Quadrature interferometry for plasma density measurements

Summary form only given. A quadrature interferometer has been used routinely in several pulsed power experiments to measure the line-averaged electron density. The optical source is a 30 mW, continuous wave Nd-YAG laser operating at 1300 nm. The light is coupled directly to an optical fiber and split into reference and scene beams with a fiber splitter. The scene beam is transported to and from the plasma using single mode optical fibers up to 100 m in length. To simplify alignment through the plasma, we have used GRIN lenses on both the launch and receive sides of the single pass transmission diagnostic where this is possible. The quadrature optics allow for an unambiguous determination of the slope of the density changes at inflection points. Final setup of the interferometer is facilitated by looking at the Lissajous figure generated from the two quadrature components. We have used this interferometer to diagnose the background density in the Pegasus-II power flow channel, to study the plasma plume generated in foil implosion experiments, to measure the plasma blowoff during implosions, and to understand the plasma formation mechanism in a fusion target plasma system.