Supercontinuum Cavity Ring-down Spectroscopy And Its Application

This thesis deals with cavity ring down spectroscopy—a new method for making trace absorption measurements, particularly with gas-phase samples.when it is used in gas detection,we need supercontinuum source as the source of cavity ring-down spectroscopy,because that the different gas has different absorption bands..The supercontinuum light source, also known as the white light,the use of ultrashort pulse laser through a nonlinear medium high, due to the nonlinear effect to achieve a wide spectral output。When we use the supercontinuum light as the source to detect the gas-phase sample by cavity ring-down spectroscopy,we can get the quantitative live measurement of the gas-phase sample.Firstly,this paper has carried on the theoretical research of cavity ring-down spectroscopy,studied and analyzed the effect of cavity length and cavity mirrors to the experiment results.And then,we generate the supercontinuum radiation in sapphire fiber and fused silicon.In conclusion,an MLA enables high efficiency use of the available laser power in the formation of filament and SC generation,so high power can be depleted from the fundamental into the visible up to the mW/nm level.Finally,we measure the contribution of femtosecond filamentation to NO3 and O3.the result show that the generation rate of NO2 is about 103 times higher than that of NO3 at the same time.