Laser heterodyne photo-thermal spectrum telemetering device and method based on quartz tuning fork

Abstract

The invention discloses a laser heterodyne photo-thermal spectrum telemetering device and method based on a quartz tuning fork, and belongs to the technical field of atmospheric greenhouse gas sensing. Aiming at the problems of poor resolution and limited sensitivity of the existing laser heterodyne spectrum technology, optical beat frequency signals in the laser heterodyne spectrum telemetering technology are measured by adopting a photoinduced thermoelastic effect of a quartz tuning fork, and the optical beat frequency signals are measured by utilizing the characteristics of narrow bandwidth, high gain, low noise and high receiving power of the quartz tuning fork. The technology of optical power amplification, laser wavelength precise measurement and control, spectral signal averaging and the like is fused, the resolution, the signal-to-noise ratio and the optical frequency precision of a laser heterodyne spectrum are improved, the precision of key greenhouse gas telemetry data is improved, and reliable technical equipment is provided for key greenhouse gas foundation telemetry in China.

Description

Technical Field

[0001] The present invention belongs to the technical field of atmospheric greenhouse gas sensing, and in particular relates to a laser heterodyne photothermal spectrum remote sensing device and method based on a quartz tuning fork. Background Art

[0002] The calculation of the total amount of greenhouse gas emissions requires a comprehensive assessment through satellite remote sensing, airborne or spherical direct measurement, ground-based in-situ direct measurement, and ground-based remote sensing. Satellite remote sensing uses satellite-borne instruments to remotely measure the column concentration of greenhouse gases in the atmosphere. It can achieve large-scale measurements in a relatively short period of time, but its measurement accuracy is low and its life is short; airborne or spherical direct measurement uses aircraft or balloons to carry measuring instruments to directly measure the vertical profile of greenhouse gases at high altitudes. It has high vertical resolution and accuracy, and can compare and calibrate satellite or ground telemetry data. However, its measurement cost is high and long-term continuous monitoring cannot be achieved; although ground-based in-situ direct measurement has high accuracy, it can only provide gas concentration information near the observation point; ground-based remote sensing can perform high-precision continuous measurement of the atmospheric transmittance spectrum of greenhouse gases at a certain longitude and latitude, which can be used to verify satellite-borne remote sensing results. It has the advantages of simple structure, low cost, and good stability. Therefore, the accuracy of the vertical profile and column concentration of greenhouse gases obtained by ground remote sensing directly affects the accuracy of the comprehensive assessment of the final carbon monitoring.

[0003] Ground-based telemetry mainly uses Fourier transform spectrometers, which have a spectral resolution of 285MHz and a wide spectral measurement range. They can simultaneously observe multiple greenhouse gases such as CO2 and CH4. They are one of the core instruments of the total carbon column concentration observation network, but they are large in structure, high in cost, and cannot be moved flexibly. In the 1950s and 1960s, scientists discovered that heterodyne beat signals can be generated between coherent light and incoherent light, and used this technology to measure the reflection spectrum of space planets, and then developed laser heterodyne radiation technology. In 1995, M. Koide of Tohoku University in Japan used laser heterodyne technology to measure the absorption spectrum of CH4 in the atmosphere and inverted its vertical profile, forming the basic framework for measuring atmospheric transmittance spectrum based on laser heterodyne radiation. The system uses the wide bandwidth response characteristics of traditional photodetectors to measure optical beat signals, and then amplifies and bandpass filters the signal into a square-law RF detector to obtain the amplitude of the beat signal, and then measures the atmospheric transmittance spectrum. Compared with Fourier change spectroscopy, laser heterodyne technology has a simple structure, high sensitivity, low cost, easy integration and portability, and therefore has become the preferred method for atmospheric transmittance spectroscopy measurement at home and abroad.

[0004] At present, the spectral resolution of laser heterodyne spectroscopy is mainly determined by the bandwidth of the bandpass filter. In order to ensure a sufficient signal-to-noise ratio, the set bandwidth of the bandpass filter is generally in the order of hundreds of MHz to GHz, which is not a high resolution for spectral measurement. The spectral resolution can be improved by further reducing the bandwidth of the bandpass filter. However, due to the reduction in the power of the signal passing through, the signal-to-noise ratio of the atmospheric transmittance spectrum deteriorates. Therefore, the existing laser heterodyne spectroscopy technology obtains a higher spectral signal-to-noise ratio by sacrificing resolution. Therefore, how to simultaneously obtain a high signal-to-noise ratio and high spectral resolution of the atmospheric transmittance spectrum is a problem that needs to be solved urgently in this technology.

