Filamentation instability in laser produced plasmas

This chapter examines laser beam filamentation driven either by ponderomotive force or thermal expansion effects in planar and in spherical geometry at various laser wavelengths using optical probing techniques, two dimensional imaging of harmonic emission, temporally resolving the laser beam burning through thin foil targets and by x-ray photography. Topics covered include mechanisms for self-focusing, optical probing, probing by using the heating laser beam, time integrated photographs, time integrated x-ray photography, other diagnostics, optical probing observations, time integrated harmonic emission photography, laser beam break-up due to target surface non-uniformities or jetting in the coronal plasma, experiments with an annular structure in the intensity distribution on the target surface, experiments on preformed plasmas, unstable filamentation, the comparison of the experimental results with theoretical predictions, detrimental effects of laser beam filamentation for laser compression experiments, hot electron and hard x-ray production, and non-uniformities in the ablation pressure. It is demonstrated that although the filaments may have grown from initial perturbations in the laser beams, the measured spatial periodicities are in close agreement to the spatial scalelengths of the theoretically predicted most unstable modes. Includes 5 drawings and 18 photos