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Among the various attempts to understand collisionless absorption of intenseultrashort laser pulses a variety of models has been invented to describe thelaser beam target interaction. In terms of basic physics collisionlessabsorption is understood now as the interplay of the oscillating laser fieldwith the space charge field produced in the plasma. A first approach to thisidea is realized in Brunel's model the essence of which consists in theformation of an oscillating charge cloud in the vacuum in front of the target.The investigation of statistical ensembles of orbits shows that the absorptionprocess is localized at the ion-vacuum interface and in the skin layer: Singleelectrons enter into resonance with the laser field thereby undergoing a phaseshift which causes orbit crossing and braking of Brunel's laminar flow. Thisanharmonic resonance acts like an attractor for the electrons and leads to theformation of a Maxwellian tail in the electron energy spectrum. Most remarkableresults of our investigations are the Brunel-like hot electron distribution atthe relativistic threshold; the minimum of absorption at $I\lambda^2 \cong(0.3-1.2)\times 10^{21}$ W/cm$^2\mu$m$^2$, in the plasma target with theelectron density of $n_e \lambda^2\sim 10^{23}$cm$^{-3}\mu$m$^2;$ the drasticreduction of the number of hot electrons in this domain and their reappearancein the highly relativistic domain; strong coupling of the fast electron jetswith the return current through Cherenkov emission of plasmons. The hotelectron energy scaling shows a strong dependence on intensity in themoderately relativistic domain $I\lambda^2 \cong (10^{18} - 10^{20})$W/cm$^2\mu$m$^2$, a scaling in vague accordance with current publishedestimates in the range $I\lambda^2 \cong (0.14-3.5)\times 10^{21}$W/cm$^2\mu$m$^2$, and a distinct power increase beyond $I=3.5\times 10^{21}$W/cm$^2\mu$m$^2$.

Collisionless absorption, hot electron generation, and energy scaling in intense laser-target interaction