Plasma Diagnostics using Cavity Ringdown Spectroscopy Combined with Optical Emission Spectroscopy

Cavity ringdown spectroscopy (CRDS) is a sensitive absorption spectral technique and capable of measuring absolution concentration of species in a variety of environments. In recent years, CRDS has been increasingly applied for plasma diagnostics. Through measurements of high resolution spectral linewidths of selected species, plasma gas kinetic temperature and electron density profiles can be determined from the lineshape broaden components (Lorentzian and Doppler components). Determination of the distribution of particular chemical species, such as transient radicals, can help understand plasma associated chemistry. Plasma thermo-equilibrium status can be evaluated by simultaneously analyzing ringdown-based absorption and optical emission spectra of a diagnostic agent in the plasma. This talk presents three powerful approaches for plasma diagnostics: analysis of linewidth broadening of selected optical transitions, determination of density distribution profile of chemical species, and simultaneous measurements of absorption and emission spectra. Additionally, the advantages and challenging issues of CRDS for plasma diagnostics will be discussed.