a sound wave signal with specific frequency, and then a corresponding absorption spectrum is obtained.
And finally, a continuous laser frequency sweep technology. And through tuning the frequency of the continuous laser, the transmission light intensity is recorded point by point, and the high-sensitivity photoacoustic spectrum of the broadband is obtained.
The specific implementation is as follows:
example 1: to target carbon dioxide (CO)2) The absorption peak group of gas molecules in the vicinity of 2.8 μm was measured as an example. As shown in fig. 1, a 2.8 μm tunable continuous laser 2 passes through 30: 70, 70% of the light is used as the light source for photoacoustic spectroscopy detection, 30% of the light is beaten with an optical comb of 2.8 μm, the repetition frequency (i.e. comb tooth pitch) f of the optical combrSelecting 10 GHz; carrier envelope phase frequency (i.e. zero frequency) f0And is set to 0 (typically implemented by adjusting the optical comb pump optical power). And monitoring the absolute optical frequency of the continuous laser in real time by an optical frequency comb frequency calibration technology.
The infrared tunable continuous light source enters the photoacoustic detection module, and the infrared light modulated by the chopper 7 enters the light-filled CO2In the photoacoustic cell 8, the acoustic signals are captured by a microphone 9 attached to the cell wall and converted into electric signals, and the electric signals are subjected to noise suppression and phase-locked amplification and then sent to a data acquisition card for acquisition and processing. The set frequency of the chopper is also accessed to the data acquisition card to be used as a reference signal. Set a program for point-by-point acquisition and processing, and can quickly obtain CO2Corresponding spectral information.
In summary, the high-resolution photoacoustic spectrometry gas detection method based on optical frequency comb frequency calibration provided by the invention has the advantages of no background noise, no scattering reflection interference and the like of photoacoustic spectrometry technology, and can realize high-resolution and accurate identification of densely distributed molecular absorption peaks and improve the precision of spectral measurement by accurately measuring the frequency after being combined with the optical frequency comb frequency calibration method. Therefore, the method has advantages in sensitivity and selectivity, can obtain the absorption spectrum information of molecules which are difficult to distinguish when a single or a plurality of the molecules are close to each other, and simultaneously solves the problem of cross sensitivity among gas absorption peaks.
The system can realize high-sensitivity quick-response characteristic gas (such as SF) in the aspect of power grid safety maintenance6Gas and its decomposition products) spectral line parameters. The method can be used for measuring important information such as concentration, content, type and the like of the gas in a sensitive and accurate mode, and provides a way for the operation safety of a power grid and the detection of fault characteristic gas.
Details not described in this specification are within the skill of the art that are well known to those skilled in the art.
Claims (10)
1. A high-resolution photoacoustic spectroscopy gas detection system based on optical frequency comb frequency calibration is characterized in that: the device comprises an infrared comb (1), an infrared tunable continuous laser (2), a first beam splitter (3), a second beam combiner (4), an infrared photoelectric detector (5), a frequency spectrograph (6), a chopper (7), a photoacoustic cell (8) and a microphone (9), wherein the output end of the infrared comb (1) is connected with the input light path of the second beam combiner (4), the output end of the infrared tunable continuous laser (2) is connected with the input light path of the first beam splitter (3), the first output end of the first beam splitter (3) is connected with the input light path of the second beam combiner (4), the output end of the second beam combiner (4) is connected with the input light path of the infrared photoelectric detector (5), the output end of the infrared photoelectric detector (5) is connected with the electric signal input end of the frequency spectrograph (6), the output end of the first beam splitter (3) is right opposite to the light source incidence port of the photoacoustic cell (8), the chopper (7) is arranged between the output end of the first beam splitter (3) and the light source incident port of the photoacoustic cell (8), the chopper (7) is used for carrying out periodic intensity modulation on an optical signal output by the first beam splitter (3), gas to be detected is arranged in the photoacoustic cell (8), the optical signal output by the first beam splitter (3) is subjected to intensity modulation by the chopper (7) and then is emitted into the gas to be detected in the photoacoustic cell (8), and a microphone (9) is used for detecting an acoustic signal generated after the gas to be detected absorbs optical energy.
