Echo wall mode optical microcavity enhanced photo-thermal spectrum type gas sensing device and detection method

Abstract

The invention provides an echo wall mode optical microcavity enhanced photo-thermal spectrum type gas sensing device, which belongs to the technical field of micro-nano infrared gas sensing, and comprises an upper computer, a photoelectric system and a gas path system which are connected in sequence, the photoelectric system comprises an infrared sensing branch circuit, a laser excitation branch circuit and a photoelectric detection branch circuit which are processed in parallel; the gas path system comprises a gas transmission system and a gas chamber, and a WGM microcavity coupling system is fixedly arranged in the gas chamber; the infrared sensing branch, the laser excitation branch and the photoelectric detection branch are respectively connected with the upper computer and the WGM microcavity coupling system; the invention further provides an echo wall mode optical microcavity enhanced photo-thermal spectrum type gas detection method. The high quality factor (Q value) and the strong light field local characteristic of the WGM microcavity are utilized, the photothermal effect is combined, high-sensitivity detection is achieved by detecting microcell temperature change generated after gas absorbs exciting light, and the universality and the detection sensitivity of the WGM microcavity serving as a sensor are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-nano-level infrared gas sensing, and in particular to an optical microcavity gas sensing device based on a whispering gallery mode and a detection method. Background Art

[0002] Traditional small infrared spectroscopy gas sensors use high-power lasers or complex multi-reflection cavity structures to improve system sensitivity, resulting in large probes (the part where the gas interacts with the sensing material) with high volume, weight, and power consumption, making it difficult to meet the needs of special scenarios such as deep space exploration. Micro-nano sensing probes have shown great potential in this field due to their miniaturization and low power consumption. However, due to the limitations of the effective area of ​​interaction between light and gas at the micro-nano scale, the detection sensitivity of existing waveguide sensors is still relatively low. For example, Su et al. 2 A methane sensing probe was designed on a silicon wafer and a detection limit of 1% was achieved [Su P., Han Z., Kita D., et al. Monolithic on-chip mid-IR methane gas sensor with wave guide integrated detector [J]. Applied Physics Letters, 2019, 114(5): 051103.]. To improve sensitivity, researchers usually use slow light waveguide technology to enhance the interaction between light and gas using high group refractive index. However, such sensors often require millimeter-level waveguide lengths to achieve high-sensitivity detection. For example, Peng et al. used a 1mm long SOI two-dimensional photonic crystal waveguide to achieve an acetylene detection limit of 277ppm [Peng Z., Huang Y., Zheng K., et al. Slow-light-enhanced on-chip 1D and 2D photonic crystal waveguide gas sensing in near-IR with an ultrahigh interaction factor [J]. Photonics Research, 2023, 11(10): 1647-1656.]. Therefore, how to achieve high-sensitivity gas sensing while keeping the sensor probe at the micro-nano size is an urgent problem that needs to be solved in this field.

[0003] In recent years, the emergence of whispering gallery mode (WGM) optical microcavities has provided new insights into high-sensitivity gas sensing at the micron and nanoscale. WGM optical microcavities localize light intensity through total internal reflection, achieving tens of thousands of light-matter interactions at the micrometer scale. Their high quality factor and small mode volume combine to achieve high sensitivity while maintaining miniaturization. These properties allow for integration into silicon-based chips, opening the door to the development of portable gas sensors.

