A laser gas measurement method and product based on laser nonlinear output

Abstract

The application discloses a laser gas measurement method and product based on nonlinear output of a laser, and aims at the problem that a traditional TDLAS harmonic method cannot accurately measure gas concentration when obvious nonlinear effect occurs in laser output of a mid-infrared and mid-far infrared laser. An infrared laser signal passing through a gas to be measured is acquired, and the infrared laser signal is converted into an electric signal to obtain a voltage signal of the laser signal; an initial frequency of the infrared laser signal is f; the voltage signal is synchronously collected, and phase-locked amplification is performed on a 4f frequency band signal of the voltage signal to obtain a voltage curve of the 4f signal; an absorption amplitude is calculated according to a peak-to-peak value, and after correction by a calibration coefficient and temperature and gas pressure, a gas concentration is obtained. The method provided in the application can be applied to a nonlinear output laser to accurately calculate and obtain the gas concentration.

Description

Technical Field

[0001] This application relates to the field of gas detection technology, and in particular to a laser gas measurement method. Background Technology

[0002] Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology periodically scans the output wavelength of a laser to modulate the intensity of sawtooth and sinusoidal signals; this method is called Wavelength Modulation Spectroscopy (WMS). Typically, the sinusoidal modulation frequency is f, and the demodulation frequency is 2f, known as second harmonic demodulation. This absorption measurement method uses the peak-to-peak value of the second harmonic waveform as the measured value to invert and calculate the gas concentration.

[0003] The second harmonic (2f) detection method assumes that the power P of the laser output is linearly related to the driving current I, and the output wavelength λ is linearly related to the driving current I. Under this assumption, the second harmonic is considered to be only related to the gas concentration, so the gas concentration can be calculated by inversion.

[0004] For near-infrared DFB lasers, the power P and driving current I, as well as the output wavelength λ and driving current I, have a very close linear relationship. Therefore, this assumption holds true and has become the main approach for current WMS (Wave Filter Management) technology. However, for mid-infrared and mid-far-infrared lasers, the relationships between power P and driving current I, and between output wavelength λ and driving current I, are non-linear. This assumption does not hold, and calculations based on this relationship cannot accurately measure gas concentration. Therefore, a method for measuring gas concentration under non-linear conditions of laser output beams is urgently needed. Summary of the Invention

[0005] This application provides a laser gas measurement method and product based on the nonlinear output of a laser, addressing the problem that the traditional TDLAS harmonic method cannot accurately measure gas concentration when the laser output of mid-infrared and mid-far-infrared lasers exhibits significant nonlinear effects.

[0006] In a first aspect, a laser gas measurement method based on the nonlinear output of a laser, the method comprising:

[0007] The infrared laser signal passing through the gas to be tested is acquired and converted into an electrical signal to obtain the voltage signal of the laser signal; the initial frequency of the infrared laser signal is f;

[0008] The voltage signal is acquired synchronously, and the 4f frequency band signal of the voltage signal is amplified by phase lock-in to obtain the voltage curve of the 4f signal; wherein, the amplitude of the 4f frequency band signal is only related to the gas concentration;

[0009] The absorption amplitude is calculated based on the peak-to-peak value, and the gas concentration is obtained after calibration coefficients and corrections for temperature and pressure.

[0010] In the above scheme, optionally, the infrared laser signal is a mid-infrared, mid-far-infrared laser signal or a near-infrared laser signal with poor linearity.

[0011] In a second aspect, a laser gas measurement system includes: a mid-infrared laser, a long optical path gas chamber, a mid-infrared detector, a current-to-voltage amplification module, a phase-locked amplification module, an embedded control system, a laser current drive module, and a laser temperature control module.

[0012] The output optical path of the mid-infrared laser is connected to the input end of the long optical path gas chamber;

[0013] The long-path gas chamber is disposed in the optical path of the mid-infrared laser, its input end receives laser light from the mid-infrared laser, and its output detection end is connected to the input detection end of the mid-infrared detector.

