A gas parameter high-precision measurement system and method based on harmonic reconstruction principle

Abstract

This invention discloses a high-precision gas parameter measurement system and method based on the harmonic reconstruction principle, belonging to the field of data processing technology. The method includes the following steps: S1, processing the modulated transmittance signal to obtain harmonic curves from order 0 to k0; S2, obtaining the variation curves of each order harmonic with respect to the laser frequency based on the laser frequency variation signal and the harmonic curves from order 0 to k0; S3, determining the molecular absorption spectrum based on the variation curves of each order harmonic with respect to the laser frequency; S4, analyzing the molecular absorption spectrum to determine the physical parameters of the gas being measured. This invention retains the core advantages of wavelength modulation spectroscopy, such as high signal-to-noise ratio, strong anti-interference capability, and high measurement accuracy, while providing a new measurement method for high-precision calibration of spectral physical parameters, high-precision measurement of gas parameters under weak absorption conditions, and gas monitoring in complex industrial environments, effectively expanding the measurement efficiency and application scope of this technology.

Description

Technical Field

[0001] This invention belongs to the field of data processing technology, specifically relating to a high-precision gas parameter measurement system and method based on the harmonic reconstruction principle. Background Technology

[0002] In existing wavelength modulation spectroscopy (WMS) technology, the even-order harmonic curves (usually the second or fourth harmonic) obtained by phase-locked filtering are intermediate signals without clear physical meaning. They usually need to be pre-calibrated using a standard gas of known concentration under the same operating conditions, and then the concentration of the gas being measured is calculated based on the amplitude of its peak value. The operation process is complicated and can only measure the concentration of the gas.

[0003] In existing wavelength modulation spectroscopy (WMS) techniques, there is an improved method that uses the first harmonic to correct the second harmonic, eliminating the need for pre-calibration under weak absorption approximation conditions, namely the 2f / 1f calibration-free method. However, this method only uses the peak value of the harmonic signal and discards most of the information in the curve. Therefore, it can only reflect the concentration of the gas being measured under weak absorption conditions and cannot reflect other physical parameters and characteristics.

[0004] In addition, existing direct absorption spectroscopy (DAS) techniques, based on slow-scanning laser absorption signals, can obtain molecular absorption spectral functions with clear physical meaning, and directly measure information such as gas concentration, temperature, pressure, spectral line broadening, and line intensity. However, this method is easily affected by factors such as particulate matter, environmental vibration, and electromagnetic interference in actual measurements, resulting in low signal-to-noise ratio and accuracy. It is only suitable for calibrating spectral parameters under strong absorption conditions and cannot meet the high-precision measurement requirements under more demanding conditions such as weak absorption and strong interference. Summary of the Invention

[0005] To address the problem that harmonic signals obtained using wavelength modulation spectroscopy (WMS) in laser absorption spectroscopy (LAS) gas detection cannot fully reflect the physical properties and parameters of the gas being measured, this invention proposes a high-precision gas parameter measurement system and method based on the harmonic reconstruction principle.

[0006] The technical solution of the present invention is: a high-precision gas parameter measurement system based on the harmonic reconstruction principle, comprising a laser generation system, a laser detection system, and a signal acquisition and processing system;

[0007] The laser generation system is used to generate a voltage signal coupled with a slow scanning signal and a fast modulation signal, generate a driving current, and output a modulated laser signal.

[0008] The laser detection system receives the laser signal passing through the absorption gas cell optical path and the reference optical path, and obtains the target order harmonic signal through phase-locked filtering;

[0009] The signal acquisition and processing system performs spectral analysis to reproduce molecular absorption spectra.

[0010] Based on the above system, this invention also proposes a high-precision gas parameter measurement method based on the harmonic reconstruction principle, comprising the following steps:

[0011] S1. Process the modulation transmittance signal to obtain the harmonic curves of order 0 to k0;

[0012] S2. Based on the laser frequency change signal and the harmonic curves of orders 0 to k0, obtain the curves of each order of harmonics changing with the laser frequency.

[0013] S3. Determine the molecular absorption spectrum based on the curves of the change of each harmonic with the laser frequency;

[0014] S4. Analyze the molecular absorption spectrum to determine the physical parameters of the gas being measured.