[0005] In recent years, the emergence of photothermoelastic spectroscopy based on quartz tuning forks has brought new opportunities for spectral detection technology. When a modulated laser beam interacts with the target gas molecules and irradiates the surface of the tuning fork quartz crystal, local heat accumulation is formed, generating a gradient temperature field, causing deformation (strain) within the elastic range. This strain field is related to the thermal expansion coefficient of the quartz tuning fork. Then, due to the piezoelectric properties of the tuning fork, this elastic strain is converted into an electrical signal output, which contains the light intensity change signal caused by gas absorption, so that the concentration of the gas can be determined. Summary of the invention

[0006] In view of the problems of poor resolution and limited sensitivity in the existing laser heterodyne spectroscopy technology, a quartz tuning fork is used as an AC photothermal detector with the characteristics of narrow bandwidth, high gain, low noise and high receiving power. It is combined with the laser heterodyne spectroscopy technology. The present invention provides a laser heterodyne photothermal spectroscopy telemetry device and method based on a quartz tuning fork.

[0007] The principle of the present invention is as follows: the photothermoelastic effect of a quartz tuning fork is used to measure the optical beat frequency signal in laser heterodyne spectroscopy telemetry technology, and the characteristics of the tuning fork such as narrow bandwidth, high gain, low noise, and high receiving power are utilized, and technologies such as optical power amplification, precise measurement and control of laser wavelength, and spectral signal averaging are integrated to improve the resolution, signal-to-noise ratio, and optical frequency accuracy of the laser heterodyne spectrum, thereby improving the accuracy of key greenhouse gas telemetry data.

[0008] Specifically, the power-amplified sunlight and the local oscillator light source are combined and irradiated onto the surface of the quartz tuning fork AC photothermal detector, the alternating light intensity signal at the tuning fork resonance frequency is converted into an alternating electrical signal, and the electrical signal is demodulated using the tuning fork resonance frequency.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A laser heterodyne photothermal spectrum telemetry device based on a quartz tuning fork, the device comprising a sunlight collection and amplification module, a local oscillator light source wavelength precision control module, a tuning fork photothermal detection module, a data acquisition and processing module, a fiber combiner, and a fiber splitter; wherein:

[0011] The sunlight collection and amplification module includes a sunlight tracker, an optical fiber switch, a semiconductor optical amplifier, and an optical fiber light receiving device;

[0012] The working principle of the sunlight collection and amplification module is:

[0013] In optical heterodyne detection, efficient sunlight collection is the key to the laser heterodyne telemetry system, which is accomplished by the combination of a solar tracker and a fiber optic light collecting device. The camera on the solar tracker reads the solar image, and then uses the image processing algorithm to form a feedback control strategy to drive the horizontal and vertical stepper motors to achieve stable solar tracking;

[0014] The fiber optic light receiving device is a fiber optic collimator with no moving parts and a compact structure. It focuses nearly parallel sunlight onto the fiber end face through an aspheric lens, achieving the coupling of sunlight to the single-mode fiber. The collected sunlight is further passed through a fiber optic switch to add intensity modulation. The modulated sunlight is amplified in a specific band by a semiconductor optical amplifier and then enters the tuning fork-type photothermal detection module to be combined with the local oscillator light source.

[0015] The local oscillator light source wavelength precision control module includes a temperature control and flow control module, a local oscillator light source, a computer, a wavelength measurement module, and a 2mm thickness standard tool;

[0016] The working principle of the local oscillator light source wavelength precision control module is:

[0017] When a small amount of local oscillator light source is input into the wavelength measurement module through the beam splitter, the computer collects the PD signal with low noise. After calculation and feedback control strategy, the output voltage signal controls the temperature control and flow control modules to drive the local oscillator light source to output a specific wavelength, and then scans the laser wavelength in steps until the measurement band is scanned. Since the laser wavelength is controlled with high precision, the spectral signal can be averaged multiple times without distorting the line shape.

