Picosecond Thermodynamics in Underdense Plasmas Measured with Thomson Scattering.

ABSTRACT

The rapid evolutions of the electron density and temperature in a laser-produced plasma were measured using collective Thomson scattering. Unprecedented picosecond time resolution, enabled by a pulse-front-tilt compensated spectrometer, revealed a transition in the plasma-wave dynamics from an initially cold, collisional state to a quasistationary, collisionless state. The Thomson-scattering spectra were compared with theoretical calculations of the fluctuation spectrum using either a conventional Bhatnagar-Gross-Krook (BGK) collision operator or the rigorous Landau collision terms the BGK model overestimates the electron temperature by 50% in the most-collisional conditions.