Carbon-nitrogen emission cooperative measurement apparatus and method

Abstract

A carbon-nitrogen emission cooperative measurement apparatus and a method. The apparatus comprises an integrated cavity, a single-beam laser and a double-beam hybrid laser which are respectively disposed at two opposite ends of the integrated cavity, and an information acquisition and analysis system. The single-beam laser and the double-beam hybrid laser are respectively used for continuously transmitting laser beams to the integrated cavity. Use of the single-beam laser and the double-beam hybrid laser can achieve high-frequency measurement of CO2-CH4-N2O-N2 mixed gas of any concentration in the same space and time in one integrated cavity, and the concentrations of CO2, CH4 and N2O are inversed by means of the information acquisition and analysis system. The apparatus has a simple structure, satisfies the research requirements for simultaneous measurement of various greenhouse gases under the same path, greatly improves the utilization efficiency of the integrated cavity, and reduces measurement costs.

Description

A carbon and nitrogen emission collaborative detection device and method Technical Field

[0001] The present invention belongs to the field of environmental gas detection and relates to a carbon and nitrogen emission coordinated detection device and method. Background Art

[0002] Carbon dioxide, methane and nitrous oxide emissions come from numerous sources and exist simultaneously in many emission processes. Therefore, it is of great significance to develop a method with high detection sensitivity, high-frequency response characteristics and high selectivity that can identify and measure the three major greenhouse gases in the same space and time range.

[0003] P. Mahesh et al. and Gonzalez-Valencia R et al. conducted simultaneous measurements of CO2 and CH4 in the atmosphere and freshwater ecosystems, respectively. They used LGR's gas analysis equipment based on off-axis integral cavity output spectroscopy (OA-ICOS) technology. The measurement baselines for CO2 and CH4 were 10 -7 and 10 -10 DL Arévalo-Martínez et al. also used LGR equipment to simultaneously detect carbon dioxide and nitrous oxide in the ocean and atmosphere. K. Wang et al. used off-axis cavity-enhanced absorption spectroscopy (OA-CEAS) based on time-division multiplexing technology to simultaneously detect methane and carbon dioxide in the atmosphere. The high-reflectivity dielectric film cavity mirror used in OA-CEAS enables it to achieve higher detection sensitivity through more reflections, facilitating isotope detection without enrichment. However, the traditional unidirectional transmission detection mode of OA-CEAS makes it difficult to simultaneously couple more than two beams into a single integrating cavity. As a result, current research focuses on the detection of only one greenhouse gas, CO2, CH4, or N2O. A few studies have involved the simultaneous detection of all three greenhouse gases, CO2, CH4, and N2O, using OA-CEAS in the same integrating cavity. No reports have been found on the simultaneous and spatial detection of all three greenhouse gases, CO2, CH4, and N2O, using OA-CEAS in the same integrating cavity.

[0004] To this end, an embodiment of the present invention provides a bidirectional off-axis cavity enhanced absorption OA-CEAS device for simultaneous and high-frequency measurement of multiple gas components, thereby partially solving the technical problems of low utilization efficiency of integrating cavities and high detection costs in the field of multi-gas detection in the prior art. Technical Solutions

[0005] To address the shortcomings of existing technologies, a device and method for coordinated carbon and nitrogen emissions detection are provided. Based on an OA-CEAS device operating in a bidirectional off-axis cavity enhancement mode, this method enables simultaneous and spatiotemporal detection of CO2, CH4, and N2O gas molecules and their isotopic concentrations at sub-ppb levels. This method addresses the current difficulty in coupling more than two beams into a single integrating cavity for simultaneous detection of multiple greenhouse gases using unidirectional beam transmission detection. This method addresses the research need for simultaneous detection of multiple greenhouse gases along the same path, significantly improving the utilization efficiency of the integrating cavity and reducing detection costs.

[0006] To achieve the above technical objectives, the present invention provides a coordinated carbon and nitrogen emission detection device, which includes an integrating cavity, two laser groups, and an information acquisition and analysis system. The two laser groups are a single-beam laser and a dual-beam hybrid laser, respectively, disposed at opposite ends of the integrating cavity. The single-beam laser and the dual-beam hybrid laser are respectively used to continuously emit a transmission laser beam to the integrating cavity. The two laser groups can realize simultaneous and spatial high-frequency detection of a CO2-CH4-N2O-N2 gas mixture of any concentration in one integrating cavity, thereby inverting the concentrations of CO2, CH4, and N2O in the CO2-CH4-N2O-N2 gas mixture to be measured.

[0007] Two groups of lasers are placed at both ends of the integrating cavity, with two concave mirrors placed between them. The two groups of lasers continuously transmit in both directions on both sides of the integrating cavity, realizing a bidirectional continuous transmission mode of the integrating cavity and utilizing denser high-order transverse modes to improve the sensitivity of gas concentration detection.

[0008] The integrating cavity includes a gas absorption cell having a CO2-CH4-N2O-N2 mixed gas, a dual-beam hybrid laser is located at the left end of the gas absorption cell, and a single-beam laser is located at the right end of the gas absorption cell, between the dual-beam hybrid laser and the gas absorption cell; an information acquisition and analysis system is located between the single-beam laser and the gas absorption cell, and the information acquisition and analysis system includes a first concave mirror arranged on a laser path between the dual-beam hybrid laser and the gas absorption cell, and a second concave mirror arranged on a laser path between the single-beam laser and the gas absorption cell, and further includes a first filter and a first photodetector, a second filter and a second photodetector, which are sequentially connected, and the first photodetector and the second photodetector are connected to a computer via a data acquisition card; An incident hole is provided on the first concave mirror and the second concave mirror, respectively. The concave surfaces of the first concave mirror and the second concave mirror are angled at approximately 2° relative to the gas absorption cell, thereby being capable of reflecting the laser beam passing through the gas absorption cell onto the first filter and the second filter. The information acquisition and analysis system comprises a first concave mirror arranged on the optical path between the dual-beam mixing laser and the gas absorption cell, a second concave mirror arranged on the optical path between the single-beam laser and the gas absorption cell, a first filter and a first photodetector arranged in sequence on the reflected optical path of the first concave mirror, a second filter and a second photodetector arranged in sequence on the reflected optical path of the second concave mirror, an acquisition card connected to the first photodetector and the second photodetector, respectively, and a computer connected to the acquisition card.

[0009] An incident hole is provided on each of the first concave mirror and the second concave mirror. The concave surface of the first concave mirror and the concave surface of the second concave mirror are both inclined relative to the gas absorption cell at an angle of about 2°. The concave surface of the first concave mirror is used to reflect the laser beam passing through the gas absorption cell onto the first filter, and the concave surface of the second concave mirror is used to reflect the laser beam passing through the gas absorption cell onto the second filter.

[0010] The lasers emitted by the two groups of lasers are reflected multiple times by the first and second concave mirrors, thereby increasing the effective path length of the lasers in the gas absorption cell and achieving the measurement of lower concentration gases. At the same time, the laser light collected by the photodetector is emitted by the laser located on the other side of the corresponding gas absorption cell. The laser light on the same side of the photodetector is filtered by the filter and will not be collected.

[0011] Specifically, the first concave mirror allows the laser of the dual-beam hybrid laser to pass through and enter the gas absorption cell through the incident hole. The concave surface of the first concave mirror reflects the light reflected by the gas absorption cell to the first filter. The laser beam within the wavelength band of the first filter will pass through the first filter and enter the first photodetector, and the laser beam outside the wavelength band of the first filter will be reflected back to the gas absorption cell along the original path. The second concave mirror allows the laser of the single-beam laser to pass through and enter the gas absorption cell through the incident hole, and at the same time reflects the light fed back by the gas absorption cell to the second filter. In this process, the laser beam within the wavelength band of the second filter will pass through the two filters and enter the second photodetector, and the laser beam outside the wavelength band of the second filter will be reflected back to the gas absorption cell along the original path.

