Research On Gas Raman Spectroscopy Detection Technology Based On Optical Feedback Cavity Enhancement

Gas detection is an important part of environmental protection,serving various industries with rapid development at present,but the traditional gas detection technology generally has some problems such as low sensitivity,serious interference and complex structure,which seriously hinder its development.With the emergence of lasers in the last century,people have found that the combination of laser technology and gas detection can improve the detection performance of gas,which is conducive to the application of gas detection in many fields.In this paper,the optical feedback cavity enhancement technology in laser technology is combined with Raman spectroscopy technology to carry out the research of gas Raman detection technology.The paper mainly consists of the following four parts:1.Raman spectroscopy principle and laser Raman enhancement principle.Based on the microscopic collision mechanism between photons and material molecules,the characteristics of scattered photons in different types of collisions are studied in combination with the round-trip process of excited molecular energy level transition.The advantages and disadvantages of gas detection technology based on different principles are analyzed.The basic principle of gas detection based on laser Raman spectroscopy is studied,and it is determined that high power laser is the key factor to obtain gas Raman scattering signal.The principle of multi-beam interference in optical resonator is analyzed,and the basic structure of common resonator is understood.2.Basic theory and optical feedback analysis of V-type three-mirror cavity.Based on the theory of laser transmission matrix and electromagnetic theory,the stable resonance condition of the resonator is deduced,and the light intensity transmitted by the cavity and the light intensity in the cavity are deduced.In order to avoid the influence of directly reflected light on the laser,this paper selects V-type three-mirror cavity as the gas cell,analyzes the specific process of optical feedback and the influence of optical feedback on the laser combined with the principle of light injection locking,theoretically deduces the optical feedback model of V-type three-mirror cavity,and understands the basic principle of optical feedback to realize frequency locking.Matlab program simulation and experimental results were used to analyze the influence of feedback rate and feedback phase.3.Construction of a V-shaped three-mirror cavity gas Raman spectrum detection device based on optical feedback cavity enhancement.In this paper,visible light semiconductor laser is selected as the basic light source of the device.The device is under constant temperature,vibration isolation and no light environment.The output light of the laser is scanned,modulated,collimated and reshaped.In combination with wavelength modulation method,the optical feedback injection locking is realized,and the laser power in the cavity is significantly enhanced,which provides sufficient preparation for the subsequent gas Raman spectrum signal collection.4.Construction of lateral collection optical path and Raman signal analysis.The optical path of Raman spectrum signal collection was built on the side of the cavity,and the concave mirror was used to improve the collection efficiency.The parameters of spectrometer and CCD camera were set by computer software,and the Raman spectrum signals of N₂,O₂,CO₂,CO,H₂,CH₄,C₂H₂,C₂H₆,C₂H₄ and mixed gases were collected by the detection device.The Raman frequency shift of each gas was determined and the detection limit was calculated.