Method for measuring time-varying absorption based on fixed-point wavelength modulation technique

Abstract

The application provides a measurement method for reconstructing time-varying absorption based on fixed-point wavelength modulation technology, which comprises the following steps: applying a high-frequency sinusoidal scanning signal to a laser, wherein the scanning frequency is f m ; the wave number response of the laser has a nonlinear relationship with the current, and the nonlinear fitting of discrete wave numbers obtains a continuously changing wave number function v(t); the Beer-Lambert law is used to express the absorption rate α v (t) of the laser by the absorption medium; the Fourier transform and the lock-in filtering extraction are performed on α v (t) to extract the harmonic waves of the absorption rate function with time; the wave number information of the dynamic harmonic waves at any time is supplemented by numerically solving the inverse function of the wave number function at the rising edge or the falling edge, so that the absorption rate at each time is reconstructed, and the calibration-free measurement is realized. The absorption rate reconstructed by the application has a higher signal-to-noise ratio and does not reduce the time resolution of the spectrum.

Description

Technical Field

[0001] This application relates to the field of online dynamic gas measurement technology, and in particular to a measurement method and system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology. Background Technology

[0002] Tunable diode laser absorption spectroscopy (TDLAS) features high sensitivity, high time resolution, and in-situ measurement capabilities, and has been widely used in industrial gas measurement. Combining spectroscopic knowledge, TDLAS can measure gas concentration, temperature, velocity, and pressure.

[0003] Traditional TDLAS technology is a direct absorption spectroscopy method. It involves injecting a low-frequency alternating current around the center of the absorption line by exploiting the relationship between the laser wavelength and the injection current, thus obtaining a complete absorption line. This technique is called Scan-DAS. This method can reveal the complete absorption spectrum, and gas physical properties can be obtained by fitting the measured absorbance, enabling calibration-free measurements.

[0004] If the laser frequency is fixed at the center of the spectral line and the scanning signal is canceled, this method is called Fixed-Point Direct Absorption Spectrum (Fixed-DAS). This method has extremely high time resolution, reaching the microsecond or even nanosecond level. However, the complete line shape cannot be viewed during Fixed-DAS measurements; it assumes the gas follows a line shape from a database, converting the absorbance to concentration proportionally. Strictly speaking, it is not a calibration-free method.

[0005] Although Scan-DAS technology is calibration-free, its absorption information is distributed across the entire spectrum. Any noise, such as mechanical vibration, combustion oscillation, and laser wavelength jitter, will affect Scan-DAS measurements.

[0006] Fixed-DAS measurements require the laser wavelength to be precisely at the spectral apex. Therefore, before measurement, the center of the spectral line must be located using a wavelength counter or multiple reflection cells, further increasing the complexity of the measurement system. Furthermore, the spectral line center of the absorbing medium changes with temperature and pressure. For example, the center frequency of an OH radical at 1500 K and 4 atm shifts to its full width at half maximum (FWHM) at room temperature. Thus, using the room-temperature, room-pressure spectral line center for Fixed-DAS measurements will introduce a 100% measurement error. In complex measurement environments, the absorbing medium collides with various substances, resulting in a highly complex line model that deviates significantly from the known model, introducing unknown errors into Fixed-DAS measurements. Summary of the Invention

[0007] This application aims to at least partially address one of the technical problems in the related art.

[0008] Therefore, the first objective of this application is to propose a measurement method for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology, which solves the problem that the signal-to-noise ratio and time resolution of traditional laser absorption spectra cannot be simultaneously achieved, so that the reconstructed absorbance not only has a higher signal-to-noise ratio, but also does not reduce the time resolution of the spectrum.

[0009] The second objective of this application is to propose a measurement system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology.

[0010] To achieve the above objectives, the first aspect of this application proposes a method for measuring time-varying absorbance based on fixed-point-wavelength modulation technology, comprising:

[0011] A high-frequency sinusoidal scanning signal is applied to the laser, with a scanning frequency of f. m ;

[0012] The wavenumber response of a laser has a nonlinear relationship with the current. By performing nonlinear fitting on the discrete wavenumber, a continuously changing wavenumber function v(t) can be obtained.

