A resonant quartz enhanced dual optical comb photoacoustic spectroscopy gas detection device and method

Abstract

The application discloses a kind of resonance quartz enhanced dual optical comb photoacoustic spectroscopy gas detection devices, device includes dual optical comb source, acoustooptic frequency shift component, quartz resonant component, signal amplification component, phase-sensitive demodulation component and normalization component;Dual optical comb source is as the excitation light source of photoacoustic effect, it realizes real-time frequency shift by acoustooptic frequency shift component;Dual optical comb source is emitted by acoustooptic frequency shift component and after acting on gas molecule, produces multi-heterodyne sound wave, and quartz resonant component extracts resonance component therein and converts it into electrical signal;The electrical signal generated is successively processed by signal amplification component, phase-sensitive demodulation component, normalization component, and the composition discrimination of target gas and concentration inversion are realized by signal after processing.This application improves the structure and detection mode of dual optical comb photoacoustic spectroscopy, completes the resonance detection of dual optical comb photoacoustic spectroscopy, improves the detection sensitivity of system by acoustic and electrical two-stage filtering, and increases the dynamic range of system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of gas detection, and in particular to a resonant quartz-enhanced dual-comb photoacoustic spectroscopy gas detection device and method. BACKGROUND

[0002] Dual-comb is composed of two optical frequency combs with a small frequency difference. As an ideal light source, it has the characteristics of high resolution, wide spectral range, and fast measurement. Dual-comb spectroscopy is one of its typical applications. Although this technology is relatively mature, there are still some challenges. For example, different detectors need to be replaced in different wavelength bands, and the dynamic range is limited by the photoelectric detector and the Fourier transform multiplexing. As a wavelength-unselective technology, photoacoustic spectroscopy has been widely used in trace gas detection, such as atmospheric pollution detection, factory emission monitoring, and medical disease diagnosis, due to its high sensitivity, fast response, and large dynamic range. Its basic principle is to use a microphone or other acoustoelectric device as an acoustic transducer to detect the sound waves induced by the photoacoustic effect. Therefore, based on dual-comb photoacoustic spectroscopy technology, it can work in a wide wavelength range from ultraviolet to terahertz without replacing the detector.

[0003] However, in actual detection, the traditional dual-comb photoacoustic spectroscopy has some limitations. First, because multiple comb components of the dual-comb source will simultaneously excite sound waves, multiple heterodyne sound waves are generated. Since the frequency components of the multiple heterodyne sound waves are not single, a wideband microphone is usually used as an acoustic transducer. First, it has a higher noise floor than a narrowband detector, and it cannot achieve resonant detection of sound signals. Resonant accumulation of sound is very important in photoacoustic spectroscopy technology, so non-resonant detection based on a wideband microphone inevitably limits the sensitivity of the system. At the same time, since the traditional dual-comb spectroscopy and dual-comb photoacoustic spectroscopy are based on Fourier transform to process signals, such a wideband processing method limits the dynamic range and resolution of the system, and also causes the system to collect more noise, further limiting the sensitivity. SUMMARY

[0004] In order to solve the problem that the existing dual-comb optical sound spectrum cannot realize resonance enhancement of sound signals and has low detection sensitivity, a resonant quartz enhanced dual-comb optical sound spectrum gas detection device and method are provided, the structure and detection method of the dual-comb optical sound spectrum are improved, resonance enhancement of sound signals is realized, and meanwhile, the acoustic and electrical two-stage filtering mode is adopted, so that the gas detection system has a large dynamic range and high sensitivity. The dual-comb source is used as a light source, the two optical combs are frequency shifted under the action of the acousto-optic frequency shift component, so that the center frequency of the down-converted sound spectrum of the dual-comb source is adjusted in real time, and the optical sound signals of each comb tooth pair are collected by the quartz tuning fork in resonance. Compared with the dual-comb optical sound spectrum gas detection device based on a microphone, the resonance enhancement mode is adopted to increase the amplitude of the optical sound signal, and meanwhile, the noise floor is smaller, so that the sensitivity of the sensing system is improved, and the phase-sensitive detection mode is adopted instead of the Fourier transform process, which not only reduces the hardware requirements of the system, but also increases the dynamic range of the system.