[0014] The mid-infrared detector has its input detection end connected to the output detection end of the long optical path air cell, and its output end connected to the input end of the current-to-voltage amplification module.

[0015] The current-to-voltage amplifier module has its input terminal connected to the output terminal of the mid-infrared detector, and its output terminal connected to the input terminal of the lock-in amplifier module.

[0016] The phase-locked amplifier module has its input terminal connected to the output terminal of the current-to-voltage amplifier module, and its output terminal connected to the first signal terminal of the embedded control system; it is used to amplify the 4f frequency of the signal using a phase-locked amplifier.

[0017] The embedded control system has a first signal terminal connected to the output terminal of the lock-in amplifier module, a second signal terminal connected to the first signal terminal of the laser temperature control module, and an output terminal connected to the laser current drive module. It is used to control the laser temperature control module and the laser current drive module to provide temperature control and drive current modulation for the mid-infrared laser, adjust the drive current according to sawtooth wave and sine wave output frequencies f, and perform inversion calculations on the 4f frequency signal acquired by the lock-in amplifier module.

[0018] The laser current drive module has its input terminal connected to the second signal terminal of the embedded control system and its output terminal connected to the first control terminal of the mid-infrared laser.

[0019] The first signal terminal of the laser temperature control module is connected to the second signal terminal of the embedded control system, and the output terminal is connected to the second control terminal of the mid-infrared laser.

[0020] Thirdly, an embedded control system includes a memory, a processor, and a computer program stored in the memory, characterized in that the processor executes the computer program to implement the steps of the method described above.

[0021] Fourthly, a computer-readable storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, implements the steps of the method described above.

[0022] Fifthly, a computer program product includes a computer program / instructions, characterized in that the computer program / instructions, when executed by a processor, implement the steps of the method described above.

[0023] Compared with the prior art, this application has at least the following beneficial effects:

[0024] Based on further analysis and research into the problems of existing technologies, this application recognizes that the TDLAS harmonic method is based on the demodulation method of second harmonic signals. This second harmonic (2f) detection method assumes that the laser's output power P and driving current I, and the output wavelength λ and driving current I are all linearly related. Under this assumption, it is believed that the second harmonic is only related to the gas concentration, thus allowing for inverse calculation of the gas concentration. However, for mid-infrared and mid-far-infrared lasers, the power P and driving current I, and the output wavelength λ and driving current I, are non-linearly related. Therefore, this assumption does not hold, and if calculated according to this method, the gas concentration cannot be accurately measured.

[0025] Assuming that the power P of the laser output is linearly related to the driving current I and the output wavelength λ is linearly related to the driving current I, reference [1] explored the second and fourth harmonics. The ratio of the center amplitude intensity of the fourth harmonic to that of the second harmonic is only related to the modulation depth value. A modulation depth function was established. The modulation depth value under the current environment was calculated by using the modulation depth function. The modulation frequency amplitude was then adjusted to optimize the modulation depth, ensuring that the amplitude of the second harmonic signal 2f is kept at the maximum value, thereby improving the signal-to-noise ratio and measurement accuracy.

[0026] This application, through a case study of nonlinear laser output, conducts nonlinear theoretical analysis and proposes a method for measuring gas concentration using fourth harmonic signals, along with the system composition and corresponding algorithm. The proposed 4f demodulation method aims to calculate gas concentration when the laser output is nonlinear, rather than optimizing the modulation depth coefficient to obtain the optimal 2f result. Applying the proposed 4f signal demodulation method to a nonlinear output laser yields a 4f signal that is only related to the gas concentration, allowing for accurate inversion calculation of the gas concentration. This method is applicable not only to mid-infrared ICL and QCL lasers but also to other near-infrared DFB lasers with poor linearity.