[0004] Currently, WGM microcavity gas sensing is primarily based on a refractive index-sensitive mechanism, whereby gas molecule adsorption or chemical reactions cause changes in the refractive index of the medium surrounding the microcavity, which in turn causes a shift in the resonant wavelength or phase. Gas sensing is achieved by detecting these optical parameters. However, due to the extremely small sensing area of ​​the microcavity (on the order of micrometers), the detection sensitivity is limited by the effective interaction area and system noise. To this end, researchers have proposed two main enhancement strategies: functional material modification and microcavity structure optimization. In terms of functional material modification, metal organic frameworks (MOFs), polymers or nanoporous films are often used to enhance the gas adsorption capacity of the microcavity. For example, in the literature [Li C., Lohrey T., Nguyen PD, et al., Part-per-trillion trace selective gas detection using frequency locked whispering-gallery mode microtoroids, ACS Appl. Mater. Interfaces, 2022, 14: 42430-42440.], Li et al. from the University of Arizona used polymer coatings such as polyethylene glycol, polyvinyl acetate and polyvinyl alcohol to achieve ppt-level detection of ammonia, formaldehyde and DIMP, respectively; in terms of microcavity structure optimization, such as the literature [Afri MNZB, Johari AB, Ahmad AB, et al., Carbon dioxide gas sensor based on self-assembled WGM microbottle resonator coated with polymethyl methacrylate, Optoelectron. Adv. Mater.-Rapid Commun., 2024, 18(7): 319-324.], Afri et al. used a cascaded PMMA-coated microbottle cavity to increase the CO2 detection sensitivity to 1.67pm / %ppm. In addition, the invention patent with announcement number CN115200843B discloses a multi-parameter parallel detection method based on a single whispering gallery optical microcavity. By utilizing multiple resonant modes and a sensor matrix signal processing method in a single whispering gallery optical microcavity, the parallel detection of multiple parameters is achieved, solving the problem that traditional microcavity sensing mechanisms are difficult to achieve multi-parameter independent decoupling and parallel detection.

[0005] However, the aforementioned whispering gallery optical microcavity, which relies on coating with functional materials, also presents a series of problems. Firstly, the coating process is often complex, involving multiple delicate steps such as material synthesis, uniform coating, and curing, and places stringent demands on process conditions. Secondly, the type of gas detected depends largely on the properties of the coating material, requiring specific materials for different gases, limiting the versatility and flexibility of detection. These factors have become key bottlenecks hindering the further development and application of traditional microcavity gas sensing technology. Therefore, the development of new mechanisms that directly enhance the intrinsic sensing capability of microcavities without relying on surface modification has become an urgent research need. Summary of the Invention

[0006] In response to the problem of mutual restriction between sensitivity and size in existing micro-nano waveguide sensors, and the technical problem that existing whispering gallery mode (WGM) microcavity gas sensors rely on functional material coating and have poor versatility, the present invention proposes a whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device and detection method. The high Q value, small mode volume, and high temperature sensitivity of the WGM microcavity as a sensing probe are combined with the highly sensitive and highly selective infrared photothermal spectroscopy technology. The thermally induced frequency shift effect of the whispering gallery microcavity is used to measure the non-radiative thermal relaxation signal in the photothermal spectroscopy technology. The technology integrates technologies such as precise laser wavelength measurement and control and adaptive transmission spectroscopy signal processing to improve the resolution and signal-to-noise ratio of the microcavity transmission spectrum, thereby enhancing the accuracy of trace gas monitoring data. This solves the problems of mutual restriction between sensitivity and size, poor versatility, and reliance on functional material coating of micro-nano gas sensor probes.

[0007] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device comprises a host computer, a photoelectric system, and a gas circuit system connected in sequence; the photoelectric system comprises an infrared sensing branch, a laser excitation branch, and a photoelectric detection branch for parallel processing; the gas circuit system comprises a gas transmission system and a gas chamber, wherein a WGM microcavity coupling system is fixedly disposed in the gas chamber; the infrared sensing branch, the laser excitation branch, and the photoelectric detection branch are respectively connected to the host computer and the WGM microcavity coupling system; the infrared sensing branch outputs gas-absorbable near-infrared laser light according to host computer instructions, the laser excitation branch outputs output light that satisfies the resonance conditions of the microcavity and can form a whispering gallery mode according to host computer instructions, the WGM microcavity coupling system detects a photothermal signal induced by a first transmitted light obtained by the near-infrared laser and obtains a second transmitted light signal obtained by the output light that can form a whispering gallery mode, and the photoelectric detection branch transmits the photothermal signal induced by the first transmitted light and the second transmitted light signal to the host computer for data processing.

[0009] The infrared sensing branch includes an integrated laser temperature control-current driver, a distributed feedback laser, a fiber coupler and a fiber collimator connected in sequence; the integrated laser temperature control-current driver is connected to the host computer, and the fiber collimator is connected to the WGM microcavity coupling system optical path.

[0010] The infrared sensing branch further comprises a visible red light source, and the visible red light emitted by the visible red light source and the output light of the distributed feedback laser are coupled through an optical fiber coupler.