[0005] In order to realize the purpose of the present application, a resonant quartz enhanced dual-comb optical sound spectrum gas detection device is provided, which comprises a dual-comb source, an acousto-optic frequency shift component, a normalization component, a quartz resonant component, a signal amplification component and a phase-sensitive demodulation component. The acousto-optic frequency shift component is used to shift the frequency of the dual-comb source, so as to control the center frequency of the down-converted sound comb, and the down-converted frequency of each comb tooth pair is equal to the resonant frequency of the quartz tuning fork in turn. The output end of the acousto-optic frequency shift component is divided into two paths, one of which is connected with the normalization component, and the other of which is connected with the quartz resonant component. The dual-comb source generates the intensity modulation required for the optical sound effect through a multi-heterodyne process. The quartz resonant component adopts a quartz tuning fork to resonate and enhance the resonant component in the multi-heterodyne sound signal, and at the same time, the sound signal is converted into a current signal through the piezoelectric effect and is amplified, and the output end is connected with the input end of the signal amplification component. The output end of the signal amplification component is connected with the input end of the phase-sensitive demodulation component, the amplified signal is phase-sensitive detected, the resonant frequency component is further extracted from the electrical level, and the resonant frequency component is amplified again. Then, the collected multi-heterodyne optical sound spectrum is normalized. Specifically, the normalization detection component collects the comb tooth intensity background, and the amplitude of the optical sound signal demodulated by the phase-sensitive demodulation component is divided by the comb tooth intensity background collected by the normalization component to normalize the inconsistency of the comb tooth power. The amplitude of the normalized signal is linearly related to the gas concentration, the greater the gas concentration, the greater the signal amplitude, the normalized signal generated by the to-be-measured gas is compared with the signal generated by the calibration concentration, and then the to-be-measured gas concentration can be calculated, and the gas type is obtained by comparing with the standard absorption spectrum shape.

[0006] As a further improvement of the above-mentioned scheme, the double optical comb source comprises a first optical frequency comb and a second optical frequency comb, the acousto-optic modulator comprises a first acousto-optic modulator and a second acousto-optic modulator, and a function generator, the first optical frequency comb and the second optical frequency comb are connected to the first acousto-optic modulator and the second acousto-optic modulator respectively, and the function generator is used to provide a radio frequency signal for driving the first acousto-optic modulator and the second acousto-optic modulator. In order to satisfy the resonance detection of all comb teeth pairs, the frequency of the radio frequency signal output by the function generator is adjusted in real time, so that the acoustic wave frequency of each comb teeth pair is aligned with the resonance frequency of the quartz tuning fork in turn, and the resonance detection of all comb teeth pairs is completed by tuning the frequency of the radio frequency signal.

[0007] As a further improvement of the above-mentioned scheme, the normalization component comprises a photodetector and a data acquisition card, which are used to collect the intensity background of the comb teeth and perform normalization. The spectral response range of the photodetector corresponds to the spectral range of the double optical comb source.

[0008] As a further improvement of the above-mentioned scheme, the quartz resonant component comprises a quartz tuning fork (using a commercial standard quartz tuning fork) and a gas chamber component, the quartz tuning fork is used for resonance detection of the acoustic signal, and the gas chamber component is used for containing the gas to be measured. The resonance enhanced detection of the acoustic wave signal is realized by using the quartz tuning fork, the frequency shifted double optical comb source is collimated and incident into the gap between the two arms of the quartz tuning fork, which is used to maximize the photoacoustic signal and minimize the thermal noise, and the parameters such as pressure and temperature in the absorption process are controlled.

[0009] As a further improvement of the above-mentioned scheme, the signal amplification component is a preamplifier, the input end of the preamplifier is connected to the pin output of the quartz tuning fork, the current signal output by the quartz tuning fork is converted into a voltage signal, and the voltage signal is amplified.