[0027] References [1] Chen Hao, Ju Yu, Han Li. Study on the relationship between modulation depth and amplitude of higher harmonic center in TDLAS wavelength modulation method [J]. Spectroscopy and Spectral Analysis, 2021, 41(12):3676-81. Attached Figure Description

[0028] Figure 1 A nonlinear relationship diagram between laser input current and output wavelength provided in one embodiment of this application;

[0029] Figure 2 A nonlinear relationship diagram between laser input current and output light intensity provided in one embodiment of this application;

[0030] Figure 3 A structural diagram of a laser gas measurement system provided in one embodiment of this application;

[0031] Figure 4 A flowchart of a laser gas measurement system provided in one embodiment of this application;

[0032] Figure 5 This is an internal structural diagram of a computer device in one embodiment.

[0033] Among them, 1 is a mid-infrared laser; 2 is a long optical path gas chamber; 3 is an MCT mid-infrared detector; 4 is a current-to-voltage amplification module; 5 is a phase-locked loop amplification module; 6 is an embedded control system; 7 is a laser current drive module; and 8 is a laser temperature control module. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0035] In the description of this application: unless otherwise stated, the terms "first," "second," etc., are intended to distinguish the objects they refer to and do not have any particular meaning in terms of technical connotation (e.g., they should not be construed as an emphasis on importance or order). Expressions such as "comprising," "including," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0036] In one embodiment, a laser gas measurement method based on the nonlinear output of a laser includes:

[0037] The infrared laser signal passing through the gas to be tested is acquired and converted into an electrical signal to obtain the voltage signal of the laser signal; the initial frequency of the infrared laser signal is f.

[0038] The voltage signal is acquired synchronously, and the 4f band signal of the voltage signal is amplified by phase lock-in to obtain the voltage curve of the 4f signal; the amplitude of the 4f band signal is only related to the gas concentration.

[0039] The absorption amplitude is calculated based on the peak-to-peak value, and the gas concentration is obtained after calibration coefficients and corrections for temperature and pressure.

[0040] In one embodiment, the infrared laser signal is a mid-infrared, mid-far-infrared, or near-infrared laser signal with poor linearity.

[0041] The TDLAS harmonic method is based on the demodulation method of the second harmonic signal. Assuming that the power P of the laser output is linearly related to the driving current I and the output wavelength λ is linearly related to the driving current I, the reference [1] explored the second and fourth harmonics. The ratio of the center amplitude intensity of the fourth harmonic to that of the second harmonic is only related to the modulation depth value. A modulation depth function was established. The modulation depth value under the current environment was calculated by using the modulation depth function. Then, the modulation frequency amplitude was adjusted to optimize the modulation depth and ensure that the amplitude of the second harmonic signal 2f is kept at the maximum value, thereby improving the signal-to-noise ratio and measurement accuracy.

[0042] This application also proposes a 4f demodulation method, which aims to calculate the gas concentration when the laser is outputting nonlinearly, rather than optimizing the modulation depth coefficient to obtain the optimal 2f result.

[0043] Significant nonlinear effects occur after the laser output of mid-infrared ICL and QCL lasers, such as... Figure 1 and Figure 2 As shown, when sinusoidal modulation of the laser current at frequency f is used, the output current is described as follows:

[0044] I(t)=I0+ΔI cosωt (1)

[0045] In the formula, I0 represents the driving current corresponding to the gas absorption wavelength, ΔI represents the current value corresponding to the modulation wavelength, and ω=2πf.

[0046] The time variation of wavelength λ can be approximated by equation (2):

[0047]

[0048] In the formula, λ represents the laser wavelength; λ0 represents the constant term for the laser wavelength; I represents the current driving the infrared laser; and ΔI represents the current corresponding to the modulation wavelength. The varying wavelength and current parameters follow... Figure 1 The current wavelength characteristics shown are illustrated.

