Laser light absorption by a plasma with a very steep density gradient

Abstract
We investigated the behavior of reflectivity versus angle of incidence of a Cu target irradiated by 4‐ps laser pulses at 1.06 μm. From the data taken at 1013–1014 W/cm2 we show that optical resonance takes place also in the presence of very steep density gradients of the order of ∼0.15 μm. The role of collisions is discussed and illustrated by measurements taken at lower fluxes.