[0015] Furthermore, in S1, the modulated transmittance signal is subjected to circuit or digital phase-locked filtering to obtain harmonic curves of order 0 to k0.

[0016] Furthermore, in S2, the laser frequency change signal The expression is:

[0017] ;

[0018] in, The center wavelength of the laser. For wavelength modulation amplitude, For modulation frequency, For time.

[0019] Furthermore, in S3, the curves of the change of laser frequency by each order harmonic are reconstructed using Chebyshev polynomials, the transmittance-frequency curve is calculated, and the logarithm of the transmittance-frequency curve is taken to obtain the corresponding molecular absorption spectrum.

[0020] Furthermore, in S3, the expression for refactoring is:

[0021] ;

[0022] in, The result of reconstructing the normalized frequency variables. The amplitude of each harmonic of transmittance, For harmonic orders, This is a normalized frequency variable.

[0023] Furthermore, in S3, the expression for the transmittance-frequency curve is:

[0024] ;

[0025] in, For laser transmittance, The transmitted intensity of the laser. The incident intensity of the laser. Let absorptivity function, The amplitude of each harmonic of transmittance, For modulation frequency, For time, For harmonic orders, The center wavelength of the laser. For frequency.

[0026] Furthermore, in S3, the expression for the molecular absorption spectral line is:

[0027] ;

[0028] in, The amplitude of the 0th harmonic of transmittance. The amplitude of each harmonic of transmittance, The center wavelength of the laser. For wavelength modulation amplitude, For phase, For harmonic orders, Transmittance.

[0029] The beneficial effects of this invention are: while retaining the core advantages of wavelength modulation spectroscopy, such as high signal-to-noise ratio, strong anti-interference ability, and high measurement accuracy, this invention can provide new measurement methods for high-precision calibration of spectral physical parameters, high-precision measurement of gas parameters under weak absorption conditions, and gas monitoring in complex industrial sites, effectively expanding the measurement efficiency and application scope of this technology. Attached Figure Description

[0030] Figure 1 A flowchart illustrating a high-precision gas parameter measurement method based on the harmonic reconstruction principle;

[0031] Figure 2 Diagram of WMS technology system device;

[0032] Figure 3 (a) is a graph showing the relationship between frequency modulation and light intensity modulation at different frequencies of the spectral line over time;

[0033] Figure 3 (b) is a schematic diagram of the transmittance function A0~A4 harmonic signals (m=2.2);

[0034] Figure 4 Centered on points O1~O5, A0~A 10 A schematic diagram of transmittance information (m=2.2) obtained from subharmonic reconstruction;

[0035] Figure 5 Centered on 101 points, A0~A 10 A schematic diagram of transmittance information (m=2.2) obtained from subharmonic reconstruction;

[0036] Figure 6 A schematic diagram showing the transmittance function and its error obtained by reconstruction for different modulation depths and harmonic orders;

[0037] Figure 7 (a) is a graph showing the change in transmittance over time in the reconstructed absorbance function of the 7185.597 cm spectral line of water molecules;

[0038] Figure 7 (b) A0~A in the reconstructed absorption function of the 7185.597 cm⁻¹ water molecule spectrum. 12 A schematic diagram of a subharmonic signal;

[0039] Figure 7 (c) is a schematic diagram of the transmittance, absorbance and fitting residuals obtained from the reconstruction of the absorbance function of the 7185.597 cm spectral line of water molecules. Detailed Implementation

[0040] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0041] This invention provides a high-precision gas parameter measurement system based on the harmonic reconstruction principle, comprising a laser generation system, a laser detection system, and a signal acquisition and processing system;

[0042] The laser generation system is used to generate a voltage signal coupled with a slow scanning signal and a fast modulation signal, generate a driving current, and output a modulated laser signal;

[0043] The laser detection system receives the laser signal passing through the absorption gas cell optical path and the reference optical path, and obtains the target order harmonic signal through phase-locked filtering;

[0044] The signal acquisition and processing system performs spectral analysis to reproduce molecular absorption spectra.

[0045] Based on the above systems, such as Figure 1 As shown, this invention provides a high-precision measurement method for gas parameters based on the harmonic reconstruction principle, comprising the following steps:

[0046] S1. Process the modulation transmittance signal to obtain the harmonic curves of order 0 to k0;

[0047] S2. Based on the laser frequency change signal and the harmonic curves of orders 0 to k0, obtain the curves of each order of harmonics changing with the laser frequency.

