Fourier photo-thermal gas detection device and method

Abstract

The application discloses a Fourier photo-thermal gas detection device and method, and belongs to the technical field of gas detection. In view of the problems of narrow spectral response range, low power tolerance and the need for refrigeration of a light detector in an existing Fourier transform spectrum, a Fourier photo-thermal gas detection device is designed, a thermal light source is used as an excitation light source of absorption effect, the thermal light source is subjected to unified intensity modulation of wide spectrum light through an intensity modulation assembly and phase modulation through an interferometer assembly; the broadband light emitted after being subjected to double modulation is partially absorbed after acting on gas molecules, a quartz tuning fork light detector assembly effectively collects transmitted light, extracts resonance components in the transmitted light and converts the resonance components into electrical signals; the generated electrical signals are sequentially subjected to processing through a signal amplification assembly, a phase-sensitive demodulation assembly and a Fourier transform assembly, and composition discrimination and concentration inversion of a target gas are realized through the processed signals.

Description

Technical Field

[0001] This invention belongs to the field of gas detection technology, specifically relating to a Fourier transform photothermal gas detection device and method. Background Technology

[0002] Fourier transform spectroscopy (FTSS) boasts high resolution, a wide spectral range, and parallel multiplexing capabilities, making it an ideal method for gas analysis as it meets the demands of broadband gas detection and simultaneous multi-gas detection. Despite its relative maturity, several challenges remain. Commercial photodetectors, the core component of FTSS, suffer from limitations such as narrow spectral response range, low power tolerance, and the need for cooling, severely impacting FTSS performance. Quartz tuning forks, as photodetectors, exhibit a flat and sensitive response across the entire wavelength range, with no wavelength selectivity, and have been successfully used for gas detection from the visible to the infrared and even terahertz bands. Their basic principle involves light radiating onto the surface of the quartz tuning fork, which collects this light energy and converts it into heat, creating localized heat accumulation on its surface and resulting in a non-uniform temperature field distribution. Due to the photothermoelastic properties of quartz tuning forks, these temperature changes cause thermal expansion and contraction of the material, resulting in deformation (strain) within its elastic range, which is then converted into mechanical vibration of the quartz tuning fork arm. Finally, based on the piezoelectric effect of the quartz tuning fork, an electrical signal is output. Acquiring and processing this signal enables qualitative and quantitative analysis of target gas molecules. Because quartz tuning fork photodetectors can absorb light across the entire wavelength range through quartz material and its surface coating, converting it into heat for detection, they possess full-spectrum light detection potential and require no cooling. Therefore, Fourier photothermal gas detection technology can achieve broadband gas detection and simultaneous multi-gas detection, operating across the entire spectrum from ultraviolet to terahertz, without requiring detector replacement or cooling. Summary of the Invention

[0003] To address the problems of narrow spectral response range, low power tolerance, and the need for cooling in existing Fourier transform spectroscopy photodetectors, this invention provides a Fourier photothermal gas detection device and method. By improving the structure and detection method of the Fourier transform spectrum, the signal-to-noise ratio and detection spectral range are improved, providing a brand-new solution for broadband, high-resolution gas detection.

[0004] This invention uses a thermal light source as the light source and modulates its intensity using an intensity modulation component. This achieves uniform modulation of all wavelength components of the thermal light source, allowing the quartz tuning fork to collect light across a wide spectral range and achieve a flat and sensitive response through the conversion of energy such as heat and elasticity. Compared to gas detection devices based on traditional commercial photodetectors using Fourier transform spectroscopy, this invention employs a quartz tuning fork detection light operating in the several kHz range, possessing sharp resonant characteristics and strong resistance to environmental interference, to improve the spectral response range of the sensing system. By improving the structure and detection method of the Fourier transform spectrum, this invention achieves full-spectrum detection of the Fourier transform spectrum, improving the system's detection sensitivity and increasing its spectral response range.

[0005] To achieve the above objectives, the present invention employs the following technical solutions:

[0006] A Fourier transform photothermal gas detection device, the device comprising: a broadband light source, an intensity modulation component, an interferometer component, a broadband interference beam, a sample cell component, a quartz tuning fork photodetector component, a signal amplification component, a phase-sensitive demodulation component, and a Fourier transform component; wherein:

[0007] The output end of the broadband light source is connected to the input end of the intensity modulation component;

[0008] The output of the intensity modulation component is connected to the interferometer component; the intensity modulation component is used to modulate the intensity of the broadband light source so that the frequency of the periodic change in the intensity of the light source is equal to the resonant frequency of the quartz tuning fork.

