Photo-thermal gas detection device and method based on double-comb enhancement

Abstract

The invention relates to the technical field of spectrum sensing and precision measurement, in particular to a photo-thermal gas detection device and method based on double-comb enhancement, and the photo-thermal gas detection device comprises a pumping laser module, a detection laser module, a hollow-core anti-resonance optical fiber and a data acquisition module, the pump light and a first optical comb generated by the detection laser module are transmitted in the same direction in the hollow-core anti-resonance optical fiber, and the phase of the first optical comb is modulated by a photothermal effect generated after gas absorbs the pump light; and performing optical beat frequency and demodulation on the modulated first optical comb and second optical comb in a data acquisition system to obtain a photo-thermal spectrum signal. According to the invention, the wide spectrum coverage capability of the double optical combs is utilized to realize rapid parallel detection of multi-component gas, and signals are transferred to a radio frequency domain through coherent heterodyne detection, so that various noises are effectively inhibited, and the detection sensitivity, the signal-to-noise ratio and the environmental adaptability are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of spectral sensing and precision measurement, in particular to a dual comb enhanced photothermal gas detection device and method. BACKGROUND

[0002] Gas optical sensing technology has become an indispensable key means in the fields of environmental monitoring, industrial safety, medical health and national defense warning, etc. due to its non-contact measurement, excellent selectivity and real-time response capability. Among many optical sensing methods, photothermal spectroscopy technology realizes indirect measurement of gas concentration by detecting the thermal effect and the change of refractive index caused by the absorption of light energy by the gas. This method has unique advantages in trace gas detection due to its extremely low background interference.

[0003] At present, typical photothermal spectroscopy systems generally use a combination of a single-wavelength pump laser with intensity modulation and another continuous wave probe light. When the pump light wavelength is resonant with the absorption peak of the measured gas, the gas is periodically heated and induces refractive index modulation, and then the gas concentration information is demodulated through the phase or intensity change of the probe light.

[0004] However, the above-mentioned sensing scheme based on monochromatic laser is limited by its inherent technical bottlenecks:

[0005] On the one hand, its single-wavelength working mode needs to be wavelength scanned, which leads to difficulty in improving the measurement speed and cannot realize rapid multi-component gas synchronous detection;

[0006] On the other hand, the sensitivity of the system is severely limited by the intensity noise of the pump light source, the thermal noise of the detection system and environmental disturbances, and the signal-to-noise ratio improvement faces great challenges.

[0007] The above reasons make it difficult for the existing technology to meet the growing demand for high sensitivity, rapid response and multi-component simultaneous detection, especially in complex background or dynamic changing environment. SUMMARY

[0008] In order to solve the above technical problems, the present application provides a dual comb enhanced photothermal gas detection device and method.

[0009] The technical problems solved by the present application can be realized by the following technical solutions:

[0010] A dual comb enhanced photothermal gas detection device, comprising:

[0011] a pump laser module for generating pump light with a wavelength matching the absorption peak of the gas to be measured;

[0012] a detection laser module for generating a first optical comb and a second optical comb;

[0013] an air-core anti-resonant hollow fiber, an input end of the air-core anti-resonant hollow fiber being coupled with the pump light and the first optical comb, for containing the to-be-tested gas and guiding the pump light and the first optical comb to transmit in the same direction, so that a phase of the first optical comb is modulated by a photo-thermal effect excited by the pump light;

[0014] a data acquisition module, an input end of the data acquisition module being connected with an output end of the air-core anti-resonant hollow fiber and the probe laser module respectively, for performing optical beat and demodulation on the second optical comb and the modulated first optical comb, to obtain a photo-thermal spectrum signal of the to-be-tested gas.

[0015] Preferably, the probe laser module is a microcavity dual optical comb.

[0016] Preferably, the probe laser module comprises:

[0017] a microcavity optical comb generator, for generating an optical comb;

[0018] a frequency control unit, connected with the microcavity optical comb generator, for processing the optical comb, to generate and maintain a fixed repetition frequency difference between the first optical comb and the second optical comb.

[0019] Preferably, the frequency control unit comprises:

[0020] a modulator, for frequency modulating the optical comb or the split optical path;

[0021] a feedback circuit, connected with the modulator, for controlling the modulator to lock the repetition frequency difference at a preset value, according to a frequency or phase difference signal of the first optical comb and the second optical comb.

