High-sensitivity interferometry of plasmas and gases in pulsed power experiments

Accurate measurements of plasmas and gases in pulsed power devices are needed so they can be used (or avoided) as desired. This paper reviews measurements of plasmas and gases using the high-sensitivity, two-color interferometer in use at the Naval Research Laboratory (NRL) since 1993. The instrument uses two cw Nd:YAG lasers at 1.064 and 0.532 /spl mu/m wavelengths that can be aligned along the same line-of-sight to simultaneously measure electron and neutral densities. This interferometer can measure optical path changes (phase shifts) as small as 10/sup -5/ waves. The interferometer's capabilities are illustrated by several examples, including the first measurement of electrons co-moving in vacuum with an intense proton beam, detection of gas turbulence, preionization of gas from a supersonic nozzle, and gas desorption from a metal surface exposed to intense UV.