[0009] The output of the interferometer assembly is connected to the sample cell assembly; the interferometer assembly uses a Michelson interferometer to perform phase modulation on the broadband light source and obtain an intensity interferogram in the time domain, and outputs the broadband interference light.

[0010] The broadband interference beam is connected to the sample cell assembly;

[0011] The sample cell assembly contains the gas to be tested and increases the absorption path of the gas and light. Its output end is connected to the input end of the quartz tuning fork photodetector assembly.

[0012] The quartz tuning fork photodetector assembly uses a quartz tuning fork to effectively collect broadband transmitted light, realizes the conversion of light-thermal-elastic energy through the photothermoelastic effect of the quartz tuning fork, and outputs an electrical signal through the piezoelectric effect. Its output terminal is connected to the input terminal of the signal amplification assembly.

[0013] The output of the signal amplification component is connected to the input of the phase-sensitive demodulation component. The amplified signal is subjected to phase-sensitive detection to further extract the resonant frequency component from the electrical level and amplify it again.

[0014] The output of the phase-sensitive demodulation component is connected to the Fourier transform component; the Fourier transform component performs Fourier transform processing on the acquired mixed photothermal spectra over a wide spectral range to extract photothermal spectra of different wavelengths.

[0015] Specifically, by processing the frequency domain photothermal spectrum before and after passing through the gas to be tested, the absorbance signal of the gas to be tested is obtained. Its amplitude is linearly related to the gas concentration. The higher the gas concentration, the larger the signal amplitude. By comparing the signal generated by the gas to be tested with the signal generated by the calibrated concentration, the concentration of the gas to be tested can be calculated. The gas type is obtained by comparing it with the shape and wavelength position of the standard absorption spectrum.

[0016] Furthermore, the broadband light source is a thermal light source, and the intensity modulator includes a modulator (which may be an optical chopper, an acousto-optic modulator, an internal electronic modulator, etc.) and a function generator. The broadband light source is connected to the modulator, and the function generator is used to provide a radio frequency signal to drive the modulator. In order to achieve resonant detection of all wavelength components of the broadband light source, the frequency of the radio frequency signal output by the function generator is aligned with the resonant frequency of the quartz tuning fork.

[0017] Furthermore, the interferometer component is a Michelson interferometer, in which the intensity-modulated thermal light source is collimated and incident on the Michelson interferometer to perform phase modulation on the thermal light source, thereby obtaining broadband interference light with intensity variation in the time domain.

[0018] Furthermore, the sample cell assembly is a multi-pass cell used to contain the gas to be tested and to enhance the interaction length between the gas to be tested and the broadband interference light.

[0019] Furthermore, the quartz tuning fork photodetector assembly includes a quartz tuning fork and a gas chamber assembly. The quartz tuning fork is used to resonate and detect the transmitted light of broadband interference light. The gas chamber assembly is used to contain nitrogen gas to avoid environmental interference to the quartz tuning fork. The broadband interference light, after intensity modulation by the modulator and phase modulation by the Michelson interferometer, is focused and incident on the inner side of the root of the two arms of the quartz tuning fork to maximize the photothermal signal and control parameters such as pressure and temperature during the detection process.

[0020] Furthermore, the signal amplification component is a preamplifier, the input terminal of which is connected to the pin output of the quartz tuning fork. The current signal output by the quartz tuning fork is converted into a voltage signal and amplified.

[0021] Furthermore, the phase-sensitive demodulation component is a lock-in amplifier, the input of which is connected to the output of the preamplifier, and the demodulation frequency is the resonant frequency of the quartz tuning fork, thus obtaining a mixed photothermal signal for a wide spectral range.

[0022] Furthermore, the Fourier transform component includes an analog-to-digital converter and a Fourier transform electronic unit, used to perform analog-to-digital conversion and Fourier transform on the signal output by the lock-in amplifier; the input terminal of the analog-to-digital converter is connected to the output terminal of the lock-in amplifier to convert the analog signal output by the lock-in amplifier into an electronic signal; the Fourier transform electronic unit is used to perform Fourier transform on the photothermal signal to achieve extraction of mixed photothermal signals in a wide spectral range.

[0023] Furthermore, the quartz tuning fork photodetector assembly has a full-spectrum response capability.