[0011] The laser excitation branch comprises a digital laser controller, a continuously tunable single-frequency diode laser, an attenuator and a polarization controller connected in sequence; the digital laser controller is connected to the host computer, and the polarization controller is connected to the WGM microcavity coupling system.

[0012] The photoelectric detection branch includes a first photodetector and a second photodetector. The signal receiving ends of the first photodetector and the second photodetector respectively collect the photothermal signal induced by the first transmitted light of the WGM microcavity coupling system absorbed by the gas infrared and the second transmitted light signal obtained by the WGM microcavity coupling system. The signal output ends of the first photodetector and the second photodetector are both connected to the host computer.

[0013] The WGM microcavity coupling system includes a fiber cone and a WGM microcavity, which are encapsulated in the air chamber in an over-coupled state, and the polarization controller is coupled to the WGM microcavity through the fiber cone.

[0014] The gas transmission system includes a dynamic gas distribution system and a gas storage device connected in sequence. The gas storage device is connected to the gas chamber through a first pipeline, and a first valve is provided on the first pipeline.

[0015] The gas transmission system further includes a flow meter, a vacuum pump and an exhaust gas treatment device connected in sequence. The flow meter is connected to the gas chamber via a second pipeline, and a second valve is provided on the second pipeline.

[0016] A whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas detection method, comprising the following steps:

[0017] Step 1: Use the laser excitation branch to perform coarse scanning to output the output light I that can form the whispering gallery mode. After coupling with the output light I through the WGM microcavity coupling system, the photoelectric detection branch outputs a rough transmitted light spectrum.

[0018] Step 2: The host computer uses LabVIEW software to determine the fundamental mode position based on the rough transmitted light spectrum. The laser excitation branch is used to perform a fine scan centered on the fundamental mode to output the output light II that can form the whispering gallery mode. The second transmitted light signal is obtained after passing through the WGM microcavity coupling system.

[0019] Step 3: Use the gas delivery system to prepare the gas sample and inject the gas sample into the gas chamber;

[0020] Step 4: Using the infrared sensing branch to emit gas-absorbable near-infrared laser light, the gas surrounding the WGM microcavity coupling system is heated based on the non-radiative thermal relaxation effect, and a photothermal signal induced by the first transmitted light is obtained after passing through the gas chamber where the WGM microcavity coupling system is located;

[0021] Step 5: Using the photoelectric detection branch, the photothermal signal induced by the first transmitted light and the second transmitted light signal are transmitted to a host computer for data processing using LabVIEW software to establish a calibration equation;

[0022] Step 6: Inject a gas of unknown concentration into the gas chamber and obtain the concentration of the gas of unknown concentration based on the calibration equation.

[0023] The method of transmitting the photothermal signal induced by the first transmitted light and the second transmitted light signal to the host computer for data processing using LabVIEW software to establish a calibration equation is as follows: using LabVIEW software to process the second transmitted light signal to obtain a frequency shift value, performing inversion operation processing on the photothermal signal induced by the first transmitted light through LabVIEW software, and outputting the gas concentration c in the gas chamber; drawing a frequency shift and concentration relationship curve, and establishing a calibration equation based on the least squares method.

[0024] Beneficial effects of the present invention:

[0025] The present invention utilizes the gas-light-heat multi-physical field coupling mechanism to break through the bottleneck of the existing technology. The coating-free design is used to get rid of the dependence on specific functional materials and reduce the complexity of the preparation process; the dual-light path synergistic enhancement mechanism is used, and the gas to be measured generates a temperature rise through the non-radiative thermal relaxation effect after absorbing light energy, and then the WGM microcavity detects the temperature change with high precision. Through the synergistic effect of the excitation light-WGM microcavity, the WGM microcavity optical path enhancement effect is utilized to improve the detection sensitivity; it has multi-gas compatibility and does not need to rely on specific functional materials. It only needs to adjust the excitation wavelength to achieve rapid detection of different gases, solving the problem of poor versatility of traditional WGM microcavity sensors. This method not only overcomes the limitations brought by material modification, but also significantly improves the intrinsic sensing capability of the microcavity through the photothermal effect, providing a new way for the development of miniaturized, highly sensitive, and multi-component gas sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 Schematic diagram of the system structure of the present invention.

