Kollektive Energieabsorption von Mikroplasmen in starken Laserfeldern
The interaction of strong ultrashort laser pulses with atomic clusters is characterized by an efficient absorption of laser energy and unique features of energy conversion into x-rays, electrons, ions and fusion neutrons. In the present work, absorption of laser light by atomic clusters is studied in the intensity regime of outer ionization. Outer ionization refers to the emission of electrons from the cluster producing a hot collisionless plasma. Simulation methods for collisionless nanoscale plasmas in external fields are introduced. In particular, a one-dimensional point-sheet method, a two-dimensional electromagnetic particle-in-cell method and an electrostatic two- and three-dimensional particle method are presented and applied to absorption calculations for plane, cylindrical and spherical targets. Particle simulations with a regularized harmonic-core Coulomb force prove particularly efficient and can be performed for realistic spherical systems with both electron and ion motion. Absorption is studied in detail as a function of the laser frequency and intensity. Absorption by outer ionization is found to dominate at high intensities and at low frequencies below the Mie-resonance. It shows close analogy to the nonresonant absorption at a solid surface proposed by Brunel. However, it is found that the efficiency (mechanism) of energy conversion to free electrons cannot be simply predicted by this one-dimensional model. Corresponding scaling laws for 2-dimensional cylindrical and 3-dimensional spherical systems are obtained.
info:eu-repo/classification/ddc/530, Laserfeld, Cluster, Wechselwirkung, Plasma, Energieaufnahme, Physik, Mikroplasma, kollektive Absorption, intensive Laserpulse, Femtosekunden-Pulse
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