High-sensitivity micro-gas-volume gas detection device and method based on double-enhanced photo-thermal spectrum

Abstract

The invention provides a high-sensitivity micro-gas-volume gas detection device and method based on a double-enhanced photo-thermal spectrum, and relates to the field of optical sensing, and the high-sensitivity micro-gas-volume gas detection device comprises a pump light source, a detection light source, a micro-nano optical fiber ring resonance module, a filter, a photoelectric detector, a signal processing unit and a control module. According to the high-sensitivity micro-gas-volume gas detection device and method based on the double-enhanced photo-thermal spectrum, double enhancement of photo-thermal and resonance detection is realized through the micro-nano optical fiber annular resonant cavity, so that nano-upgraded gas volume can be equivalent to an absorption optical path of dozens of meters, and the detection accuracy is improved. Therefore, high-sensitivity gas measurement under the condition of tiny gas flow is realized.

Description

Technical Field

[0001] The present invention relates to the field of optical sensing, and in particular to a highly sensitive small amount of gas detection device and method based on double enhanced photothermal spectroscopy. Background Art

[0002] At present, in the field of gas measurement, gas detection based on absorption spectroscopy technology has a relatively simple system, short absorption path, lack of signal amplification means, and high gas volume requirements. Along with absorption spectroscopy, photoacoustic effect and photothermal effect will also occur. Although the absorption path of photoacoustic effect is short, the photoacoustic signal is amplified thousands of times through the resonance of the acoustic cavity, which improves the accuracy of gas measurement. However, the acoustic resonance frequency of the photoacoustic spectrum itself is unstable and easily affected by acoustic noise. The mechanism of photothermal spectroscopy is that gas absorbs light to generate heat, which in turn causes the refractive index to change. The change in refractive index can reflect the gas concentration. Photothermal spectroscopy not only has high measurement accuracy, but also good stability, which is suitable for high-sensitivity gas detection needs. However, the gas volume that can be provided in many application scenarios is very limited, but the accuracy and sensitivity of gas detection are very high. In respiratory analysis and disease diagnosis in the medical and health field, it is necessary to detect extremely trace target compounds, such as volatile organic compounds (VOCs), from the patient's exhaled gas for the diagnosis of diseases such as lung cancer and diabetes. Specific locations in environmental monitoring, such as soil pores, groundwater wells, or near plant leaves, also require trace gas sampling, such as monitoring methane emissions in the soil or gas exchange between plants and the atmosphere. These places can only provide very small amounts of gas samples. In the case of very limited gas volume, improving detection sensitivity is of great significance. In addition, in the chromatographic measurement of transformers, the content of various abnormal gases is very low, resulting in a small amount of gas output, but the accuracy requirements for the gas are very high. Using a small amount of gas to achieve high-precision measurement is extremely important for the health status detection of transformers.

[0003] In view of the problems existing in the above application fields, a dual-enhanced photothermal spectroscopy gas detection method and device are proposed, which can achieve high-sensitivity gas measurement based on tiny gas amounts. Summary of the invention

[0004] The purpose of the present invention is to provide a highly sensitive and tiny amount of gas detection device and method based on double-enhanced photothermal spectroscopy. Through a micro-nano optical fiber ring resonator, a resonance method and signal detection dual enhancement are realized, so that a micro-nano optical fiber ring of hundreds of microns can be equivalent to an absorption optical path of tens of meters, thereby realizing highly sensitive gas measurement under tiny amounts of gas.

[0005] To achieve the above object, the present invention provides a highly sensitive small amount of gas detection device based on double enhanced photothermal spectroscopy, comprising: The laser current controller enables the pump light laser to generate tunable pulse light, so that the detection light is scanned near the resonance wavelength of the micro-nano optical fiber ring; The laser temperature controller is used to control the operating temperature of the pump light laser and adjust the wavelength of the pump light to match the gas absorption wavelength; The pump light laser generates pump light, and the light energy is absorbed by the characteristic gas to generate photothermal energy, releasing heat energy; The detection light laser generates detection light, and the resonant wavelength of the micro-nano optical fiber ring can be found during the wavelength scanning process; The wavelength division multiplexer couples the pump light and the probe light into the micro-nano fiber ring resonator; The micro-nano fiber ring resonator allows the pump light to be repeatedly coupled and transmitted in the micro-nano fiber ring and interact with the gas, thereby generating an enhanced photothermal signal; for the detection light, the detection process of the photothermal signal is resonantly amplified, forming a double enhancement phenomenon; The narrowband filter converts the spectral changes of the probe light into changes in light intensity; The photoelectric detector converts the resonant detection light signal into an electrical signal for the back-end processing unit to demodulate the gas concentration information; The phase-locked amplifier amplifies the signal of the detection light after photoelectric detection, and obtains the second harmonic proportional to the gas concentration through demodulation; The laser current controller is also used to superimpose a sine wave on the driving current. The driving current is used for wavelength scanning so that the pump wavelength corresponds to the gas absorption wavelength. The sine wave is used for wavelength modulation to improve the signal-to-noise ratio.