[0010] As a further improvement of the above-mentioned scheme, the phase-sensitive demodulation component is a lock-in amplifier, the input end of the lock-in amplifier is connected to the output end of the preamplifier, the demodulation frequency is the resonance frequency of the quartz tuning fork, and the photoacoustic signal used for representing the gas concentration is obtained.

[0011] A detection method of a resonance type quartz enhanced double optical comb photoacoustic spectroscopy gas device, characterized by comprising the following steps:

[0012] Step one: filling the gas sample to be measured into the gas chamber of the quartz resonant component;

[0013] Step two: connecting the first optical frequency comb and the second optical frequency comb to the first acousto-optic modulator and the second acousto-optic modulator respectively, performing frequency offset in the optical domain for the double optical comb source, and combining the two optical frequency combs after frequency offset to obtain the double optical comb;

[0014] Step three: the double optical comb after being split, one part is connected with the photodetector to eliminate the influence of uneven power distribution of different combs and normalize the absorption spectrum, and the other part is collimated to the gap between the two arms of the quartz tuning fork and interacts with the gas molecules therein to generate a multi-heterodyne sound wave through the photoacoustic effect, and due to the piezoelectric effect of the quartz tuning fork, the resonance component in the multi-heterodyne sound wave is detected by the quartz tuning fork and an electric signal is output from the pin thereof;

[0015] Step four: the multi-heterodyne sound wave is amplified through a preamplifier, and then the amplified electric signal is demodulated through a lock-in amplifier;

[0016] Step five: the signal demodulated by the lock-in amplifier and the output of the photodetector are collected through a data acquisition card, the signal is normalized and analyzed, and the type and concentration of the gas are inversely calculated.

[0017] The beneficial effects of the present application are:

[0018] Compared with the prior art, the resonant quartz enhanced double optical comb photoacoustic spectroscopy gas detection device and method provided by the present application uses a quartz tuning fork as an acoustic transducer to realize resonant detection of multi-heterodyne photoacoustic spectroscopy. The shift frequency of the two optical frequency combs is adjusted through an acousto-optic shift frequency component, so that each comb tooth is equal to the resonance frequency of the quartz tuning fork in turn after down-conversion of the acoustic frequency. Therefore, after the intensity-modulated double optical comb source interacts with the gas molecules through the multi-heterodyne process, a multi-heterodyne sound wave is generated due to the photoacoustic effect, and the acoustic component resonating with the quartz tuning fork will be acoustically enhanced. On the basis of acoustically filtering the environmental noise, the amplitude of the photoacoustic signal can be effectively improved, and the sensitivity of the system is further improved. At the same time, the signal amplification component amplifies the signal output by the quartz tuning fork, and further adopts a lock-in amplifier for phase-sensitive demodulation. In this process, the noise level is reduced and the signal-to-noise ratio of the system is improved, and finally the photoacoustic signal representing the concentration and type of the measured gas is obtained. Such resonant detection and acoustic and electrical two-stage filtering improve the detection sensitivity of the system and increase the dynamic range of the system. In summary, the present application has important scientific and engineering application value. BRIEF DESCRIPTION OF DRAWINGS

[0019] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings, in which:

[0020] Figure 1 It is a schematic diagram of the resonant quartz enhanced double optical comb photoacoustic spectroscopy gas detection device of the present application;

[0021] Figure 2 It is a schematic diagram of the acousto-optic shift frequency component of the present application;

[0022] Figure 3A schematic diagram of collimated incidence of a dual optical comb source into a quartz tuning fork according to the present application. DETAILED DESCRIPTION

[0023] The present application provides a resonant quartz enhanced dual optical comb photoacoustic spectroscopy gas detection device, as shown in the figure, comprising a first optical frequency comb 1 and a second optical frequency comb 2, a first acousto-optic modulator 3 and a second acousto-optic modulator 4, a photodetector 5, a gas cell assembly 6, a quartz tuning fork 7, a preamplifier 8, a lock-in amplifier 9, a data acquisition card 10, and a function generator 11, wherein: Figure 1

