High power laser guiding in a capillary discharge waveguide at LBNL

We will present progress on guiding experiments of a high power, short pulse laser in a capillary discharge waveguide. In the experiments, capillaries are used that are produced by laser machining 200-400 micron slots in sapphire plates. The capillary is then filled with hydrogen gas (1-9 10$^{18}$cm$^{3})$ and fully ionized by an electric discharge. Ohmic heating and diffusion create a parabolic plasma density profile that is ideally suited to guide the laser beam. Past experiments have shown guiding efficiencies of up to 90{\%}, with clean Gaussian mode profiles [1]. We will present progress towards guiding record-high intensities (10$^{18 }$W/cm$^{2}$ and above) in these structures using the LOASIS laser system at LBNL, focusing on a regime where relativistic guiding effects start playing a role. Applications of this waveguide as an accelerating structure in a Laser Wakefield Accelerator will be discussed. This work is supported by US DoE, DE-AC02-05CH11231 and in part by the Research Councils UK, Basic Technology Program (GR/R88090), DOE/NNSA under UNR grant DE-FC52-01NV14050, NSF, and AFOSR. [1] D. J. Spence, A. Butler, S. M. Hooker, J. Opt. Soc. Am. B, \textbf{20}, p138, 2003