Cavity Ring Down Spectroscopy measurements of Ar-II velocity distribution functions

The WVU helicon source group routinely uses laser induced florescence (LIF) to measure the ion velocity distribution function (ivdf) of argon plasmas. We are constructing a continuous wave Cavity Ring Down Spectroscopy (cw-CRDS) system that will provide an alternate approach to measuring the ivdf. CRDS is a proven, ultra-sensitive, laser absorption technique that will provide sufficient resolution to measure the Doppler broadened absorption line of Argon and other plasma species. We will use a CW tunable diode laser at 668.43 nm, pumping the Ar-II metastable 3d$^{4}$F$_{7/2}$ level to the 4p$^{4}$D$_{5/2}$ level, to gather data from our steady state, high density, helicon plasma source CHEWIE (the Compact HElicon Waves and Instabilities Experiment). The cw-CRDS data will then be compared to LIF measurements. Once optimized for the Ar-II transition, we will use a similar experimental configuration to complete the difficult measurement of the ivdf for He-II transition at 1012.36 nm. This report will present completed design schematics for the CRDS system as well as initial data gathered through the early stages of operation.