Abstract
The thresholds for self-focusing (filamentation) of a laser beam in a laser-produced plasma have been computed for propagation of nanosecond duration pulses in short (cr where Ncr is the critical density) multiply ionised absorbing plasmas. The authors also report results of an experimental study where they have observed filamentary structures in the X-ray emission from aluminium plasmas accompanied by an increase in the divergence of the light transmitted through them. Both observations indicate self-focusing has occurred at an intensity near to that predicted by the computer code, this being approximately=1013-1014 W cm-2 for nanosecond duration pulses in plasmas formed by irradiating light solids (Z<or=13).