[0024] A Fourier transform photothermal gas detection method, the method comprising the following steps:

[0025] Step 1: Fill the multi-pass cell with the gas sample to be tested;

[0026] Step 2: Connect the thermal light source to the modulator and perform intensity modulation on all wavelength components of the thermal light source at a uniform frequency. The modulation frequency is equal to the resonant frequency of the quartz tuning fork.

[0027] Step 3: The intensity-modulated thermal light source is incident on the Michelson interferometer, and the broadband light source is phase-modulated. By scanning the moving mirror in the Michelson interferometer, broadband interference light with a regular intensity change in the time domain is obtained.

[0028] Step 4: The broadband interference light is collimated and incident on the multi-pass cell, where it interacts with the gas molecules and is partially absorbed.

[0029] Step 5: The transmitted broadband interference light is focused and incident on the inner side of the root of the two arms of the quartz tuning fork. Due to the photothermoelastic and piezoelectric effects of the quartz tuning fork, the light energy of the broadband interference light is completely absorbed by the quartz tuning fork and converted into heat detection, and an electrical signal is output from its pins.

[0030] Step 6: Amplify the mixed photothermal signal using a preamplifier, and then demodulate the amplified electrical signal using a lock-in amplifier;

[0031] Step 7: Perform analog-to-digital conversion on the demodulated signal from the lock-in amplifier, then perform Fourier transform on the signal to obtain the spectrum in the frequency domain, analyze the signal, and infer the type and concentration of the gas.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] Compared with existing technologies, the present invention provides a Fourier photothermal gas detection device and method that uses a quartz tuning fork as a photodetector to achieve flat and sensitive detection of broadband light. An intensity modulation component uniformly modulates the thermal light source, ensuring that the periodic variation frequency of heat accumulation on the surface of the quartz tuning fork for each wavelength component of the broadband light source equals the resonant frequency of the quartz tuning fork. A Michelson interferometer is used to phase-modulate the broadband light source and convert it into broadband interference light in the time domain. Therefore, the quartz tuning fork, through thermoelastic and piezoelectric effects, responds non-selectively and flatly to the intensity-modulated and interfered broadband transmitted light, and can also resonate to increase the amplitude of the photothermal signal, thereby improving the system's sensitivity. Simultaneously, a signal amplification component amplifies the signal output from the quartz tuning fork and further uses a lock-in amplifier for phase-sensitive demodulation. This process reduces noise levels and improves the system's signal-to-noise ratio. Then, a Fourier transform component converts the photothermal signal output from the lock-in amplifier into a digital signal and further performs Fourier transform processing to finally obtain a frequency-domain photothermal signal characterizing the concentration and type of the gas to be measured. This resonant detection method, along with Fourier transform, enables broadband gas detection and simultaneous multi-gas detection, thus expanding the system's applicability. In summary, this invention has significant scientific and engineering application value. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a Fourier photothermal gas detection device according to the present invention; wherein: thermal light source-1, modulator-2, function generator-3, Michelson interferometer-4, broadband interference light-5, multi-pass cell-6, gas chamber assembly-7, quartz tuning fork-8, preamplifier-9, lock-in amplifier-10, analog-to-digital converter-11, and Fourier transform electronic unit-12;

[0035] Figure 2 This is a schematic diagram of the broadband interference light focusing incident on the quartz tuning fork of the present invention. Detailed Implementation

[0036] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.

[0037] This invention provides a Fourier transform photothermal gas detection device, such as... Figure 1 As shown, it includes a thermal light source 1, a modulator 2, a function generator 3, a Michelson interferometer 4, a broadband interference light 5, a multi-pass cell 6, a gas cell assembly 7, a quartz tuning fork 8, a preamplifier 9, a lock-in amplifier 10, an analog-to-digital converter 11, and a Fourier transform electronic unit 12.

[0038] The thermal light source 1 undergoes uniform intensity modulation of all wavelength components of the light source 1 via modulator 2. By changing the frequency of the function generator 3, the frequency of the periodic change in broadband light intensity is altered, ensuring that the frequencies of all wavelength components of the broadband light equal the resonant frequency of the quartz tuning fork 8. The intensity-modulated broadband light enters the Michelson interferometer 4, where it undergoes phase modulation and interference, outputting broadband interference light 5, which then enters the multipass cell 6 to interact with the gas under test. The transmitted light is focused and incident on the inner sides of the roots of the two arms of the quartz tuning fork 8, as shown... Figure 2 As shown. The quartz tuning fork 8 effectively collects light energy, and the electrical signal output generated through the thermoelastic and piezoelectric effects is connected to the preamplifier 9, and then sent to the lock-in amplifier 10 for demodulation. The demodulated signal is sent to the analog-to-digital converter 11 to be converted into a digital signal, and finally the digital signal is sent to the Fourier transform electronic unit 12 for Fourier transform.

