Fourier photo-thermal gas detection device and method

Abstract

The invention discloses a Fourier photo-thermal gas detection device and method, and belongs to the technical field of gas detection. Aiming at the problems of narrow spectral response range, low power tolerance, need of refrigeration and the like of an optical detector in the conventional Fourier transform spectrum, a Fourier photo-thermal gas detection device is designed, and a thermal light source is used as an excitation light source of an absorption effect; uniform intensity modulation of wide-spectrum light is achieved through the intensity modulation assembly, and phase modulation is achieved through the interferometer assembly. Broadband light emitted through double modulation is partially absorbed after acting with gas molecules, and a quartz tuning fork optical detector assembly effectively collects transmission light, extracts resonance components in the transmission light and converts the resonance components into electrical signals. The generated electrical signal is processed by the signal amplification assembly, the phase-sensitive demodulation assembly and the Fourier transform assembly in sequence, and component discrimination and concentration inversion of the target gas are realized by the processed signal.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas detection, and in particular relates to a Fourier photothermal gas detection device and method. Background Art

[0002] Fourier transform spectroscopy has the characteristics of high resolution, wide spectral range, parallel multiplexing, etc. It can meet the needs of broadband gas detection and synchronous detection of multiple gases, and is an ideal method for material analysis. Although the technology is relatively mature, it still has some challenges. As the core component of Fourier transform spectroscopy technology, commercial photodetectors have limitations such as narrow spectral response range, low power tolerance, and the need for refrigeration, which seriously affect the performance of Fourier transform spectroscopy. As a photodetector, the quartz tuning fork has a flat and sensitive response to the full band of light and has no wavelength selectivity for light. It has been successfully used as a photodetector to realize gas detection from visible to infrared and even terahertz bands. The basic principle is that light radiates to the surface of the quartz tuning fork, which collects the light energy and converts it into heat, forming local heat accumulation on its surface, resulting in an uneven distribution of the temperature field. Due to the photothermal elastic properties of the quartz tuning fork, these temperature changes cause thermal expansion and contraction of the material, causing deformation (strain) within the elastic range and then converting 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, and the acquisition and processing of the electrical signal can realize qualitative and quantitative analysis of the target gas molecules. Because the quartz tuning fork photodetector can absorb the full-band light through the quartz material and the coating material on its surface and convert it into heat for detection, it has the potential for full-spectrum detection of light and does not require refrigeration. Therefore, Fourier photothermal gas detection technology can realize broadband gas detection and synchronous detection of multiple gases, and can work in the full spectrum range from ultraviolet to terahertz, without the need to replace the detector and without refrigeration. Summary of the invention

[0003] In view of the problems of narrow spectral response range, low power tolerance and need for cooling of light detectors in existing Fourier transform spectroscopy, the present invention provides a Fourier photothermal gas detection device and method; by improving the structure and detection method of Fourier transform spectroscopy, the signal-to-noise ratio and detection spectral range are improved, providing a new solution for broadband and high-resolution gas detection.

[0004] The present invention uses a thermal light source as a light source, and modulates the intensity of the thermal light source under the action of an intensity modulation component, thereby achieving uniform modulation of all wavelength light components of the thermal light source, so that the quartz tuning fork collects light of all wavelength components in a wide spectral range and achieves a flat and sensitive response through the conversion of energy such as heat and elastic force. Compared with the Fourier transform spectroscopy gas detection device based on traditional commercial light detectors, a quartz tuning fork detection light that works within a few kHz range, has sharp resonance characteristics, and has strong resistance to environmental interference is used to improve the spectral response range of the sensing system. The present invention completes the full spectrum detection of the Fourier transform spectrum by improving the structure and detection method of the Fourier transform spectrum, improves the detection sensitivity of the system, and increases the spectral response range of the system.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A Fourier photothermal gas detection device, comprising: a broadband light source, an intensity modulation component, an interferometer component, a broadband interference light, 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 end 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 of the intensity of the light source is equal to the resonance frequency of the quartz tuning fork;

