Focussing of laser beams by means of a z-pinch formed plasma guiding system

It is shown that during a capillary discharge, plasma channels for guiding light from high-power lasers are temporarily formed. The experiments are performed with alumina capillaries of 2-mm radius and 14-cm length filled with about 100 Pa of helium, methane or hydrogen. The transmission of probe light is enhanced due to light guiding by a factor up to 20 during a time window of 5 ns. The results indicate the formation of a first channel, when the shock wave reaches the axis, and of a second channel after the reflection of the shock wave on the axis. Compared to simple focussing by a lens, in the guiding device the intensity-length product: increases by almost two orders of magnitude. Guiding is achieved over 180 times the Rayleigh length.