[0022] Preferably, the modulator is an electro-optic modulator or an acousto-optic modulator.

[0023] Preferably, the first optical comb is a probe optical comb, and the second optical comb is a reference optical comb.

[0024] Preferably, the pump laser module is a mid-infrared tunable laser.

[0025] Preferably, a core of the air-core anti-resonant hollow fiber is an air channel, and a gas inlet and a gas outlet are arranged on a tube wall of the air-core anti-resonant hollow fiber, to form a flowing to-be-tested gas sample cell.

[0026] Preferably, the data acquisition module comprises:

[0027] A beam combiner is connected to the probe laser module and the hollow-core anti-resonant fiber respectively, and is used for spatially combining the second optical comb with the modulated first optical comb to obtain a combined light;

[0028] A photodetector is connected to the beam combiner, and is used for converting the combined light into a beat frequency electrical signal;

[0029] A signal processor is connected to the photodetector, and is used for performing fast Fourier transform on the beat frequency electrical signal to generate the photothermal optical spectrum signal.

[0030] The application further provides a dual-comb enhanced photothermal gas detection method, which is applied to the dual-comb enhanced photothermal gas detection device.

[0031] In step S1, the pump light and the first optical comb are coupled into the hollow-core anti-resonant fiber filled with the to-be-detected gas in the same direction, the periodic photothermal effect is generated by exciting the gas molecules by using the pump light, and the phase of the first optical comb is modulated;

[0032] In step S2, the modulated first optical comb and the second optical comb are spatially combined and heterodyne interfered to generate a beat frequency electrical signal;

[0033] In step S3, the beat frequency electrical signal is digitally collected and spectrum-analyzed, the photothermal optical spectrum signal representing the gas absorption characteristics is extracted, and the to-be-detected gas concentration is determined based on the photothermal optical spectrum signal.

[0034] Beneficial effects: the dual optical combs and the hollow-core anti-resonant fiber are introduced, the spectral wide coverage capability of the dual optical combs is used to replace the traditional single-wavelength scanning, the rapid synchronous detection of multi-component gas is realized, the photothermal signal is converted to the radio frequency domain by optical beating by using the coherence characteristics of the dual optical combs, the pump light intensity noise and the detection thermal noise are effectively suppressed, the detection sensitivity and the signal-to-noise ratio are greatly improved, and the rapid, high-precision and multi-component detection capability of trace gas in a complex dynamic environment is significantly enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a device structure schematic diagram of the application;

[0036] Figure 2 is a hollow-core anti-resonant fiber schematic diagram of the application;

[0037] Figure 3 is a dual-comb differential detection principle diagram of the application;

[0038] Figure 4 is a method flowchart of the application.

[0039] Label explanation: 1, pump laser module; 2, probe laser module; 21, first optical comb; 22, second optical comb; 3, hollow core anti-resonant fiber; 31, gas inlet; 32, gas outlet; 4, data acquisition module. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the scope of protection of the present application.

[0041] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0042] The present application will be further described below with reference to the drawings and specific embodiments, but is not limited to the present application.

[0043] In recent years, in order to solve the spectral bandwidth limitation of monochromatic light source, researchers try to introduce optical frequency comb with wide spectral coverage to replace the traditional monochromatic light source, and develop double comb optical thermal spectrum technology combined with double optical comb pumping and hollow fiber enhancement, but such method still needs to rely on independent continuous wave probe laser and complex interference optical path, the serial scanning mode, the sensitivity to system stability and noise have not been fundamentally changed, there are still significant deficiencies in detection efficiency, long-term stability and robustness in actual environment, which is difficult to meet the growing application demand for high-speed, high-sensitivity and high-stability gas sensing.

[0044] Therefore, with reference to Figure 1 The present application provides a kind of based on double comb enhanced optical thermal gas detection device, comprising:

[0045] Pump laser module 1, for generating pump light with wavelength matching the absorption peak of the gas to be measured;

[0046] Probe laser module 2, for generating first optical comb 21 and second optical comb 22;

[0047] Hollow core anti-resonant fiber 3, the input end of the hollow core anti-resonant fiber 3 is coupled with the pump light and the first optical comb 21, for accommodating the gas to be measured and guiding the pump light and the first optical comb 21 to transmit in the same direction, so that the phase of the first optical comb 21 is modulated by the photothermal effect excited by the pump light;

[0048] A data acquisition module 4, an input end of the data acquisition module 4 is connected with an output end of the probe laser module 2 and the hollow-core anti-resonant fiber 3 respectively, and is used for optical beat frequency and demodulation of the second optical comb 22 and the modulated first optical comb 21, so as to obtain the optical thermal spectrum signal of the gas to be measured.