[0018] The core of the technology is to construct a monotonic function of output voltage and laser wavelength, also known as the discrimination function. The measured laser forms two beams after passing through a double-sided reflector, and then enters the standard tool at different angles, forming two pairs of transmitted and reflected light, which are detected by the PD detector respectively. The theoretical waveforms of the transmission PD11 and reflection PD21 of the first beam of light, and the transmission PD12 and reflection PD22 waveforms of the second beam of light have a π phase shift with the first beam of light. The discrimination function of the first beam of light can be calculated by PD11 / PD12, mainly to eliminate the influence of laser power fluctuations; in addition, in order to expand the wavelength measurement range, it is necessary to introduce the discrimination function of the second beam of light to complement the discrimination function of the first beam of light. In order to achieve accurate wavelength measurement, in addition to using ULE materials, the standard tool also needs to accurately control the temperature of the entire wavelength measurement module with an accuracy better than 0.01°C. Finally, the discrimination function is calibrated using a wavelength meter or other wavelength measurement methods, and then the wavelength is determined by measuring the voltage.

[0019] The tuning fork type photothermal detection module includes a quartz tuning fork, a function generator, a transimpedance preamplifier, and a lock-in amplifier;

[0020] The working principle of the tuning fork type photothermal detection module is:

[0021] The local oscillator light source and the sunlight are focused to the root of the quartz tuning fork through the optical fiber combiner and the optical fiber light receiving device, one signal input end of the transimpedance preamplifier is connected to one electrode of the quartz tuning fork, and the other signal input end is connected to the other electrode of the quartz tuning fork and then grounded;

[0022] The synchronous signal input terminal of the phase-locked amplifier is connected to the synchronous signal output terminal of the function generator, so as to ensure that the demodulation signal frequency of the phase-locked amplifier is the same as the modulation signal frequency of the function generator.

[0023] The quartz tuning fork is a sensor element with strong noise immunity. Depending on the structural design, its resonant frequency can be in the order of tens of kHz, the response bandwidth can be in the order of Hz, and the quality factor can be greater than 10 4 , and it also has the advantages of high tolerance to optical power, detection without wavelength selectivity, and small size. It is used as an AC photothermal detector in the present invention. The optical signal of the broadband beat frequency of sunlight and local laser is output by the fiber collimator, and the total optical power is in the order of W, which is directly irradiated on the root surface of the quartz tuning fork. Due to the photothermoelastic effect, the tuning fork only has a high gain response to the beat frequency signal of its resonant frequency, and the photocurrent generated by the piezoelectric effect is converted into a voltage signal by the transimpedance preamplifier. The voltage signal is sent to the phase-locked amplifier and demodulated by the resonant frequency signal of the quartz tuning fork generated by the function generator to obtain the amplitude of the optical beat frequency signal of this frequency.

[0024] The data acquisition and processing module includes a data acquisition card and a computer;

[0025] The working principle of the data acquisition and processing module is: the signal input end of the data acquisition card is connected to the signal output end of the phase-locked amplifier, and the RS232 interface of the data acquisition card is connected to the signal acquisition port of the computer.

[0026] Furthermore, the wavelength measurement module is a 2mm thick standard tool made of ULE material, with 25% reflective film coated on both end faces, a free spectrum range of 50GHz, a cavity mode width of 25GHz, and uses the rising or falling edge of its transmission mode to measure the relative wavelength of the laser.

[0027] Furthermore, the wavelength measurement module uses a 2mm thickness standard tool to measure and control the laser wavelength in real time; the tuning fork type photothermal detection module uses a quartz tuning fork instead of a photodetector as an AC photothermal detector to achieve high-sensitivity measurement of alternating light signals; the detection bandwidth of the phase-locked amplifier is 1kHz-100kHz.

[0028] Furthermore, the sunlight collection and amplification module adds a bandpass filter near the wavelength of the local oscillator light source in front of the optical fiber light receiving device. Since the bandwidth of sunlight is very wide, unnecessary light can be filtered out to improve the signal-to-noise ratio of the detection system.