[0009] The output end of the interferometer component is connected to the sample cell component; the interferometer component performs phase modulation on the broadband light source through a Michelson interferometer and obtains an intensity interference pattern in the time domain, and outputs the broadband interference light;

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

[0011] The sample pool assembly contains the gas to be tested and increases the absorption path of the gas and light, and its output end is connected to the input end of the quartz tuning fork light detector 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 photothermal effect of the quartz tuning fork, and outputs an electrical signal through the piezoelectric effect, and its output end is connected to the input end of the signal amplification assembly;

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

[0014] The output end of the phase-sensitive demodulation component is connected to the Fourier transform component; the Fourier transform component performs Fourier transform processing on the collected mixed photothermal spectrum within a wide spectrum range to extract photothermal spectra of different light wavelengths.

[0015] Specifically, by processing the frequency domain photothermal spectrum before and after the gas to be tested, the absorbance signal of the gas to be tested is obtained. The amplitude of the absorbance signal is linearly related to the gas concentration. The greater the gas concentration, the greater 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, and the type of gas is obtained by comparing with the shape and wavelength position of the standard absorption spectrum.

[0016] Furthermore, the broadband light source is a thermal light source, the intensity modulator includes a modulator (which may be an optical chopper, an acousto-optic modulator, an internal electronic modulation, 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 satisfy the requirement of 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, and the intensity-modulated thermal light source is collimated and incident on the Michelson interferometer to perform phase modulation on the thermal light source to obtain broadband interference light with intensity variation in the time domain.

[0018] Furthermore, the sample cell assembly is a multi-pass cell for containing the gas to be measured and enhancing the interaction length between the gas to be measured and the broadband interference light.

[0019] Furthermore, the quartz tuning fork photodetector assembly includes a quartz tuning fork and an air chamber assembly. The quartz tuning fork is used to resonate and detect the transmitted light of the broadband interference light. The air chamber assembly is used to contain nitrogen to prevent environmental interference with the quartz tuning fork. The broadband interference light after modulator intensity modulation and Michelson interferometer phase modulation is focused and incident on the inner side of the roots 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 amplifying component is a preamplifier, the input end of the preamplifier is connected to the pin output of the quartz tuning fork, and 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 phase-locked amplifier, the input end of the phase-locked amplifier is connected to the output end of the preamplifier, the demodulation frequency is the resonance frequency of the quartz tuning fork, and a mixed photothermal signal is obtained for a wide spectral range.

[0022] Furthermore, the Fourier transform component includes an analog-to-digital converter and a Fourier transform electronic unit, which are used to perform analog-to-digital conversion and Fourier transform on the signal output by the phase-locked amplifier; the input end of the analog-to-digital converter is connected to the output end of the phase-locked amplifier to convert the analog signal output by the phase-locked 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 within a wide spectral range.

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

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

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

[0026] Step 2: The thermal light source is connected to the modulator, and all wavelength components of the thermal light source are modulated at a uniform frequency, where the modulation frequency is equal to the resonance frequency of the quartz tuning fork;

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

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

[0029] Step 5: The transmitted broadband interference light is focused and incident on the inner side of the roots of the two arms of the quartz tuning fork. Due to the photothermoelastic effect and piezoelectric effect 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 pin;

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

[0031] Step 7: Perform analog-to-digital conversion on the signal demodulated by the phase-locked amplifier, and then perform Fourier transform on the signal to obtain a spectrum in the frequency domain. Analyze the signal to invert the type and concentration of the gas.