[0013] The Beer-Lambert law is used to represent the absorptivity α of the absorbing medium to the laser. v (t);

[0014] For absorption rate α v (t) Perform Fourier transform and phase-locked filtering to extract the X and Y axis components of the dynamic harmonics, thereby achieving decoupling of time and wave number;

[0015] At any given time, the dynamic harmonics contain harmonic information of the absorption rate but not wavenumber information of the absorption rate. By numerically solving the inverse function of the wavenumber function at the rising or falling edge, the wavenumber information of the absorption rate at each time is supplemented, and the absorption rate at each time is reconstructed.

[0016] Calibration-free measurement is achieved based on the reconstructed absorbance at each moment.

[0017] To achieve the above objectives, a second aspect of the present invention provides a measurement system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology, comprising:

[0018] The signal application module is used to apply a high-frequency sinusoidal scanning signal to the laser, with a scanning frequency of f. m ;

[0019] The wavenumber fitting module is used because the wavenumber response of a laser has a nonlinear relationship with the current. It performs nonlinear fitting on discrete wavenumbers to obtain a continuously changing wavenumber function v(t).

[0020] The absorption spectrum representation module is used to represent the absorptivity α of the absorbing medium to laser light using the Beer-Lambert law. v (t);

[0021] The absorption spectrum processing module is used to process the absorption rate α. v (t) Perform Fourier transform and phase-locked filtering to extract the X and Y axis components of the dynamic harmonics, thereby achieving decoupling of time and wave number;

[0022] The absorption spectrum reconstruction module is used to obtain harmonic information of the dynamic harmonics at any time, including the absorption rate, but not the wavenumber information of the absorption rate. It supplements the wavenumber information of the absorption rate at each time by numerically solving the inverse function of the wavenumber function at the rising or falling edge, and reconstructs the absorption rate at each time.

[0023] The calibration-free measurement module is used to achieve calibration-free measurement based on the reconstructed absorbance at each time step.

[0024] This application presents a method for reconstructing time-varying absorbance based on fixed-point wavelength modulation (Fixed-WMS) technology. This method utilizes the high temporal resolution of Fixed-point wavelength modulation (Fixed-WMS) to apply a high-frequency sinusoidal modulation signal to the laser and extract the harmonics of the absorbance function over time. By numerically solving for the inverse function of the laser's wavenumber response and substituting the dynamic harmonics into the Fixed-WMS formula, a spectrum can be reconstructed at each time point. This reconstructed absorbance not only has a higher signal-to-noise ratio but also does not reduce the temporal resolution of the spectrum.

[0025] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0026] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a flowchart illustrating a method for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology, as provided in Embodiment 1 of this application.

[0028] Figure 2 A schematic diagram of the spectral distribution of the absorption spectrum when a high-frequency scanning signal is applied;

[0029] Figure 3 This is a technical roadmap of an embodiment of this application;

[0030] Figure 4 This is a schematic diagram of a shock tube device according to an embodiment of this application;

[0031] Figure 5 The wavenumber calibration results for the 2.93μm laser in this application embodiment;

[0032] Figure 6 This is a schematic diagram of the light intensity signal and pressure signal 10ms before and after the reflected shock wave in an embodiment of this application;

[0033] Figure 7 The time-varying absorbance and 1.5ms slice plot are reconstructed using this application;

[0034] Figure 8 This is a comparison chart of the H2O concentration measured in this application and the results of scan-DAS measurement;

[0035] Figure 9 This is a schematic diagram of a measurement system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology, provided as an embodiment of this application. Detailed Implementation

[0036] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0037] The following describes, with reference to the accompanying drawings, a method and system for measuring time-varying absorbance based on fixed-point-wavelength modulation technology.

[0038] Figure 1 This is a schematic flowchart of a method for measuring time-varying absorbance based on fixed-point-wavelength modulation technology, as provided in Embodiment 1 of this application.

[0039] like Figure 1 As shown, the measurement method for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology includes the following steps:

[0040] Step 101: Apply a high-frequency sinusoidal scanning signal to the laser, with a scanning frequency of f. m ;

[0041] Step 102: The wavenumber response of the laser has a nonlinear relationship with the current. The continuously changing wavenumber function v(t) is obtained by nonlinear fitting of the discrete wavenumber.

