Instability of filamentation and backscatter in laser produced plasmas

Optical observations of laser light (lambda = 0.53 μm) transmitted through thin foil targets suggests that self-focussed light filaments form and decay on a time scale of about 10 ps. In addition time resolved spectra of backscattered radiation show fine scale time modulations with a periodicity of 5 to 20 ps. This backscattered laser light is turned off shortly after the plasma becomes underdense indicating that it originates from plasma densities close to critical. Several models are discussed which may explain the observations. (author)