[0012] The wavelength ranges of the first filter and the second filter are different. The wavelength of the laser beam emitted by the dual-beam hybrid laser is within the wavelength range of the first filter, and the wavelength of the laser beam emitted by the single-beam laser is within the wavelength range of the second filter.

[0013] During this process, the laser beam within the wavelength range of the second filter will pass through the two filters and enter the second photodetector, while the laser beam outside the wavelength range of the second filter will be reflected back into the gas absorption cell along the original path. During this process, the first filter reflects the light emitted by the first and second quantum cascade lasers and reflected by the first concave mirror on the left side of the gas absorption cell, while the second filter reflects the laser light emitted by the laser and reflected by the second concave mirror on the right side of the gas absorption cell.

[0014] in:

[0015] The computer collects the voltage signal of the first photodetector and / or the second photodetector through the acquisition card, and the computer calculates the concentration of CO2, CH4, N2O, etc. in the CO2-CH4-N2O-N2 mixed gas to be measured based on the voltage signal.

[0016] Furthermore, the carbon and nitrogen emission collaborative detection device also includes a sine wave generator, a sawtooth wave generator, an adder and a collimator, and the dual-beam hybrid laser includes a first laser controller, a second laser controller, a first quantum cascade laser, a second quantum cascade laser and a beam combiner;

[0017] The outputs of the sine wave generator and the sawtooth wave generator are subjected to signal superposition processing by an adder to generate a laser driving signal. The adder is used to output the laser driving signal to the first laser controller or the second laser controller. The first laser controller is connected to the first quantum cascade laser, and the second laser controller is connected to the second quantum cascade laser. The output ends of the first quantum cascade laser and the second quantum cascade laser are connected to a collimator pointing to the left end of the gas absorption cell through a beam combiner.

[0018] The sine wave generator is a phase-locked amplifier, the sawtooth wave generator is a function generator, and the first quantum cascade laser and the second quantum cascade laser are both DFB tunable semiconductor lasers.

[0019] Furthermore, the single-beam laser includes a third laser controller and a third quantum cascade laser connected to the third laser controller. The adder is used to output the laser driving signal to the third laser controller. The output end of the third quantum cascade laser points to the right end of the gas absorption cell.

[0020] Furthermore, the wavelengths of the laser beams used to test CO2, CH4, and N2O are 4353.9 nm, 3211.3 nm, and 4567 nm, respectively, while the wavelengths of the laser beams emitted by the first quantum cascade laser, the second quantum cascade laser, and the third quantum cascade laser correspond one-to-one to 4353.9 nm, 3211.3 nm, and 4567 nm, respectively.

[0021] Furthermore, the technical parameters of the first photodetector and the second photodetector are: the response band is 3000nm-5000nm, and the technical parameters of the data acquisition card are: 2-channel 12-bit D / A output, 8-channel phase-difference analog input, 1-channel 16-bit counter, and 16-channel programmable switch quantities.

[0022] Furthermore, the three lasers are a first quantum cascade laser, a second quantum cascade laser, and a third quantum cascade laser, and all three lasers are DFB tunable semiconductor lasers;

[0023] Furthermore, the first laser controller outputs a driving current signal under the drive of the laser driving signal to control the output of the first quantum cascade laser 7, and / or the second laser controller outputs a driving current signal under the drive of the laser driving signal to control the output of the second quantum cascade laser, and / or the third laser controller outputs a driving current signal under the drive of the laser driving signal to control the output of the third quantum cascade laser; the capacitor in the bias device Bias-Tee is used to filter out the DC bias in the Gaussian white noise signal, and superimpose the broadband high-frequency white noise signal of 5 MHz-2 GHz, -10 dBm emitted by the white noise source on the driving current signal to prevent the laser injection current from being biased, and also protect the normal operation of the laser group.

[0024] Further, the white noise source includes a lock-in amplifier, a signal generator, and a radio frequency noise source;

[0025] The lock-in amplifier and the signal generator superimpose the signals through an adder to form a laser driving signal. The radio frequency noise source adds radio frequency noise with a power of -10 dBm to the laser driving signal. The radio frequency noise is filtered through a low-pass filter and input into the bias device together with the driving current signal. The driving current signal superimposed with the radio frequency noise after passing through the bias device is used to control the operation of the first quantum cascade laser, the second quantum cascade laser, or the third quantum cascade laser.

[0026] Among them, the modulation signal of the laser consists of two parts:

[0027] A portion of the modulation signal is formed by adding a sine wave generated by a lock-in amplifier and a triangular wave generated by a signal generator to serve as a laser driving signal, and the portion of the modulation signal is sent to at least one of the first laser controller, the second laser controller, and the third laser controller; and

[0028] Another part of the modulation signal is a white noise signal emitted by the radio frequency noise source. After passing through a low-pass filter, this part of the modulation signal is superimposed with the driving current signal generated by one of the first laser controller, the second laser controller, and the third laser controller through a bias device to control the first quantum cascade laser or the second quantum cascade laser.

[0029] The sine wave and the triangle wave are superimposed by the adder to realize the wavelength modulation of the signal, and the white noise signal emitted by the radio frequency noise source is used to suppress the cavity mode noise of the integral cavity.

[0030] Furthermore, the first concave mirror and the second concave mirror are both silver-coated concave spherical mirrors.

[0031] Furthermore, the length of the gas absorption cell is 30 cm.

[0032] A detection method of a carbon and nitrogen emission collaborative detection device, the steps of which are as follows:

[0033] The gas absorption cell is filled with the mixed gas to be tested, including CO2 (carbon dioxide), CH4 (methane), N2O (nitrous oxide) and N2 (nitrogen);

[0034] The output terminals of the sine wave generator and the sawtooth wave generator are connected to the adder and the input terminal of the data acquisition card respectively;

[0035] Connecting the adder output to the first laser controller input, the second laser controller input, or the third laser controller 6 input;

[0036] The output end of the first laser controller is connected to the first quantum cascade laser, and the output end of the second laser controller is connected to the second quantum cascade laser. The laser beams output by the first quantum cascade laser and the second quantum cascade laser pass through a beam combiner. The light passing through the beam combiner passes through a collimator and then passes through a first concave reflector, a gas absorption cell, a second concave reflector, a first filter, and a first photodetector in sequence.

[0037] The output end of the third laser controller is connected to the third quantum cascade laser. The laser beam output by the third quantum cascade laser passes through the collimator, and then passes through the second concave reflector, the gas absorption cell, the first concave reflector, the second filter, and is incident on the second photodetector.

[0038] A high-frequency sinusoidal modulation signal is loaded into the injection current of at least one of the first laser controller, the second laser controller, and the third laser controller, so that the laser beam output by at least one of the first laser controller, the second laser controller, and the third laser controller undergoes sinusoidal jitter near its optical frequency, and a signal with a very narrow bandwidth near the second harmonic of the modulation frequency is extracted during signal demodulation;

[0039] Loading a low-frequency sawtooth wave into at least one of the injection currents of the first laser controller, the second laser controller, and the third laser controller so that the central wavelength output by the dual-beam hybrid laser can completely scan the gas absorption spectrum;

[0040] The output ends of the first photodetector and the second photodetector are both connected to the input end of the data acquisition card, and the output end of the data acquisition card is connected to the input end of the computer; the two absorption light signals are converted into voltage signals after passing through the first photodetector and the second photodetector and are collected by the data card. The computer uses LabVIEW software to obtain the signals through the acquisition card and then sends them to the digital phase lock. According to the different modulation frequencies of the dual-beam hybrid laser and the single-beam laser, the voltage signals detected by the first photodetector and the second photodetector are demodulated respectively. The second harmonic signal obtained by demodulation at the double frequency according to the corresponding modulation frequency by the phase-locked amplifier is subjected to wavelet denoising and Kalman filtering to obtain the second harmonic signals of the CO2, CH4 and N2O absorption spectra;