[0024] The first optical frequency comb 1 and the second optical frequency comb 2 are frequency shifted by the first acousto-optic modulator 3 and the second acousto-optic modulator 4, respectively. By changing the frequency of the function generator 11, the center frequency of the down-converted audio comb is changed, and each comb tooth is sequentially made to have a frequency equal to the resonance frequency of the quartz tuning fork 7, as shown in the figure. After frequency shifting, the first optical frequency comb 1 and the second optical frequency comb 2 are combined to form a dual optical comb source, part of which enters the photodetector 5 to convert the optical signal to an electrical signal, and the comb tooth intensity background is obtained and sent to the data acquisition card 10 for signal normalization, and the other part enters the gas cell assembly 6 and is collimated to be incident on the gap between the arms of the quartz tuning fork 7, as shown in the figure. Figure 2 Figure 3 After the gas molecules near the arms of the quartz tuning fork 7 interact with the dual optical comb source, they release sound waves to the surrounding through thermal relaxation, and the electrical signal output of the quartz tuning fork 7 is connected to the preamplifier 8, and then sent to the lock-in amplifier 9 for demodulation, and the demodulated signal is sent to the data acquisition card.

[0025] The specific implementation process is as follows:

[0026] Step 1: Change the difference between the frequencies applied to the first acousto-optic modulator 3 and the second acousto-optic modulator 4 from small to large, so as to change the frequency of the down-converted audio comb of the dual optical comb source, so that each comb tooth of the dual optical comb source is sequentially equal to the resonance frequency of the quartz tuning fork 7.

[0027] Step 2: The low-frequency envelope generated by the mixing of the first optical frequency comb 1 and the second optical frequency comb 2 serves as the necessary intensity modulation for generating photoacoustic effect. Due to the photoacoustic effect, the interaction between the dual optical comb source and the gas molecules produces multiple heterodyne sound waves, and the quartz tuning fork 7 extracts the resonant component. In order to achieve effective detection and minimize detection noise, the dual optical comb source needs to be collimated through the gap between the two arms of the quartz tuning fork 7, as shown in the figure. Figure 3

[0028] Step 3: Use the lock-in amplifier 9 to perform first harmonic demodulation on the output of the preamplifier 8, and the demodulation frequency is the resonance frequency of the quartz tuning fork.​​​

[0029] Step four: the output of the photodetector 5 and the output of the lock-in amplifier are sent to the data acquisition card 10 at the same time, and the signal is normalized to eliminate the uneven comb background.

[0030] Step five: the normalized signal amplitude is linearly related to the gas concentration, the normalized signal generated by the to-be-detected gas is compared with the signal generated by the calibration concentration, and then the to-be-detected gas concentration can be calculated, and the type of gas is obtained by comparison with the standard absorption spectrum shape.

[0031] In the present application, the low-frequency envelope generated by the mixing process of the first optical frequency comb 1 and the second optical frequency comb 2 will be used as the necessary intensity modulation for generating the photoacoustic signal, thereby generating a multi-heterodyne acoustic wave. The acoustic component in the multi-heterodyne acoustic wave that resonates with the quartz tuning fork 7 will be resonantly accumulated due to the high Q value of the quartz tuning fork 7, which improves the detection sensitivity compared with the non-resonant mode.

[0032] In the present application, the first optical frequency comb 1 and the second optical frequency comb 2 are generated by splitting the same continuous light source through electro-optic modulation, and the difference between the repetition frequencies of the first optical frequency comb 1 and the second optical frequency comb 2 is provided as: the resonance frequency of the quartz tuning fork 7 divided by the number of combs.

[0033] In the present application, the frequency offset scheme provided is: the adjustment range of the difference between the first acousto-optic modulator 3 and the second acousto-optic frequency shifter 4 is from 1 / 2 of the resonance frequency of the quartz tuning fork 7 to 3 / 2 of the resonance frequency of the quartz tuning fork 7.