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

[0033] Compared with the prior art, the present invention provides a Fourier photothermal gas detection device and method, which uses a quartz tuning fork as a light detector to achieve flat and sensitive detection of wide-spectrum light. The thermal light source is uniformly modulated by the intensity modulation component, so that the periodic change frequency of the heat accumulated by each wavelength component of the broadband light source on the surface of the quartz tuning fork is equal to the resonance frequency of the quartz tuning fork. The broadband light source is phase modulated and converted into broadband interference light in the time domain by a Michelson interferometer. Therefore, the quartz tuning fork will respond to the broadband transmitted light after intensity modulation and interference non-selectively and flatly through the thermoelastic effect and the piezoelectric effect, and can also resonantly increase the amplitude of the photothermal signal, thereby improving the sensitivity of the system. At the same time, the signal amplification component amplifies the signal output by the quartz tuning fork, and further uses a phase-locked amplifier for phase-sensitive demodulation. In this process, the noise level is reduced and the system signal-to-noise ratio is improved. Then, the Fourier transform component converts the photothermal signal output by the phase-locked amplifier into a digital signal, and further performs Fourier transform processing, and finally obtains a frequency domain photothermal signal that characterizes the concentration and type of the gas to be measured. Such resonance detection and Fourier transform methods realize wideband gas detection and multi-gas synchronous detection, and improve the application range of the system. In summary, the present invention has important scientific and engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of a Fourier photothermal gas detection device of 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, Fourier transform electronic unit-12;

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

[0036] In order to gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description of the present invention. However, the present invention has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the comprehensive understanding of the disclosure of the present invention.

[0037] The present invention provides a Fourier transform optical thermal gas detection 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 chamber assembly 7, a quartz tuning fork 8, a preamplifier 9, a phase-locked amplifier 10, an analog-to-digital converter 11, and a Fourier transform electronic unit 12.

[0038] The thermal light source 1 uniformly modulates the intensity of all wavelength components of the thermal light source 1 through the modulator 2. By changing the frequency of the function generator 3, the frequency of the periodic change of the broadband light intensity is changed, so that the frequency of all wavelength components of the broadband light is equal to the resonance frequency of the quartz tuning fork 8. The broadband light after intensity modulation enters the Michelson interferometer 4, which performs phase modulation and interference on the broadband light and outputs broadband interference light 5, which then enters the multi-pass cell 6 to interact with the gas to be measured. The transmitted light is focused and incident on the inner side of the roots of the two arms of the quartz tuning fork 8, as shown in FIG. Figure 2 The quartz tuning fork 8 effectively collects light energy, and through the thermoelastic effect and the piezoelectric effect, the generated electrical signal output is connected to the preamplifier 9, and then sent to the phase-locked amplifier 10 for demodulation, and 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 gas sample to be tested into the multi-pass cell 6;

[0041] Step 2: The thermal light source 1 is connected to the modulator 2, and all wavelength components of the thermal light source 1 are modulated with a uniform intensity frequency. The driving frequency of the function generator 3 is adjusted and applied to the modulator 2, so as to change the frequency of the intensity modulation of the thermal light source, so that the frequency of the broadband light intensity change is equal to the resonance frequency of the quartz tuning fork 8;

[0042] 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, and a broadband interference light 5 with a regular intensity change in the time domain is obtained through scanning of the moving mirror in the Michelson interferometer 4;

[0043] Step 4: The broadband interference light 5 is collimated and incident on 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 on the inner side 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 components through the conversion of light-heat-elastic energy, resonates and amplifies them, and converts them into electrical signals for output. In order to achieve effective detection, the broadband interference light needs to be focused on the inner side of the roots of the two arms of the quartz tuning fork 8, such as Figure 2 As shown;

[0045] Step 6: Use the lock-in amplifier 10 to perform primary harmonic demodulation on the output of the preamplifier 9, and the demodulation frequency is the resonance frequency of the quartz tuning fork;

[0046] Step 7: The output of the lock-in amplifier 10 is sequentially sent to 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 to be measured in the frequency domain;

[0047] Step 8: Pure nitrogen is filled into the multi-pass cell, and the reference spectrum is obtained by detection. The absorbance signal of the gas to be tested is obtained according to the gas absorbance formula. The signal amplitude is linearly related to the gas concentration. The absorbance signal of the gas to be tested is compared with the signal generated by the calibration concentration to calculate the concentration of the gas to be tested. The type of gas is obtained by comparing the spectral wavelength position and the shape of the standard absorption spectrum.