[0039] The specific implementation process is as follows:

[0040] Step 1: Fill the multi-pass cell 6 with the gas sample to be tested;

[0041] Step 2: Connect thermal light source 1 to modulator 2, perform intensity modulation of all wavelength components of thermal light source 1 at a uniform frequency, adjust the driving frequency of function generator 3 and apply it to modulator 2, thereby changing the frequency of thermal light source intensity modulation so that the frequency of broadband light intensity change is equal to the resonant frequency of quartz tuning fork 8.

[0042] Step 3: The intensity-modulated thermal light source 1 is incident on the Michelson interferometer 4, and the broadband light source is phase-modulated. By scanning the moving mirror in the Michelson interferometer 4, broadband interference light 5 with regular intensity changes in the time domain is obtained.

[0043] Step 4: The broadband interference light 5 is collimated and incident into the multi-pass cell 6, so that the light energy at a specific wavelength of the broadband light is absorbed;

[0044] Step 5: The transmitted broadband interference light 5 is focused onto the inner sides of the roots of the two arms of the quartz tuning fork 8. The quartz tuning fork 8 effectively collects all the light energy, extracts the resonant component through the conversion of light-thermal-elastic energy, amplifies it, and converts it into an electrical signal output. To achieve effective detection, the broadband interference light needs to be focused onto the inner sides of the roots of the two arms of the quartz tuning fork 8, such as... Figure 2 As shown;

[0045] Step 6: Use lock-in amplifier 10 to perform a harmonic demodulation on the output of preamplifier 9. The demodulation frequency is the resonant frequency of the quartz tuning fork.

[0046] Step 7: The output of the lock-in amplifier 10 is sequentially fed into the analog-to-digital converter 11 and the Fourier transform electronic unit 12 for Fourier transform processing to obtain the photothermal spectrum of the gas under test in the frequency domain.

[0047] Step 8: Fill the multi-pass cell with pure nitrogen and obtain the reference spectrum. Process the gas absorbance according to the gas absorbance formula to obtain the absorbance signal of the gas to be tested. The signal amplitude is linearly related to the gas concentration. By comparing the absorbance signal of the gas to be tested with the signal generated by the calibration concentration, the concentration of the gas to be tested can be calculated. The gas type is obtained by comparing the position of the spectral wavelength and the shape of the standard absorption spectrum.

[0048] In this invention, modulator 2 modulates the intensity necessary for generating photothermal signals across all wavelengths of broadband light, thereby producing a mixed thermal signal over a wide spectral range. Due to the high Q value of the quartz tuning fork 8, the thermal signal will be resonantly accumulated, which improves detection sensitivity compared to non-resonant methods.

[0049] In this invention, due to the narrow resonant properties of the quartz tuning fork 8, the function generator 3 drives the modulator 2 to achieve fine adjustment of the intensity modulation frequency.

[0050] In this invention, the quartz tuning fork 8 can absorb light across the entire wavelength range and convert it into heat for detection through quartz material and its surface coating material. Therefore, it has the potential for full-spectrum light detection and does not require cooling.

[0051] In this invention, broadband light is phase-modulated and interfered by a Michelson interferometer 4 through step scanning to obtain broadband interference light 5. The mixed photothermal signal generated by the broadband interference light is then used to pick up the photothermal signal of single-frequency light through a Fourier transform scheme.