[0049] Specifically, in the embodiment of the present application, in order to solve the problems of the existing dual-comb optical thermal spectrum technology, such as the need for external probe light and complex interference structure, the essence of the detection mode is still serial, the system is sensitive to noise and environmental disturbance, and the like, the first optical comb 21 is directly introduced into the hollow-core anti-resonant fiber 3 as the probe light, and is co-axially transmitted with the pump light to generate collinear phase modulation, and then is beat with the homologous second optical comb 22, so that the alignment difficulty and additional noise caused by the independent continuous wave probe laser and the complex spatial interference light path are effectively avoided, and the all-fiber and collinear integrated parallel optical thermal spectrum detection is realized.

[0050] Specifically, the homologous dual-comb collinear enhanced optical thermal spectrum detection architecture maximizes the spatial overlap and interaction efficiency of the pump light and the probe light (the first optical comb 21) through collinear transmission; the natural multi-wavelength parallel detection capability of the dual-comb is utilized, so that the wide spectrum information can be obtained at one time without scanning; through optical heterodyne beat, the low-frequency optical thermal phase modulation signal is efficiently transferred and demodulated to the radio frequency domain which is easy to process, so that the detection speed, long-term stability and robustness to environmental interference of the system are fundamentally improved.

[0051] As a preferred embodiment of the present application, the pump laser module 1 is a mid-infrared tunable laser.

[0052] Specifically, in order to fully excite and utilize the strong intrinsic absorption of the target gas molecules in the mid-infrared band (especially the molecular vibration-rotation absorption spectrum), so as to realize high-sensitivity and high-selectivity detection of various trace gases, in the embodiment of the present application, a narrow-line-width and fast-tunable laser in the mid-infrared band is preferably used as a pump light source. The core feature of the pump light source is that the wavelength can be accurately and quickly tuned to the resonance wavelength of one or more characteristic absorption peaks of the gas to be measured.

[0053] In specific work, the laser can be controlled by a wavelength scanning and locking driving circuit:

[0054] Firstly, scanning is performed in a wide spectrum range to identify and locate the target absorption peak;

[0055] Subsequently, the laser wavelength is accurately locked at the center of the selected absorption peak, or is periodically scanned in a small range according to the detection requirement.

[0056] This wavelength selectivity and tuning capability, combined with the long optical path enhancement effect provided by hollow anti-resonant fiber, greatly enhances the excitation efficiency of the photothermal effect.

[0057] When a precisely resonant pump light periodically (usually generated by a built-in or external intensity modulator) irradiates a gas, the gas molecules absorb the light energy and transition from their ground state. This energy is then converted into heat through non-radiative relaxation processes (such as collisions), generating a spatially periodic temperature field distribution within the optical fiber that is synchronized with the modulation frequency. The periodic variation of this temperature field directly leads to in-phase and frequency-synchronized modulation of the gas's refractive index.

[0058] This process is the core physical mechanism of the photothermal effect, providing a high-contrast signal source for subsequent measurement of refractive index changes (i.e., phase changes) using a probe optical comb. This mid-infrared pumping scheme, because it directly acts on the "fingerprint" absorption region of molecules, not only significantly improves the sensitivity and selectivity of detection, but also provides a key physical basis for realizing the distinguishable detection of multi-component gases (through sequential or parallel tuning of pump wavelengths).

[0059] In a preferred embodiment of the present invention, the detection laser module 2 is a microcavity dual optical comb.

[0060] To fundamentally simplify the system configuration, improve long-term operational stability, and optimize its core coherent detection performance, this invention preferably employs a dual optical comb generated by a single optical microcavity as the detection light source. The microcavity dual optical comb is generated by simultaneously exciting and locking two optical frequency combs with different repetition frequencies within the same high-quality factor (high Q value) microresonant cavity. In this embodiment, these two optical combs are respectively configured as a first optical comb 21 (serving as signal light, entering the sensing fiber) and a second optical comb 22 (serving as local reference light, directly entering the data acquisition module).