[0048] S3. Determine the molecular absorption spectrum based on the curves of the change of each harmonic with the laser frequency;

[0049] S4. Analyze the molecular absorption spectrum to determine the physical parameters of the gas being measured.

[0050] This invention establishes a novel, high-precision, calibration-free pressure / concentration measurement algorithm based on wavelength modulation. The method first reconstructs the transmittance information within a specific frequency range (i.e., frequency modulation depth) using the harmonic signals corresponding to each frequency of the spectrum. Then, it averages the transmittance in the frequency overlap region, finally obtaining the transmittance function and taking its logarithm to obtain the absorptivity function, thereby calculating the gas pressure / concentration.

[0051] This invention takes into account the importance of the absorbance function (directly determining gas temperature, concentration, spectral parameters, etc.) and the advantages of wavelength modulation (high sensitivity and strong anti-interference ability). Based on wavelength modulation, a high-precision, calibration-free absorbance function reconstruction method is established, eliminating the complicated calibration process and expanding the application scope of the technology.

[0052] By extracting a portion of points along the slow-scanning wavelength as the center point for reconstructing transmittance, and then using the harmonic components obtained from high-frequency modulation, combined with Chebyshev polynomials, the transmittance over a range of twice the modulation depth wavenumber is reconstructed. Since the reconstructed ranges of each center point overlap, averaging the overlapping portions yields a relatively accurate reconstructed transmittance, which is then used to calculate the accurate absorbance function. This method enables simultaneous measurement of gas pressure / concentration.

[0053] This invention improves wavelength modulation spectroscopy, which not only obtains the complete absorbance but also removes high-frequency noise through harmonic detection. Compared with the direct absorption method, the measurement accuracy is significantly improved. Especially at low concentrations, the noise of the direct absorption method is relatively large, and the transmittance reconstruction method is more effective in removing noise.

[0054] In this embodiment of the invention, in S1, the modulated transmittance signal is subjected to circuit or digital phase-locked filtering to obtain harmonic curves of order 0 to k0.

[0055] In this embodiment of the invention, in S2, the laser frequency change signal The expression is:

[0056] ;

[0057] in, The center wavelength of the laser. For wavelength modulation amplitude, For modulation frequency, For time.

[0058] In this embodiment of the invention, in S3, the curves of the change of laser frequency by each order harmonic are reconstructed using Chebyshev polynomials, the transmittance-frequency curve is calculated, and the logarithm of the transmittance-frequency curve is taken to obtain the corresponding molecular absorption spectrum.

[0059] In this embodiment of the invention, in S3, the expression for reconstruction is:

[0060] ;

[0061] in, The result of reconstructing the normalized frequency variables. The amplitude of each harmonic of transmittance, For harmonic orders, This is a normalized frequency variable.

[0062] In this embodiment of the invention, in S3, the expression for the transmittance-frequency curve is:

[0063] ;

[0064] in, For laser transmittance, The transmitted intensity of the laser. The incident intensity of the laser. Let absorptivity function, The amplitude of each harmonic of transmittance, For modulation frequency, For time, For harmonic orders, The center wavelength of the laser. For frequency.

[0065] In this embodiment of the invention, in S3, the expression for the molecular absorption spectrum is:

[0066] ;

[0067] in, The amplitude of the 0th harmonic of transmittance. The amplitude of each harmonic of transmittance, The center wavelength of the laser. For wavelength modulation amplitude, For phase, For harmonic orders, Transmittance.

[0068] In one embodiment of the present invention, the measurement system mainly consists of a laser generation system, a laser detection system, and a signal acquisition and processing system. The core algorithm for reconstructing the transmittance within a specific frequency range (i.e., modulation depth) based on the harmonic signals corresponding to a certain frequency of the gas spectral line, obtaining a series of transmittance information in different frequency ranges by scanning the entire absorption spectral line at low frequency, and finally superimposing the transmittance of the frequency overlapping region to obtain the absorption cross section is implemented on the computer in the processing system.

[0069] The laser generation system includes a signal generator, a diode laser and its drive controller. The signal generator can generate a voltage signal coupled with a slow scanning signal and a fast modulation signal. After being input to the laser controller, it generates a drive current, which drives the diode laser to output the modulated laser signal.