[0042] In this embodiment, a high-frequency sinusoidal scanning signal is applied to the laser, with a scanning frequency of f. m Due to the nonlinear relationship between the laser's wavenumber response and the current, the laser's output wavenumber v(t) has a series of expansions in the frequency domain, expressed as:

[0043]

[0044] in, The center wavenumber of the laser [cm] -1 ], and These represent the hysteresis phase of the wavenumber response relative to the light intensity on the x and y axes, respectively.

[0045] This embodiment captures the nonlinear response of the laser wavenumber under high-frequency scanning excitation by preserving the wavenumber response of the laser at higher harmonics, making the reconstructed absorption spectrum more reflective of the physical state of the gas and laying a good foundation for subsequent fitting and calculation work.

[0046] Step 103: Use Beer-Lambert's law to express the absorptivity α of the absorbing medium to the laser. v (t);

[0047] In this embodiment, the set scanning frequency f m This is high enough that the spectrum of the absorption rate presents as a series concentrated in ±kf m Frequency clusters, such as Figure 2 As shown, the spectrum is not only in ±kf m There is a distribution, and also a distribution at frequencies around it, because the thermodynamic parameters change with time, within ±kf. m The nearby spectrum carries time-varying information about the absorption rate.

[0048] In this embodiment, according to Beer-Lambert's law, the absorptivity of the absorbing medium for laser light can be expressed as:

[0049]

[0050] Among them, I t I0 and I0 represent the intensities of the transmitted and incident light, respectively; p is the gas pressure [atm]; x represents the concentration of the absorbing component; L is the absorption path length [cm]; and S(T) is the linear intensity [cm]. -2 ·atm -1 The last four terms combined are called the integral area, which is the integral of a spectral line with respect to the wavenumber. It represents the influence of gas thermodynamic parameters on absorption intensity, and in this embodiment, it is expressed as k[cm]. -1 ]. It is the linear function of this transition [cm] -1 This is typically represented using the Voigt line type, which is the convolution of the Gaussian and Lorentz line types.

[0051] Step 104, regarding the absorption rate α v(t) Perform Fourier transform and phase-locked filtering to extract the X and Y axis components of the dynamic harmonics, thereby achieving decoupling of time and wave number;

[0052] In this embodiment, the absorbance is first subjected to a Fourier transform to obtain its real Fourier coefficients H. k and J k :

[0053]

[0054] Where H k J k It is α v The cosine and sine components of the spectrum. Where δ0 = 1, this is because the Fourier integral of higher-order terms reduces general energy, δ n =2 (n>0), N represents the discrete sequence α v The number of points contained in (t). In actual operation, H k J k This can be obtained through a Fast Fourier Transform. The original absorbance function can then be expanded using a Real Fourier Transform from the above equation:

[0055]

[0056] In this embodiment, an ideal low-pass filter is used to... Figure 2 The X and Y axis components of the dynamic harmonics are obtained by extracting each frequency cluster in the signal.

[0057]

[0058] Among them, Z n,X and Z n,Y These are the X-axis and Y-axis components of the nth dynamic harmonic, f s f m These represent the sampling frequency and the modulation frequency, respectively, with λ representing the modulation frequency f. m In the discrete spectrum, λ = Nf m / f s .

[0059] When calculating the 0th dynamic harmonic, the lower limit of the summation in the above formula should be 0. λ also determines the number of sine (cosine) waves participating in each dynamic harmonic reconstruction process. β takes the value (0, 0.5], representing the width of the ideal low-pass filter. When β is 0.5, it represents a scanning frequency with half the width. Based on the dynamic characteristics of the measurement conditions, the filter width can be shortened to remove inter-band noise.

[0060] This embodiment extracts harmonics from the original absorbance data by introducing the harmonic formula of Fixed-WMS technology, distributing the frequency information of the absorbance to each harmonic, and by appropriately shortening the filter width, it can retain the time-domain information of the absorbance while eliminating inter-band noise caused by non-ideal experimental factors, thus giving each dynamic harmonic an extremely high signal-to-noise ratio.