[0029] Furthermore, the tuning fork type heterodyne photothermal detection module also involves that in the traditional photothermoelastic spectroscopy, laser is always used as the light source, and the quartz tuning fork has a small light receiving area, so the structure of the quartz tuning fork needs to be redesigned to adapt to sunlight excitation.

[0030] A laser heterodyne photothermal spectroscopy telemetry method based on a quartz tuning fork, the method comprising the following steps:

[0031] Step 1: Use a solar tracker to achieve stable solar tracking. The sunlight collected by the optical fiber light receiving device is modulated by the optical fiber switch. The modulated sunlight is amplified by a semiconductor optical amplifier and then combined with the local oscillator light source by a fiber combiner.

[0032] Step 2: The local oscillator light source emits a laser beam driven by the temperature control and fluid control modules. The local oscillator light source is able to completely scan the gas absorption line by adjusting the current value given by the computer. The low-power part is then sent to the wavelength measurement module through the optical fiber beam splitter. The high-power part and the sunlight after the optical fiber beam splitter 11 and the combined beam are combined again through the optical fiber beam combiner 10. The computer performs low-noise acquisition on the PD signal. After calculation and feedback control strategy, the output voltage signal is used to control the local oscillator light source to output a specific wavelength, and then the laser wavelength is scanned step by step until the measurement band is scanned.

[0033] Step 3: The combined local oscillator light source and sunlight are focused by the fiber combiner, and the focused light beam is directly irradiated to the root of the quartz tuning fork to generate a photothermal signal; due to the photothermoelastic effect, the quartz tuning fork only has a high gain response to the beat frequency signal of its resonant frequency, and the photocurrent generated by the piezoelectric effect is converted into a voltage signal by the transimpedance preamplifier;

[0034] Step 4: The transimpedance preamplifier amplifies the received voltage signal and transmits it to the lock-in amplifier. The lock-in amplifier demodulates the voltage signal. The demodulation process is divided into mixing and filtering. The piezoelectric signal is transmitted to the data acquisition card after mixing and filtering.

[0035] Step 5: The data acquisition card transmits the collected heterodyne signal to the LabView program in the computer, and after calculation and processing, the corresponding gas whole-layer atmospheric transmittance spectrum is obtained;

[0036] Step 6: Repeat steps 1-5 to achieve continuous measurement of the atmospheric transmittance spectrum under clear weather conditions.

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] 1. Quartz tuning forks can replace traditional photodetectors to obtain extremely high detection sensitivity, because tuning forks are a sensor element with strong noise immunity. At room temperature and standard atmospheric pressure, its quality factor is greater than 10 4 , weak signals can be enhanced by resonance inside it, and the noise removal ability is extremely strong, because the response frequency band of the tuning fork is only a few Hz;

[0039] 2. The quartz tuning fork has an extremely wide spectral response range. Based on its non-wavelength selectivity, it can receive all light waves from visible to infrared bands, avoiding the problem of replacing different detectors when measuring different gases;

[0040] 3. The quartz tuning fork has a large measurement dynamic range, based on receiving watt-level optical power in the linear range without saturation. However, the saturation effect of the photodetector limits the efficiency of heterodyne detection. A high signal-to-noise ratio is obtained by increasing the incident light power.

[0041] 4. Using a quartz tuning fork as an AC photothermal detector can obtain a spectral resolution of the kHz order. The resolution obtained by traditional heterodyne detection technology is in the hundreds of MHz order, which improves the spectral resolution by 3 orders of magnitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of the structure of the quartz tuning fork in the present invention;

[0043] Figure 2 It is a structural schematic diagram of the device of the present invention;

[0044] Figure 3 This is a schematic diagram of a wavelength precision control module of the present invention;

[0045] Figure 4 It is a theoretical waveform diagram of the frequency discrimination function in the local oscillator light source wavelength precision measurement module in the present invention;

[0046] Figure 5 This is the heterodyne signal diagram output by the lock-in amplifier;

[0047] Figure 6 This is the gas transmittance spectrum after computer processing. DETAILED DESCRIPTION

[0048] 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.

