Study On Multi-component Sensing Of Trace Gas In Laser Intracavity Based On QEPAS

In recent years,sudden environmental pollution accidents caused by toxic and harmful gases have not only posed a serious threat to human health and life safety,but also caused huge losses to national property.Therefore,it is extremely crucial for trace gas to establish rapid and accurate detection and analysis methods.At present,photoacoustic spectroscopy technology has the problems of single detection component and low detection limit,which can not meet the requirements of the industry.Photoacoustic spectroscopy based on quartz enhanced laser intracavity has the advantages of strong anti-interference ability,good selectivity,high detection sensitivity and low background noise.It has important research significance in the field of multicomponent trace gas detection.In this paper,a multi-component gas sensing system based on ring cavity erbium-doped fiber laser is designed by using quartz enhanced photoacoustic spectroscopy(QEPAS)technology.The amplified spontaneous emission(ASE)spectrum of C band and L band erbium-doped fiber laser has carried on the simulation analysis,ASE spectral output power is obtained,and on the experiment by changing the length of the erbium-doped fiber explored under different pump power of the size of the laser output power,the length of C band and L band erbium-doped fiber is determined.In order to realize the output of multiple wavelengths of the laser and avoid the mode competition between multiple wavelengths,the time-dividing operation of the C-band and L-band intracavity is realized by optical switching,which can effectively use the laser power and reduce the loss of each wavelength at the same time.Aiming at the design and optimization of multi-component gas sensing system,the“On-Beam” tuning fork structure is used to detect the photoacoustic signal,and the response frequency of the quartz tuning fork is 32.758 k Hz at room temperature.The grating of each wavelength is scanned by piezoelectric ceramic driving,and the variation trend of driving voltage with wavelength is obtained.Based on time division multiplexing technology,the gas time-dividing detection is realized by controlling the on-off switching of optical switch and multiple fiber gratings.According to the different positions of tuning fork gas cell,three gas sensing structures are proposed,and the three structures are experimentally explored.Comparing the experimental results,an optimal multi-component gas detection system is proposed,which greatly improves the intensity of photoacoustic signal.Taking acetylene and carbon dioxide as examples,experiments are carried out under normal temperature and pressure using multi-component gas sensing system based on intracavity erbium-doped fiber laser,the linear fitting and minimum detection limit of acetylene are 0.9996 and 0.229 ppm respectively,and the linear fitting degree and minimum detection limit of carbon dioxide are 0.9966 and 158.74 ppm respectively,which proves that the system has good linear response and high sensitivity.