[0028] Figure 2 It is the transmission spectrum signal of the rough scanning process of the present invention.

[0029] Figure 3 This is an actual test diagram of the transmission spectrum signal frequency shift of the present invention, blue: before ventilation; red: after ventilation.

[0030] Figure 4 This is a simulation diagram of the frequency shift of the transmission spectrum signal, blue: before ventilation; red: after ventilation. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] A whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device, such as Figure 1 As shown, it includes a host computer, a photoelectric system and a gas circuit system connected in sequence; the photoelectric system includes an infrared sensing branch, a laser excitation branch and a photoelectric detection branch for parallel processing; the gas circuit system includes a gas transmission system and an air chamber, and a WGM microcavity coupling system is fixedly installed in the air chamber; the infrared sensing branch, the laser excitation branch and the photoelectric detection branch are respectively connected to the host computer and the WGM microcavity coupling system.

[0034] The infrared sensing branch is used to output near-infrared laser that can be absorbed by gas according to the instructions of the host computer;

[0035] The laser excitation branch is used to output the outgoing light that meets the resonance conditions of the microcavity and can form the whispering gallery mode according to the instructions of the host computer;

[0036] The gas transmission system is used to control the transmission of detection gas;

[0037] The gas chamber is used to contain the detection gas;

[0038] The WGM microcavity coupling system is used to process the outgoing light emitted by the laser excitation branch based on the whispering gallery mode optical microcavity gas sensing principle and the near-infrared laser based on the infrared photothermal spectroscopy gas sensing principle to obtain the second transmitted light signal and the photothermal signal induced by the first transmitted light respectively;

[0039] The present invention introduces infrared photothermal spectroscopy (PTS) gas sensing technology into the field of whispering gallery mode (WGM) microcavity gas sensing, and from the perspective of a breakthrough in the sensing mechanism, converts traditional direct gas sensing into indirect gas sensing. Since the infrared absorption process of the gas causes non-radiative thermal relaxation, which changes the ambient temperature, the highly sensitive temperature sensing characteristics of the WGM microcavity can be utilized. By detecting the optical mode shift of the WGM microcavity caused by the heat change generated by the gas absorption process, the absorbance can be inferred, and then the gas concentration information can be obtained. Whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing technology combines the high-sensitivity temperature sensing advantages of the whispering gallery mode microcavity with the high-sensitivity gas sensing advantages of photothermal spectroscopy technology, which helps to improve the accuracy of measurement data of micro-nano gas sensors.

[0040] The photoelectric detection branch is used to collect the photothermal signal induced by the first transmitted light and the second transmitted light signal. The photothermal signal induced by the first transmitted light is used to obtain the light intensity attenuation of the infrared sensing branch and then perform gas concentration inversion. The second transmitted light signal is used to obtain the frequency shift information of the output light from the laser excitation branch.

[0041] The host computer uses the LabVIEW signal processing platform to control the parameters of the infrared sensing branch and laser excitation branch in the photoelectric system, receive and process the photothermal signal induced by the first transmitted light and the second transmitted light signal collected by the photodetector, invert the gas concentration, and establish a calibration equation for concentration and frequency shift to complete the system's automated control and data analysis.

[0042] The infrared sensing branch includes an integrated laser temperature control-current driver (LDTC0520, Wavelength), a distributed feedback laser (DFB) (DFB-1653.7, Mianyang All-Optical Communication Technology Co., Ltd.), a fiber coupler (TW1550R3A1, Thorlabs), and a fiber collimator (50-1550A-APC, Thorlabs), which are connected in sequence. The integrated laser temperature control-current driver is connected to the host computer, and the fiber collimator is connected to the optical path of the WGM microcavity coupling system. The infrared sensing branch also includes a visible red light source, and the visible red light emitted by the visible red light source and the output light of the distributed feedback (DFB) laser are coupled through the fiber coupler.

[0043] The integrated laser temperature control-current driver is used to adjust the driving voltage signal and temperature value to match the output band of the distributed feedback (DFB) laser with the infrared absorption band of the gas to be measured;

[0044] A distributed feedback (DFB) laser is used to emit a near-infrared light source to excite the gas to be measured, thereby changing the ambient temperature by generating a non-radiative thermal relaxation effect. In this embodiment, a distributed feedback (DFB) laser with a central wavelength of 1653.7 nm is used.