[0049] The principle of the present invention is as follows: the photothermoelastic effect of a quartz tuning fork is used to measure the optical beat frequency signal in the laser heterodyne spectroscopy telemetry technology, and the characteristics of the quartz tuning fork such as narrow bandwidth, high gain, low noise, and high receiving power are utilized, and the optical power amplification, laser wavelength precision measurement and control, and spectral signal averaging technologies are integrated to improve the resolution, signal-to-noise ratio, and optical frequency accuracy of the laser heterodyne spectrum, thereby improving the accuracy of key greenhouse gas telemetry data.

[0050] Specifically, the power-amplified sunlight and the local oscillator light source are combined and irradiated onto the surface of the quartz tuning fork AC photothermal detector, the alternating light intensity signal at the tuning fork resonance frequency is converted into an alternating electrical signal, and the electrical signal is demodulated using the tuning fork resonance frequency.

[0051] A laser heterodyne photothermal spectrum telemetry device based on a quartz tuning fork, the device comprising a sunlight collection and amplification module, a local oscillator light source wavelength precision control module, a quartz tuning fork photothermal detection module, a data acquisition and processing module, a fiber combiner 10, and a fiber splitter 11; wherein:

[0052] The sunlight collection and amplification module includes a sunlight tracker 1, an optical fiber light collecting device 2, an optical switch 3, and a semiconductor optical amplifier 4.

[0053] The working principle of the sunlight collection and amplification module is:

[0054] In optical heterodyne detection, efficient sunlight collection is the key to the laser heterodyne telemetry system, which is accomplished by the combination of a solar tracker and an optical fiber light collecting device. The camera on the solar tracker 1 reads the solar image, and then uses the image processing algorithm to form a feedback control strategy to drive the horizontal and vertical stepper motors to achieve stable solar tracking;

[0055] The optical fiber receiving device 2 is an optical fiber collimator with no moving parts and a compact structure. It focuses nearly parallel sunlight onto the end face of the optical fiber through an aspheric lens to achieve coupling of sunlight to the single-mode optical fiber, and further passes the collected sunlight through an optical switch 3 to add intensity modulation; the modulated sunlight is amplified in a specific band by a semiconductor optical amplifier 4 and then enters the tuning fork type photothermal detection module to be combined with the local oscillator light source.

[0056] The local oscillator light source wavelength precision control module includes a temperature control and flow control module 5, a local oscillator light source 6, a microcomputer 7, a wavelength measurement module 8, and a 2 mm thickness standard tool 9;

[0057] The working principle of the local oscillator light source wavelength precision control module is:

[0058] When a small part of the local oscillator light source is input into the wavelength measurement module 8 through the beam splitter 11, the computer 7 performs low-noise acquisition on the PD signal, and after calculation and feedback control strategy, the output voltage signal controls the temperature control and flow control module 5 to drive the local oscillator light source to output a specific wavelength, and then step-scans the laser wavelength until the measurement band is scanned. Since the laser wavelength is controlled with high precision, the spectral signal can be averaged multiple times without distorting the line shape.

[0059] The core of the technology is to construct a monotonic function of output voltage and laser wavelength, also known as the discrimination function. The measured laser forms two beams after passing through a double-sided reflector, and then enters the standard tool at different angles, forming two pairs of transmitted and reflected light, which are detected by the PD detector respectively. The theoretical waveforms of the transmission PD11 and reflection PD21 of the first beam of light, and the transmission PD12 and reflection PD22 waveforms of the second beam of light have a π phase shift with the first beam of light. The discrimination function of the first beam of light can be calculated by PD11 / PD12, mainly to eliminate the influence of laser power fluctuations; in addition, in order to expand the wavelength measurement range, it is necessary to introduce the discrimination function of the second beam of light to complement the discrimination function of the first beam of light. In order to achieve accurate wavelength measurement, in addition to using ULE materials, the standard tool also needs to accurately control the temperature of the entire wavelength measurement module with an accuracy better than 0.01°C. Finally, the discrimination function is calibrated using a wavelength meter or other wavelength measurement methods, and then the wavelength is determined by measuring the voltage.

[0060] The tuning fork type photothermal detection module includes a quartz tuning fork 12, a function generator 13, a transimpedance preamplifier 14, and a lock-in amplifier 15;

[0061] The working principle of the tuning fork type photothermal detection module is:

[0062] The local oscillator light source and the sunlight pass through the optical fiber combiner 10 and then through the optical fiber light receiving device 2 to be focused to the root of the quartz tuning fork 12. One signal input end of the transimpedance preamplifier 14 is connected to one electrode of the quartz tuning fork, and the other signal input end is connected to the other electrode of the quartz tuning fork and then grounded.

