Experimental study of preformed plasmas using the Titan laser at LLNL

In ultra-high intensity ($>$10$^{19}$ W/cm$^{2})$ ultra-short ($\sim $picosecond scale) pulsed laser plasma experiments, the main irradiating pulses are usually preceded by nanosecond scale of pre-pulses, due to amplified stimulus emission (ASE). The ASE generates pre-plasma, which is often characterized by its scale-length, the spatial decay length of the plasma density. These preformed plasmas are believed to play an important role in laser-plasma interactions and in accelerating charged particles, such as electrons. To better understand their role in producing charged particle beams in laser-solid target interactions, we have investigated, using optical interferometry, pre-plasmas produced by a controlled nanosecond-long pulse laser and also ones created by the ASE of the short-pulse Titan laser at Lawrence Livermore National Laboratory. I will present the optical interferometry data and compare the characteristics of pre-plasmas from both the LP and ASE cases.