[0061] Step 105: At any given time, the dynamic harmonics contain harmonic information of the absorption rate but not wavenumber information of the absorption rate. The wavenumber function is numerically solved to obtain the inverse function of the wavenumber function at the rising or falling edge, thereby supplementing the wavenumber information of the absorption rate at each time and reconstructing the absorption rate at each time.

[0062] In this embodiment, the dynamic harmonic Z constructed above... n (t) is independent of the wavenumber, achieving decoupling between time and wavenumber. At any given time, the dynamic harmonics contain harmonic information from the absorption rate function, but lack wavenumber information. The inverse function of the wavenumber function at the rising (falling) edge is obtained through numerical solution:

[0063] x = f -1 (v)

[0064] This allows for the addition of wavenumber information to the absorptivity at each time step, thereby reconstructing the absorptivity at each time step. The formula for reconstructing the absorptivity is:

[0065]

[0066] Where n takes values ​​ranging from 0, 1, 2, ..., f s / 2f m -1. In the actual spectrum, the highest harmonic of the absorption rate is f. s / 2f m However, the frequency clusters of this harmonic are too close to the maximum effective range of the FFT spectrum, and are usually incomplete, so they should be discarded. Therefore, the maximum value of n is f. s / 2f m -1.

[0067] This embodiment uses the synthesis formula of Fixed-WMS, substituting the values ​​of dynamic harmonics at each time point, to reconstruct a spectrum at each time point. By numerically solving the inverse function of the wavenumber response, the nonlinear characteristics of the wavenumber response can be preserved to the greatest extent, making the reconstructed spectrum more closely match the actual curve.

[0068] Step 106: Perform calibration-free measurement based on the reconstructed absorbance at each time step.

[0069] The measurement method for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology in this application embodiment employs, as follows: Figure 3The illustrated approach utilizes the high temporal resolution of Fixed-WMS (Fixed-Point Wavelength Modulation) to apply a high-frequency sinusoidal modulation signal to the laser, extracting the time-varying harmonics of the absorbance function and reconstructing the time-varying absorbance. This reconstructed absorbance not only has a higher signal-to-noise ratio but also does not reduce the temporal resolution of the spectrum.

[0070] By using a shock tube device to generate time-varying thermodynamic parameters and applying a 50kHz sinusoidal scan to a laser, this application can reconstruct the process of H2O absorptivity changing within the millisecond range. Figure 4 A schematic diagram of the shock tube experimental setup is shown. The shock tube is divided into a high-pressure section and a low-pressure section by aluminum foil. Before the experiment, the inside of the shock tube is evacuated to a vacuum using a vacuum pump. A mixture of 1% methanol and 2% O2 gas is introduced into the low-pressure section and diluted with 97% argon gas. High-pressure gas is introduced into the high-pressure section to cause the diaphragm to rupture, forming a shock wave that compresses the gas in the low-pressure section. The methane / hydrogen mixture is rapidly ignited after compression, gradually releasing H2O. A pair of CaF2 optical windows are placed near the end face of the low-pressure section, through which a 2.93 μm laser is directed into the shock tube. The laser absorption spectrum of H2O is acquired within 10 ms before and after the formation of the reflected shock wave, and the data is processed using this application.

[0071] First, the wavenumber of the 2.93 μm laser was calibrated. The wavenumber variation of the laser under a 50 kHz scan was determined using a 72.65 mm long single-crystal GeFP interferometer. The interference signal and wavenumber calibration results are as follows: Figure 5 As shown, when the wavenumber changes monotonically, the wavenumber interval between adjacent interference peaks is 0.01631 cm⁻¹. -1 When the wavenumber reaches an extreme value, the wavenumbers on both sides of the extreme value are equal. It can be seen that the phase difference between the change in the interference envelope (light intensity change) and the wavenumber change is approximately π. Based on this principle, assigning values ​​to the relative wavenumbers of the interference peaks can transform them into a discrete wavenumber sequence, i.e., the triangular scatter plot in the figure. Using the expression for the laser's output wavenumber expanded in the frequency domain, a nonlinear fit is performed on the discrete wavenumbers to obtain a continuously changing wavenumber function, taking f... m The fifth harmonic of the fitted residuals has a standard deviation of 7.0e-4cm. -1 This indicates that using a continuous function to represent wavenumber changes results in almost no error.

