Plasma parameters of a capillary plasma channel for laser guiding

Optical guiding of an ultrashort and intense laser pulse with long interaction length is important in many applications such as laser-driven plasma accelerators. To overcome this limitation, a waveguide which has a refractive index profile like an optical fiber is required [1]. We demonstrated the production of an optical waveguide in a capillary discharge-produced plasma using a cylindrical capillary. Plasma parameters of its waveguide were characterized by use of both a Normarski laser interferometer and a hydrogen plasma line spectrum. A space-averaged maximum temperature of 3.3 eV with electron densities of the order of $10^{17}$ cm$^{-3}$ was observed at a discharge time of 150 ns and a maximum discharge current of 200 A. An ultrashort, intense laser pulse was guided by use of this plasma channel. \\[4pt] [1] T. Higashiguchi $et$ $al$., Rev. Sci. Instrum. 81, 046109 (2010).