EXPERIMENTAL IDENTIFICATION OF 'VACUUM HEATING' AT FEMTOSECOND-LASER-IRRADIATED METAL SURFACES

摘要

The non-linear "vacuum heating" absorption mechanism proposed by Brunei and subsequently included in numerous theoretical discussions of the interaction of intense laser pulses with sharply bounded metal surfaces has been experimentally observed. The absorption is unique to p-polarized pulses at oblique angles of incidence with peak intensity above 10~(14) W/cm~2. The observed absorption scales as (Iλ~2 )~(0.64) and reaches 20% at 10~(15) W/cm~2. The absorption occurs when L≤x_(osc), where L is the scale length of a density gradient present at the surface and x_(osc) is the quiver amplitude in the laser field. The value of L has been measured in order to confirm the L≤x_(osc) regime. Conventional resonance absorption is negligible in this regime.