Study On Cavity Ring-down Spectroscopy Technology And Its Application

Cavity ring-down spectroscopy is an important kind of high sensitivity detection technology which is widely used in atmospheric chemistry analysis, industrial process control, spectrum detection of micro molecular and atomic system, biological sciences research, macro atmospheric environment monitoring, weak absorption detection, etc. The study of frequency domain cavity ring-down spectroscopy belongs to the category of cavity enhanced spectroscopy technology in spectrum detection.Firstly, the steady-state output of optical resonant cavity is studied. And then the dynamic response of cavity is mainly studied by taking the cavity as a linear and time invariant system, the ultra-short pulse as impulse function and through the approach of signal processing. The mathematical description obtained could fit any form of injected light waves. From the perspective of signal processing, the traditional P-CRDS and CW-CRDS could be considered as observation of impulse response and step response respectively. In the end of this chapter, some simulations of the dynamic response of cavity are done.Secondly, the cavity response to linear frequency chirped light-wave has been studied in the condition of low chirp, by taking the cavity as a fixed comb filter. The Fourier analysis of light power passing through cavity has been made and an analytic description has been given, which reveals the fact that the signal spectrum of light power is related to the absorption spectrum of material inside cavity. Based on this theoretic analysis, a new approach of cavity ring-down spectroscopy, called Frequency Domain Cavity Ring-Down Spectroscopy, has been put forward. Besides, the influence of light line-width is analyzed by mathematical description. The simulation results clearly show the spectral attenuation trend of different line-widths. This provides theoretical basis for the selection of laser.Finally, after introducing the various types of optical resonant cavity, a visibility sensor based on frequency domain cavity ring-down spectroscopy is designed. This sensor can absolutely meet the requirements when driving.