[0052] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A Fourier transform photothermal gas detection device, characterized in that, The device includes: a broadband light source, an intensity modulation component, an interferometer component, a broadband interference beam, a sample cell component, a quartz tuning fork photodetector component, a signal amplification component, a phase-sensitive demodulation component, and a Fourier transform component; wherein: The output end of the broadband light source is connected to the input end of the intensity modulation component; The output terminal of the intensity modulation component is connected to the interferometer component; The output end of the interferometer assembly is connected to the sample cell assembly; The broadband interference beam is connected to the sample cell assembly; The sample cell assembly contains the gas to be tested and increases the absorption path of the gas and light. Its output end is connected to the input end of the quartz tuning fork photodetector assembly. The output terminal of the quartz tuning fork photodetector assembly is connected to the input terminal of the signal amplification assembly; The quartz tuning fork photodetector assembly includes a quartz tuning fork (8) and a gas chamber assembly (7). The quartz tuning fork (8) is used to detect the energy of broadband interference light (5), and the gas chamber assembly (7) is used to contain nitrogen gas to avoid environmental interference to the quartz tuning fork (8). The transmitted broadband interference light is focused and incident on the inner side of the root of the two arms of the quartz tuning fork. Due to the photothermoelastic and piezoelectric effects of the quartz tuning fork, the light energy of the broadband interference light is completely absorbed by the quartz tuning fork and converted into heat detection, and an electrical signal is output from its pins. The output terminal of the signal amplification component is connected to the input terminal of the phase-sensitive demodulation component; The output of the phase-sensitive demodulation component is connected to the Fourier transform component; The Fourier transform component performs Fourier transform processing on the acquired mixed photothermal spectra over a wide spectral range to extract photothermal spectra of different wavelengths.

2. The Fourier transform photothermal gas detection device according to claim 1, characterized in that: The broadband light source is a thermal light source (1). The intensity modulation component includes a modulator (2) and a function generator (3). The function generator (3) is used to provide a radio frequency signal to drive the modulator (2). The frequency of the radio frequency signal is tuned so that all wavelength components of the thermal light source (1) are resonantly detected.

3. The Fourier transform photothermal gas detection device according to claim 2, characterized in that: The interferometer component is a Michelson interferometer (4), which is used to perform phase modulation on the thermal light source (1) and obtain an intensity interferogram in the time domain, and output broadband interference light (5).

4. The Fourier transform photothermal gas detection device according to claim 3, characterized in that: The sample cell assembly is a multi-pass cell (6) used to contain the gas to be tested and to increase the interaction length between the gas to be tested and the broadband interference light (5).

5. The Fourier transform photothermal gas detection device according to claim 4, characterized in that: The signal amplification component is a preamplifier (9), and the input terminal of the preamplifier (9) is connected to the pin output of the quartz tuning fork (8).

6. The Fourier transform photothermal gas detection device according to claim 5, characterized in that: The phase-sensitive demodulation component is a lock-in amplifier (10), and the input terminal of the lock-in amplifier (10) is connected to the output terminal of the preamplifier (9).

7. The Fourier transform photothermal gas detection device according to claim 6, characterized in that: The Fourier transform component includes an analog-to-digital converter (11) and a Fourier transform electronic unit (12) for performing analog-to-digital conversion and Fourier transform on the signal output by the lock-in amplifier (10).

8. The Fourier transform photothermal gas detection device according to claim 7, characterized in that: The quartz tuning fork photodetector assembly has full-spectrum response capability.

9. A Fourier transform photothermal gas detection method, characterized in that: The method is implemented based on a Fourier transform photothermal gas detection device according to any one of claims 1-8, and includes the following steps: Step 1: Fill the multi-pass cell (6) with the gas sample to be tested; Step 2: Connect the thermal light source (1) to the modulator (2) and perform intensity modulation of all wavelength components of the thermal light source (1) at a uniform frequency. The modulation frequency is equal to the resonant frequency of the quartz tuning fork. Step 3: The intensity-modulated thermal light source (1) is incident on the Michelson interferometer (4) to perform phase modulation on the broadband light source. Through the scanning of the moving mirror in the Michelson interferometer (4), broadband interference light (5) with regular intensity changes in the time domain is obtained. Step 4: Broadband interference light (5) is collimated into the multi-pass cell (6) and interacts with the gas molecules therein, and is partially absorbed; Step 5: The transmitted broadband interference light (5) is focused and incident on the inner side of the root of the two arms of the quartz tuning fork (8). Due to the photothermoelastic effect and piezoelectric effect of the quartz tuning fork (8), the light energy of the broadband interference light (5) is completely absorbed by the quartz tuning fork (8) and converted into heat detection, and an electrical signal is output from its pins. Step 6: The mixed photothermal signal is amplified by a preamplifier (9), and then the amplified electrical signal is demodulated by a lock-in amplifier (10); Step 7: Perform analog-to-digital conversion on the demodulated signal from the lock-in amplifier (10), then perform Fourier transform on the signal to obtain the spectrum in the frequency domain, analyze the signal, and infer the type and concentration of the gas.

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