[0061] This design, by using a microcavity dual optical comb integrated on a single chip as the detection light source, first achieves complete integration and homogenization of the system's core light source. It not only ensures the natural frequency stability and ultra-low relative noise between the two detection optical combs through chip-level physical packaging, thus completely eliminating the need for the large femtosecond laser array and complex active phase-locked feedback circuit that traditional dual-comb systems rely on, but also fundamentally liberates the system from an optical platform sensitive to vibration and temperature drift, greatly improving the robustness and long-term operational stability of the device.

[0062] Further, the deep integration of the microcavity dual-comb with the architecture of the present application, through its inherent high coherence comb teeth and GHz-level high repetition rate characteristics, directly empowers high-performance heterodyne detection: high coherence ensures high signal-to-noise ratio when performing frequency mixing with modulated signal light (first optical comb 21), and high frequency repetition rate naturally pushes the demodulated radio frequency spectral signal to a clean frequency band far from various low-frequency noises (such as pump light intensity noise, circuit 1 / f noise, and environmental disturbances), thereby significantly expanding the detection sensitivity and dynamic range of the system in principle.

[0063] Finally, this innovative choice at the level of the light source enables the device to achieve miniaturization, chipization, and full solidification of the overall system architecture while inheriting the core advantages of dual-comb technology, such as wide-spectrum parallelism and fast detection. This marks a fundamental leap in the technology path from a laboratory precision optical platform to a field-ready instrument, laying a solid technical foundation for building a gas sensing terminal that truly possesses high sensitivity, fast response capability, and is suitable for long-term stable operation in complex environments.

[0064] As a preferred embodiment of the present application, the detection laser module 2 comprises:

[0065] A microcavity optical frequency comb generator for generating an optical frequency comb;

[0066] A frequency control unit connected to the microcavity optical frequency comb generator for processing the optical frequency comb to generate and maintain a fixed repetition frequency difference between the first optical comb 21 and the second optical comb 22.

[0067] Specifically, in order to accurately generate and long-term stably maintain the fixed and known repetition frequency difference necessary for dual-comb heterodyne detection while taking advantage of the high integration of microcavity optical frequency combs, a precise frequency control unit is introduced in the embodiment of the present application. The frequency control unit processes the original optical frequency comb output by the microcavity generator, aiming to actively generate a small frequency offset, thereby deriving two sets of frequency combs that "slide" at a stable rate in the time domain and can be accurately aligned in the frequency domain, serving as the first optical comb 21 for signal detection and the second optical comb 22 for local reference, respectively.

[0068] Further specifically, in the embodiment of the present application, the frequency control unit comprises:

[0069] A modulator for frequency modulating the optical frequency comb or the optical path after beam splitting;

[0070] A feedback circuit connected to the modulator for controlling the modulator to lock the repetition frequency difference at a preset value based on the frequency or phase difference signal of the first optical comb 21 and the second optical comb 22.

[0071] Specifically, the modulator usually adopts an acousto-optic frequency shifter (AOM) or an electro-optic phase modulator. Its working mode can be two:

[0072] One is to split the original optical frequency comb output by the microcavity generator as a whole, and then select one path (for example, the path for generating the second optical comb 22) to apply a fixed frequency offset;

[0073] Another more optimal way is to perform periodic frequency modulation associated with the comb mode on the common path of the optical frequency comb before splitting (for example, by a modulation source locked to the free spectral range of the microcavity), thereby physically exciting a secondary optical comb (i.e., the second optical comb 22) with a precise repetition frequency difference.

[0074] And the feedback circuit is the core of the control unit, which synchronously receives a small part of the light signals from the first optical comb 21 and the second optical comb 22 through a high-speed photodetector, and extracts the coherent beat frequency signal between them. The frequency of the beat frequency signal is the embodiment of the actual repetition frequency difference.

[0075] The feedback circuit compares the actual frequency with the preset value provided by a very stable RF reference source (such as an atomic clock or a GPS disciplined crystal oscillator) to generate an error signal. The error signal is used to drive the modulator in real time and accurately, dynamically adjusting the frequency shift or modulation depth, thereby forming a closed servo control loop to lock the repetition frequency difference on the preset target value.

[0076] This active locking mechanism effectively compensates for the slight frequency drift of the microcavity itself due to environmental temperature, pump power fluctuations and other factors, ensuring the spectral stability of the system during long-term operation and the reliability of the measurement data. It is a key technical support to ensure that the device realizes high-precision and high-repeatability gas concentration quantitative analysis.