[0072] Figure 6 The data shows light intensity and pressure signals 10 ms before and after the formation of the reflected shock wave. At 0 ms, the reflected shock wave forms, methanol is instantaneously heated and compressed, and ignites approximately 0.25 ms later, releasing H2O molecules. (The gray line is shown as I...) tAbsorption peaks begin to appear. The solid black line represents the pre-collected background light intensity, which serves as I0 in the frequency domain expansion of the laser's output wavenumber. t Substituting I0 into the frequency domain expansion expression of the laser's output wavenumber, we obtain the raw absorptivity of the scan-DAS. The black dashed line represents the pressure signal monitored by a sensor at the same location in the shock tube, synchronized with the absorptivity, used to calculate the H2O concentration.

[0073] Using the obtained raw scan-DAS absorbance as the input signal, the data is reconstructed using this application, and the resulting time-varying absorbance is as follows: Figure 7 As shown, the filter bandwidth is set to 5kHz and the time resolution to 400kHz. Voigt fitting is performed on the absorption peak at each time step to obtain the instantaneous integrated absorbance κ(t), from which the change in H2O concentration over time can be inferred. The expression for the Voigt function is:

[0074]

[0075] in, Δv L and Δv D These represent Lorentz and Doppler broadenings, respectively. Doppler broadening can be obtained through temperature, while Lorentz broadening is the quantity to be fitted. Figure 7 The right side shows a slice at 1.5ms, comparing the signal-to-noise ratio (SNR) of the reconstructed spectrum and the original scan-DAS spectrum. It can be seen that the SNR of the reconstructed spectrum at this time is 106.8, a 53% improvement compared to the original scan-DAS spectrum. Furthermore, the best-fit curves of the two almost completely overlap, indicating that this application did not lose any spectral information from the original data.

[0076] By fitting the H2O spectrum at each moment, the process of H2O concentration changing over time can be obtained. Figure 8 The results show the fitted H2O concentration and the concentration measured by scan-DAS, and also include predicted concentrations from two internationally popular chemical kinetic mechanisms. Figure 8 The dashed line and telephone line represent internationally popular chemical mechanism prediction curves. The reconstructed H2O concentration in this application shows an extremely high degree of agreement with the mechanism prediction curve, proving that the reconstructed H2O absorbance has real physical significance and is capable of measuring rapid physicochemical dynamic processes in the millisecond range. Furthermore, compared with the original scan-DAS, the concentration measured in this application improves the signal-to-noise ratio without reducing the temporal resolution.

[0077] To achieve the above embodiments, this application also proposes a measurement system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology.

[0078] Figure 9 This is a schematic diagram of a measurement system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology, provided as an embodiment of this application.

[0079] like Figure 9 As shown, the measurement system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology includes:

[0080] The signal application module is used to apply a high-frequency sinusoidal scanning signal to the laser, with a scanning frequency of f. m ;

[0081] The wavenumber fitting module is used because the wavenumber response of a laser has a nonlinear relationship with the current. It performs nonlinear fitting on discrete wavenumbers to obtain a continuously changing wavenumber function v(t).

[0082] The absorption spectrum representation module is used to represent the absorptivity α of the absorbing medium to laser light using the Beer-Lambert law. v (t);

[0083] The absorption spectrum processing module is used to process the absorption rate α. v (t) Perform Fourier transform and phase-locked filtering to extract the X and Y axis components of the dynamic harmonics, thereby achieving decoupling of time and wave number;

[0084] The absorption spectrum reconstruction module is used to obtain harmonic information of the dynamic harmonics at any time, including the absorption rate, but not the wavenumber information of the absorption rate. It supplements the wavenumber information of the absorption rate at each time by numerically solving the inverse function of the wavenumber function at the rising or falling edge, and reconstructs the absorption rate at each time.

[0085] The calibration-free measurement module is used to achieve calibration-free measurement based on the reconstructed absorbance at each time step.