[0070] The laser output from the laser is split into two paths via a beam splitter fiber, passing through the absorption gas chamber optical path and the reference optical path respectively. The absorption gas chamber can be a single-pass or multi-pass chamber, achieving an absorption optical path of ~10 cm to ~100 m, depending on the requirements. The reference optical path can measure the compensation signal of the external optical path, or it can be connected to an interferometer to measure the laser wavelength signal.

[0071] The laser detection system receives the laser signal passing through the optical path and obtains the target order harmonic signal through phase-locked filtering. This system typically consists of several laser detectors and a lock-in amplifier.

[0072] Signal acquisition and processing systems typically consist of an oscilloscope (or data acquisition card) and a computer. The oscilloscope or acquisition card collects the electrical signals measured by the laser detection system into data, which is then input into the computer for processing. Core algorithms are then used for spectrum analysis to reproduce molecular absorption spectra.

[0073] Based on the laser absorption signal measured by the experimental system, the molecular absorption spectrum can be reproduced through the following steps:

[0074] (1) Perform circuit or digital phase-locked filtering on the experimentally measured modulation transmittance signal τ(t) to obtain the harmonic curves A of the 0~k0 order. k (t) (k=0,1,…k0).

[0075] (2) Combining the measured laser frequency change signal ν(t), the curves A of the change of each order harmonic with respect to the laser frequency are obtained. k (ν)(k=0,1,…k0)。

[0076] (3) The obtained harmonic-frequency curve set is reconstructed using Chebyshev polynomials, and the transmittance-frequency curve τ(ν) in a specific frequency range (i.e. frequency modulation depth) is calculated. Then, the logarithm is taken to obtain the corresponding molecular absorption spectrum α(ν).

[0077] (4) Analyze the obtained molecular absorption spectral line α according to the spectroscopic theory, calculate the physical parameters such as the concentration, temperature and pressure of the gas being measured, or study its absorption characteristics such as spectral line intensity and broadening.

[0078] The instantaneous wavelength of the laser is given by the following formula, where, [cm -1 ] represents the center wavelength of the laser, a[cm -1 ] represents the wavelength modulation amplitude, ω represents the modulation frequency, and the modulation coefficient is defined as m = a / Δv, where Δv is the half-width and half-height of the spectral line.

[0079] (1);

[0080] When a monochromatic laser beam passes through the gas medium being measured, according to the Beer-Lambert absorption law, the laser transmittance and its Fourier series expansion are as follows:

[0081] (2);

[0082] Once the transmittance is measured in the experiment, its logarithm can be used to obtain the core parameter of TDLAS—the absorption rate function.

[0083] (3);

[0084] From formula (1), we can obtain:

[0085] (4);

[0086] make: , ,but:

[0087] (5);

[0088] Substituting formula (5) into formula (2), we obtain the following formula for reconstructing the transmittance function: (6).

[0089] In formula (6), for a fixed frequency, transmittance information within the frequency range of -a to a (i.e., modulation depth) can be reconstructed. Preliminary experimental results show that compared with the traditional direct absorption method, WM-RAS improves the measurement accuracy of the absorptivity function by about an order of magnitude. At this time, the pseudo-residual is mainly caused by the laser's own intensity instability, optical path interference, etc., and the standard deviation reaches 10. -5This method is expected to provide a new measurement approach for high-precision calibration of spectral physical parameters, high-precision measurement of gas parameters under weak absorption conditions, and gas monitoring in complex industrial environments.

[0090] This invention is based on wavelength modulation spectroscopy (WMS) technology and designs a highly versatile algorithm. By reconstructing and averaging the harmonic signal through spectrum analysis, the gas absorption cross section can be obtained for spectroscopic analysis and to calculate the physical parameters or properties of the gas being measured, such as temperature, pressure, and absorption line intensity.

[0091] like Figure 2 As shown, the wavelength modulation spectroscopy system mainly includes a signal generator, a laser driver controller, a diode laser, a beam splitter fiber, an absorption gas chamber, a reference optical path, a laser detector, a lock-in amplifier, an oscilloscope or data acquisition card, and a computer. The optical path from left to right in the diagram represents the laser beam emitted by the laser, split, and then entering the absorption gas chamber and reference optical paths respectively. The electrical connections indicate that the slow-scan and high-frequency modulation coupled signals output by the signal generator are loaded onto the laser by the driver controller, and the signal measurement and processing are completed by the detection and acquisition unit. The wavelength modulation spectrum, laser absorption spectrum, and tunable diode laser absorption spectrum in the diagram are all wavelength modulation spectra, laser absorption spectra, and tunable diode laser absorption spectra, respectively.

