Interaction experiments of laser light with low density supercritical foams at the AEEF ABC facility

Experiments have been performed on the interaction physics of laser light w ith polystyrene and agar-agar foams having average densities higher than cr itical. The experiments have been performed at the ABC facility of the Asso ciazione EURATOM-ENEA sulla Fusione, in Frascati. The main addressed topics have been energy coupling (balance), diffusion of energy into the target, plasma and dense phase dynamics, and harmonics generation. The laser light (lambda = 1.054 mum) was focused by a F/1 lens to produce on the target sur face about 1.6 X 10(14) W/cm(2) (approximate to 10(15) W/cm(2) in the waist , set about 100 mum inside the target). Experiments have shown efficient en ergy coupling (>80%) to be attributed to cavity formation in the low densit y foam (efficient light absorption) and good mechanical coupling of the pla sma trapped in the cavity to the dense phase (ablation pressure work). Heat diffusion possibly plays a transitory role in the initial stages of the in teraction (300-500 ps). Time integrated harmonics measurements revealed a b lue-shifted 2 omega and a red-shifted 5/2 omega.