[0049] Appearance Figure 1 , Figure 2When nonlinear effects occur, and the modulation wavelength range is very small, the time variation of laser power P can be approximated by equation (3). Nonlinear effects refer to the nonlinear relationship between the laser power P of the infrared laser and the driving current I, and between the output wavelength λ and the driving current I.

[0050] P(t) = P0 + Δ P cosωt+Δ 2P cos 2 ωt (3)

[0051] In the formula, P(t) represents the relationship between laser power and time, and P0 represents laser power; This represents the second harmonic generated due to the nonlinearity of laser power. This indicates the third harmonic generated due to the nonlinearity of laser power;

[0052] According to Beer-Lambert's absorption law, the power of the beam absorbed by the gas under small signal conditions is approximately given by equation (4):

[0053] P T (t)=P(t)exp[-α(t)]=P(t)[1-α(t)] (4)

[0054] In the formula, α(t) represents the gas absorption coefficient produced at the gas absorption wavelength; P T P(t) represents the beam power absorbed by the gas; P(t) represents the relationship between laser power and time.

[0055] During gas measurement, the output wavelength of the infrared laser scans near the gas absorption wavelength α, therefore the absorption coefficient also changes with time, as shown in (5):

[0056] α(t)=α0+α1 cosωt+α2 cos 2 ωt (5)

[0057] In the formula, α0 represents the absorption coefficient constant; and This represents the dynamic change in the absorption coefficient.

[0058] According to formulas (3)-(5), we can obtain:

[0059] P T (t)=(P0+Δ P cosωt+Δ 2P cos 2 ωt)(1-α0-α1cosωt-α2cos 2 ωt) (6)

[0060] In the formula, P T (t) represents the beam power absorbed by the gas; P0 represents the laser power; ΔP This represents the second harmonic generated due to the nonlinearity of laser power; Δ 2P This represents the third harmonic generated due to the nonlinearity of laser power; α1 and α2 represent the dynamic variation of the absorption coefficient.

[0061] When the voltage amplitude of the signal received by the photodetector is less than the voltage amplitude of the photodetector's cutoff signal, and simultaneously the voltage amplitude of the signal received by the photodetector is greater than the voltage amplitude of the noise, the received signal of the photodetector is proportional to the transmission power: s(t) = ξP T (t), where ξ represents the efficiency of the photodetector. Using the trigonometric identity, the signal can be expressed in the following form as equation (7):

[0062]

[0063] In the formula, s(t) represents the signal absorbed by the photodetector; ξ represents the efficiency of the photodetector; P T (t) represents the beam power absorbed by the gas; P0 represents the laser power; Δ P This represents the second harmonic generated due to the nonlinearity of laser power; Δ 2P α represents the third harmonic generated due to the nonlinearity of laser power; α0 represents the absorption coefficient constant; α1 and α2 represent the dynamic variation of the absorption coefficient; ω, 2ω and 3ω represent the first, second and third harmonics generated due to gas absorption, respectively.

[0064] Typical WMS measurements are performed under second harmonic conditions. Given the current-power relationship as shown in equation (3), the values ​​of the constant components in equation (7), as well as the amplitudes of the first harmonic ω, second harmonic 2ω, and third harmonic 3ω generated by gas absorption, are complex combinations of various parameters. The amplitude of the second harmonic 2ω depends not only on the gas concentration but also on Δ, which is independent of the gas absorption concentration. 2P Parameters. From equation (7), it can be seen that the amplitude of the fourth harmonic 4ω is directly proportional to α2 and proportional to the gas concentration. Therefore, under the above conditions, choosing the 4f signal is better than the 2f signal, and a more accurate gas concentration can be obtained.

[0065] This application presents a laser gas measurement method based on the nonlinear output of a laser, which can be applied not only to mid-infrared ICL and QCL lasers, but also to other near-infrared DFB lasers with poor linearity.

