Plasmas produced in laser-heated foam

Summary form only given, as follows. Laser-heated foam offers possibility of producing a large plasma with a density much lower than that resulting from laser-heating of a solid. Such plasmas may be of interest as a gain medium in X-ray lasers or as a long-scale-length plasma source for the study of parametric instabilities. Preliminary results of a study exploring the deposition of a 2.3 ns, 0.53 /spl mu/m laser pulse in Agar (CH/sub 2/O) suggest that, for a sufficiently small focal spot, the laser beam propagates into the foam target by strong self-focusing. This yields a plasma filament inside the foam with a diameter less than 50 /spl mu/m and a length exceeding 400 /spl mu/m.