Plasma plume influence on laser pulse evolution in capillary discharge waveguides

Gas-filled capillary discharge waveguide is an useful medium for investigating high-power laser-plasma interactions over extended lengths because guiding can increase the interaction length to many Rayleigh lengths. The role of the gas plasma plume at the entrance of a CDW in increasing the laser intensity is under investigation. Experimentally have been performed different measurements of the plasma density profiles in the region adjacent to exit plane of capillary. Simulations of laser pulse evolution in this region, employing simulation codes and analytical functions, show that relativistic self-focusing may lead to an increase of the pulse intensity compared to the case without the plume. Measurements show that the on-axis plasma density over this region is close to that inside the waveguide (~1018 cm-3). Here the laser beam converges to the smallest focal spot and relativistic self-focusing leads to an increase in the laser intensity. If injection is guaranteed to occur early, the required length would only be of the order of 3-8 mm for our parameters, with important advantages of a lower discharge voltages for gas breakdown, and an easier alignment of laser beam