[0045] The fiber coupler is used to couple the visible red light and the output light of the distributed feedback (DFB) laser;

[0046] The fiber collimator is used to collimate and adjust the output angle and position of the coupled light to illuminate the vicinity of the WGM microcavity;

[0047] A visible red light source is used to couple with the output light of a distributed feedback (DFB) laser for subsequent observation of the position of the photothermal field.

[0048] The laser excitation branch includes a digital laser controller (DLC) (DLC, TOPTICA), a continuously tunable single-frequency diode laser (CTL) (CTL1430-1720nm, TOPTICA), an attenuator (1550APC / FC, Qianhai Xunka Optoelectronic Communication Equipment Co., Ltd.) and a polarization controller (FPC562, Thorlabs), which are connected in sequence; the digital laser controller (DLC) is connected to the host computer, and the polarization controller is connected to the WGM microcavity coupling system.

[0049] A digital laser controller (DLC) is used to adjust the wavelength and scanning pattern of the continuously tunable single-frequency diode laser (CTL) to match the microcavity size. In this embodiment, the wavelength range is 1512-1514 nm, and the microcavity diameter is 53.2 μm.

[0050] A continuously tunable single-frequency diode laser (CTL) is used to emit continuously tunable output light, which is coupled to the WGM microcavity via the evanescent field.

[0051] The attenuator is used to reduce the output light power to prevent high-power laser from damaging the microcavity, fiber taper, and photoelectric detection equipment. At the same time, it enables the coupling system to operate in the linear region to ensure the stability of the second transmitted light signal (such as the fundamental mode position and Q value).

[0052] The polarization controller is used to adjust the polarization direction of the outgoing light to match the polarization sensitivity of the fiber taper and photodetector, thereby reducing coupling loss.

[0053] The photoelectric detection branch includes a first photodetector (PDA30B2, Thorlabs) and a second photodetector (PDA05CF2, Thorlabs). The signal receiving ends of the first photodetector and the second photodetector respectively collect the first transmitted light induced photothermal signal and the second transmitted light signal obtained by the WGM microcavity coupling system. The signal output ends of the first photodetector and the second photodetector are both connected to the host computer.

[0054] The WGM microcavity coupling system includes an optical fiber taper and a WGM microcavity, which are encapsulated in the air chamber in an over-coupled state, and the polarization controller is coupled to the WGM microcavity through the optical fiber taper.

[0055] The gas transmission system includes a dynamic gas distribution system (MR-DF2, Beijing Minnit Environmental Protection Equipment Co., Ltd.) and a gas storage device connected in sequence. The gas storage device is connected to the gas chamber through a first pipeline, and a first valve is provided on the first pipeline; the gas transmission system also includes a flow meter, a vacuum pump and an exhaust gas treatment device connected in sequence. The flow meter (LEZWB, Shengjie Instrument Technology Co., Ltd.) is connected to the gas chamber through a second pipeline, and a second valve is provided on the second pipeline.

[0056] Example 2

[0057] A whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas detection method, comprising the following steps:

[0058] S1: The fiber taper was prepared by flame drawing and the WGM microcavity was prepared by CO2 laser melting.

[0059] S2: A continuously tunable single-frequency diode laser (CTL) is driven by a digital laser controller (DLC) in a coarse scanning mode with a scanning range greater than a free spectral range (FSR). The output laser power is reduced by an attenuator, and the polarization state of the output light is adjusted by a polarization controller. A second transmitted light signal is obtained by coupling the WGM microcavity with the fiber taper. The second transmitted light signal is collected by a second photodetector and processed by the LabVIEW software of the host computer to output the transmitted light spectrum in the coarse scanning mode.

[0060] S3: Observe the transmitted light spectrum in coarse scanning mode, determine the fundamental mode position using LabVIEW software, and drive a continuously tunable single-frequency diode laser (CTL) in fine scanning mode to scan within a range centered on the fundamental mode. Adjust the coupling between the fiber taper and the WGM microcavity to an overcoupled state, and adjust the polarization controller to maximize the Q value of the WGM microcavity. (This program, written in LabVIEW, includes initial processing (SG filtering), background fitting (nonlinear least squares algorithm), automatic half-height search algorithm, and Q value calculation.) During use, UV glue is used to solidify the fiber taper holder and the WGM microcavity holder to encapsulate the WGM microcavity coupling system.