2. The gas detection system based on optical-frequency comb frequency scaling with high resolution photoacoustic spectroscopy of claim 1, wherein: the microphone is characterized by further comprising a phase-locked amplifier (10) and a data acquisition card (11), wherein the signal output end of the microphone (9) is connected with the input end of the phase-locked amplifier (10), the output end of the phase-locked amplifier (10) is connected with the input end of the data acquisition card (11), and the set frequency signal output end of the controller of the chopper (7) is connected with the input end of the data acquisition card (11).
3. The gas detection system based on optical-frequency comb frequency scaling with high resolution photoacoustic spectroscopy of claim 1, wherein: the infrared tunable continuous laser (2) is used for outputting the frequency f to be measuredcwThe infrared optical comb (1) is used for outputting infrared optical comb signals subjected to frequency calibration, and the infrared photoelectric detector (5) is used for beating the infrared continuous laser signals and the infrared optical comb signals to obtain beating signals fbCaptured and recorded in a spectrum analyzer (6), the spectrum analyzer (6) is used for utilizing infrared continuous laser signals and beat frequency signals fbAnd calibrating the frequency f to be measured in the infrared continuous laser signal by an optical combcwThe measurement is performed.
4. The gas detection system based on optical-frequency comb frequency scaling with high resolution photoacoustic spectroscopy of claim 3, wherein: the frequency output by the infrared tunable continuous laser (2) is fcwAfter intensity modulation is carried out on the infrared continuous laser signal by the chopper (7), the infrared continuous laser signal is emitted into the gas to be detected in the photoacoustic cell (8), and a microphone (9) is used for detecting a sound wave signal generated after the gas to be detected absorbs optical energy.
5. The gas detection system based on optical-frequency comb frequency scaling with high resolution photoacoustic spectroscopy of claim 4, wherein: the acoustic wave signals are amplified by a phase-locked amplifier (10), collected by a data acquisition card (11), and the photoacoustic spectrum intensity signals of the gas to be detected are obtained by using a photoacoustic spectrum detection method.
6. A high-resolution photoacoustic spectrometry gas detection method based on optical frequency comb frequency calibration is characterized by comprising the following steps:
step 1: the output of the infrared tunable continuous laser (2) is fcwThe infrared continuous laser signal is output by the infrared comb (1), the infrared continuous laser signal is input to the second beam combiner (4) through the first beam splitter (3), and a beat frequency signal f is obtained by beating the infrared continuous laser signal and the infrared comb signal in the second beam combiner (4)b；
Step 2: the infrared photoelectric detector (5) converts the beat frequency signal fbCaptured and recorded in a spectrum analyzer (6);
and step 3: the spectrum analyzer (6) utilizes the infrared continuous laser signal and the beat frequency signal fbAnd calibrating the frequency f to be measured in the infrared continuous laser signal by an optical combcwCarrying out measurement;
and 4, step 4: the output frequency of the infrared tunable continuous laser (2) is fcwAfter intensity modulation is carried out on the infrared continuous laser signal by the chopper (7), the infrared continuous laser signal is emitted into gas to be detected in the photoacoustic cell (8), and a microphone (9) is used for detecting a sound wave signal generated after the gas to be detected absorbs optical energy and converting the sound wave signal into a sound wave electric signal;
and 5: the acoustic wave electric signals are amplified by a phase-locked amplifier (10), collected by a data acquisition card (11), and the photoacoustic spectrum intensity signals of the gas to be detected are obtained by using a photoacoustic spectrum detection method;
step 6: and (2) adjusting the wavelength or frequency of the infrared laser output by the infrared tunable continuous laser (2) by adopting a continuous laser frequency sweeping method to realize wavelength or frequency scanning in a broadband spectrum range, and simultaneously, measuring the frequency of the tuned continuous laser in real time by using the optical comb calibration method of the steps 1-3 to obtain a broadband photoacoustic spectrogram with frequency corresponding to the photoacoustic signal amplitude one by one, thereby realizing the spectrum detection of the decomposition product of the multi-component sulfur hexafluoride electrical equipment.
