Evidence of filamentation (self-focusing) of a laser beam propagating in a laser-produced aluminium plasma

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 (< = 180 μm thick), high-density (0.05-0.9 Nsub(cr) where Nsub(cr) is the critical density) multiply ionised absorbing plasmas. Results are also reported of an experimental study in which filamentary structures have been observed 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 equal to 1013-1014 W cm-2 for nanosecond duration pulses in plasmas formed by irradiating light solids (Z < = 13). (author)