[0041] The different modulation frequency parameters of the dual-beam hybrid laser and the single-beam laser are 30Hz, 1V sawtooth wave superimposed on 12kHz, 150mV sine wave and 10Hz, 100mV sawtooth wave superimposed on 8kHz, 50mV sine wave;

[0042] A series of CO2-CH4-N2O-N2 mixed gas absorption spectra with different concentrations within the setting range of the dual-beam hybrid laser and the single-beam laser were tested, and the spectral line pairs with high correlation were selected. The relationship model between the second harmonic peak value and the corresponding concentration was established for these spectral line pairs. The direct absorption and second harmonic signals of the corresponding gases were simulated and fitted with the actual measured signals to obtain the following corresponding models, which are Y CO2 =1.827X CO2 +0.189, Y CH4 =0.00286X CH4 +0.30475, Y N2O =0.185X N2O +0.208, where Y represents the corresponding gas concentration and X represents the second harmonic peak-to-peak value. For a CO2-CH4-N2O-N2 mixed gas of any concentration, the concentration of at least one of CO2, CH4 and N2O can be inverted using the relationship model between the calibrated second harmonic peak-to-peak value and the corresponding concentration.

[0043] A method for collaboratively measuring the concentration of carbon and nitrogen emission gases by a carbon and nitrogen emission collaborative detection device comprises the following steps:

[0044] Step A. Determine the optimal structural parameters of the curvature radius of the first concave mirror 12 and the second concave mirror 16, the spacing and angle between the concave reflector and the cavity mirror in the integrating cavity, and the optimal positions of the first photodetector 15 and the second photodetector 18 using optical design software;

[0045] Step B. Establishing atmospheric transmittance models for CO2, CH4, and N2O molecules and their selected isotope molecules, and selecting spectral detection windows and target spectral line combinations suitable for simultaneous detection of CO2, CH4, and N2O molecules and their isotope molecules for each of the three greenhouse gases;

[0046] Step C. The sine wave generator generates a high-frequency sine wave, the sawtooth wave generator generates a low-frequency triangular wave, and a dual-beam hybrid laser and a single-beam laser are used to receive the superposition signal of the high-frequency sine wave and the low-frequency triangular wave respectively to work and generate laser beams respectively; wherein, the first quantum cascade laser and the second quantum cascade laser of the dual-beam hybrid laser with similar wavelengths are placed on the same side, and the two laser beams are coupled through a fiber coupler, and then collimated by a collimator 11, and then coupled through the incident hole on the concave reflector on the same side of the integrating cavity according to the appropriate position and off-axis angle. The third quantum level laser of the single beam laser is set on the other side of the integrating cavity, and after being collimated by the collimator, it is coupled into the integrating cavity according to the appropriate position and off-axis angle through the incident hole on the concave reflector on the same side of the integrating cavity; the two laser beams enter from both sides of the integrating cavity, and respectively pass through the integrating cavity with the gas to be detected, and are converged and reflected by the concave reflector on the side of the exit cavity mirror. The opposite beam is filtered out by the narrow band filter of the corresponding wavelength, received by the photodetector, and demodulated by the phase-locked amplifier to obtain two spectral lines corresponding to CO2 (the two spectral lines are consistent with the CO2 emission). 16 O 12 C 16 O and 16 O 13 C 16 O respectively), two spectral lines corresponding to CH4 (these two spectral lines correspond to 12 CH4 and 13 CH4) and three spectral lines corresponding to N2O (the three spectral lines are 14 N2 16 O. 14 N 15 N 16 O and 15 N 14 N 16 O respectively);

[0047] Step D. For the two spectral lines corresponding to CO2, two spectral lines corresponding to CH4, and three second harmonic signals corresponding to N2O obtained for the target greenhouse gas, background signals are removed to obtain absorption-related signals corresponding to the seven spectral lines. To improve system sensitivity, a pentavalent wavelet denoising method is used to reduce noise in the WMS-2f signal measured by the photodetector;

[0048] Step E. Based on the pressure and temperature information in the integrating cavity, obtaining the absorption state signals in the second harmonic signals of the spectral lines corresponding to CO2, CH4 and N2O respectively under the same temperature and pressure environment;

[0049] Step F: Perform inversion calculations on the peak values ​​of the absorption-related signals corresponding to CO2, CH4, N2O and some of their isotopes to obtain the concentrations of CO2, CH4 and N2O, respectively.

[0050] Furthermore, the optimal structural parameters in step A are determined using the following method:

[0051] Matlab was used to simulate and analyze the intracavity light field using an eccentric Gaussian beam. The intracavity light field in the bidirectional mode can be described by the sum of the incident light fields on both sides:

[0052] ,

[0053] ,

[0054] At this time, the light field of the light spot after any N reflections on the cavity mirror can be obtained from the light field matrix M of the first light spot

[0055] ,

[0056] By calculating the vector sum of all the light fields on the cavity mirror, the total light field emitted by the cavity mirror on one side of the integrating cavity can be obtained. ,

[0057] Then the transmittance spectrum on one side of the integrating cavity is obtained from the output and input power

[0058] ,

[0059] To improve computational efficiency, the cavity mirror is divided into a series of grids during the simulation process. Only the light field at the grid points is considered during calculations, and the total power is obtained by multiplying the irradiance at the grid points by the area of ​​the grid. By varying parameters such as cavity length, cavity mirror curvature radius, incident beam diameter, off-axis angle of the incident light on both sides, and incident position, Airy functions are used to simulate and analyze the intracavity light field and transmittance spectrum under various conditions. By balancing the optimal optical path with the optimal signal-to-noise ratio, the optimal structural parameters for the bidirectionally coupled detection mode are obtained.

[0060] Furthermore, the target spectral line selection criteria in step B are suitable for the spectral detection window and target spectral line combination for simultaneous detection of the molecule and its isotope molecules as follows:

[0061] Step B1. The selected absorption line combinations of CO2, CH4 and N2O molecules and their isotopes should be distributed within 2 cm -1 Within the range to ensure full coverage by a single scan of the laser;

[0062] Step B2. Based on the absorption band distribution of each molecule and its isotope, analyze the band mixing effect between each band to ensure that the spacing between the spectral lines in each combination is not less than 0.1 cm -1 , ensuring that the spectral line mixing at normal pressure will not affect the measurement accuracy;

[0063] Step B3. The absorption line strength of each spectral line in each combination is as high as possible to ensure that the system has good detection sensitivity;

[0064] Step B4. Considering the isotopic abundance of each molecule, the absorption depths of the individual spectral lines within the combination should not differ significantly, ensuring a good signal-to-noise ratio for all detected spectral lines.

[0065] Step B5. Ensure that each spectral line combination is free from absorption interference from other molecules with high atmospheric abundance.

[0066] Step B6. The lower energy level of each selected spectral line should be as small as possible, thereby effectively reducing the impact of line intensity changes caused by ambient temperature changes on measurement accuracy.

