The optical pumping of liquid active media

Abstract

The excitation of liquids to produce optical amplification depends on a number of factors associated with the molecular properties and the intra molecular structure of liquids. The most important factors determining the efficiency of the activation process are the lifetimes of the states which decay to produce laser transitions and the various mechanisms by which the excitation may be by-passed, for example, by the excitation of triplet states of dyes.In a given column of excited liquid, the optical gain of the column will depend on the population inversion, the column length and the reflectivities of the mirrors defining the optical cavity. The latter mirror reflectivity may be enhanced by non linear optical processes in the liquid in the course of which hypersonic waves may be stimulated, or a stationary wave of thermal origin may be brought into existance which could introduce a periodicity of refractive index into the column.The purpose of this investigation is to design and develop a very fast flashlamp pumped dye laser system which will have an active lasing time period >100 ns so that triplet state population and any major thermal effects become less important. The design parameters for ultrafast ultra violet lights sources are also investigated.The first part of the thesis considers the criteria required for the efficient optical excitation of a liquid and describes the design and construction of fast light sources. The properties of strip line pulsers are considered in detail, and the results from a series of prototype devices are evaluated. These include specially designed coaxial flash lamps as well as the usual linear type. Preliminary experiments and problems associated with achieving lasing output from rhodamine 6G are discussed.