[0066] In one embodiment, reference Figure 3 A laser gas measurement system, comprising: a mid-infrared laser, a long optical path gas chamber, a mid-infrared detector, a current-to-voltage amplification module, a lock-in amplification module, an embedded control system, a laser current drive module, and a laser temperature control module;

[0067] The mid-infrared laser's output optical path is connected to the input end of a long-path gas cell;

[0068] The long-path gas cell is set in the optical path of the mid-infrared laser. Its input end receives the laser light from the mid-infrared laser, and its output detection end is connected to the input detection end of the mid-infrared detector.

[0069] The mid-infrared detector has its input detection end connected to the output detection end of the long optical path gas cell, and its output end connected to the input end of the current-to-voltage amplifier module.

[0070] The current-to-voltage amplifier module has its input terminal connected to the output terminal of the mid-infrared detector, and its output terminal connected to the input terminal of the lock-in amplifier module.

[0071] The phase-locked amplifier module has its input terminal connected to the output terminal of the current-to-voltage amplifier module, and its output terminal connected to the first signal terminal of the embedded control system; it is used to amplify the 4f frequency of the signal using a phase-locked amplifier.

[0072] An embedded control system has a first signal terminal connected to the output terminal of a lock-in amplifier module, a second signal terminal connected to the first signal terminal of a laser temperature control module, and an output terminal connected to a laser current drive module. This system controls the laser temperature control module and the laser current drive module to provide temperature control and drive current modulation for the mid-infrared laser, adjusts the drive current according to sawtooth and sine wave output frequencies f, and performs inversion calculations on the 4f frequency signal acquired by the lock-in amplifier module.

[0073] The laser current drive module has its input terminal connected to the second signal terminal of the embedded control system and its output terminal connected to the first control terminal of the mid-infrared laser.

[0074] The first signal terminal of the laser temperature control module is connected to the second signal terminal of the embedded control system, and the output terminal is connected to the second control terminal of the mid-infrared laser.

[0075] refer to Figure 3 The embedded control system 6 controls the laser current drive module 7 and the laser temperature control module 8 to provide temperature control and drive current modulation for the mid-infrared laser 1. The drive current is adjusted according to the sawtooth wave and sine wave f frequencies. The mid-infrared laser 1 outputs the modulated wavelength λ according to the modulated current, and the optical power P changes accordingly. The laser beam illuminates the long-path gas chamber 2, where the gas absorbs the energy of the beam. The optical signal is converted into a current signal at the current-to-voltage amplification module 4, and then into a voltage signal. This voltage signal is then amplified at the 4f frequency by the lock-in amplification module 5, amplifying the 4f signal excited by f. The embedded control system 6 acquires the curve of the 4f signal, and the gas concentration is obtained through inversion calculation using software. The mid-infrared laser 1 is an ICL or QCL mid-infrared laser, directly emitting light from TO.

[0076] In one embodiment, a control method for a laser gas measurement system is also provided. This method is based on a laser gas measurement system and refers to... Figure 4 Under the control of the laser temperature control module 8, the laser temperature control is normal (meaning that the output wavelength λ0 corresponds to the gas absorption wavelength). The embedded control system 6 controls the laser current drive module 7 to output sawtooth waves and sine waves with a frequency of f. The current-to-voltage amplification module 4 synchronously acquires the corresponding 4f signal. After one scan, the voltage curve of the 4f signal is obtained. The absorption amplitude is calculated according to the peak-to-peak value. After calibration coefficients and corrections for temperature and gas pressure, the gas concentration is obtained.

