Vacuum heating vs skin layer absorption of intense fs laser pulses

Crossing of the narrow skin layer in solid targets by electrons in a time shorter than a laser cycle represents one of the numerous collisionless absorption mechanisms of intense laser-matter interaction [1, 2, 3]. This kinetic effect is studied by a test particle approach in an energy interval extending into the relativistic domain. Three main results obtained are the strong dependence of the energy gain by the single particle on the instant of injection relative to the phase of the light wave, the reflection of the particles primarily contributing to absorption well in front of the target, and absorption hardly exceeding the 10% limit. The simulation results shed new light on “vacuum heating”. Looking through the enormous amount of theoretical papers that have appeared on ultrashort intense light pulse interaction with dense matter three aspects emerge,