[0092] like Figure 3 As shown in (a), the relationship between frequency modulation and intensity modulation at different frequency positions of the spectral line and time is presented. In the figure, the vertical axis "transmittance" represents transmittance, and the horizontal arrow next to "time" indicates the direction of time variation; O1, O2, O3, O4, and O5 represent the five selected characteristic frequency points; M1, M2, M3, and M4 represent the modulation boundary points corresponding to different frequency positions; 0.25 cm⁻¹, 0.42 cm⁻¹, 0.50 cm⁻¹, 0.58 cm⁻¹, and 0.75 cm⁻¹ in the figure represent the frequency positions of the corresponding characteristic points. The black curve represents the transmittance envelope of the absorption line, the red curve represents the frequency modulation trajectory changing with time, and the blue curve represents the transmittance response near different frequency points.

[0093] like Figure 3 As shown in (b), the 0th to 4th harmonic signals of the transmittance function with modulation coefficient m=2.2 are presented. In the figure, the vertical axis “Harmonic” represents the harmonic amplitude, and the horizontal axis “Frequency (cm⁻¹)” represents the frequency; A0, A1, A2, A3, and A4 represent the 0th, 1st, 2nd, 3rd, and 4th harmonic components, respectively; H0, H2, and H4 represent the even-order harmonic characteristic values ​​extracted near the center frequency. This figure shows that different orders of harmonics respond differently to the shape of the absorption line, providing a basis for subsequent transmittance reconstruction.

[0094] like Figure 4 As shown, the results of reconstructing transmittance information using harmonics A0 to A10 centered at points O1 to O5 are presented. Subfigures (a) to (c) correspond to the local reconstruction results centered at Q1, Q2, and Q3, respectively, and subfigure (d) shows the overall reconstruction result after superimposing the local results. In the figure, "Reconstruction Result" represents the reconstruction curve, "Transmittance" represents the theoretical transmittance curve, and ν1, ν2, ν3, ν4, and ν5 represent different center frequency positions. This figure illustrates that by performing local reconstruction at multiple center points and stitching and averaging the overlapping areas, a complete transmittance function can be recovered.

[0095] like Figure 5 As shown, the results of reconstructing transmittance information using harmonics A0 to A10, centered at 101 points, are presented. Subplot (a) shows the 3D reconstruction result; subplot (b) shows the local reconstruction coverage area corresponding to different center points, with color bars indicating transmittance magnitude; subplot (c) shows the final transmittance curve obtained by averaging the overlapping areas. In the figure, No.41, No.51, and No.61 represent different center point numbers, O represents the center position of the absorption line, and 0.4 cm⁻¹ and 0.6 cm⁻¹ represent example boundary frequencies. This figure shows that as the number of center points increases, the continuity and accuracy of the reconstruction results further improve.

[0096] like Figure 6 As shown, the transmittance functions and their errors obtained from reconstruction under different modulation depths and harmonic orders are presented. Subplot (a) corresponds to modulation coefficient m=2.2, and subplot (b) corresponds to modulation coefficient m=1.1. In each figure, the upper vertical axis "Transmittance" represents transmittance, the lower vertical axis "Residual" represents the residual, and the horizontal axis "Frequency (cm⁻¹)" represents frequency. "Theoretical Value" represents the theoretical curve. H0~H4, H0~H6, H0~H8, and H0~H12 represent the results of reconstruction using harmonics of orders 0 to 4, 0 to 6, 0 to 8, and 0 to 12, respectively. This figure illustrates that as the harmonic order involved in reconstruction increases, the transmittance fitting result is closer to the theoretical value, and the overall residual decreases.

[0097] like Figure 7 As shown in (a), the transmittance versus time curve in the reconstruction results of the 7185.597 cm⁻¹ spectral line of water molecules is presented. In the figure, the vertical axis “Transmittance” represents transmittance, and the horizontal axis “Time (s)” represents time. The curve reflects the periodic change of the transmittance signal over time under the combined effect of slow scanning and high-frequency modulation.