[0067] Furthermore, the inversion of the concentration in step F is carried out in the following steps:

[0068] Step F1. For the vacuum treatment of the integrating chamber, CO2, CH4, N2O, and N2 are used to prepare CO2-CH4-N2O-N2 mixed gases of different concentrations. The integrating chamber is filled with 450ppm-2ppm-0.4ppm, 600ppm-3ppm-0.5ppm, 700ppm-4ppm-0.6ppm, 800ppm-5ppm-0.7ppm, and 900ppm-6ppm-0.8ppm of carbon dioxide-methane-nitrous oxide-nitrogen (CO2-CH4-N2O-N2) mixed gases, respectively;

[0069] Step F2. Synchronously collect the outgoing signal, triangular wave signal, and sine wave signal after multiple reflections of the mixed gas, demodulate the collected signal from the sample integrating cavity at the corresponding sine wave modulation frequency, and obtain the desired second harmonic signal of the CO2-CH4-N2O-N2 mixed gas;

[0070] Step F3. Calibrate the system: Give the relationship between the second harmonic signal peak height and concentration at the five concentrations in step F1; perform polynomial fitting on the peak heights at the five concentrations measured in step F1 to obtain the calibration formula:

[0071] X=-1.2722+65.3014X P-504.2734 XP 2 +2444.9629 XP 3

[0072] Where: X represents the corresponding gas concentration, P represents the peak-to-peak value of the second harmonic, and the peak-to-peak value of the second harmonic represents the peak height of the WMS-2f signal. The parameters are obtained by first calibrating the system with a set of gases of known concentration to obtain the relationship between the peak height of the WMS-2f signal and the concentration (called the calibration formula). During measurement, the concentration of the measured gas is inverted by the calibration formula. The experiment measured 5 concentrations of CO2-CH4-N2O-N2 mixed gas and calibrated the system. The relationship between the peak height of the WMS-2f signal obtained under the above 5 concentrations and the concentration is obtained, and the linear correlation R 2 =0.991. A cubic polynomial was fitted to the peak heights at all measured concentrations, and the correlation obtained was R 2 =0.996;

[0073] At this point, the system calibration is completed, and the calibration formula is the following cubic polynomial:

[0074]

[0075] Step F4. Measure the CO2-CH4-N2O-N2 mixed gas of any concentration, and use the calibration formula in step F3 to invert the concentration of at least one of the gases CO2, CH4, and N2O in the CO2-CH4-N2O-N2 mixed gas to be measured. Beneficial effects

[0076] 1. The present invention utilizes an integrating cavity based on a bidirectional cavity enhancement mode to achieve simultaneous and spatial detection of three greenhouse gases, namely CO2, CH4 and N2O, and some of their isotopes, greatly improving the utilization efficiency of the integrating cavity, achieving a fast response time, saving detection costs, and expanding the application range of OA-CEAS equipment.

[0077] 2. This device uses frequency division multiplexing assisted wavelength modulation absorption spectroscopy technology for detection, which can achieve the simultaneous coupling of multiple lasers in the same integrating cavity.

[0078] 3. By placing a concave mirror, the light beam reflected by the first concave mirror is reflected back into the integrating cavity again, which plays the role of light intensity re-injection.

[0079] 4. Using RF white noise to perturb the laser's operating linewidth, the longitudinal mode noise suppression technology uses RF white noise to perturb the laser's modulated current, reducing the laser's coherence by changing its output spectral linewidth. This weakens or even eliminates the interference effect when the beams overlap within the cavity, depriving the laser of the possibility of coupling resonance with the integrating cavity, thereby suppressing noise and improving the signal-to-noise ratio. The introduction of frequency division multiplexing and wavelength modulation technology can greatly enhance the system's detection sensitivity. These features not only improve the system's detection performance but also effectively reduce the system's measurement costs.

[0080] Advantages: The bidirectional transmission mode within the integrating cavity helps improve detection sensitivity by utilizing denser high-order transverse modes. However, since narrow-linewidth lasers also generate a large number of longitudinal modes within the integrating cavity, the longitudinal mode noise is exacerbated when multiple lasers operate together. This paper proposes a longitudinal mode noise suppression technique based on RF white noise perturbing the laser's operating linewidth. This technique uses RF white noise to perturb the laser's modulation current, weakening the laser's coherence by changing its output spectral linewidth. This weakens or even eliminates the interference effect when the beams overlap within the cavity, making it impossible for the laser to couple and resonate with the integrating cavity. The signal output by the RF white noise source is filtered by a low-pass filter and then input into the laser circuit through a Bias-Tee. Together with the controller, it controls the laser's output, thereby changing the linewidth of its output spectrum. This paper combines theory and experiment to analyze the relationship between the laser's operating linewidth, the integrating cavity mode noise, and the integrated output signal signal-to-noise ratio under white noise of different powers and frequencies, and obtains the optimal RF noise modulation parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] FIG1 is a schematic structural diagram of a carbon and nitrogen emission collaborative detection device according to the present invention;

[0082] FIG2 is a schematic diagram of a noise suppression method for a dual-beam hybrid laser according to the present invention.

[0083] FIG3 is a schematic diagram of the carbon and nitrogen emission coordinated measurement method of the present invention.

[0084] In the figure: 1—sine wave generator, 2—sawtooth wave generator, 3—adder, 4—first laser controller, 5—second laser controller, 6—third laser controller, 7—first quantum cascade laser, 8—second quantum cascade laser, 9—third quantum cascade laser, 10—beam combiner, 11—collimator, 12—first concave mirror, 13—gas absorption cell, 14—first filter, 15—first photodetector, 16—second concave mirror, 17—second filter, 18—second photodetector, 19—data acquisition card, 20—computer. Modes for Carrying Out the Invention

[0085] The present invention will be further explained below with reference to the accompanying drawings.

[0086] By precisely selecting the detection spectral lines, two laser groups can simultaneously detect all detectable molecules and their isotopes. A coordinated carbon and nitrogen emissions detection device is provided that achieves simultaneous high-frequency and spatial detection of three important greenhouse gases: CO2 (carbon dioxide), CH4 (methane), and N2O (nitrous oxide) within the same integrating cavity.

[0087] The present invention adopts the following technical solution: a carbon and nitrogen emission collaborative detection device for simultaneously monitoring three gases: CO2, CH4 and N2O.

[0088] The device includes an integrating cavity, a single-beam laser and a double-beam hybrid laser respectively arranged at opposite ends of the integrating cavity, and an information acquisition and analysis system. The single-beam laser and the double-beam hybrid laser are respectively used to continuously emit transmission laser beams to the integrating cavity; the integrating cavity includes a gas absorption cell with a CO2-CH4-N2O-N2 mixed gas, the double-beam hybrid laser is located at the left end of the gas absorption cell, and the single-beam laser is located at the right end of the gas absorption cell; the information acquisition and analysis system includes a first concave mirror arranged on the optical path between the double-beam hybrid laser and the gas absorption cell, A second concave mirror is placed on the optical path between the single-beam laser and the gas absorption cell, a first filter and a first photodetector are arranged in sequence on the reflected optical path of the first concave mirror, a second filter and a second photodetector are arranged in sequence on the reflected optical path of the second concave mirror, an acquisition card is connected to the first photodetector and the second photodetector respectively, and a computer is connected to the acquisition card; an incident hole is provided on the first concave mirror and the second concave mirror respectively, the concave surface of the first concave mirror and the concave surface of the second concave mirror are both inclined relative to the gas absorption cell, and the concave surface of the first concave mirror is used to pass through the gas absorption cell. The laser beam of the absorption cell is reflected onto the first filter, and the concave surface of the second concave mirror reflects the laser beam passing through the gas absorption cell onto the second filter; the first concave mirror allows the laser of the dual-beam hybrid laser to pass through and enter the gas absorption cell through the incident hole, and the concave surface of the first concave mirror reflects the light reflected by the gas absorption cell to the first filter. The laser beam within the wavelength range of the first filter will pass through the first filter and enter the first photodetector, and the laser beam outside the wavelength range of the first filter will be reflected back to the gas absorption cell along the original path; the second concave mirror allows the single-beam hybrid laser to pass through the incident hole The laser of the dual-beam hybrid laser passes through and enters the gas absorption cell, and at the same time reflects the light fed back by the gas absorption cell to the second filter. In this process, the laser beam within the wavelength range of the second filter will pass through the two filters and enter the second photodetector, and the laser beam outside the wavelength range of the second filter will be reflected back to the gas absorption cell along the original path. The wavelength ranges of the first filter and the second filter are different. The wavelength of the laser beam emitted by the dual-beam hybrid laser is within the wavelength range of the first filter, and the wavelength of the laser beam emitted by the single-beam laser is within the wavelength range of the second filter.