[0077] As a preferred embodiment of the present application, the first optical comb 21 is a probe optical comb, and the second optical comb 22 is a reference optical comb.

[0078] Specifically, in order to extract and demodulate the weak refractive index modulation signal generated by the gas to be measured in the co-linear photo-thermal detection architecture of the present application in the highest signal-to-noise ratio, in the embodiments of the present application, the roles of the double optical combs are clearly functionally divided and path configured:

[0079] The first optical comb 21 is used as a probe optical comb, which is coupled into the hollow-core anti-resonant optical fiber filled with the gas to be measured together with the pump light, and its phase directly carries the gas concentration information modulated by the periodic photo-thermal effect;

[0080] Meanwhile, the second optical comb 22 is taken as a reference optical comb, which is transmitted to the data acquisition module directly via an independent, stable and gas-unmodulated optical path (short optical fiber or free space).

[0081] The physical basis of this division is that the probe optical comb undergoes the same physical process as the pump light in the sensing optical fiber, and its spectrum phase is "coded" with the target information; while the reference optical comb always remains "pure", and its phase only reflects the intrinsic and slow phase noise of the laser. When the two are optically beat on the photodetector of the data acquisition module, the intrinsic phase noise common to both is highly correlated and cancels out, while the rapid and periodic phase modulation caused by gas absorption only exists in the probe optical comb and is differentially amplified and converted into an RF signal that is easy to process. This heterodyne differential detection mechanism is the core physical principle of the present application, which can extract the weak gas signal from strong environmental interference and laser inherent noise.

[0082] As a preferred embodiment of the present application, the core of the hollow core anti-resonant fiber 3 is an air channel, and a gas inlet 31 (Gas in) and a gas outlet 32 (Gas out) are arranged on the wall of the hollow core anti-resonant fiber 3 to form a flowing gas sample cell.

[0083] Specifically, in order to overcome the problems of static gas sampling being susceptible to gas adsorption / desorption, reaction consumption and concentration gradient, and to achieve rapid response, continuous and real-time monitoring of the sensing unit to the gas environment, in the embodiment of the present application, with reference to Figure 2 The hollow core anti-resonant fiber HC-ARF is designed and integrated as a dynamic and continuous flowing gas sample cell; on the cladding structure of the optical fiber, a gas inlet 31 and a gas outlet 32 are respectively opened at a specific position (usually close to both ends of the optical fiber) through precision machining or packaging process.

[0084] The target gas continuously flows into the air core channel of the optical fiber from the inlet under the driving of an external micro-pump or pressure difference, fully interacts with the laser (i.e. pump light / probe light) transmitted therein, and then flows out from the outlet.

[0085] This flow cell design brings multiple key advantages:

[0086] Firstly, it ensures that the gas sample in the sensing area is always in a state of rapid renewal, which greatly shortens the response time (time constant) of the system to the change of gas concentration, enabling it to track the dynamically changing gas environment;

[0087] Secondly, continuous flow effectively avoids the long-term adsorption accumulation or consumption of target gas molecules on the inner wall of the optical fiber, ensuring the accuracy and long-term stability of the measurement;

[0088] At the same time, it is also convenient to introduce standard gas for online calibration or zero calibration;

[0089] In addition, the flow design also reduces the harsh requirements for sealing and initial filling accuracy, improves the practicability and reliability of the system.

[0090] This embodiment combines the inherent long optical path and strong light field restriction advantages of optical fiber with dynamic sampling capability to jointly construct an efficient, sensitive and rapid response miniaturized gas sensing core unit.

[0091] As a preferred embodiment of the present application, the data acquisition module 4 comprises:

[0092] A beam combiner is connected to the probe laser module 2 and the hollow-core anti-resonant optical fiber 3, respectively, for spatially combining the second optical comb 22 with the modulated first optical comb 21 to obtain a combined light;

[0093] A photodetector is connected to the beam combiner for converting the combined light into a beat frequency electrical signal;

[0094] A signal processor is connected to the photodetector for performing fast Fourier transform on the beat frequency electrical signal to generate the photothermal spectroscopy signal.