[0061] Q value judgment:

[0062]

[0063] Where FWHM is the full width at half maximum, and λ is the resonant wavelength. The narrower the full width at half maximum, the greater the Q value.

[0064] S4: A dynamic gas distribution system is used to prepare a gas sample, and a vacuum pump and a flow meter are used to inject the gas into the gas chamber containing the WGM microcavity coupling system at a constant flow rate. In this embodiment, the gas is methane gas.

[0065] S5: Use an integrated laser temperature control-current driver to drive a distributed feedback laser (DFB) to emit a near-infrared laser beam. Adjust the driving voltage signal and temperature value so that the distributed feedback laser (DFB) can completely scan the gas absorption line. Use a fiber coupler to couple the near-infrared laser with visible red light. The coupled light is focused and collimated by a fiber collimator and then irradiated near the WGM microcavity. Due to the frequency shift effect of the whispering gallery mode microcavity on temperature, the second transmitted light signal collected by the second photodetector will undergo a frequency shift. The collimated beam position is adjusted by the fiber collimator, and the position of the WGM microcavity packaging system is adjusted by the three-dimensional translation stage so that the WGM microcavity is in the maximum temperature gradient area, that is, the frequency shift value of the second transmitted light signal is maximized. The collimated beam position and the microcavity coupling system position are fixed.

[0066] S6: The photothermal signal induced by the first transmitted light is collected by the first photodetector, the photothermal signal induced by the first transmitted light is inverted and processed by the host computer LabVIEW software platform, and the gas concentration c value in the gas chamber is output as a reference.

[0067] Inversion calculation formula:

[0068]

[0069] Wherein, I is the intensity of transmitted light, I0 is the intensity of incident light, α is the absorption coefficient, and L is the optical path length of light in the medium. In this embodiment, α is a constant that is related to the gas environment and the absorption band. The optical path length L of the gas has no reflection in the experiment, and the length of the gas chamber corresponds to the optical path length of effective absorption.

[0070] S7: The second transmitted light signal is collected by the second photodetector, and the second transmitted light signal is processed by the host computer LabVIEW software platform to obtain a frequency shift value.

[0071] S8: looping steps S6-S7, drawing a frequency shift versus concentration relationship graph, establishing a calibration equation based on the least squares method, and adjusting the calibration equation parameters in the LabVIEW software.

[0072] like Figure 2 As shown in the experimental figure, the transmission spectrum obtained when the packaged microcavity sensor probe is coarsely scanned in the long wavelength range and the selected refined scanning range.

[0073] like Figure 3 As shown in the experimental figure, the encapsulated microcavity sensor probe is used to detect gas. When 500ppmv methane gas is injected into the gas chamber, the spectrum line will shift by 2.7pm.

[0074] like Figure 4 As shown in the simulation diagram, the transmission spectrum of a microcavity with a diameter of 5μm will shift when the ambient temperature is changed.

[0075] S9: injecting a gas of unknown concentration into the gas chamber through step S4, and obtaining the concentration of the gas of unknown concentration based on the established calibration equation.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device, characterized in that: The invention comprises a host computer, a photoelectric system and a gas circuit system connected in sequence; the photoelectric system comprises an infrared sensing branch, a laser excitation branch and a photoelectric detection branch for parallel processing; the gas circuit system comprises a gas transmission system and an air chamber, wherein a WGM microcavity coupling system is fixedly arranged in the air chamber; the infrared sensing branch, the laser excitation branch and the photoelectric detection branch are respectively connected to the host computer and the WGM microcavity coupling system; the infrared sensing branch outputs near-infrared laser absorbable by gas according to the instruction of the host computer, the laser excitation branch outputs outgoing light that meets the resonance condition of the microcavity and can form an echo gallery mode according to the instruction of the host computer, the WGM microcavity coupling system detects a photothermal signal induced by a first transmitted light obtained by the near-infrared laser and obtains a second transmitted light signal obtained by the outgoing light that can form the echo gallery mode, and the photoelectric detection branch transmits the photothermal signal induced by the first transmitted light and the second transmitted light signal to the host computer for data processing.

