Enhanced Backscatter with a Structured Laser Pulse

A large-amplitude backscatter instability, consistent with Brillouin, occurs when a prepulse plasma is formed ahead of a high-irradiance (${10}^{15}$-${10}^{16}$ W/${\mathrm{cm}}^2$) Nd-laser pulse. These results indicate that temporally structured laser pulses suggested for laser pellet implosion may also encounter large backscatter.