[0006] Preferably, the micro-nano optical fiber ring allows part of the pump light to propagate around the micro-nano optical fiber in the form of an evanescent field, so that the pump light contacts the gas and is then absorbed by the gas; at the same time, the pump light that is not absorbed by the gas can be coupled back into the micro-nano optical fiber ring to participate in the next light-matter interaction; at the same time, the micro-nano optical fiber ring also causes the detection light to resonate in the micro-nano optical fiber ring.

[0007] Preferably, the wavelength of the pump light corresponds to the wavelength of the absorption spectrum of the gas being measured.

[0008] Preferably, the wavelength range of the detection light covers the resonant wavelength range of the micro-nano optical fiber ring.

[0009] Preferably, the resonance range of the micro-nano optical fiber ring is related to the diameter and photothermal intensity of the micro-nano optical fiber ring.

[0010] Preferably, the diameter of the micro-nano optical fiber is used to determine the size of the evanescent field, the coupling loss and the transmission loss of the detection light.

[0011] Preferably, the method further comprises a processing unit for realizing functions of data collection, filtering and data processing, and obtaining a corresponding gas concentration signal through calculation of the optical signal.

[0012] Preferably, the micro-nano optical fiber ring resonator also includes another configuration in which a planar optical waveguide resonant structure or a micro-ring resonant cavity is used instead.

[0013] Preferably, the driving current of the pump light also includes another setting without superimposing a sine wave.

[0014] A highly sensitive and minute amount of gas detection method based on double enhanced photothermal spectroscopy comprises the following steps: By controlling the temperature, the pump light is placed near the absorption peak of acetylene gas; the current controller uses the driving current to scan the wavelength near the absorption peak, and at the same time superimposes a sine wave on the driving current; A wavelength division multiplexer is used to couple the pump light and the probe light into the micro-nano fiber ring resonator; The photothermal spectrum resonance of the pump light is formed in the micro-nano optical fiber ring, which changes the equivalent refractive index of the micro-nano optical fiber ring; the equivalent refractive index is amplified by the resonance of the detection light, and the spectrum of the detection light is shifted; The spectrum changes of the detection light are converted into light intensity changes through a narrow-band filter; The signal of the detection light after photoelectric detection is phase-locked and amplified, and the second harmonic proportional to the gas concentration is obtained by demodulation; The processing unit calculates the second harmonic optical signal to obtain a corresponding gas concentration signal.

[0015] Therefore, the present invention adopts the above-mentioned highly sensitive small amount gas detection device and method based on double enhanced photothermal spectroscopy, and the technical effects are as follows: (1) In terms of enhancing the interaction between light and gas, the high energy density of micro-nano optical fiber and the long equivalent optical path of the ring resonator can be utilized; in terms of enhancing the detection of gas absorption signals, resonant amplification is introduced into the photothermal refractive index detection for the first time. Double resonance is realized in the same micro-nano optical fiber ring, with novel theory and compact structure. After double resonance amplification, the micro-nano optical fiber ring of 100 microns can be equivalent to an absorption optical path of tens of meters, and it is expected to achieve ultra-high measurement accuracy of ppt level under the condition of nanoliter gas volume.

[0016] (2) The stability of the micro-nano optical fiber resonant structure is a key factor of the system. There are two difficulties. First, the highly sensitive resonant ring is prone to detuning problems caused by operating point offset. To address this problem, a thermal balance control method is proposed. Based on the closed-loop feedback control theory of the photothermal effect, the direction of detuning is determined by wavelength scanning, and then the direction of temperature deviation is determined. Then, the wavelength scanning frequency is dynamically adjusted to keep the heat generation in a constant state and control the resonance point of the resonant ring to remain unchanged.

