Research On Detection Of Methane By Cavity Ring-down Spectropy Based On DFB Laser

Methane is a major greenhouse gas with flammability and explosibility,thus it is regarded as an integral area of research in environmental inspection and other scientific explorations alike.Moreover,in a multitude of applications real time on-line tests on the concentration of methane are also an important part.This paper is focused on trace gas inspection by means of cavity ring-down spectroscopy both theoretically and experimentally.The set-up for narrow line-width DFB laser is established,and the influential factors for the cavity ring-down is analyzed in the purpose of measuring methane's concentration online.This technique has drawn increasing attention because of its high sensitivity and identifiability in spectroscopy.As the technology of trace gas inspection is still advancing,and air pollution is becoming worse,a highly sensitive inspection technique on trace gas is worthy to be presented and rewarding to be applied.First of all,an array of factors for the performance of optical cavity ring-down spectroscopy is analyzed respectively,such as cavity length,reflector,cut-off time of laser and so on.Particularly,the effect of the cut-off time on inspection data variation is derived from treatment of the intra-cavity energy formulae.Furthermore,a spectroscopy approach based on DFB CW laser source is introduced.The spectroscopy system structure is simplified through wave-length modulation electrically,mode matching and laser cut-off.A method of quadruple ring-cavity structure is proposed and its work principles of main parts are presented.Lastly,experimental results with a CW laser source are covered including spectrum data acquisition,and data analysis to obtain methane concentration under laboratory condition.Stability of inspection by scanning the overtone band of methane's absorption spectrum is accounted,and the methane's concentration is obtained under laboratory condition.