[0086] Furthermore, in the embodiments of this application, the output wavenumber v(t) of the laser is expressed as:

[0087]

[0088] Where v represents the center wavenumber of the laser, and i represents the wavenumber response at f m The component at the i-th harmonic, a i Let b represent the coefficients of the cosine component of the i-th harmonic component, where t is time t and b is the coefficient of the i-th harmonic component. i The coefficients of the sinusoidal component representing the i-th harmonic are given. and These represent the hysteresis phase of the wavenumber response relative to the light intensity on the x-axis and y-axis, respectively.

[0089] Specifically, in the embodiments of this application, according to the Beer-Lambert law, the absorptivity α of the absorbing medium to the laser is... v (t) is represented as:

[0090]

[0091] Among them, I t Let I0 and I0 be the intensities of the transmitted and incident light, respectively; p be the gas pressure; x be the concentration of the absorbing component; L be the absorption path length; and S(T) be the linear intensity. The combination of p, x, L, and S(T) represents the integral area, denoted as k(t). It is a linear function of the transition, represented using the Voigt linear style.

[0092] Furthermore, in the embodiments of this application, the absorption rate α... v (t) Perform Fourier transform and phase-locked filtering to extract the X and Y axis components of the dynamic harmonics, including:

[0093] Perform an FFT on the absorbance to obtain its real Fourier coefficients H. k and J k for:

[0094]

[0095] Among them, H k J k It is α v The cosine and sine components of the spectrum, δ k For k=2, k>1, when k=0, δ k Let 1, N represent discrete sequence α v (t) The number of points contained in the sequence;

[0096] Using an ideal low-pass filter, the X-axis and Y-axis components of the dynamic harmonics are extracted from each frequency cluster, and expressed as follows:

[0097]

[0098] Among them, Z n,x (t), Z n,y (t) represents the dynamic harmonic Z of the nth time at time t. n X-axis and Y-axis components of (t), Z n,X Z n,Y These are the X and Y axis components of the nth dynamic harmonic, β represents the width of the ideal low-pass filter, and λ represents the modulation frequency f. m In the discrete spectrum, λ = Nf m / f s .

[0099] Specifically, in this embodiment, the inverse function of the wavenumber function at the rising or falling edge is numerically solved, and expressed as:

[0100] x = f -1 (v)

[0101] The formula for the remodeling absorption rate is:

[0102]

[0103] Among them, Z n,x (t), Z n,y (t) represents the dynamic harmonic Z of the nth time at time t. n The X and Y axis components of (t), f s Indicates the sampling frequency.

[0104] It should be noted that the foregoing explanation of the measurement method embodiment for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology also applies to the measurement system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology in this embodiment, and will not be repeated here.

[0105] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0106] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0107] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

[0108] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0109] It should be understood that various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0110] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0111] Furthermore, the functional units in the various embodiments of this application can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0112] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A method for measuring time-varying absorbance based on fixed-point-wavelength modulation technology, characterized in that, include: A high-frequency sinusoidal scanning signal is applied to the laser, with a scanning frequency of... ; The wavenumber response of a laser has a nonlinear relationship with the current. A continuously varying wavenumber function can be obtained by nonlinearly fitting the discrete wavenumber. ; The Beer-Lambert law is used to describe the absorptivity of the absorbing medium for laser light. ; Regarding absorption rate Fourier transform and phase-locked filtering are performed to extract the X and Y axis components of the dynamic harmonics, thus achieving decoupling between time and wavenumber. At any given time, the dynamic harmonics contain harmonic information of the absorption rate but not wavenumber information of the absorption rate. By numerically solving the inverse function of the wavenumber function at the rising or falling edge, the wavenumber information of the absorption rate at each time is supplemented, and the absorption rate at each time is reconstructed. Calibration-free measurement is achieved based on the reconstructed absorbance at each moment; According to Beer-Lambert's law, the absorptivity of the absorbing medium to the laser is... Represented as: in, , These represent the intensities of the transmitted light and the incident light, respectively. It is gas pressure. Indicates the concentration of the absorbent component. It is the absorption optical path. It's a strong line. , , , The combination of these is the integral area, denoted as: , It is a linear function of the transition, represented using the Voigt linear style; The absorption rate Fourier transform and phase-locked filtering are performed to extract the X and Y axis components of the dynamic harmonics, including: Perform an FFT on the absorbance to obtain its real Fourier coefficients. and for: in, , yes The cosine and sine components of the spectrum, For 2, k>1, when k=0 Take 1, Represents discrete sequence The number of points contained in the sequence; By using an ideal low-pass filter, dynamic harmonics are obtained by extracting each frequency cluster. The X-axis and Y-axis components are represented as follows: in, , for Second-rate Dynamic harmonics The X-axis and Y-axis components, Indicates the sampling frequency. This represents the width of an ideal low-pass filter. Indicates modulation frequency Index in the discrete spectrum .