[0017] (3) It can be used in situations where the gas volume is extremely small and high measurement accuracy is required, such as breathing gas and transformer oil chromatography. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of a highly sensitive small amount of gas detection method based on double-enhanced photothermal spectroscopy provided in this embodiment; Figure 2 A schematic diagram of the resonant cavity frequency feedback control locking principle based on thermal control provided in this embodiment; Figure 3 This is the system principle block diagram. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0020] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0021] Light source selection: The pump light laser should have a wavelength corresponding to the gas being measured, and the output power should be greater than 10 mW. The detection light can use a semiconductor laser with a wavelength of 1550 nm or 1310 nm as the light source, and the output power should be greater than 1 mW.

[0022] Construction of micro-nano fiber ring: A ring resonator is made using a silica fiber with a diameter of 1 micron (μm), and the circumference of the ring is about 1 centimeter (cm).

[0023] Signal processing configuration: Equipped with high-performance preamplifier, bandpass filter and demodulation circuit to ensure signal integrity and reliability.

[0024] Control software development: Write a set of control software that integrates light source control, data acquisition, signal processing and other functions, and simplify the operation process through a graphical user interface.

[0025] Detector configuration: Use a highly sensitive photodiode as a detector to ensure that weak photothermal effect signals can be captured.

[0026] Embodiment 1 A highly sensitive and minute amount of gas detection method based on double enhanced photothermal spectroscopy comprises the following steps: Design and application of laser controller The laser current controller enables the pump light laser to generate tunable pulse light, so that the probe light scans near the resonant wavelength of the micro-nano fiber ring. Specifically: Modulation frequency: The modulation frequency can be set to 1 kilohertz (kHz).

[0027] Modulation mode: External modulation is adopted, that is, the working state of the modulator is controlled by an external signal to realize the modulation of the light source beam.

[0028] The thermal balance control method is specifically embodied in: the laser temperature controller is used to control the temperature of the pump light laser so that the pump light is near the absorption peak of acetylene gas; the current controller uses the driving current to scan the wavelength near the absorption peak, and at the same time superimposes a sine wave on the driving current. The sine wave is used for wavelength modulation to improve the signal-to-noise ratio.

[0029] A wavelength division multiplexer is used to couple the pump light and the probe light into the micro-nano fiber ring resonator; a photothermal spectrum resonance of the pump light is formed in the micro-nano fiber ring, and the equivalent refractive index of the micro-nano fiber ring is changed; the equivalent refractive index is amplified by the resonance of the probe light, and the spectrum of the probe light is shifted; The micro-nano optical fiber ring allows part of the pump light to propagate around the micro-nano optical fiber in the form of an evanescent field, allowing the pump light to come into contact with the gas and then be absorbed by the gas; at the same time, the pump light that is not absorbed by the gas can be coupled back into the micro-nano optical fiber ring to participate in the next light-matter interaction; at the same time, the micro-nano optical fiber ring also allows the detection light to have a smaller transmission loss and a higher coupling efficiency, ensuring that it resonates in the micro-nano optical fiber ring.

[0030] There are three ways to determine the diameter of micro-nano optical fiber: setting it according to the wavelength of pump light and probe light; setting it according to the excitation efficiency of pump light and gas; setting it according to the resonance efficiency of probe light.

[0031] Construction and optimization of micro-nano fiber ring resonance module The micro-nano fiber ring resonance module is one of the core components of the present invention, and its function is to use the ring resonant cavity to make the pump light oscillate repeatedly in the cavity to enhance the interaction between light and gas. Specifically: Material selection: Silicon dioxide (SiO2) is selected as the material of micro-nano optical fiber because of its excellent optical transmission performance and chemical stability, refractive index of about 1.44, and loss coefficient <0.01dB / cm.

[0032] Size design: The diameter of the micro-nano fiber ring is designed to be 1 micron (μm), the total length of the ring resonator is 1 centimeter (cm), and the optical path gain is about 10 4 , to provide a sufficiently long optical path and enhance the interaction between light and gas.