[0089] in:

[0090] The computer collects the voltage signals of the first photodetector and / or the second photodetector through the acquisition card, and calculates the concentrations of CO2, CH4, N2O, etc. in the CO2-CH4-N2O-N2 mixed gas to be measured based on the voltage signals.

[0091] The length of the gas absorption cell is 30 cm.

[0092] The gas absorption tank is filled with a mixture of carbon dioxide, methane, nitrous oxide and nitrogen.

[0093] The first and second concave mirrors are both silver-coated concave spherical mirrors.

[0094] The coordinated detection device for carbon and nitrogen emissions also includes a narrow-band filter that can serve as the first filter and the second filter. The first filter corresponding to the wavelength of the opposite laser beam is placed in front of the first photodetector, and the second filter corresponding to the wavelength of the opposite laser beam is placed in front of the second photodetector. At the same time, the filter can be used to reflect the light beam outside the bandpass wavelength, thereby achieving a re-injection enhancement effect on the light beam on this side.

[0095] As a preferred technical solution of the present invention: the first quantum cascade laser, the second quantum cascade laser and the third quantum cascade laser all adopt DFB tunable semiconductor lasers. Example

[0096] As shown in Figures 1 and 2, the carbon and nitrogen emission coordinated detection device of the present invention includes a laser group, a gas absorption cell and an information acquisition and analysis system.

[0097] Specifically, the carbon and nitrogen emission collaborative detection device includes a sine wave generator 1, a sawtooth wave generator 2, an adder 3, a first laser controller 4, a second laser controller 5, a third laser controller 6, a first quantum cascade laser 7, a second quantum cascade laser 8, a third quantum cascade laser 9, a combiner 10, a collimator 11, a first filter 14, and a second filter 17. Sine wave generator 1 is a function generator RIGOL DG1000Z1. The technical parameters are as follows: the sine wave frequency is 12 kHz, and a function signal generator model F05 can be selected. The technical parameters of sawtooth wave generator 2 are as follows: the sawtooth wave frequency is 30 Hz, and a function signal generator model F05 can be selected. The technical parameters of the laser controller are as follows: the temperature adjustment range is 20-30 °C, the step size is 0.5 °C, and the accuracy is 0.005 °C. The current tuning range is 20-110 mA, and the accuracy is 0.001 mA. An ITC-4002QCL controller can be selected. The technical parameters of the first quantum cascade laser 7 are as follows: the central wavelength is 3.3 μm, and the maximum output power is 5 mW. The technical parameters of the second quantum cascade laser 8 are as follows: the central wavelength is 4.3 μm, and the maximum output power is 5 mW. The technical parameters of the third quantum cascade laser 9 are as follows: the central wavelength is 4.5 μm, and the maximum output power is 5 mW.

[0098] In this embodiment, the gas absorption cell is filled with a mixture of carbon dioxide, methane, nitrous oxide, and nitrogen. The concentrations of carbon dioxide, methane, and nitrous oxide can be calculated based on the volume ratios of carbon dioxide, methane, and nitrous oxide, respectively. The long-range gas absorption cell 13 comprises a cylindrical cavity made of Pyrex glass with a volume of 3.2 L. The ends of the cylindrical cavity are provided with a light inlet and a light outlet. The sides of the cylindrical cavity are provided with an air extraction port and an air inlet, both of which are equipped with needle valves. A discrete concave mirror is positioned near each end of the cylindrical cavity, with a distance of 55 cm between the two discrete concave mirrors.

[0099] The information acquisition and analysis system includes a first photodetector 15, a second photodetector 18, a data acquisition card 19, and a computer 20. The technical specifications of the first and second photodetectors 15 and 18 are as follows: a response band of 1200-1800 nm, and 2011-type InGaAs photodetectors are available. The data acquisition card 19 also features a PCI bus, plug-and-play support, two 12-bit D / A outputs, eight phase-difference analog inputs, a 16-bit counter, and 16 programmable switches. The acquisition and conversion functions support various triggering modes, and an AC6115 data acquisition card is available.

[0100] Working principle:

[0101] Working principle of the present invention:

[0102] Step F1. Vacuum the sample cell pipes and prepare carbon dioxide-methane-nitrous oxide-nitrogen gas mixtures of varying concentrations using carbon dioxide, methane, nitrous oxide, and high-purity nitrogen. Fill the sample cell with carbon dioxide-methane-nitrous oxide-nitrogen (CO2-CH4-N2O-N2) gas mixtures at concentrations of 450 ppm-2 ppm-0.4 ppm, 600 ppm-3 ppm-0.5 ppm, 700 ppm-4 ppm-0.6 ppm, 800 ppm-5 ppm-0.7 ppm, and 900 ppm-6 ppm-0.8 ppm, respectively.

[0103] Step F2. Synchronously collect the outgoing signal after multiple reflections from the sample, as well as the triangular wave signal and the sine wave signal, and demodulate the collected signal from the sample cell at the corresponding sine wave modulation frequency to obtain the desired second harmonic signal of the target gas;

[0104] Step F3. Calibrate the system to obtain the relationship between the peak height of the second harmonic signal and the concentration at the five concentrations in step E; perform a polynomial fit on the peak heights at all measured concentrations to obtain a calibration formula;

[0105] Step F4. Measure the CO2-CH4-N2O-N2 mixed gas of any concentration using the calibration formula in step F3: X = -1.2722 + 65.3014X P - 504.2734 XP 2 +2444.9629 XP 3 , and the concentration of the CO2-CH4-N2O-N2 mixed gas to be measured is inverted.

[0106] The outputs of sine wave generator 1 and sawtooth wave generator 2 are connected to adder 3 and the input of data acquisition card 19, respectively. The output of adder 3 is connected to the input of laser controller 4. The output of first laser controller 4 is connected to first quantum cascade laser 7, and the output of second laser controller 5 is connected to second quantum cascade laser 8. The light output from first quantum cascade laser 7 and second quantum cascade laser 8 passes through beam combiner 10. After passing through collimator 11, the light passes through first concave reflector 12, gas absorption cell 13, second concave reflector 16, first filter 14, and first photodetector 15. The output of third laser controller 6 is connected to third quantum cascade laser 9. After passing through the collimator, the light from third quantum cascade laser 9 is incident on second concave reflector 16, gas absorption cell 13, first concave reflector 12, second filter 17, and second photodetector 18 in sequence. The outputs of first and second photodetectors are both connected to the input of the data acquisition card, which in turn connects to the input of a computer. This invention uses frequency division multiplexing and wavelength modulation spectroscopy. This is achieved by loading a high-frequency sinusoidal modulation signal into the laser's injection current, causing the laser output to sinusoidally jitter near its optical frequency. During signal demodulation, only a narrow bandwidth signal near the second harmonic of the modulation frequency is extracted, achieving a tuning range close to the absorption line of the target gas. This suppresses noise signals in most other frequency bands and significantly improves the signal-to-noise ratio.

[0107] At the same time, a lower-frequency sawtooth wave is added to the laser's injection current, allowing the laser's output center wavelength to completely scan the gas absorption spectrum. The two absorption light signals are converted into voltage signals by a photodetector and collected by a data card, ultimately being sent to a computer 20 for processing. Using LabVIEW, the signals are acquired through the acquisition card and fed into a digital phase-locked system. The signals are demodulated based on the different modulation frequencies of the two lasers. Subsequently, the collected signals undergo wavelet denoising and Kalman filtering to obtain the second harmonic signals of each detection spectrum line.

[0108] First, a series of CO2-CH4-N2O-N2 mixed gas spectra of different concentrations within the laser setting range were tested, and some spectral line pairs with high correlation were selected. Models were established for these spectral line pairs to invert the concentrations of carbon monoxide and methane, and obtain a calibration formula. The CO2-CH4-N2O-N2 mixed gas of arbitrary concentration was measured, and the calibration formula was used to invert the concentrations of the measured gases CO2, CH4 and N2O.