2. The method as described in claim 1, characterized in that, laser output wavenumber Represented as: in, Indicates the center wavenumber of the laser. Indicates the wavenumber response at The i Components at the second harmonic. express i The coefficients of the cosine component of the second harmonic component. For a moment, express i The coefficients of the sinusoidal component of the second harmonic component. and These represent the hysteresis phase of the wavenumber response relative to the light intensity on the x-axis and y-axis, respectively.

3. The method as described in claim 1, characterized in that, The method of numerically solving for the inverse function of the wavenumber function at the rising or falling edge is expressed as: The formula for the remodeling absorption rate is: 。 4. A measurement system for reconstructing time-varying absorbance based on fixed-point-wavelength modulation technology, characterized in that, include: The signal application module is used to apply a high-frequency sinusoidal scanning signal to the laser, with a scanning frequency of [missing information]. ; The wavenumber fitting module is used because the wavenumber response of a laser has a nonlinear relationship with the current. It performs nonlinear fitting on discrete wavenumbers to obtain a continuously changing wavenumber function. ; The absorption spectrum representation module is used to represent the absorptivity of the absorbing medium to laser light using Beer-Lambert's law. ; The absorption spectrum processing module is used to process the absorption rate. Fourier transform and phase-locked filtering are performed to extract the X and Y axis components of the dynamic harmonics, thus achieving decoupling between time and wavenumber. The absorption spectrum reconstruction module is used to obtain harmonic information of the dynamic harmonics at any time, including the absorption rate, but not the wavenumber information of the absorption rate. It supplements the wavenumber information of the absorption rate at each time by numerically solving the inverse function of the wavenumber function at the rising or falling edge, and reconstructs the absorption rate at each time. A calibration-free measurement module is used to achieve calibration-free measurement based on the reconstructed absorbance at each time step; According to Beer-Lambert's law, the absorptivity of the absorbing medium to the laser is... Represented as: in, , These represent the intensities of the transmitted light and the incident light, respectively. It is gas pressure. Indicates the concentration of the absorbent component. It is the absorption optical path. It's a strong line. , , , The combination of these is the integral area, denoted as: , It is a linear function of the transition, represented using the Voigt linear style; The absorption rate Fourier transform and phase-locked filtering are performed to extract the X and Y axis components of the dynamic harmonics, including: Perform an FFT on the absorbance to obtain its real Fourier coefficients. and for: in, , yes The cosine and sine components of the spectrum, For k=2, k>1, when k=0 Take 1, Represents discrete sequence The number of points contained in the sequence; Using an ideal low-pass filter, the X-axis and Y-axis components of the dynamic harmonics are extracted from each frequency cluster, and expressed as follows: in, , for Second-rate Dynamic harmonics The X-axis and Y-axis components, This represents the width of an ideal low-pass filter. Indicates modulation frequency Index in the discrete spectrum , The sampling frequency.

5. The system as described in claim 4, characterized in that, laser output wavenumber Represented as: in, Indicates the center wavenumber of the laser. Indicates the wavenumber response at The i Components at the second harmonic. express i The coefficients of the cosine component of the second harmonic component. For a moment, express i The coefficients of the sinusoidal component of the second harmonic component. and These represent the hysteresis phase of the wavenumber response relative to the light intensity on the x-axis and y-axis, respectively.

6. The system as described in claim 5, characterized in that, The method of numerically solving for the inverse function of the wavenumber function at the rising or falling edge is expressed as: The formula for the remodeling absorption rate is: 。

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