[0033] In order to achieve the dual resonance effect, the length of the micro-nano optical fiber L Should meet: ml pump =n pump L and nλ prob =n prob L ,in, l pump and l prob are the wavelengths of the pump light and the probe light, respectively. n pump and n prob are the equivalent refractive indices of the pump light and the probe light, respectively, m and n is a positive integer. By adjusting the length of the micro-nano optical fiber L and the core diameter so that both the pump light and the probe light meet the resonance conditions at the same time.

[0034] (1); Among them, Δ n eff It represents the refractive index change caused by the photothermal effect and thermal expansion effect. Indicates the central wavelength of the probe light. The change in the resonant wavelength relative to the central wavelength of the probe light, Δ L Indicates the change in length of the micro-nano optical fiber caused by photothermal generation.

[0035] Coupling efficiency control: coupling coefficient R prob →0.9999, by optimizing the matching of core and cladding diameters, a reflectivity of nearly 99.99% is achieved.

[0036] Resonant cavity quality factor Q: target Q>10 6 , ensuring the accumulation of highlight energy.

[0037] Free spectral range (FSR): FSR = c / (2 n eff L ), by adjusting L Ensure a balance between measurement range and resolution.

[0038] Enhancement mechanism: By optimizing the geometric parameters of the ring resonator, such as the radius of curvature, core size, etc., the best light energy accumulation effect can be achieved.

[0039] Secondary amplification: A resonance amplification mechanism is introduced into the resonance module to achieve secondary amplification of the photothermal effect by enhancing the detection of gas absorption signals.

[0040] Photothermal enhancement and secondary amplification mechanism: By solving the heat conduction equation, the temperature distribution of the micro-nano optical fiber and its surrounding gas can be obtained. When the pump light is transmitted in the optical fiber, the photothermal effect will cause the local temperature to rise, thereby changing the refractive index of the optical fiber and the surrounding gas. The change in refractive index caused by the temperature increase will cause the optical path of the optical fiber to change, thereby affecting the propagation characteristics of light. These changes not only enhance the interaction between light and gas, but also increase the amplification of the optical signal through the resonance effect. The optical path change caused by temperature and the nonlinear effect in the optical fiber work together to achieve enhanced amplification of the optical signal. In addition, controlling factors such as pump light power, optical fiber geometric parameters and reflectivity can help further optimize the gain effect and achieve more efficient optical signal amplification.

[0041] Solving the heat conduction equation: The temperature distribution around the micro-nano optical fiber and itself is described by the following equation: (2); (3); in, represents the density of air, is the specific heat capacity of air, is the thermal conductivity of air, represents the temperature gradient, which indicates the rate of change of temperature in space. represents the convection term, α c is the gas absorption coefficient, P pump represents the pump light power, represents the radial distance from the light source, i represents the angle component in polar coordinates, I nom-evaa ( r , i ) represents polar coordinates ( r , i ) under the unit space radiation intensity distribution, represents the time correlation function, which is used to represent the modulation of laser power in time or other time-varying effects, Indicates the density of materials such as micro-nano optical fibers, represents the specific heat capacity of the optical fiber, Represents the thermal conductivity of the optical fiber.

[0042] By solving equations (2) and (3), we can obtain the temperature distribution in the micro-nano waveguide and the surrounding air, and then we can obtain the refractive index change in the air and the micro-nano waveguide. n effBoth the thermo-optic effect and the thermal expansion effect will cause the refractive index to change. Therefore, the refractive index change here is divided into the refractive index change of the air around the micro-nano optical fiber, the refractive index change of the micro-nano optical fiber itself, and the change of the length of the micro-nano optical fiber caused by the refractive index change. For the convenience of analysis, the three are expressed as equivalent refractive index. n eff express.

[0043] Equivalent optical path after resonance enhancement L eff , magnification for: (4); (5); in, l represents the wavelength of pump light, or It represents the coupling coefficient, that is, the coupling efficiency of light transmission in micro-nano optical fiber, the equivalent reflectivity of pump light and detection light R pump = R probe =99.99%, signal amplification factor β Up to 2×10 8 To further improve the equivalent reflectivity of pump light and probe light, β Improve accordingly.

[0044] The spectrum changes of the detection light are converted into light intensity changes through a narrow-band filter; The signal of the detection light after photoelectric detection is phase-locked and amplified, and the second harmonic proportional to the gas concentration is obtained by demodulation; The processing unit calculates the second harmonic optical signal to obtain a corresponding gas concentration signal.