[0109] As shown in FIG3 , the present invention designs a method for collaboratively measuring carbon and nitrogen emissions, which specifically includes the following steps:

[0110] Step A. Determine the optimal structural parameters of the curvature radius of the first concave mirror and the second concave mirror, the spacing and angle between the concave reflector and the cavity mirror in the integrating cavity, and the optimal positions of the first photodetector and the second photodetector using optical design software;

[0111] Step B. Establishing atmospheric transmittance models for CO2, CH4, and N2O molecules and their selected isotope molecules, and selecting spectral detection windows and target spectral line combinations suitable for simultaneous detection of CO2, CH4, and N2O molecules and their isotope molecules for each of the three greenhouse gases;

[0112] Step C. The sine wave generator generates a high-frequency sine wave, the sawtooth wave generator generates a low-frequency triangular wave, and a dual-beam hybrid laser and a single-beam laser are used to receive the superposition signal of the high-frequency sine wave and the low-frequency triangular wave respectively to work and generate laser beams respectively; wherein, the first quantum cascade laser and the second quantum cascade laser of the dual-beam hybrid laser with similar wavelengths are placed on the same side, and the two laser beams are coupled through a fiber coupler, and then collimated by a collimator 11, and then coupled through the incident hole on the concave reflector on the same side of the integrating cavity according to the appropriate position and off-axis angle. The third quantum level laser of the single beam laser is set on the other side of the integrating cavity, and after being collimated by the collimator, it is coupled into the integrating cavity according to the appropriate position and off-axis angle through the incident hole on the concave reflector on the same side of the integrating cavity; the two laser beams enter from both sides of the integrating cavity, and respectively pass through the integrating cavity with the gas to be detected, and are converged and reflected by the concave reflector on the side of the exit cavity mirror. The opposite beam is filtered out by the narrow band filter of the corresponding wavelength, received by the photodetector, and demodulated by the phase-locked amplifier to obtain two spectral lines corresponding to CO2 (the two spectral lines are consistent with the CO2 emission). 16 O 12 C 16 O and 16 O 13 C 16 O respectively), two spectral lines corresponding to CH4 (these two spectral lines correspond to 12 CH4 and 13CH4) and three spectral lines corresponding to N2O (the three spectral lines are 14 N2 16 O. 14 N 15 N 16 O and 15 N 14 N 16 O respectively);

[0113] Step D. For the two spectral lines corresponding to CO2, two spectral lines corresponding to CH4, and three second harmonic signals corresponding to N2O obtained for the target greenhouse gas, background signals are removed to obtain absorption-related signals corresponding to the seven spectral lines. To improve system sensitivity, a pentavalent wavelet denoising method is used to reduce noise in the WMS-2f signal measured by the photodetector;

[0114] Step E. Based on the pressure and temperature information in the integrating cavity, obtaining the absorption state signals in the second harmonic signals of the spectral lines corresponding to CO2, CH4 and N2O respectively under the same temperature and pressure environment;

[0115] Step F: Perform inversion calculations on the peak values ​​of the absorption-related signals corresponding to CO2, CH4, N2O and some of their isotopes to obtain the concentrations of CO2, CH4 and N2O, respectively.

[0116] Furthermore, the optimal structural parameters in step A are determined using the following method:

[0117] Matlab was used to simulate and analyze the intracavity light field using an eccentric Gaussian beam. The intracavity light field in the bidirectional mode can be described by the sum of the incident light fields on both sides:

[0118] ,

[0119] ,

[0120] At this time, the light field of the light spot after any N reflections on the cavity mirror can be obtained from the light field matrix M of the first light spot

[0121] ,

[0122] By calculating the vector sum of all the light fields on the cavity mirror, the total light field emitted by the cavity mirror on one side of the integrating cavity can be obtained.

[0123] ,

[0124] Then the transmittance spectrum on one side of the integrating cavity is obtained from the output and input power

[0125] ,

[0126] To improve computational efficiency, the cavity mirror is divided into a series of grids during the simulation process. Only the light field at the grid points is considered during calculations, and the total power is obtained by multiplying the irradiance at the grid points by the area of ​​the grid. By varying parameters such as cavity length, cavity mirror curvature radius, incident beam diameter, off-axis angle of the incident light on both sides, and incident position, Airy functions are used to simulate and analyze the intracavity light field and transmittance spectrum under various conditions. By balancing the optimal optical path with the optimal signal-to-noise ratio, the optimal structural parameters for the bidirectionally coupled detection mode are obtained.

[0127] Furthermore, specifically, the criteria followed in selecting the target spectral line in step B are as follows: the spectral detection window and target spectral line combination suitable for simultaneous detection of the molecule and its isotope molecules are:

[0128] Step B1. The selected absorption line combinations of CO2, CH4 and N2O molecules and their isotopes should be distributed within 2 cm -1 Within the range to ensure full coverage by a single scan of the laser;

[0129] Step B2. Based on the absorption band distribution of each molecule and its isotope, analyze the band mixing effect between each band to ensure that the spacing between the spectral lines in each combination is not less than 0.1 cm -1 , ensuring that the spectral line mixing at normal pressure will not affect the measurement accuracy;

[0130] Step B3. The absorption line strength of each spectral line in each combination is as high as possible to ensure that the system has good detection sensitivity;

[0131] Step B4. Considering the isotopic abundance of each molecule, the absorption depths of the individual spectral lines within the combination should not differ significantly, ensuring a good signal-to-noise ratio for all detected spectral lines.

[0132] Step B5. Ensure that each spectral line combination is free from absorption interference from other molecules with high atmospheric abundance.

[0133] Step B6. The lower energy level of each selected spectral line should be as small as possible, thereby effectively reducing the impact of line intensity changes caused by ambient temperature changes on measurement accuracy.

[0134] Further, specifically, the inversion of the concentration in step F is carried out in the following steps:

[0135] Step F1. For the vacuum treatment of the integrating chamber, CO2, CH4, N2O, and N2 are used to prepare CO2-CH4-N2O-N2 mixed gases of different concentrations. The integrating chamber is filled with 450ppm-2ppm-0.4ppm, 600ppm-3ppm-0.5ppm, 700ppm-4ppm-0.6ppm, 800ppm-5ppm-0.7ppm, and 900ppm-6ppm-0.8ppm of carbon dioxide-methane-nitrous oxide-nitrogen (CO2-CH4-N2O-N2) mixed gases, respectively;

[0136] Step F2. Synchronously collect the outgoing signal, triangular wave signal, and sine wave signal after multiple reflections of the mixed gas, demodulate the collected signal from the sample integrating cavity at the corresponding sine wave modulation frequency, and obtain the desired second harmonic signal of the CO2-CH4-N2O-N2 mixed gas;

[0137] Step F3. Calibrate the system: Give the relationship between the second harmonic signal peak height and concentration at the five concentrations in step F1; perform polynomial fitting on the peak heights at the five concentrations measured in step F1 to obtain the calibration formula:

[0138] X=-1.2722+65.3014X P-504.2734 XP 2 +2444.9629 XP 3

[0139] Where: X represents the corresponding gas concentration, P represents the peak-to-peak value of the second harmonic, and the peak-to-peak value of the second harmonic represents the peak height of the WMS-2f signal. The parameters are obtained by first calibrating the system with a set of gases of known concentration to obtain the relationship between the peak height of the WMS-2f signal and the concentration (called the calibration formula). During measurement, the concentration of the measured gas is inverted by the calibration formula. The experiment measured 5 concentrations of CO2-CH4-N2O-N2 mixed gas and calibrated the system. The relationship between the peak height of the WMS-2f signal obtained under the above 5 concentrations and the concentration is obtained, and the linear correlation R 2 =0.991. A cubic polynomial was fitted to the peak heights at all measured concentrations, and the correlation obtained was R 2 =0.996;

[0140] At this point, the system calibration is completed, and the calibration formula is the following cubic polynomial:

[0141]

[0142] Step F4. Measure a CO2-CH4-N2O-N2 mixed gas of any concentration, and use the calibration formula in step F3 to invert the concentration of at least one of CO2, CH4, and N2O in the CO2-CH4-N2O-N2 mixed gas to be measured.

