High-precision ultrafast detection of acetylene combustion process based on time-frequency mapping

Abstract

The application discloses a kind of high-precision ultrafast detection methods of acetylene combustion process based on time-frequency mapping, including time domain stretching, time-frequency mapping and dynamic combustion detection three parts, utilize single optical frequency comb as light source, after dispersion element and Mach-Zehnder interferometer, form the spread pulse of multiple oscillation frequencies, finally realize the high-precision detection of acetylene gas dynamic combustion process in the single pulse period of oscilloscope, and obtain analysis in frequency domain through time-frequency mapping curve, effectively solve the high requirements such as high stability and mutual coherence of previous fast high-precision acquisition system and double-comb light source.

Description

Technical Field

[0001] This invention belongs to the field of gas detection, specifically relating to a high-precision ultrafast detection method for the acetylene combustion process based on time-frequency mapping. Technical Background

[0002] Ultrafast spectroscopy is an important tool for understanding the composition of matter, molecular evolution, and dynamics. It plays a vital role not only in basic sciences such as physics, chemistry, and biomedicine, but also in applications such as gas tracking and leak warning. In recent years, optical frequency combs have become a focus of researchers due to their excellent characteristics such as ultrashort pulse width, ultrafast repetition frequency, and ultrahigh peak power. They have also provided new technical means for ultrafast spectroscopy measurements, such as cavity ring-down technique, Fourier transform method, and multiheterodyne measurement using optical frequency combs as light sources. However, these methods are often limited by high-precision acquisition systems and the high stability and mutual coherence of dual-comb light sources. Therefore, in order to solve the above-mentioned problems related to detection, acquisition, and light sources, a high-precision ultrafast detection method for the acetylene combustion process based on time-frequency mapping is proposed. This method utilizes the high repeatability of a single optical frequency comb and the time-domain stretching characteristics of dispersion-compensating optical fibers to achieve the recording and analysis of transient phenomena. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems in the prior art and provide a high-precision ultrafast detection method for the acetylene combustion process based on time-frequency mapping. Utilizing a single optical frequency comb as the light source avoids the high requirements for locking the repetition and offset frequencies of dual optical frequency combs. Furthermore, the high repeatability of the optical frequency comb enables detection rates down to the nanosecond level. Dispersion-compensating optical fibers are used to stretch ultrashort pulses in the time domain. This period broadening reduces the need for photodetectors and oscilloscopes for acquisition and resolution, making it possible to analyze and record transient phenomena within ultra-short time intervals. By using pulses containing multiple oscillation frequencies to find the time-frequency mapping curve, high-precision measurement is achieved.

[0004] The technical solution adopted in this invention is: high-precision ultrafast detection of the acetylene combustion process based on time-frequency mapping, including:

[0005] A time-domain stretching module, which is used to stretch femtosecond pulses emitted by a single optical frequency comb to the nanosecond level, includes an optical frequency comb, a tunable filter, a dispersion-compensating fiber, and a power amplifier.

[0006] The time-frequency mapping module is used to form interference fringes with multiple oscillation frequencies and to find the time-frequency mapping curve. It includes a beam splitter, an attenuator, an electrically driven fiber delay line, and a coupler.

[0007] A dynamic combustion detection module, used to obtain transient phenomena of acetylene gas combustion, includes a shaper, an acetylene-oxygen combustion cell, a spectrometer, a photodetector, and an oscilloscope;

[0008] In the time-domain stretching module, the optical frequency comb is sequentially connected to a tunable filter, a dispersion-compensating fiber, and a power amplifier to obtain a stretched pulse. The stretched pulse enters the time-frequency mapping module, is split into two paths by a beam splitter, one path passes through an attenuator, and the other path passes through an electric fiber delay line. The two paths are then combined in a coupler to obtain a probe light. The probe light enters the dynamic combustion detection module, passes through a shaper and an acetylene-oxygen combustion cell, and is first transmitted to a spectrometer to obtain spectral information. Then, the spectrometer is replaced by a photodetector and an oscilloscope to obtain dynamic combustion information.

[0009] Furthermore, the dispersion-compensating fiber broadens the femtosecond pulses emitted by the optical frequency comb to a repetition period, completely recording the transient phenomenon of acetylene gas combustion within one period, thereby achieving nanosecond-level ultrafast detection and reducing the requirements for the acquisition and resolution capabilities of photodetectors and oscilloscopes.

[0010] Furthermore, the dispersion-compensating fiber can be modeled as a linear time-invariant system, treating dispersions of different orders as subsystems, and the overall transfer function is the product of the transfer functions of each subsystem:

[0011]

[0012] Where β n is the mode propagation function of n-order dispersion, w is the center frequency of the optical pulse, and L is the length of the dispersion-compensating fiber.

[0013] When the dispersion-compensating fiber exhibits only first-order and second-order dispersion, the outputs in the frequency domain and time domain are as follows:

[0014] A1(w)=H1(w)A0(w) (2)

[0015]

[0016] in, It is the inverse Fourier transform of H1(w), h0 is the complex amplitude, and t R =t-β1L, A0(w) is the input pulse.