[0048] In the present invention, the modulator 2 modulates the intensity necessary for generating the photothermal signal as all wavelength components of the broadband light, thereby generating a mixed thermal signal in 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 the detection sensitivity compared to the non-resonant method.

[0049] In the present invention, due to the narrow resonance 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 the present invention, the quartz tuning fork 8 can absorb the full-band light and convert it into heat for detection through the quartz material and the coating material on its surface, so it has the potential for full-spectrum detection of light and does not require refrigeration.

[0051] In the present invention, the broadband light is phase modulated and interfered by the Michelson interferometer 4 through step scanning to obtain the broadband interference light 5. The hybrid photothermal signal generated by the broadband interference light is realized by the Fourier transform scheme to realize the photothermal signal pickup of the single-frequency light.

[0052] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A Fourier photothermal gas detection device, characterized in that: The device comprises: a broadband light source, an intensity modulation component, an interferometer component, a broadband interference light, a sample cell component, a quartz tuning fork light detector 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 end of the intensity modulation component is connected to the interferometer component; The output end of the interferometer component is connected to the sample cell component; The broadband interference light is connected to the sample cell assembly; The sample pool assembly contains the gas to be tested and increases the absorption path of the gas and light, and its output end is connected to the input end of the quartz tuning fork light detector assembly; The output end of the quartz tuning fork light detector assembly is connected to the input end of the signal amplification assembly; The output end of the signal amplification component is connected to the input end of the phase-sensitive demodulation component; The output end of the phase-sensitive demodulation component is connected to the Fourier transform component; The Fourier transform component performs Fourier transform processing on the collected mixed photothermal spectrum within a wide spectral range to extract photothermal spectra of different light wavelengths.

2. A Fourier photothermal gas detection device according to claim 1, characterized in that: The broadband light source is a thermal light source (1), and the intensity modulation component comprises a modulator (2) and a function generator (3). The function generator (3) is used to provide a radio frequency signal for driving the modulator (2), and to tune the frequency of the radio frequency signal so as to complete resonance detection of all wavelength components of the thermal light source (1).

3. A Fourier 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 interference pattern in the time domain, and output broadband interference light (5).

4. A Fourier 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 measured and to increase the interaction length between the gas to be measured and the broadband interference light (5).

5. A Fourier photothermal gas detection device according to claim 4, characterized in that: The quartz tuning fork light detector assembly comprises a quartz tuning fork (8) and an air chamber assembly (7); the quartz tuning fork (8) is used to detect the energy of broadband interference light (5); and the air chamber assembly (7) is used to contain nitrogen to prevent the environment from interfering with the quartz tuning fork (8).

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

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

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

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

10. A Fourier photothermal gas detection method, characterized in that: The method comprises the following steps: Step 1: Filling the gas sample to be tested into the multi-pass cell (6); Step 2: The thermal light source (1) is connected to the modulator (2), and all wavelength components of the thermal light source (1) are modulated at a uniform frequency, wherein the modulation frequency is equal to the resonance frequency of the quartz tuning fork; Step 3: The intensity-modulated thermal light source (1) is incident on a Michelson interferometer (4) to perform phase modulation on the broadband light source, and a broadband interference light (5) with a regularly changing intensity in the time domain is obtained by scanning a moving mirror in the Michelson interferometer (4); Step 4: The broadband interference light (5) is collimated and incident on 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 sides of the roots of the two vibration 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 pin; Step 6: amplify the mixed photothermal signal through a preamplifier (9), and then demodulate the amplified electrical signal through a lock-in amplifier (10); Step 7: Perform analog-to-digital conversion on the demodulated signal of the lock-in amplifier (10), then perform Fourier transform on the signal to obtain a spectrum in the frequency domain, analyze the signal, and invert the type and concentration of the gas.

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