[0077] Combination Figure 4 In this embodiment, the laser gas measurement system is initialized. The laser temperature control module 8 is used to drive the mid-infrared laser 1 to control the temperature. The system checks whether the temperature control is normal (i.e., whether the output wavelength λ0 corresponds to the gas absorption wavelength). If the temperature control is abnormal, the process ends and the laser temperature control module 8 is readjusted. If the temperature control is normal, the laser current drive module 7 is controlled to output sawtooth waves and sine waves at a frequency of f. After the laser passes through the long optical path gas chamber 2, it is detected by the MCT mid-infrared detector 3. The current-to-voltage amplification module 4 synchronously collects the signal. After one scan, the voltage curve of the signal is obtained. The phase-locked amplification module 5 is used to amplify the frequency band with an output wavelength of 4f. The embedded control system 6 collects the voltage value of the 4f harmonic signal. The system checks whether the sawtooth wave array scan is complete. If the scan is not complete, the data is collected repeatedly. When the scan is complete, the peak-to-peak value of the 4f signal within the sawtooth wave scan period is calculated. The gas concentration is calculated by combining the calibration coefficients. The calculation results are corrected for temperature and pressure and then output.

[0078] In one embodiment, an embedded control system is provided, the internal structure of which can be shown in the following diagram. Figure 5 As shown, the computer device includes a processor, memory, communication interface, and human-computer interaction interface (such as a combination of monitor, keyboard, and mouse, or a touchscreen) connected via a system bus. The processor provides computing and control capabilities, and the communication interface is used for wired or wireless communication with external terminals. Wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. The computer device loads and runs a computer program to implement the aforementioned laser gas measurement method based on the nonlinear output of a laser.

[0079] Those skilled in the art will understand that Figure 5The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0080] In one embodiment, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, implements the steps of the methods described in the above embodiments.

[0081] In one embodiment, a computer program product is also provided, including a computer program / instructions that, when executed by a processor, implement the steps of the methods described in the embodiments above.

[0082] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method of laser gas measurement based on the non-linear output of a laser, characterized in that, The method comprises the following steps: An infrared laser signal passing through the gas to be measured is obtained and converted into an electrical signal to obtain a voltage signal of the laser signal; The initial frequency of the infrared laser signal is ; Synchronously acquire voltage signals and analyze the voltage signals. The frequency band signal is amplified by phase lock-in to obtain The voltage curve of the signal; wherein, the The amplitude of the frequency band signal is only related to the gas concentration; the absorption amplitude is calculated according to the peak-to-peak value, and the gas concentration is obtained after calibration coefficients and corrections for temperature and gas pressure. Specifically, this includes: using a lock-in amplifier module to output a wavelength of... Phase-locked amplification is performed in the frequency band, and data is collected using an embedded control system. Harmonic signal voltage value; determine whether the sawtooth wave array scan is complete, and repeat data acquisition if the scan is not complete; when the scan is complete, calculate the sawtooth wave scan period. The peak-to-peak value of the signal is used to calculate the gas concentration by combining the calibration coefficients. The calculation results are then corrected for temperature and pressure and output. wherein, when the frequency is Laser current sinusoidal modulation, output current description: （1） In the formula, indicates the driving current corresponding to the gas absorption wavelength, indicates the current value corresponding to the modulation wavelength, ; Wavelength The time variation of the wavelength is expressed by (2) as follows: （2） In the formula, represents the laser wavelength; represents a constant term of the laser wavelength; represents a current driving the infrared laser, represents a current corresponding to the modulation wavelength; When the nonlinear effect occurs, the time variation of the laser power is expressed by equation (3) when the modulation wavelength range is smaller than a predetermined range, and the nonlinear effect indicates that the laser power of the infrared laser is nonlinear with respect to the driving current , the output wavelength , and the driving current , （3） wherein represents the change of the laser power over time, represents the laser power; represents the second harmonic due to the nonlinearity of the laser power; represents the third harmonic due to the nonlinearity of the laser power; According to the Beer-Lambert absorption law, the light beam power absorbed by the gas under small signal is formula (4): （4） In the formula, represents the gas absorption coefficient generated at the gas absorption wavelength; represents the light beam power of the gas absorption; represents the change relationship of the laser power with time; When measuring a gas, the output wavelength of the infrared laser is scanned around the wavelength of absorption of the gas so that the absorption coefficient also varies with time, as in (5): （5） wherein represents an absorption coefficient constant; and represents a dynamic change portion of the absorption coefficient; According to formulas (3)-(5), formula (6) is obtained: （6） wherein represents the light beam power absorbed by the gas; represents the laser power; represents the second harmonic generated due to laser power nonlinearity; represents the third harmonic generated due to laser power nonlinearity; and represents the dynamic part of the absorption coefficient; When the voltage amplitude of the signal received by the photodetector is < the voltage amplitude of the cutoff signal of the photodetector, and the voltage amplitude of the signal received by the photodetector is > the voltage amplitude of the noise, the signal received by the photodetector is proportional to the transmission power: where represents the efficiency of the photodetector, using the trigonometric identity relationship, the signal is expressed in the following form as equation (7): （7） wherein represents the photo detector absorption signal; represents the efficiency of the photo detector; represents the light beam power absorbed by the gas; represents the laser power; represents the second harmonic generated due to laser power nonlinearity; represents the third harmonic generated due to laser power nonlinearity; represents the absorption coefficient constant; and represents the dynamic part of the absorption coefficient; , and represent the first, second and third harmonics generated due to gas absorption, respectively; Given the characteristics of the current-power relationship as shown in equation (3), the values ​​of the constant components of equation (7) and the first harmonic generated by gas absorption. Second harmonic and third harmonic The amplitude is a complex combination of various parameters; among them, the second harmonic... The amplitude depends not only on the gas concentration, but also on factors independent of the gas absorption concentration. Parameters; according to equation (7), the fourth harmonic amplitude and It is directly proportional to the gas concentration.

