Polarisation dependence of multiphoton spectroscopy
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Group theoretical techniques are used to analyse the polarisation dependence of multiphoton processes. The analysis is sufficiently general to be applied to all point group symmetries and in a wide variety of physical situations. For two photon spectroscopy, a method is developed for extracting the maximum information available from polarisation studies. It is shown that measurements involving circular polarisations of the light beams are always required to determine all the parameters contributing to the intensities. Detailed results are given for the case of time reversal even interactions for electric dipole coupling. The analysis is applied to non resonant vibrational Raman scattering in the presence of degenerate electronic states. Existing selection rules are extended allowing a proof that symmetric and antisymmetric amplitude terms do not interfere. Complete tables of selection rules are given for both oriented and random scatterers. Non linear effects are also considered. Diagram techniques provide an efficient method for separating the geometrical factors which contribute to the hyper Raman scattering intensity. New symmetry restrictions are postulated for the four photon C.A.R.S. process. Handed effects are also considered and in particular natural and induced circular dichroism. Both the M.C.D. and E.C.D. spectra are shown to be isotropic or axially symmetric in certain point groups.