[0143] The above-described technical solution designs a coordinated carbon and nitrogen emissions measurement method, based on the bidirectionally coupled detection mode OA-CEAS, capable of simultaneously detecting the concentrations of three important greenhouse gases, CO2, CH4, and N2O, and some of their molecular isotopes, at the ppb level. The technical features of the above embodiments may be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as these technical features do not conflict with each other, they should be considered within the scope of this specification.

[0144] The above-described embodiments merely represent several embodiments of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A carbon and nitrogen emission coordinated detection device, characterized in that: The device comprises an integrating cavity, a single-beam laser and a double-beam hybrid laser respectively arranged at two opposite ends of the integrating cavity, and an information acquisition and analysis system, wherein the single-beam laser and the double-beam hybrid laser are respectively used to continuously emit a transmission laser beam to the integrating cavity; The integrating cavity includes a gas absorption cell having a CO2-CH4-N2O-N2 mixed gas, a double-beam mixing laser is located at the left end of the gas absorption cell, and a single-beam laser is located at the right end of the gas absorption cell; The information acquisition and analysis system comprises a first concave mirror arranged on the optical path between the dual-beam hybrid laser and the gas absorption cell, a second concave mirror arranged on the optical path between the single-beam laser and the gas absorption cell, a first filter and a first photodetector arranged in sequence on the reflected optical path of the first concave mirror, a second filter and a second photodetector arranged in sequence on the reflected optical path of the second concave mirror, an acquisition card connected to the first photodetector and the second photodetector respectively, and a computer connected to the acquisition card; The first concave mirror and the second concave mirror are respectively provided with incident holes, the concave surface of the first concave mirror and the concave surface of the second concave mirror are both arranged obliquely relative to the gas absorption cell, the concave surface of the first concave mirror is used to reflect the laser beam passing through the gas absorption cell onto the first filter, and the concave surface of the second concave mirror is used to reflect the laser beam passing through the gas absorption cell onto the second filter; The first concave mirror allows the laser of the dual-beam hybrid laser to pass through and enter the gas absorption cell through the incident hole. The concave surface of the first concave mirror reflects the light reflected by the gas absorption cell to the first filter. The laser beam within the wavelength band of the first filter will pass through the first filter to enter the first photodetector, and the laser beam of the laser outside the wavelength band of the first filter will be reflected back to the gas absorption cell along the original path. The second concave mirror allows the laser of the single-beam laser to pass through and enter the gas absorption cell through the incident hole, and at the same time reflects the light fed back by the gas absorption cell to the second filter. In this process, the laser beam within the wavelength band of the second filter will pass through the two filters to enter the second photodetector, and the laser beam of the laser outside the wavelength band of the second filter will be reflected back to the gas absorption cell along the original path. The first filter and the second filter have different wavelength ranges, the wavelength of the laser beam emitted by the dual-beam hybrid laser is within the wavelength range of the first filter, and the wavelength of the laser beam emitted by the single-beam laser is within the wavelength range of the second filter; in: The computer collects the voltage signal of the first photodetector and / or the second photodetector through the acquisition card, and the computer calculates the concentration of CO2, CH4, N2O, etc. in the CO2-CH4-N2O-N2 mixed gas to be measured based on the voltage signal.

2. The carbon and nitrogen emission coordinated detection device according to claim 1, characterized in that: The carbon-nitrogen emission collaborative detection device further includes a sine wave generator, a sawtooth wave generator, an adder and a collimator, and the dual-beam hybrid laser includes a first laser controller, a second laser controller, a first quantum cascade laser, a second quantum cascade laser and a beam combiner; The outputs of the sine wave generator 1 and the sawtooth wave generator are processed by signal superposition through an adder to generate a laser driving signal. The adder is used to output the laser driving signal to the first laser controller or the second laser controller. The first laser controller is connected to the first quantum cascade laser, and the second laser controller is connected to the second quantum cascade laser. The output ends of the first quantum cascade laser 7 and the second quantum cascade laser are connected to a collimator pointing to the left end of the gas absorption cell through a beam combiner. The sine wave generator 1 is a phase-locked amplifier, the sawtooth wave generator is a function generator, and the first quantum cascade laser and the second quantum cascade laser are both DFB tunable semiconductor lasers.

3. The carbon and nitrogen emission coordinated detection device according to claim 2, characterized in that: The single-beam laser includes a third laser controller and a third quantum cascade laser connected to the third laser controller. The adder is used to output a laser driving signal to the third laser controller. The output end of the third quantum cascade laser points to the right end of the gas absorption cell.

4. The carbon and nitrogen emission coordinated detection device according to claim 3, characterized in that: The first laser controller outputs a driving current signal under the drive of the laser driving signal to control the output of the first quantum cascade laser 7, and / or the second laser controller outputs a driving current signal under the drive of the laser driving signal to control the output of the second quantum cascade laser, and / or the third laser controller outputs a driving current signal under the drive of the laser driving signal to control the output of the third quantum cascade laser; the capacitor of the bias device is used to filter out the DC bias in the white noise signal, and superimpose the white noise signal emitted by the white noise source with the driving current signal.

5. The carbon and nitrogen emission coordinated detection device according to claim 4, characterized in that: White noise sources include lock-in amplifiers, signal generators, and RF noise sources; The phase-locked amplifier and the signal generator process the signals by adding a signal to form a laser driving signal; the radio frequency noise source adds radio frequency noise to the laser driving signal, and the radio frequency noise is filtered by a low-pass filter and input into the bias device together with the driving current signal. The driving current signal superimposed with the radio frequency noise after passing through the bias device is used to control the first quantum cascade laser, the second quantum cascade laser or the third quantum cascade laser to work; Among them, the modulation signal of the laser consists of two parts: A part of the modulation signal is superimposed by a sine wave generated by a phase-locked amplifier and a triangular wave generated by a signal generator through an adder to serve as a laser driving signal, and the part of the modulation signal is sent to at least one of the first laser controller, the second laser controller and the third laser controller; and, Another part of the modulation signal is a white noise signal emitted by a radio frequency noise source. After passing through a low-pass filter, the modulation signal is superimposed with a driving current signal generated by one of the first laser controller, the second laser controller and the third laser controller through a bias device to control the first quantum cascade laser or the second quantum cascade laser. The sine wave and the triangle wave are superimposed by the adder to achieve the wavelength modulation of the signal, and the white noise signal emitted by the radio frequency noise source is used to suppress the integrated cavity mode noise.

6. The carbon and nitrogen emission coordinated detection device according to claim 1, characterized in that: The first concave mirror and the second concave mirror are both silver-coated concave spherical mirrors; the length of the gas absorption cell is 30 cm.

