Investigation of the interaction of subpicosecond KrF laser pulses with a preformed carbon plasma

Abstract

The interaction of a subpicosecond KrF laser pulse with a preformed carbon plasma of various scale lengths is investigated. Two different interaction geometries are chosen. In the first one the propagation vector of the short pulse has a component along the density gradient of the preformed plasma (angle of incidence is 45°). In the second geometry the propagation direction of the short pulse is perpendicular to the density gradient of the preplasma (angle of incidence is 90°). The emitted soft X-ray spectrum in the wavelength interval from 10 to 700 Å is observed while changing several parameters of the experiment. It is found that the emission in the “short” wavelength part under 200 Å results from the radiation of ions created by collisional heating near the critical density region. The “long” wavelength part above 200 Å, enhanced up to a maximal factor of 20, is mainly produced by radiating particles field—ionized up to the He-like carbon state in the high-intensity laser field. The “short” wavelength part is missing in the case of 90° angle of incidence because there is no interaction with the critical layer that results in an insufficient collisional heating.