[0045] Design and implementation of signal processing unit The signal processing unit is used to amplify, filter and demodulate the weak electrical signal received by the detector to obtain a clear detection signal and demodulate the gas concentration. Specifically: Amplifier circuit: Use a high-gain low-noise amplifier to ensure that weak signals can be effectively amplified without introducing additional noise.

[0046] Filter circuit: Use a bandpass filter to filter out noise in irrelevant frequency bands and retain useful signals.

[0047] Demodulation circuit: The demodulation circuit restores the modulated signal to the original signal for subsequent analysis.

[0048] Function and implementation of control module The control module is responsible for coordinating the operation process of the entire system, including light source modulation, data acquisition, and signal processing. Specifically: Software platform: Use LabVIEW development platform to write control software to realize functions such as light source modulation and data acquisition.

[0049] Coordination mechanism: By writing control logic, ensure the coordinated work between the light source, modulator, and signal processing unit.

[0050] User interface: A user-friendly interface is designed to facilitate operators to set system parameters and view measurement results.

[0051] Figure 3 The schematic diagram of the system structure for light intensity detection is shown in Figure 1. A sine wave is superimposed on the wavelength scanning driving current to suppress system noise, and then a lock-in amplifier is used to extract the second harmonic in the light intensity signal to demodulate the gas concentration.

[0052] In order to verify the effect of the present invention, an actual measurement experiment was carried out: Experimental preparation: Place a small amount of the gas to be tested in a closed container and maintain a constant temperature inside the container to avoid the influence of temperature changes on the measurement results.

[0053] System construction: Build the experimental system according to the above design plan and ensure that all components are connected correctly.

[0054] Experimental operation: Turn on the light source, convert the light beam into a modulated signal through the modulator, and then enter the micro-nano fiber ring resonance module. Finally, the detector captures the signal and transmits it to the signal processing unit.

[0055] Data analysis: Use the signal processing unit to process the collected data and analyze the changes in gas concentration.

[0056] Result verification: By comparing the changes in signal intensity before and after the experiment, and comparing the results with those of traditional detection methods, the superior performance of the present invention in trace gas detection was confirmed.

[0057] Through the detailed description of the above specific implementation methods, the present invention provides a method and device for realizing high-sensitivity tiny gas volume measurement based on double-enhanced photothermal spectroscopy of micro-nano optical fiber rings, which not only improves the detection sensitivity, but also simplifies the operation process and has broad application prospects.

[0058] like Figure 1 As shown, as a preferred embodiment of the present invention, this embodiment provides a highly sensitive and small amount of gas detection device based on double enhanced photothermal spectroscopy, including a pump light source, a detection light source, a micro-nano optical fiber ring resonance module, a signal processing unit, a control module, etc.; Figure 2The modulation method of photothermal spectrum is used to control the thermal balance of the micro-nano fiber ring, so that the resonant frequency of the micro-nano fiber ring is stabilized within a certain range. Then the frequency sweep of the pump light is used to correspond to the cavity frequency within this range. The specific method is: the wavelength of the pump light is periodically controlled by the driving current to scan near the gas absorption peak, and the direction of the wavelength change of the resonant ring detuning is determined by scanning the wavelength near the gas absorption peak. The temperature can be estimated from the direction of the wavelength detuning change. When the temperature is low, the scanning cycle is increased, and when the temperature is high, the scanning cycle is reduced to stabilize the temperature within a smaller range, ensuring that the pump light scans the absorption peak within the resonant range.

