STUDY OF ATOMIC COLLISION PROCESSES WITH LASER RADIATION AND CHARGED PARTICLE IMPACT

Abstract

The work reported in this thesis (entitled 'STUDY OF ATOMIC COLLISION PROCESSES WITH LASER RADIATION AND CHARGED PARTICLE IMPACT') deals with the study of three types of the scattering processes. First is the laser assisted inelastic scattering of electrons with atomic targets. Second is.the elastic scattering of electrons and positrons by atomic targets at inter-mediate energies and the third is the inelastic scattering of electrons by He+ ion in a dense plasma. The thesis has been written in seven chapters. In Chapter 1 of the thesis' we give a general intro-duction of the subject and the various approximation methods used in studies on atomic collision processes. In Chapter 2, the laser assisted excitation hydrogen (1s-2s) and helium (11S-21S) atoms by electron impact is studied. We treat the laser atom interaction in dipole plus quadrupole approximation. The quadrupole contribution is found to be significant at the laser frequencies in the vicinity of the quadrupole allowed transitions. In Chapter 31, we study the excitation of forbidden transitions in lithium (2s-3s) and sodium - iv - (3s-4s) by electron impact in a resonant laser field. The frequency of the laser is chosen to match with either the transition frequency 2s-2p for lithium or 3s-3p for sodium. The laser field is assumed to be circularly polarized. For one photon absorption the total cross section at various laser intensities and incident energies are presented. In Chapter 4, the first order space translation approximation (STA.1)as given by Brandi etal [Phys. Rev. A17, 1900 (1978) and Phys. Rev. A19, 1058 (1979)] to study the electron-hydrogen scattering in a laser field is analysed. STA 1 is shown to be inadequate and a second order space translation approximation (STA 2) is presented. In Chapter 5, the elastic scattering of electrons and positrons by helium (11S) atom and in Chapter 6, the elastic scattering of electrons and positrons by hydrogen (ls) and lithium (2s) atoms at intermediate energies are investigated. In these chapters, we use the two potential approach. The distortion of the projectile and target polarisation are considered. For electron scattering, the exchange effect is also included. In Chapter 7, the electron impact excitation of ls-2s,ls-2p and 2s-2p transitions in He+ ion in a dense plasma is investigated. The collision strengths for these processes are obtained using the two potential model alongwith the Debye—Hbckel model of plasma screening.