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 with polystyrene and agar–agar foams having average densities higher than critical. The experiments have been performed at the ABC facility of the Associazione 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 (λ = 1.054 μm) was focused by a F/1 lens to produce on the target surface about 1.6 × 1014 W/cm2 (≈1015 W/cm2 in the waist, set about 100 μm inside the target). Experiments have shown efficient energy coupling (>80%) to be attributed to cavity formation in the low density foam (efficient light absorption) and good mechanical coupling of the plasma trapped in the cavity to the dense phase (ablation pressure work). Heat diffusion possibly plays a transitory role in the initial stages of the interaction (300–500 ps). Time integrated harmonics measurements revealed a blue-shifted 2ω and a red-shifted 5/2ω.