Dynamics of intense laser channel formation in an underdense plasma

Abstract

Efficient guiding and propagation of multi-keV x-rays in plasmas can be achieved by dynamically modifying the media through plasma channel formation. The dynamics of plasma channel formation is studied in preformed underdense plasma irradiated by a high intensity laser. This is done by a two-dimensional model coupling laser propagation to a relativistic particle-in-cell model. For laser intensity of 1020W∕cm2 and a laser beam width of 5μm the channel formation proceeds on a time scale of 60–70fs in uniform plasma with density 1018cm−3. The channel closes shortly after the rear of the laser pulse has passed due to Coulomb attraction from the ion core. Electron cavitation occurs only if the laser intensity is above a certain threshold intensity and the laser pulse duration exceeds 100fs. X-ray generation and propagation is feasible for ultrarelativistic laser pulses with small beam width, less than ∼20μm, and duration of more than 100fs.