4 J un 2 00 6 Collisionless energy absorption in nanoplasma layer in regular and stochastic regimes .

Collisionless energy absorption in 1D nanoplasma layer is considered. Straightforward classical calculation of the absorption rate in action-angle variables is presented. In regular regime the result obtained is the same as in [4], but deeper insight is possible now due to the technique used. Chirikov criterion of the chaotic absorption regime is written out. Col-lisionless energy absorption rate in nanoplasma layer is calculated in stochastic regime. 1 Collisionless absorption in regular regime. One of the novel problems of laser-matter interaction is the problem of energy absorption in nanometer targets subjected to an ultrashort (up to few picosec-ond) intence (10 13 −10 17 W/cm 2) laser fields. During such interaction hot (up to several keV energy) classical plasma bounded in nanoscale volume is produced, which has a life time of about hundreds of femtoseconds. This is dense plasma with the electron density of 10 23 cm −3 and more. Such systems are used to be called nanoplasma since first experiments of intense short laser interaction with three-dimensional nanobodies (atomic Van-der-Vaals clusters) were hold in 1996 [1]. Nanobodies are known to absorb much more compared to traditional targets like gas or even bulk. The great amount of energy contained in tiny volume results in breakdown, birth of energetic particles and high harmonics generation [2, 3]. Different mechanisms of absorption were suggested to explain such phenomena. They are inner ionization, inverse bremsstrahlung effect, vacuum heating, collisionless heating and some others a bit more sophisticated. As far as nanoplasma is a strongly bounded system with the width much less than laser wave length, the most interesting mechanism of energy absorption in it is collisionless heating in self-consistent potential. It was considered recently in one-dimensional systems corresponded to irradiated films and more deeply in three-dimesional systems which correspond to nanoclusters; the important role of it in the absorption process was evidently shown (for 1D situation see [4]).