Thomson scattering from a shock front

Abstract

We have obtained a Thomson scattering spectrum in the collective regime by scattering a probe beam from a shock front, in an experiment conducted at the Omega laser at the Laboratory for Laser Energetics. The probe beam was created by frequency converting a beamline at Omega to a 2ns pulse of 0.263μm light, focused with a dedicated optical focusing system. The diagnostic system included collecting optics, spectrometer, and streak camera, with a scattering angle of 101°. The target included a primary shock tube, a 20-μm-thick beryllium drive disk, 0.3-μm-thick polyimide windows mounted on a secondary tube, and a gas fill tube. Detected acoustic waves propagated parallel to the target axis. Ten laser beams irradiated the beryllium disk with 0.351μm light at 5×1014W∕cm2 for 1ns starting at to, driving a strong shock through argon gas at ρo=1mg∕cc. The 200J probe beam fired at t=19ns for 2ns, and at t=20.1ns a 0.3ns signal was detected. We attribute this signal to scattering from the shocked argon, before the density increased above critical due to radiative collapse.