Gas Detection Using Fast Linear-Frequency-Modulated Lasers

In people's daily production and life,explosion accidents caused by methane leakage,large amounts of harmful gases,and chemical gas leaks from the factory are incessant,prompting people to constantly explore more reliable and accurate gas detection methods to prevent the occurrence of these dangerous events.Common gas detection methods include optical detection,chemical detection.Compared with other detection methods,optical detection has the advantages of high sensitivity and easy operation.This paper studies one of the optical detection methods.The main focus of the work is to use external modulation technology,single sideband modulation technology and four-wave mixing principle to obtain a faster sweep frequency and wider spectral coverage.Research on technology.The experimental system uses MATLAB to write a program as the source of the Arbitrary Waveform Generator?AWG?signal data for program control output,producing a linearly rapidly changing signal.Using an external modulation technique,the EOM?Electro-Optic Modulator,EOM?is used as an intensity modulator to load the signal from the AWG onto the laser to obtain a fast linearly varying source with a linearity<10^-4 and a sweep rate of the order of MHz.In order to make the utilization of the light source higher,and obtain a larger sweep range and wider spectral coverage,the single sideband linear sweeping technology and the four-wave mixing principle are applied to the gas detection technology to build a perfect light source.A measurement system for generating and gas absorption spectroscopy.After realizing the output of the dual-mode and single-mode light source,the four-wave mixing principle is introduced into the experiment to do the four-wave mixing and the second-four-wave mixing,respectively,to obtain the double-frequency and quad-frequency.After the obtained light source enters the gas pool,the absorption spectrum of the gas is generated due to the mutual interaction of the light wave and the gas molecules.The measurement of gas concentration is based on the spectra we acquired and the Beer-Lambert law.According to the relatively stable wavelength range of the distributed feedback laser?DFB?provided by the laboratory,the acetylene gas in the absorption band around 1530.37nm will be tested for acetylene gas under different pressures.The absorption spectrum was inverted to an acetylene gas concentration of 99.24%.The measurement results are compared with the theoretical simulation results,and compared with the traditional gas sensing detection methods,the advantages and application prospects are analyzed.