Inelastische Prozesse in ultra-kurzer Laser-Materie-Wechselwirkung

Abstract

Within the framework of this thesis particle-in-cell (PIC) simulations of relativistic laser matter interaction have been developed including inelastic processes such as field and electron collisional ionization, binary collisions and bremsstrahlung. The code LPIC is a 1D3V PIC code with one spatial and three velocity dimensions. The implementation for field ionization is based on the ADK tunneling formula by Ammosov, Delone and Krainov or alternatively on the ''barrier suppression ionization'' model. Energy conservation throughout this process is realized by a fictitious ionization current withdrawing the ionization energy from the field. The electron collisional ionization is also energy conserving The binary Coulomb collisions are treated in a way that is equivalent to the Fokker-Planck operator in Landau form. With this code the ionization dynamics of a 1 #mu#m thick helium gas layer at slightly overcritical density (2n"c) using a six cycles long laser pulse with an intensity of 9 x 10"1"6 W/cm"2 is studied focusing on the time-dependence and clear identification of the different ionization mechanisms. Of particular importance is a new field ionization mechanism via quasi-static space charge separation fields generated by fast electrons leading especially at the rear surface of the target to directed electric fields of the same order of magnitude as the laser field amplitude. The feedback of the ionization on the reflected and transmitted pulse and the importance of collisional ionization are discussed. The fields at the rear side are characterized in space and time and compared to the ones at the front surface and systematic variations of the laser intensity and target density are investigated. With regard to an experimental realization a solid target is studied also. A 395 nm thick boron foil is irradiated with 10"1"8 W/cm"2 under 31 . The rearside electric field is quasi-static, parallel to the target normal and shows over a period of several laser cycles field strengths of the same order of magnitude as the laser amplitude (10"1"2 V/m). This field might be used to build a high Z ion source for heavy ion accelerators. (orig.)Available from TIB Hannover: RN 5339(248) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman