Laser-plasma Interaction Studies Using above Critical Density Gas Jet Plasmas and a Multi-tw Co2 Laser*

CO2 laser-plasma interaction provides a unique parameter space for particle acceleration in a gas jet plasma taking place at a critical plasma density ncr ~ 10 cm and even at higher densities (3~10 ncr) of 10μm radiation. Here we report the latest results of our study of electron acceleration in a wide range of plasma densities 1~10 ncr using a multi-TW CO2 laser system at the UCLA Neptune Laboratory. To gain insight into plasma density profile evolution during ~120 ps long CO2 laser-plasma interaction, we used laser interferometry with two 1 ps, 532 nm probe pulses with variable delay of 5~120 ps. The knowledge of spatial distribution of accelerated electron beam transported through the overdense gas plasma is critically important for minimizing laser beam filamentation and for understanding influence of other laser-plasma instabilities. This should allow for optimization of CO2 laser driven shock wave acceleration of low-divergence monoenergetic ion beams [1].