[0017] There is a mapping relationship between the output in the time domain and the frequency domain. When only the second-order dispersion is considered, the mapping factor is a linear factor, i.e., β2L. When higher-order dispersion is considered, the mapping factor is often nonlinear.

[0018] The broadened pulse is processed by a time-frequency mapping module to obtain a probe light containing multiple oscillation frequencies. The peak point of the probe light is found in a spectrometer and an oscilloscope, and a nonlinear polynomial fitting is performed to complete the search for the time-frequency mapping curve. Thus, the time-domain signal detected by the oscilloscope can be converted into the frequency domain for analysis.

[0019] The beneficial effects of this invention are:

[0020] This invention proposes a high-precision ultrafast detection of the acetylene combustion process based on time-frequency mapping. Optical frequency combs provide new technical means for ultrafast spectral measurements, such as cavity ring-down spectroscopy, Fourier transform, and multiheterodyne measurement using optical frequency combs as light sources. Among these, cavity ring-down spectroscopy is most notable for its insensitivity to laser intensity noise and jitter, exhibiting high accuracy and sensitivity with increasing effective absorption distance. However, it places high demands on the response of photodetectors. Fourier transform spectroscopy inherits the multi-channel, wide-spectrum, and high-resolution characteristics of traditional Fourier transform infrared spectrometers, but high-speed scanning measurements require sophisticated servo systems and fast, high-precision data acquisition systems. Dual-frequency comb multiheterodyne spectroscopy can achieve ultrafast spectral detection at millisecond-level speeds, but it is often limited by the high stability and mutual coherence of the dual-frequency comb light source. Therefore, this invention proposes to use a single optical frequency comb as a light source, and to find time-frequency mapping curves by forming broadened pulses of various oscillation frequencies through dispersion-compensating optical fibers and Mach-Zehnder interferometers, thereby achieving high-precision transient monitoring of the acetylene gas combustion process and overcoming the difficulties in the prior art. Attached Figure Description

[0021] Figure 1 Schematic diagram of the high-precision ultrafast detection structure for the acetylene combustion process based on time-frequency mapping in this invention:

[0022] Attached image captions:

[0023] 1--Time Domain Stretching Module 11--Optical Frequency Comb

[0024] 12--Tunable filter 13--Dispersion compensation fiber

[0025] 14--Power Amplifier 2--Time-Frequency Mapping Module

[0026] 15--Beam splitter 16--Attenuator

[0027] 17--Electric fiber optic delay line 3--Dynamic combustion detection module

[0028] 18--Coupler 19--Shaper

[0029] 20--Acetylene-Oxygen Combustion Pool 21--Spectrometer

[0030] 22--Photodetector 23--Oscilloscope Detailed Implementation

[0031] To further understand the invention's content, features, and effects, the following embodiments are provided, along with detailed descriptions in conjunction with the accompanying drawings:

[0032] like Figure 1 As shown, a high-precision ultrafast detection structure for the acetylene combustion process based on time-frequency mapping is characterized by comprising:

[0033] The time-domain stretching module 1 is used to stretch the femtosecond pulses emitted by a single optical frequency comb to the nanosecond level, and includes an optical frequency comb 11, a tunable filter 12, a dispersion compensation fiber 13, and a power amplifier 14.

[0034] The time-frequency mapping module 2 is used to form interference fringes with multiple oscillation frequencies and to find the time-frequency mapping curve. It includes a beam splitter 15, an attenuator 16, an electric fiber delay line 17, and a coupler 18.

[0035] The dynamic combustion detection module 3 is used to obtain the transient phenomenon of acetylene gas combustion, and includes a shaper 19, an acetylene-oxygen combustion pool 20, a spectrometer 21, a photodetector 22, and an oscilloscope 23.

[0036] In the time-domain stretching module 1, the optical frequency comb 11 is connected in sequence to the tunable filter 12, the dispersion compensation fiber 13, and the power amplifier 14 to obtain a stretched pulse. The stretched pulse enters the time-frequency mapping module 2, and is split into two paths by the beam splitter 15. One path passes through the attenuator 16, and the other path passes through the motorized fiber delay line 17. The two paths are combined in the coupler 18 to obtain the probe light. The probe light enters the dynamic combustion detection module 3, and after passing through the shaper 19 and the acetylene-oxygen combustion pool 20, it is first transmitted to the spectrometer 21 to obtain the spectral information. Then, the spectrometer 21 is replaced by the photodetector 22 and the oscilloscope 23 to obtain the dynamic combustion information.

[0037] The dispersion-compensating fiber 13 broadens the femtosecond pulses emitted by the optical frequency comb 11 to a repetition period, completely recording the transient phenomenon of acetylene gas combustion within one period, thereby achieving nanosecond-level ultrafast detection and reducing the requirements for the acquisition and resolution capabilities of the photodetector 22 and the oscilloscope 23.