[0095] Specifically, in order to extract the spectral phase information modulated by the gas photothermal effect from the optical heterodyne interference signal with high precision and high efficiency, in the embodiment of the present application, a set of parallel spectral signal demodulation scheme based on fast Fourier transform is designed and implemented. Figure 3 The working process is as follows:

[0096] First, the beam combiner spatially superimposes the pure local reference optical comb (Reference, corresponding to the second optical comb 22) from the probe laser module 2 and the probe optical comb (Probe, corresponding to the first optical comb 21) output from the hollow-core anti-resonant optical fiber 3, which has carried gas modulation information in phase, to form coaxial transmission of combined light.

[0097] The combined light then enters a high-speed, high-bandwidth photodetector; due to the stable repetition frequency difference between the two optical combs, each pair of teeth (the mth tooth of the reference optical comb and the nth tooth of the probe optical comb) on the photodetector will be coherently superimposed, producing a radio frequency beat signal; all the radio frequency signals produced by the comb tooth pairs together form a radio frequency comb with a frequency range covering from nearly zero to the bandwidth of the photodetector; after being digitized by a high-speed analog-to-digital converter, the beat frequency electrical signal is sent to a signal processor.

[0098] The processor applies a fast Fourier transform (FFT) to the collected time series signal, converts it from the time domain to the frequency domain, and thus obtains a radio frequency comb spectrum composed of a large number of discrete spectral lines.

[0099] In this spectrum, the slight phase modulation of each comb tooth of the probe comb caused by the thermal effect of the pump light is converted into the amplitude and phase change of the corresponding radio frequency beat spectrum line. By reading and analyzing the photo-thermal spectrum signal (as shown in the figure "PTS signal") of all the spectral lines in the entire radio frequency comb in parallel, the high-resolution, wide-band photo-thermal spectrum near the gas absorption band corresponding to the wavelength of the pump light can be reconstructed at one time in a single measurement.

[0100] This process efficiently and in parallel converts and amplifies the slow and weak optical phase modulation caused by gas absorption into the radio frequency domain, which is easy to process, and is the core data processing mechanism of the device to realize high-speed and high-sensitivity multi-component spectral detection.

[0101] Referring Figure 4 , the application also includes a dual-comb enhanced photo-thermal gas detection method applied to the dual-comb enhanced photo-thermal gas detection device as described above, comprising:

[0102] Step S1, the pump light and the first optical comb 21 are coupled into the hollow-core anti-resonant optical fiber 3 filled with the gas to be measured in the same direction, the periodic photo-thermal effect is generated by using the pump light to excite the gas molecules, and the phase of the first optical comb 21 is modulated;

[0103] Step S2, the modulated first optical comb 21 and the second optical comb 22 are spatially combined and heterodyne interfered to generate a beat electric signal;

[0104] Step S3, the beat electric signal is digitally collected and spectrum-analyzed, the photo-thermal spectrum signal representing the gas absorption characteristics is extracted, and the concentration of the gas to be measured is determined based on the photo-thermal spectrum signal.

[0105] In summary, the application realizes a new type of high-performance gas sensing system through the innovative architecture of deep integration of mid-infrared pump excitation of molecular fingerprint absorption, microcavity dual-comb parallel coherent detection, and hollow-core anti-resonant optical fiber enhanced photo-thermal interaction.

[0106] Compared with the prior art, the application has the following advantages:

[0107] Ultra-high sensitivity and signal-to-noise ratio: the photo-thermal effect is enhanced by the hollow-core optical fiber to realize long optical path and high power density, and the statistical average effect (in the case of classical shot noise, the improvement factor is about times, N is the effective comb tooth number) of the dual-comb parallel detection is combined, the system noise is effectively suppressed, and the detection limit is significantly reduced.

[0108] Fast multi-component and wideband detection capability: using thousands of comb teeth of dual optical combs as natural parallel detection channels, wide spectrum information is obtained at one time, completely getting rid of the serial working mode of wavelength scanning in traditional technology, realizing the millisecond to second level fast response of gas concentration change and multi-component simultaneous detection.

[0109] Excellent stability and environmental robustness: using the chip integrated microcavity dual comb as the light source, the natural frequency stability and ultra-low relative noise are obtained; combined with the collinear heterodyne detection technology, the common mode noise (such as vibration, temperature drift and laser intensity noise) is effectively eliminated, so that the system can still maintain long-term stable operation in complex field environment.