[0063] The synchronization signal input terminal of the lock-in amplifier 15 is connected to the synchronization signal output terminal of the function generator 13 to ensure that the demodulation signal frequency of the lock-in amplifier is the same as the modulation signal frequency of the function generator.

[0064] The quartz tuning fork is a sensor element with strong noise immunity. Depending on the structural design, its resonant frequency can be in the order of tens of kHz, the response bandwidth can be in the order of Hz, and the quality factor can be greater than 10 4 , and it also has the advantages of high tolerance to optical power, detection without wavelength selectivity, and small size. It is used as an AC photothermal detector in the present invention. The optical signal of the broadband beat frequency of sunlight and local laser is output by the fiber collimator, and the total optical power is in the order of W, which is directly irradiated on the root surface of the quartz tuning fork. Due to the photothermoelastic effect, the tuning fork only has a high gain response to the beat frequency signal of its resonant frequency, and the photocurrent generated by the piezoelectric effect is converted into a voltage signal by the transimpedance preamplifier. The voltage signal is sent to the phase-locked amplifier and demodulated by the tuning fork resonance frequency signal generated by the function generator to obtain the amplitude of the optical beat frequency signal of this frequency.

[0065] The data acquisition and processing module includes a data acquisition card 16 and a computer 17;

[0066] The working principle of the data acquisition and processing module is as follows: the signal input end of the data acquisition card 16 is connected to the signal output end of the phase-locked amplifier 15 , and the RS232 interface of the data acquisition card 16 is connected to the signal acquisition port of the computer 17 .

[0067] Furthermore, the wavelength measurement module 7 is a 2mm thick standard tool 8 made of ULE material, with 25% reflective film coated on both end faces, a free spectrum range of 50GHz, a cavity mode width of 25GHz, and uses the rising or falling edge of its transmission mode to measure the relative wavelength of the laser.

[0068] Furthermore, the wavelength measurement module 7 performs real-time measurement and control of the laser wavelength; the tuning fork type photothermal detection module utilizes a quartz tuning fork 11 instead of a photodetector as an AC photothermal detector to achieve highly sensitive measurement of alternating optical signals; and the detection bandwidth of the phase-locked amplifier 14 is 1kHz-100kHz.

[0069] Furthermore, the sunlight collection and amplification module adds a bandpass filter near the wavelength of the local oscillator light source in front of the optical fiber light receiving device 2. Since the bandwidth of sunlight is very wide, unnecessary light can be filtered out to improve the signal-to-noise ratio of the detection system.

[0070] Furthermore, the tuning fork type heterodyne photothermal detection module also involves that in the traditional photothermoelastic spectroscopy, laser has been used as the local oscillator light source. The quartz tuning fork has a small light receiving area, and the structure of the quartz tuning fork needs to be redesigned to adapt to sunlight excitation.

[0071] A laser heterodyne photothermal spectroscopy telemetry method based on a quartz tuning fork, the method comprising the following steps:

[0072] Step 1: Use the sunlight tracker 1 to achieve stable sun tracking, collect the sunlight collected by the optical fiber light receiving device 2, and modulate the sunlight through the optical switch 3; the modulated sunlight is amplified by the semiconductor optical amplifier 4, and then combined with the local oscillator light source through the optical fiber combiner 10, as shown in FIG. Figure 2 As shown by the red line;

[0073] Step 2: The local oscillator light source 6 emits a laser beam driven by the temperature control and fluid control module 5. The temperature control and fluid control module 5 is adjusted to set a given current value so that the local oscillator light source can completely scan the gas absorption line. The low-power part is then sent to the wavelength measurement module 8 through the optical fiber beam splitter 11. The high-power part and the combined sunlight after the optical fiber beam splitter 11 are combined again through the optical fiber beam combiner 10. Figure 2 As shown by the yellow line; when the local oscillator light source is input to the wavelength measurement module 8, the microcomputer 7 performs low-noise acquisition on the PD signal, and after calculation and feedback control strategy, the output voltage signal is used to control the local oscillator light source to output a specific wavelength, and then the laser wavelength is scanned step by step until the measurement band is scanned;

