Formation of laser plasma channels in a stationary gas

Plasma channels with nonuniformity of about ±3.5% have been produced by a 0.3 J, 100 ps laser pulses in a nonflowing gas, contained in a cylindrical chamber. The laser beam passed through the chamber along its axis via pinholes in the chamber walls. Plasma channels with an electron density in the range of 1018 - 1019 cm-3 were formed in pure He, N2, Ar, and Xe. A uniform channel forms in an optimal pressure range at a certain time delay, depending on the gas molecular weight. The interaction of the laser beam with the gas leaking out of the chamber through the pinholes was not significant. However, the formation of the ablative plasma on the walls of pinholes by the wings of radial profile of the laser beam plays an important role in the plasma channel formation and its uniformity. A low-current glow discharge initiated in the chamber improves the uniformity of the plasma channel slightly, while a high-current arc discharge leads to overdense plasma near the front pinhole and further refraction of the laser beam. These results indicate the potential for using nonflowing gas targets to create uniform plasma channels.