[0110] System integration and practical prospect: the core optical components (microcavity dual comb, hollow optical fiber) are developed towards miniaturization and all-fiber direction, avoiding complex spatial light path and precise optical platform, significantly reducing the volume, cost and debugging difficulty of the system, laying a solid foundation for the field deployment and portable application in the fields of environmental monitoring, industrial safety, medical diagnosis and the like.

[0111] The above only describes the preferred embodiments of the present application, and does not limit the implementation and protection scope of the present application. For those skilled in the art, it should be realized that any equivalent replacement and obvious change made by applying the contents of the present application description and drawings should be included in the protection scope of the present application.

Claims

1. A dual comb enhanced photothermal gas detection device, comprising: Comprise: a pump laser module (1) for generating pump light with a wavelength matching an absorption peak of a gas to be measured; a probe laser module (2) for generating a first optical comb (21) and a second optical comb (22); an air-core anti-resonant hollow fiber (3) having an input end coupled with the pump light and the first optical comb (21), for containing a gas to be measured and guiding the pump light and the first optical comb (21) to co-propagate, so that the phase of the first optical comb (21) is modulated by the photothermal effect excited by the pump light; a data acquisition module (4) having an input end connected with the output end of the probe laser module (2) and the air-core anti-resonant hollow fiber (3) respectively, for performing optical beating and demodulation on the second optical comb (22) and the modulated first optical comb (21) to obtain a photothermal spectrum signal of the gas to be measured.

2. The dual comb enhanced photothermal gas detection device according to claim 1, wherein, The probe laser module (2) is a microcavity dual optical comb.

3. The dual grating enhanced photothermal gas detection device of claim 2, wherein, The probe laser module (2) comprises: a microcavity optical frequency comb generator for generating an optical frequency comb; a frequency control unit connected with the microcavity optical frequency comb generator, for processing the optical frequency comb to generate and maintain a fixed repetition frequency difference between the first optical comb (21) and the second optical comb (22).

4. The dual grating enhanced photothermal gas detection device of claim 3, wherein, The frequency control unit comprises: a modulator for frequency modulating the optical frequency comb or the split optical path; a feedback circuit connected with the modulator, for controlling the modulator to lock the repetition frequency difference at a preset value according to a frequency or phase difference signal of the first optical comb (21) and the second optical comb (22).

5. The dual- comb enhanced photothermal gas detection device according to claim 4, wherein, The modulator is an electro-optic modulator or an acousto-optic modulator.

6. The dual- comb enhanced photothermal gas detection device of claim 1, wherein, The first optical comb (21) is a probe optical comb, and the second optical comb (22) is a reference optical comb.

7. The dual- comb enhanced photothermal gas detection device of claim 1, wherein, The pump laser module (1) is a mid-infrared tunable laser.

8. The dual- comb enhanced photothermal gas detection device of claim 1, wherein, The core of the air-core anti-resonant hollow fiber (3) is an air channel, and the air-core anti-resonant hollow fiber (3) is provided with a gas inlet (31) and a gas outlet (32) on the tube wall, for forming a flowing gas sample cell.

9. The dual- comb enhanced photothermal gas detection device of claim 1, wherein, The data acquisition module (4) comprises: a beam combiner connected with the probe laser module (2) and the air-core anti-resonant hollow fiber (3) respectively, for spatially combining the second optical comb (22) and the modulated first optical comb (21) to obtain a combined light; a photodetector connected with the beam combiner, for converting the combined light into a beat frequency electrical signal; a signal processor connected with the photodetector, for performing fast Fourier transform on the beat frequency electrical signal to generate the photothermal spectrum signal.

10. A dual comb enhanced photothermal gas detection method, comprising: Applied to the dual-comb enhanced photothermal gas detection device according to any one of claims 1-9, comprising: Step S1, co-coupling the pump light and the first optical comb (21) into the air-core anti-resonant hollow fiber (3) filled with the gas to be measured, using the pump light to excite the periodic photothermal effect of the gas molecules, and modulating the phase of the first optical comb (21); Step S2, modulated first optical comb (21) and second optical comb (22) are combined and heterodyne interfered to generate beat frequency electric signal; Step S3, the beat frequency electric signal is digitized, collected and spectrum analyzed, and optothermal spectrum signal representing gas absorption characteristics is extracted, and the concentration of the to-be-measured gas is determined based on the optothermal spectrum signal.

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