[0074] Step 3: The combined local oscillator light source and sunlight are focused by the optical fiber combiner 10, and the focused light beam is directly irradiated to the root of the quartz tuning fork 12 to generate a photothermal signal; due to the photothermoelastic effect, the quartz tuning fork only has a high gain response to the beat frequency signal of its resonance frequency, and the photocurrent generated by the piezoelectric effect is converted into a voltage signal by the transimpedance preamplifier 14;

[0075] Step 4: The transimpedance preamplifier 14 amplifies the received voltage signal and transmits it to the lock-in amplifier 15. The lock-in amplifier 15 demodulates the voltage signal. The demodulation process is divided into mixing and filtering. The piezoelectric signal is transmitted to the data acquisition card 16 after mixing and filtering.

[0076] Step 5: The data acquisition card 16 transmits to the LabView program in the computer 17, and after calculation and processing, the corresponding gas whole layer atmospheric transmittance spectrum is obtained. Figure 6 As shown, the heterodyne signal collected by the phase-locked amplifier 15 is as follows: Figure 5 As shown;

[0077] Step 6: Repeat steps 1-5 to achieve continuous measurement of the atmospheric transmittance spectrum under clear weather conditions.

[0078] 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 laser heterodyne photothermal spectroscopy telemetry device based on a quartz tuning fork, characterized in that: The device comprises a sunlight collection and amplification module, a local oscillator light source wavelength precision control module, a tuning fork type photothermal detection module, a data acquisition and processing module, an optical fiber combiner (10), and an optical fiber splitter (11); wherein: The sunlight collection and amplification module comprises a sunlight tracker (1), an optical fiber light collecting device (2), an optical switch (3), and a semiconductor optical amplifier (4); The local oscillator light source wavelength precision control module comprises a temperature control and flow control module (5), a local oscillator light source (6), a microcomputer (7), a wavelength measurement module (8), and a 2 mm thickness standard tool (9); The tuning fork type photothermal detection module comprises a quartz tuning fork (12), a function generator (13), a transimpedance preamplifier (14), and a lock-in amplifier (15); The data acquisition and processing module comprises a data acquisition card (16) and a computer (17).

2. According to the quartz tuning fork-based laser heterodyne photothermal spectroscopy telemetry device of claim 1, it is characterized in that: The working principle of the sunlight collection and amplification module is: The camera on the solar tracker (1) reads the solar image, and then uses the image processing algorithm to form a feedback control strategy to drive the motors in the solar tracker (1) in the horizontal and vertical directions to achieve stable solar tracking; The optical fiber light receiving device (2) is an optical fiber collimator, which has no moving parts and a compact structure. It focuses nearly parallel sunlight onto the end face of the optical fiber through an aspheric lens to achieve coupling of sunlight to the single-mode optical fiber, and further passes the collected sunlight through an optical switch (3) to add intensity modulation. The modulated sunlight is amplified in a specific wavelength band by a semiconductor optical amplifier (4) and then enters a quartz tuning fork photothermal detection module to be combined with a local oscillator light source (6).

3. According to claim 2, a laser heterodyne photothermal spectroscopy telemetry device based on a quartz tuning fork is characterized in that: The working principle of the local oscillator light source wavelength precision control module is: When a small portion of the local oscillator light source (6) is input into the wavelength measurement module (8) through the beam splitter (11), the microcomputer (7) performs low-noise acquisition on the PD signal, and after calculation and feedback control strategy, outputs a voltage signal to control the temperature control and flow control module (5) to drive the local oscillator light source (6) to output a specific wavelength, and then step-scans the laser wavelength until the measurement band is scanned.

4. According to the quartz tuning fork-based laser heterodyne photothermal spectroscopy telemetry device of claim 3, it is characterized in that: The working principle of the tuning fork type photothermal detection module is: The local oscillator light source (6) and the sunlight are focused to the root of the quartz tuning fork (12) through the optical fiber combiner (10); one signal input end of the transimpedance preamplifier (14) is connected to an electrode of the quartz tuning fork, and the other signal input end is connected to the other electrode of the quartz tuning fork and then grounded; The synchronization signal input terminal of the phase-locked amplifier (15) is connected to the synchronization signal output terminal of the function generator (13), ensuring that the demodulation signal frequency of the phase-locked amplifier is the same as the modulation signal frequency of the function generator.