7. A detection method using the carbon and nitrogen emission coordinated detection device according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: The gas absorption cell is filled with the mixed gas to be detected, including CO2, CH4, N2O and N2; The output ends of the sine wave generator and the sawtooth wave generator are connected to the adder and the input end of the data acquisition card respectively; Connecting the adder output terminal to the first laser controller input terminal, the second laser controller input terminal, or the third laser controller input terminal; The output end of the first laser controller is connected to the first quantum cascade laser, and the output end of the second laser controller is connected to the second quantum cascade laser. The laser beams output by the first quantum cascade laser and the second quantum cascade laser pass through a beam combiner. The light passing through the beam combiner passes through a first concave reflector, a gas absorption cell, a second concave reflector, a first filter, and a first photodetector in sequence after passing through a collimator. The output end of the third laser controller is connected to the third quantum cascade laser. The laser beam output by the third quantum cascade laser passes through the collimator, and then passes through the second concave reflector, the gas absorption cell, the first concave reflector, and the second filter in sequence to be incident on the second photodetector. A high-frequency sinusoidal wave modulation signal is loaded into at least one injection current of the first laser controller, the second laser controller and the third laser controller, so that the laser beam output by at least one of the first laser controller, the second laser controller and the third laser controller performs sinusoidal jitter near its optical frequency, and a signal with a very narrow bandwidth near the second harmonic of the modulation frequency is extracted when demodulating the signal; Loading a low-frequency sawtooth wave into at least one of the injection currents of the first laser controller, the second laser controller, and the third laser controller, so that the central wavelength output by the dual-beam hybrid laser can completely scan the gas absorption spectrum; The output ends of the first photodetector and the second photodetector are both connected to the input end of the data acquisition card, and the output end of the data acquisition card is connected to the input end of the computer; the two absorption light signals are converted into voltage signals after passing through the first photodetector and the second photodetector and are collected by the data card, and the computer uses LabVIEW software to obtain the signal through the acquisition card and then sends it to the digital phase lock, and according to the different modulation frequencies of the dual-beam hybrid laser and the single-beam laser, the voltage signals detected by the first photodetector and the second photodetector are demodulated respectively, and the second harmonic signal obtained by demodulation at the double frequency according to the corresponding modulation frequency by the phase-locked amplifier is subjected to wavelet denoising and Kalman filtering to obtain the second harmonic signals of the CO2, CH4 and N2O absorption spectra; The different modulation frequency parameters of the dual-beam hybrid laser and the single-beam laser are 30Hz, 1V sawtooth wave superimposed on 12kHz, 150mV sine wave and 10Hz, 100mV sawtooth wave superimposed on 8kHz, 50mV sine wave; A series of absorption spectra of CO2-CH4-N2O-N2 mixed gases with different concentrations within the setting range of the dual-beam hybrid laser and the single-beam laser were tested, and the spectral line pairs with high correlation were selected. The relationship model between the peak value of the second harmonic and the corresponding concentration was established for these spectral line pairs, and the direct absorption and second harmonic signals of the corresponding gases were simulated. The signals were fitted with the actual measured signals, and the following corresponding models were obtained, which are Y CO2 =1.827X CO2 +0.189, Y CH4 =0.00286X CH4 +0.30475, Y N2O =0.185X N2O +0.208, where Y represents the corresponding gas concentration and X represents the peak-to-peak value of the second harmonic. The CO2-CH4-N2O-N2 mixed gas of any concentration is measured, and the concentration of at least one of the gases among CO2, CH4 and N2O can be inverted by using the relationship model between the calibrated second harmonic peak-to-peak value and the corresponding concentration.

8. A method for collaboratively measuring carbon and nitrogen emission gas concentrations using the carbon and nitrogen emission collaborative detection device according to any one of claims 1 to 6, characterized in that: The steps include: Step A. Determine the optimal structural parameters of the curvature radius of the first concave mirror and the second concave mirror, the spacing and angle between the concave reflector and the cavity mirror in the integrating cavity, and the optimal position of the first photodetector and the second photodetector by optical design software; Step B. Establishing atmospheric transmittance models of CO2, CH4, and N2O molecules and their selected isotope molecules, and selecting spectral detection windows and target spectral line combinations suitable for simultaneous detection of CO2, CH4, and N2O molecules and their isotope molecules for the three greenhouse gases, respectively; Step C. The sine wave generator 1 generates a high-frequency sine wave, the sawtooth wave generator generates a low-frequency triangular wave, and a dual-beam hybrid laser and a single-beam laser are used to receive superposition signals of the high-frequency sine wave and the low-frequency triangular wave respectively to work and generate laser beams respectively; wherein, the first quantum cascade laser and the second quantum cascade laser of the dual-beam hybrid laser with similar wavelengths are placed on the same side, and the two laser beams are coupled through a fiber coupler, and then collimated by a collimator, and then coupled into the integrating cavity according to a suitable position and off-axis angle through an incident hole on the concave reflector on the same side of the integrating cavity; the single-beam laser is coupled into the integrating cavity according to a suitable position and off-axis angle. The third quantum level laser of the beam laser is arranged on the other side of the integrating cavity, and after being collimated by the collimator, it is coupled into the integrating cavity according to the appropriate position and off-axis angle through the incident hole on the concave reflector on the same side of the integrating cavity; the two laser beams enter from both sides of the integrating cavity, and after passing through the integrating cavity with the gas to be detected, they are converged and reflected by the concave reflector on the side of the exit cavity mirror, and the opposite beams are filtered out by the narrow band filter of the corresponding wavelength, and are received by the photodetector and demodulated by the phase-locked amplifier to obtain two spectral lines corresponding to CO2, two spectral lines corresponding to CH4 and three spectral lines corresponding to N2O; Step D. For the two spectral lines corresponding to CO2, two spectral lines corresponding to CH4, and three second harmonic signals corresponding to N2O obtained for the target greenhouse gas, the background signals are removed respectively to obtain the absorption-related signals corresponding to the seven spectral lines, and the five-valent wavelet denoising method is used to reduce the noise in the WMS-2f signal measured by the photodetector; Step E. Based on the air pressure and temperature information in the integration cavity, the absorption state signals in the second harmonic signals of the spectral lines corresponding to CO2, CH4 and N2O respectively under the same temperature and air pressure environment are obtained; Step F: Invert and calculate the peak values ​​of the absorption-related signals corresponding to CO2, CH4, N2O and some of their isotopes to obtain the concentrations of CO2, CH4 and N2O respectively.

9. The method for collaboratively measuring carbon and nitrogen exhaust gas concentration according to claim 8, characterized in that: The standard followed by the target spectral line selection in step B is the spectral detection window and target spectral line combination suitable for simultaneous detection of the molecule and its isotope molecule: Step B1. The selected absorption line combinations of CO2, CH4 and N2O molecules and their isotopes should be distributed in the range of 2 cm -1 within the scope; Step B2. Based on the absorption band distribution of each molecule and its isotope, analyze the band-head mixing effect between each band to ensure that the interval between the spectral lines in each combination is not less than 0.1 cm -1 ; Step B3. The absorption line strength of the spectral lines in each combination is as high as possible to ensure that the system has good detection sensitivity; Step B4. Under the premise of considering the isotopic abundance of each molecule, the absorption depth of each spectral line in the combination cannot differ too much, ensuring that all detection spectral lines have a good signal-to-noise ratio; Step B5. Try to avoid absorption interference from other molecules with high content in the atmosphere in each spectral line combination; Step B6. The lower energy level of each selected spectral line should be as small as possible, thereby effectively reducing the impact of line intensity changes caused by ambient temperature changes on measurement accuracy.

10. The method for collaboratively measuring carbon and nitrogen exhaust gas concentration according to claim 9, characterized in that: The inversion of concentration in step F is as follows: Step F1. For the vacuum treatment of the integral chamber, CO2, CH4, N2O and N2 are used to prepare CO2-CH4-N2O-N2 mixed gases of different concentrations; Step F2. synchronously collect the outgoing signal, triangular wave signal and sine wave signal after multiple reflections of the mixed gas, demodulate the collected signal from the sample integration cavity at the corresponding sine wave modulation frequency, and obtain the desired second harmonic signal of the CO2-CH4-N2O-N2 mixed gas; Step F3. Calibrate the system: give the relationship between the peak height of the second harmonic signal at 5 concentrations in step F1 and the concentration; perform polynomial fitting on the peak heights at 5 concentrations in step F1 to obtain a calibration formula, and calculate the concentration of at least one of CO2, CH4 and N2O in the CO2-CH4-N2O-N2 mixed gas to be measured according to the calibration formula; Step F4. Measure the CO2-CH4-N2O-N2 mixed gas of any concentration, and use the calibration formula in step F3 to invert the concentration of at least one of CO2, CH4 and N2O in the CO2-CH4-N2O-N2 mixed gas to be measured.

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