2. The method of claim 1, wherein the laser gas measurement based on laser nonlinear output is characterized by, The method comprises the following steps: The infrared laser signal is a mid-infrared, mid-far-infrared laser signal or a near-infrared laser signal with poor linearity.

3. A laser gas measurement system for implementing the method of any one of claims 1-2, characterized by The method comprises the following steps: The mid-infrared laser, the long optical path gas chamber, the mid-infrared detector, the current-to-voltage amplification module, the lock-in amplification module, the embedded control system, the laser current driving module, and the laser temperature control module; The output end of the mid-infrared laser is optically connected to the input end of the long optical path gas chamber. The long optical path gas chamber is arranged on the optical path of the mid-infrared laser, receives laser from the mid-infrared laser at the input end, and is connected to the input end of the mid-infrared detector at the output end. The input end of the mid-infrared detector is connected to the output end of the long optical path gas chamber, and the output end is connected to the input end of the current-to-voltage amplification module. The input end of the current-to-voltage amplification module is connected to the output end of the mid-infrared detector, and the output end is connected to the input end of the lock-in amplification module. The lock-in amplification module has an input end connected to an output end of the current-voltage conversion and amplification module, and an output end connected to a first signal end of the embedded control system, and is used for lock-in amplification of signals with different frequencies. frequencies. The first signal end of the embedded control system is connected to the output end of the lock-in amplification module, the second signal end is connected to the first signal end of the laser temperature control module, and the output end is connected to the laser current driving module. The laser temperature control module and the laser current drive module are used for providing temperature control and drive current modulation of the mid-infrared laser, and outputting according to sawtooth wave and sine wave Frequency-adjusted drive current And the lock-in amplification module collected to Frequency signal inversion calculation; The input end of the laser current driving module is connected to the second signal end of the embedded control system, and the output end is connected to the first control end of the mid-infrared laser. The first signal end of the laser temperature control module is connected to the second signal end of the embedded control system, and the output end is connected to the second control end of the mid-infrared laser.

4. An embedded control system, comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method of any one of claims 1-2.

5. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the method of any one of claims 1-2.

6. A computer program product comprising computer programs / instructions, characterized in that, The computer program / instruction is executed by the processor to implement the steps of the method of any one of claims 1-2.

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