5. According to claim 4, a laser heterodyne photothermal spectroscopy remote sensing device based on a quartz tuning fork is characterized in that: The working principle of the data acquisition and processing module is as follows: the signal input end of the data acquisition card (16) is connected to the signal output end of the phase-locked amplifier (15), and the RS232 interface of the data acquisition card (16) is connected to the signal acquisition port of the computer (17).

6. The laser heterodyne photothermal spectroscopy telemetry device based on a quartz tuning fork according to claim 5, characterized in that: The wavelength measurement module (8) is a 2 mm thick standard tool (9) made of ULE material, with 25% reflection film coated on both end faces, a free spectrum range of 50 GHz, a cavity mode width of 25 GHz, and uses the rising or falling edge of its transmission mode to measure the relative wavelength of the laser.

7. The laser heterodyne photothermal spectroscopy telemetry device based on a quartz tuning fork according to claim 6, characterized in that: The wavelength measurement module (8) uses a 2 mm thick standard tool (9) to measure and control the laser wavelength in real time. The two end surfaces are plated with a 25% reflective film. Its free spectrum region is 50 GHz, and the cavity mode width is 25 GHz. The rising or falling edge of its transmission mode is used to measure the relative wavelength of the laser. The tuning fork type photothermal detection module uses a quartz tuning fork (12) instead of a photodetector as an AC photothermal detector to achieve high-sensitivity measurement of alternating light signals. The detection bandwidth of the phase-locked amplifier (15) is 1 kHz-100 kHz.

8. The laser heterodyne photothermal spectroscopy telemetry device based on a quartz tuning fork according to claim 7, characterized in that: The sunlight collection and amplification module is used to improve the signal-to-noise ratio of the remote sensing device.

9. A laser heterodyne photothermal spectroscopy telemetry method based on a quartz tuning fork, characterized in that: The method comprises the following steps: Step 1: Track sunlight using a sunlight tracker (1), collect sunlight collected by an optical fiber light receiving device (2), and modulate the sunlight through an optical switch (3); amplify the power of the modulated sunlight through a semiconductor optical amplifier (4), and then combine the sunlight with a local oscillator light source through an optical fiber combiner (10); Step 2: The local oscillator light source (6) emits a laser beam driven by the temperature control and fluid control module (5). The given current value of the temperature control and fluid control module (5) is adjusted to make the local oscillator light source (6) completely scan the gas absorption line, and then the low-power part is sent to the wavelength measurement module (8) through the optical fiber beam splitter (11). The high-power part and the sunlight after the beam is combined through the optical fiber beam splitter (11) are combined again through the optical fiber beam combiner (10) to complete the beam combination; when the local oscillator light source (6) is input to the wavelength measurement module (8), the microcomputer (7) performs low-noise acquisition on the PD signal, and after calculation and feedback control strategy, the output voltage signal is used to control the local oscillator light source to output a specific wavelength, and then the laser wavelength is scanned step by step until the measurement band is scanned; Step 3: The combined local oscillator light source and sunlight are focused by the optical fiber combiner (10), and the focused light beam is directly irradiated to the root of the quartz tuning fork (12), generating a photothermal signal; due to the photothermoelastic effect, the quartz tuning fork only has a high gain response to the beat frequency signal of its resonance frequency, and the photocurrent generated by the piezoelectric effect is converted into a voltage signal by the transimpedance preamplifier (14); Step 4: The transimpedance preamplifier (14) amplifies the received voltage signal and transmits it to the lock-in amplifier (15). The lock-in amplifier (15) demodulates the voltage signal. The demodulation process is divided into mixing and filtering. The voltage signal is transmitted to the data acquisition card (16) after mixing and filtering. Step 5: The data acquisition card (16) transmits the collected heterodyne signal to the LabView program in the computer (17) and obtains the corresponding gas whole-layer atmospheric transmittance spectrum after calculation and processing; Step 6: Repeat steps 1-5 to achieve continuous measurement of the atmospheric transmittance spectrum under clear weather conditions.

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