Theoretical And Experimental Studies In Visible Laser Spectroscopy

In this thesis, two different aspects of the interaction of radiation with molecules are studied. First, a previously-derived exact solution to the time-dependent Schroedinger equation describing the interaction between a sinusoidally-oscillating field and an N-level atomic or molecular system is used to examine the temporal and steady-state behaviour of a five-level model molecular system. Secondly, the technique of polarization labelling spectroscopy is used to study the E 0(,g)(\u27+) state of the iodine molecule.;The behaviour of the five-level system, consisting of a ground state and four nearly degenerate excited states, is studied for various experimental conditions, and for single- and three-photon transitions. From these calculations, it is possible to predict some aspects of the behaviour of molecules in laser radiation fields of varying intensities. When the laser intensity is strong, the excited states behave like a single band. When the laser intensity is weak, an interpretation in terms of individual two-level systems is possible. The multi-photon results show that an underlying interaction between levels persists even when the spectrum appears to consist of well-separated peaks.;The introduction of differing individual relaxation terms for the energy levels is discussed, and it is shown that the previous formalism for the undamped temporal results, with some modifications, can be used to describe the damped systems. A uniform damping model is used to demonstrate how peaks in a steady-state spectrum corresponding to transitions with differing temporal behaviour can be differently damped. Generally, the temporal behaviour of the undamped system is useful for predicting the results in the damped examples.;In polarization labelling spectroscopy, only probe laser radiation corresponding to labelled transitions is recorded, so the technique is very useful in simplifying otherwise complicated molecular spectra. In this work, the technique has been used in a two-photon excitation experiment to study the E state of the iodine molecule. Although iodine has been studied extensively, the ion-pair states are only now being well-characterized. The results of the polarization labelling experiments presented here are used to obtain better determinations of the molecular constants describing the E state