[0038] The dispersion-compensating fiber 13 can be modeled as a linear time-invariant system, with dispersions of different orders considered as subsystems. The overall transfer function is the product of the transfer functions of each subsystem.

[0039]

[0040] Where β nis the mode propagation function of n-order dispersion, w is the center frequency of the optical pulse, and L is the length of dispersion-compensating fiber 13.

[0041] When the dispersion-compensating fiber 13 exhibits only first-order and second-order dispersion, its outputs in the frequency and time domains are as follows:

[0042] A1(w)=H1(w)A0(w) (2)

[0043]

[0044] in, It is the inverse Fourier transform of H1(w), h0 is the complex amplitude, and t R =t-β1L, A0(w) is the input pulse.

[0045] There is a mapping relationship between the output in the time domain and the frequency domain. When only the second-order dispersion is considered, the mapping factor is a linear factor, i.e., β2L. When higher-order dispersion is considered, the mapping factor is often nonlinear.

[0046] The broadened pulse is processed by the time-frequency mapping module 2 to obtain a probe light containing multiple oscillation frequencies. The peak point of the probe light is found in the spectrometer 21 and oscilloscope 23, and a nonlinear polynomial fitting is performed to complete the search of the time-frequency mapping curve. Thus, the time-domain signal detected by the oscilloscope 23 can be converted into the frequency domain for analysis.

[0047] The motorized fiber optic delay line 17 can be used to adjust the delay time between the two paths and change the density between the oscillation frequencies of the probe light, thereby ensuring high precision.

[0048] The attenuator 16 can be used to adjust the energy difference between the two paths, thereby changing the stripe contrast between the spectrometer 21 and the oscilloscope 23.

[0049] In summary, the high-precision ultrafast detection of the acetylene combustion process based on time-frequency mapping of the present invention achieves a nanosecond-level detection rate by utilizing the high repeatability of a single optical frequency comb 11, reduces the high requirements on the acquisition system by utilizing the time-domain stretching characteristics of the dispersion-compensating fiber 13, and ensures high precision by using time-frequency mapping curves of multiple oscillation frequencies in the spectrometer 21 and oscilloscope 23. This makes it possible to record transient phenomena in an ultra-short time and has broad application prospects in ultrafast spectral detection.

[0050] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these modifications are within the scope of protection of the present invention.

Claims

1. A high-precision ultrafast detection device for the acetylene combustion process based on time-frequency mapping, characterized in that, include: The time-domain stretching module (1) is used to stretch the femtosecond pulses emitted by a single optical frequency comb to the nanosecond level, and includes an optical frequency comb (11), a tunable filter (12), a dispersion compensation fiber (13), and a power amplifier (14). The time-frequency mapping module (2) is used to form interference fringes with multiple oscillation frequencies and to find time-frequency mapping curves. It includes a beam splitter (15), an attenuator (16), an electric fiber delay line (17), and a coupler (18). The dynamic combustion detection module (3), which is used to obtain the transient phenomenon of acetylene gas combustion, includes a shaper (19), an acetylene-oxygen combustion cell (20), a spectrometer (21), a photodetector (22), and an oscilloscope (23): In the time-domain stretching module (1), the optical frequency comb (11) is connected in sequence to the tunable filter (12), the dispersion compensation fiber (13), and the power amplifier (14) to obtain a stretched pulse. The stretched pulse enters the time-frequency mapping module (2), and is split into two paths by the beam splitter (15). One path passes through the attenuator (16), and the other path passes through the motorized fiber delay line (17). The two paths are combined in the coupler (18) to obtain the probe light. The probe light enters the dynamic combustion detection module (3), and after passing through the shaper (19) and the acetylene-oxygen combustion pool (20), it is first transmitted to the spectrometer (21) to obtain the spectrum information. Then, the spectrometer (21) is replaced by the photodetector (22) and the oscilloscope (23) to obtain the dynamic combustion information.

2. The high-precision ultrafast detection device for acetylene combustion process based on time-frequency mapping according to claim 1, characterized in that, The dispersion-compensating fiber (13) broadens the femtosecond pulses emitted by the optical frequency comb (11) to a repetition period, and records the transient phenomenon of acetylene gas combustion completely within one period, thereby realizing nanosecond-level ultrafast detection and reducing the requirements for the acquisition and resolution capabilities of the photodetector (22) and oscilloscope (23).

3. The high-precision ultrafast detection device for acetylene combustion process based on time-frequency mapping according to claim 1, characterized in that, The broadened pulse is processed by the time-frequency mapping module (2) to obtain a probe light containing multiple oscillation frequencies. The peak point of the probe light is found in the spectrometer (21) and oscilloscope (23) and nonlinear polynomial fitting is performed to complete the search of the time-frequency mapping curve, thereby converting the time domain signal detected by the oscilloscope (23) into the frequency domain for analysis.

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