[0098] like Figure 7As shown in (b), the corresponding harmonic signals from A0 to A12 are presented. The upper part of the vertical axis represents "transmittance," and the lower part represents "harmonics," indicating the transmittance baseline and the amplitude of each harmonic order, respectively. The horizontal axis "time (s)" represents time; A0 to A12 represent the 0th to 12th harmonic components. This figure shows that near the 7185.597 cm⁻¹ spectral line of the water molecule, different harmonic orders carry absorption characteristic information, which can be used as input for transmittance reconstruction.

[0099] like Figure 7 As shown in (c), the reconstructed transmittance, absorbance, and their fitting residuals are presented. In the figure, the left ordinate "Transmittance" represents transmittance, the right ordinate "Absorbance" represents absorbance, and the horizontal axis "Frequency (cm⁻¹)" represents frequency. "Transmittance" is the experimental transmittance curve, "Absorbance" is the absorbance curve converted from transmittance, "Voyt Fit" and "Roentgen Fit" represent the fitting results obtained by the two fitting methods, respectively, and "Residual" represents the fitting residual. This figure illustrates that the proposed method can accurately reconstruct absorption spectra with a small fitting error.

[0100] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A high-precision gas parameter measurement system based on the harmonic reconstruction principle, characterized in that, This includes a laser generation system, a laser detection system, and a signal acquisition and processing system; The laser generating system is used to generate a voltage signal coupled with a slow scanning signal and a fast modulation signal, generate a driving current, and output a modulated laser signal. The laser detection system receives the laser signal passing through the absorption gas chamber optical path and the reference optical path, and obtains the target order harmonic signal through phase-locked filtering; The signal acquisition and processing system performs spectral analysis to reproduce molecular absorption lines.

2. A high-precision measurement method for gas parameters based on the harmonic reconstruction principle, characterized in that, Includes the following steps: S1. Process the modulation transmittance signal to obtain the harmonic curves of order 0 to k0; S2. Based on the laser frequency change signal and the harmonic curves of orders 0 to k0, obtain the curves of each order of harmonics changing with the laser frequency. S3. Determine the molecular absorption spectrum based on the curves of the change of each harmonic with the laser frequency; S4. Analyze the molecular absorption spectrum to determine the physical parameters of the gas being measured.

3. The high-precision gas parameter measurement method based on the harmonic reconstruction principle according to claim 2, characterized in that, In step S1, the modulated transmittance signal is subjected to phase-locked filtering by circuit or digital means to obtain harmonic curves of order 0 to k0.

4. The high-precision gas parameter measurement method based on the harmonic reconstruction principle according to claim 2, characterized in that, In S2, the laser frequency change signal The expression is: ； in, The center wavelength of the laser. For wavelength modulation amplitude, For modulation frequency, For time.

5. The high-precision gas parameter measurement method based on the harmonic reconstruction principle according to claim 2, characterized in that, In step S3, the Chebyshev polynomial is used to reconstruct the curves of the change of laser frequency by each order harmonic, calculate the transmittance-frequency curve, and take the logarithm of the transmittance-frequency curve to obtain the corresponding molecular absorption spectrum.

6. The high-precision gas parameter measurement method based on the harmonic reconstruction principle according to claim 5, characterized in that, In S3, the expression for reconstruction is: ； in, The result of reconstructing the normalized frequency variables. The amplitude of each harmonic of transmittance, For harmonic orders, This is a normalized frequency variable.

7. The high-precision gas parameter measurement method based on the harmonic reconstruction principle according to claim 5, characterized in that, In S3, the expression for the transmittance-frequency curve is: ； in, For laser transmittance, The transmitted intensity of the laser. The incident intensity of the laser. Let absorptivity function, The amplitude of each harmonic of transmittance, For modulation frequency, For time, For harmonic orders, The center wavelength of the laser. For frequency.

8. The high-precision gas parameter measurement method based on the harmonic reconstruction principle according to claim 5, characterized in that, In S3, the expression for the molecular absorption spectral line is: ； in, The amplitude of the 0th harmonic of transmittance. The amplitude of each harmonic of transmittance, The center wavelength of the laser. For wavelength modulation amplitude, For phase, For harmonic orders, Transmittance.

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