[0059] Therefore, the present invention adopts the above-mentioned high-sensitivity and small-volume gas detection device and method based on double-enhanced photothermal spectroscopy, and realizes double enhancement of resonance method and signal detection through a micro-nano optical fiber ring resonator, so that a micro-nano optical fiber ring of hundreds of microns can be equivalent to an absorption light path of tens of meters, thereby realizing high-sensitivity gas measurement under tiny gas volumes.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A highly sensitive and small amount of gas detection device based on dual enhanced photothermal spectroscopy, characterized in that: include The laser current controller enables the pump light laser to generate tunable pulse light, so that the detection light is scanned near the resonance wavelength of the micro-nano optical fiber ring; The laser temperature controller is used to control the operating temperature of the pump light laser and adjust the wavelength of the pump light to match the gas absorption wavelength; The pump light laser generates pump light, and the light energy is absorbed by the characteristic gas to generate photothermal energy, releasing heat energy; The detection light laser generates detection light, and the resonant wavelength of the micro-nano optical fiber ring can be found during the wavelength scanning process; The wavelength division multiplexer couples the pump light and the probe light into the micro-nano fiber ring resonator; The micro-nano fiber ring resonator allows the pump light to be repeatedly coupled and transmitted in the micro-nano fiber ring and interact with the gas, thereby generating an enhanced photothermal signal; for the detection light, the detection process of the photothermal signal is resonantly amplified, forming a double enhancement phenomenon; The narrowband filter converts the spectral changes of the probe light into changes in light intensity; The photoelectric detector converts the resonant detection light signal into an electrical signal for the back-end processing unit to demodulate the gas concentration information; The phase-locked amplifier amplifies the signal of the detection light after photoelectric detection, and obtains the second harmonic proportional to the gas concentration through demodulation; The laser current controller is also used to superimpose a sine wave on the driving current. The driving current is used for wavelength scanning so that the pump wavelength corresponds to the gas absorption wavelength. The sine wave is used for wavelength modulation to improve the signal-to-noise ratio.

2. According to claim 1, a highly sensitive and small amount of gas detection device based on dual enhanced photothermal spectroscopy is characterized in that: The micro-nano optical fiber ring allows part of the pump light to propagate around the micro-nano optical fiber in the form of an evanescent field, allowing the pump light to come into contact with the gas and then be absorbed by the gas; at the same time, the pump light that is not absorbed by the gas can be coupled back into the micro-nano optical fiber ring to participate in the next light-matter interaction; at the same time, the micro-nano optical fiber ring also causes the detection light to resonate in the micro-nano optical fiber ring.

3. According to claim 1, a highly sensitive and small amount of gas detection device based on dual enhanced photothermal spectroscopy is characterized in that: The wavelength of the pump light corresponds to the wavelength of the absorption spectrum of the gas being measured.

4. According to claim 1, a highly sensitive and small amount of gas detection device based on dual enhanced photothermal spectroscopy is characterized in that: The wavelength range of the detection light covers the resonance wavelength range of the micro-nano optical fiber ring.

5. According to claim 1, a highly sensitive and small amount of gas detection device based on dual enhanced photothermal spectroscopy is characterized in that: The resonance range of the micro-nano fiber ring is related to the diameter and photothermal intensity of the micro-nano fiber ring.

6. The highly sensitive and small amount gas detection device based on dual enhanced photothermal spectroscopy according to claim 1 is characterized in that: The diameter of micro-nano optical fiber is used to determine the size of the evanescent field, the coupling loss of the detection light, and the transmission loss.

7. The highly sensitive and small amount gas detection device based on dual enhanced photothermal spectroscopy according to claim 1 is characterized in that: It also includes a processing unit to realize the functions of data collection, filtering and data processing, and obtains the corresponding gas concentration signal through calculation of the optical signal.

8. The highly sensitive and minute amount gas detection device based on dual enhanced photothermal spectroscopy according to claim 1 is characterized in that: The micro-nano fiber ring resonator also includes another configuration in which a planar optical waveguide resonant structure or a micro-ring resonant cavity is used instead.

9. The highly sensitive and small amount gas detection device based on dual enhanced photothermal spectroscopy according to claim 1 is characterized in that: The driving current of the pump light also includes another setting in which a sine wave is not superimposed.

10. A highly sensitive and small amount of gas detection method based on dual enhanced photothermal spectroscopy, characterized in that: The following steps are involved: By controlling the temperature, the pump light is placed near the absorption peak of acetylene gas; The current controller uses the drive current to scan the wavelength near the absorption peak and superimposes a sine wave on the drive current; A wavelength division multiplexer is used to couple the pump light and the probe light into the micro-nano fiber ring resonator; The photothermal spectrum resonance of the pump light is formed in the micro-nano optical fiber ring, which changes the equivalent refractive index of the micro-nano optical fiber ring; the equivalent refractive index is amplified by the resonance of the detection light, and the spectrum of the detection light is shifted; The spectrum changes of the detection light are converted into light intensity changes through a narrow-band filter; The signal of the detection light after photoelectric detection is phase-locked and amplified, and the second harmonic proportional to the gas concentration is obtained by demodulation; The processing unit calculates the second harmonic optical signal to obtain a corresponding gas concentration signal.

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