[0034] In the present application, the beam splitting scheme provided by the dual-comb source is: 1% enters the photodetector 5, and 99% is collimated to be incident between the gap of the two arms of the quartz tuning fork 7.

[0035] The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments can be combined with each other to form new embodiments. The above embodiments are only used to illustrate the technical solutions of the present application and not to limit them, and any modification or equivalent replacement that does not deviate from the spirit and scope of the present application should be covered in the scope of the technical solutions of the present application.

Claims

1. A resonant quartz-enhanced dual-comb photoacoustic spectroscopy gas detection device, characterized in that: The system includes a dual optical comb source, an acousto-optic frequency shifter, a normalization component, a quartz resonator, a signal amplification component, and a phase-sensitive demodulation component. The output of the dual optical comb source is connected to the input of the acousto-optic frequency shifter. The output of the acousto-optic frequency shifter is divided into two paths: one connected to the normalization component, and the other connected to the quartz resonator. The output of the quartz resonator is connected to the input of the signal amplification component. The output of the signal amplification component is connected to the input of the phase-sensitive demodulation component. The output of the phase-sensitive demodulation component is connected to the normalization component. The dual optical comb source includes... The device includes a first optical frequency comb and a second optical frequency comb. The acousto-optic frequency shifting component includes a first acousto-optic modulator, a second acousto-optic modulator, and a function generator. The first and second optical frequency combs are respectively connected to the first and second acousto-optic modulators. The function generator is used to provide radio frequency signals to drive the first and second acousto-optic modulators. The frequency of the tuned radio frequency signal is used to achieve resonance detection for all comb tooth pairs. The quartz resonant component includes a quartz tuning fork and a gas chamber component. The quartz tuning fork is used to resonate and detect the acoustic signal, and the gas chamber component is used to contain the gas to be tested.

2. The resonant quartz-enhanced dual-comb photoacoustic spectroscopy gas detection device according to claim 1, characterized in that: The normalization component includes a photodetector and a data acquisition card, used to acquire the intensity background of the comb teeth and perform normalization.

3. The resonant quartz-enhanced dual-comb photoacoustic spectroscopy gas detection device according to claim 2, characterized in that: The signal amplification component is a preamplifier, and the input terminal of the preamplifier is connected to the pin output of the quartz tuning fork.

4. The resonant quartz-enhanced dual-comb photoacoustic spectroscopy gas detection device according to claim 3, characterized in that: The phase-sensitive demodulation component is a lock-in amplifier, and the input of the lock-in amplifier is connected to the output of the preamplifier.

5. The resonant quartz-enhanced dual-comb photoacoustic spectroscopy gas detection device according to claim 4, characterized in that: The spectral response range of the photodetector corresponds to the spectral range of the dual optical comb source.

6. A detection method using the resonant quartz-enhanced dual-comb photoacoustic spectroscopy gas device as described in claim 5, characterized in that: The steps include the following: Step 1: Fill the gas sample to be tested into the gas chamber of the quartz resonator component; Step 2: The first optical frequency comb and the second optical frequency comb are connected to the first acousto-optic modulator and the second acousto-optic modulator, respectively, to perform frequency shifting in the optical domain of the dual optical comb source. After frequency shifting, the two optical frequency combs are combined into a dual optical comb. Step 3: After the beam is split, one part of the dual optical comb is connected to a photodetector to eliminate the influence of uneven power distribution between different comb teeth and normalize the absorption spectrum. The other part is collimated into the gap between the two arms of the quartz tuning fork and interacts with the gas molecules therein to generate multiheterodyne sound waves through photoacoustic effect. Due to the piezoelectric effect of the quartz tuning fork, the resonant component in the multiheterodyne sound waves is detected by the quartz tuning fork and outputs an electrical signal from its pins. Step 4: Amplify the multiheterodyne sound wave through a preamplifier, and then demodulate the amplified electrical signal through a lock-in amplifier; Step 5: Acquire the demodulated signal from the lock-in amplifier and the output of the photodetector using a data acquisition card, normalize the signal, analyze the signal, and deduce the type and concentration of the gas.

Images