2. The whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to claim 1, characterized in that: The infrared sensing branch includes an integrated laser temperature control-current driver, a distributed feedback laser, a fiber coupler and a fiber collimator connected in sequence; the integrated laser temperature control-current driver is connected to the host computer, and the fiber collimator is connected to the WGM microcavity coupling system optical path.

3. The whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to claim 2, characterized in that: The infrared sensing branch further comprises a visible red light source, and the visible red light emitted by the visible red light source and the output light of the distributed feedback laser are coupled through an optical fiber coupler.

4. The whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to any one of claims 1 to 3, characterized in that: The laser excitation branch comprises a digital laser controller, a continuously tunable single-frequency diode laser, an attenuator and a polarization controller connected in sequence; the digital laser controller is connected to the host computer, and the polarization controller is connected to the WGM microcavity coupling system.

5. The whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to claim 4, characterized in that: The photoelectric detection branch includes a first photodetector and a second photodetector. The signal receiving ends of the first photodetector and the second photodetector respectively collect the photothermal signal induced by the first transmitted light of the WGM microcavity coupling system absorbed by the gas infrared and the second transmitted light signal obtained by the WGM microcavity coupling system. The signal output ends of the first photodetector and the second photodetector are both connected to the host computer.

6. The whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to any one of claims 1 to 3 or 5, characterized in that: The WGM microcavity coupling system includes a fiber cone and a WGM microcavity, which are encapsulated in the air chamber in an over-coupled state, and the polarization controller is coupled to the WGM microcavity through the fiber cone.

7. The whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to claim 1, characterized in that: The gas transmission system includes a dynamic gas distribution system and a gas storage device connected in sequence. The gas storage device is connected to the gas chamber through a first pipeline, and a first valve is provided on the first pipeline.

8. The whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to claim 7, characterized in that: The gas transmission system further includes a flow meter, a vacuum pump and an exhaust gas treatment device connected in sequence. The flow meter is connected to the gas chamber via a second pipeline, and a second valve is provided on the second pipeline.

9. A whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas detection method, using the whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to claim 1, characterized in that: Including steps: Step 1: Use the laser excitation branch to perform coarse scanning to output the output light I that can form the whispering gallery mode. After coupling with the output light I through the WGM microcavity coupling system, the photoelectric detection branch outputs a rough transmitted light spectrum. Step 2: The host computer uses LabVIEW software to determine the fundamental mode position based on the rough transmitted light spectrum. The laser excitation branch is used to perform a fine scan centered on the fundamental mode to output the output light II that can form the whispering gallery mode. The second transmitted light signal is obtained after passing through the WGM microcavity coupling system. Step 3: Use the gas delivery system to prepare the gas sample and inject the gas sample into the gas chamber; Step 4: Using the infrared sensing branch to emit gas-absorbable near-infrared laser light, the gas surrounding the WGM microcavity coupling system is heated based on the non-radiative thermal relaxation effect, and a photothermal signal induced by the first transmitted light is obtained after passing through the gas chamber where the WGM microcavity coupling system is located; Step 5: Using the photoelectric detection branch, the photothermal signal induced by the first transmitted light and the second transmitted light signal are transmitted to a host computer for data processing using LabVIEW software to establish a calibration equation; Step 6: Inject a gas of unknown concentration into the gas chamber and obtain the concentration of the gas of unknown concentration based on the calibration equation.

10. The whispering gallery mode optical microcavity enhanced photothermal spectroscopy gas sensing device according to claim 9, characterized in that: The method of transmitting the photothermal signal induced by the first transmitted light and the second transmitted light signal to the host computer for data processing using LabVIEW software to establish a calibration equation is as follows: using LabVIEW software to process the second transmitted light signal to obtain a frequency shift value, performing inversion operation processing on the photothermal signal induced by the first transmitted light through LabVIEW software, and outputting the gas concentration c in the gas chamber; drawing a frequency shift and concentration relationship curve, and establishing a calibration equation based on the least squares method.

Images