7. The method for detecting gas by high-resolution photoacoustic spectroscopy based on frequency scaling of an optical-frequency comb according to claim 6, wherein: the infrared comb signal refers to a broadband infrared light source with a spectral range of 3 toThe spectrum of the optical comb is distributed in a comb-tooth shape within 12 mu m, namely the spectrum consists of N frequency teeth or comb teeth which are distributed at equal intervals, N is any integer, wherein 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 f0The frequency spacing of comb teeth adjacent to each other is frThen, the absolute frequency of the nth comb is expressed as: f. ofn＝f0+nfrWherein 0 is<n<N；
The infrared photoelectric detector (5) is used for detecting beat frequency signal fbThe detection mode is that the frequency to be measured is fcwThe infrared continuous laser signal and the infrared optical comb signal are overlapped in space and then enter an infrared photoelectric detector (5), the output signal of the infrared photoelectric detector (5) is connected with a spectrum analyzer (6), and the frequency of the beat frequency detection output signal is fb＝|fcw-fn|，fbMeasured by a spectrum analyzer.
8. The method for detecting gas by high-resolution photoacoustic spectroscopy based on frequency scaling of an optical-frequency comb according to claim 7, wherein: the infrared optical comb signal subjected to frequency calibration refers to f of the optical combrThe frequency is determined by means of an infrared photodetector 5 and a frequency meter in such a way that the optical comb pulse repetition frequency is measured; f of optical comb0The frequency, i.e. the carrier envelope phase frequency, is determined by means of an f-2f self-referencing technique, i.e. a comb f whose frequency is lower than the central frequency of the optical combn1＝f0+n1·fr，fn1The frequency of the n1 th comb tooth of the optical comb is defined, n1 is an ordinal number and is a positive integer, any comb tooth with the frequency lower than the center frequency of the optical comb is subjected to frequency doubling through a nonlinear crystal to generate the frequency of 2fn1＝2f0+2n1·frThen the frequency-doubled light and the comb teeth f of the optical comb which are higher than the center frequency of the optical combn2＝f0+2·n1·frPerforming beat frequency detection, fn2Is the frequency of n2 comb teeth of the optical comb, n2 is an ordinal number and a positive integer, corresponds to any comb tooth with the frequency higher than the center frequency of the optical comb, and one comb tooth can always be found to satisfy n1 that n2 is equal to 2 times, and the frequency f 'is obtained'b＝2fn1-fn2＝f0Of the beat signal, f'bIs at a frequency fn1And a frequency of fn2The frequency of the beat frequency signal between the comb teeth of the optical comb can be directly measured by a frequency spectrograph, and the frequency of the beat frequency signal is f0Frequency;
at known f0And frThereafter, in order to measure fcwThe number n of comb teeth is determined, and the infrared continuous laser signal is roughly measured in advance by a spectrum analyzer (6) or an optical wavelength meter and then by an inequality 0<|fcw-(f0+nfr)|<fr/2 estimating the value of the integer n, using f measured by the spectrum analyzer (6)bBy beat frequency detection formula fb＝|fcw-(f0+nfr) I accurately calculate fcwOf (c) is detected.
9. The method for detecting gas by high-resolution photoacoustic spectroscopy based on frequency scaling of an optical-frequency comb according to claim 8, wherein: the decomposition product of the sulfur hexafluoride electrical equipment is electrical equipment fault characteristic gas with infrared absorption characteristics.
10. The method for detecting gas by high-resolution photoacoustic spectroscopy based on frequency scaling of an optical-frequency comb according to claim 6, wherein: in the step 5, the infrared continuous laser signal is modulated by the intensity of the chopper and then irradiates into a photoacoustic cell (8) containing gas to be detected, gas molecules absorb infrared light with the frequency v and then are excited to generate energy level transition, the excited molecules return to the ground state through nonradiative transition and convert absorbed light energy into heat energy, as incident light is periodically modulated by the chopper, the temperature, namely the pressure, can also periodically change, a microphone (9) is used for receiving the sound wave signal and converting the sound wave signal into an electric signal, and the electric signal is sent into a data acquisition card (11) for signal processing after being subjected to noise suppression and amplification by a phase-locked amplifier (10).
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