TIME-RESOLVED FLUORESCENCE AS A DIRECT EXPERIMENTAL APPROACH TO THE STUDY OF EXCITATION AND IONIZATION PROCESSES IN DIFFERENT ATOM RESERVOIRS

Several examples of laser-excited, time-resolved fluoresence waveforms are discussed to show how the essential parameters describing the interaction between the radiation and the atomic system can be directly evaluated. The results reported here have been experimentally obtained, with relatively fast detection electronics, in different atom reservoirs operated at atmospheric pressure, that is, an air-acetylene flame, an inductively coupled argon plasma and a graphite furnace. It is shown that the study of the complete temporal evolution (i.e., during and after excitation) of the population density of selected atonic levels, directly pumped by the laser or collisionally coupled to the laser-excited level, can provide important information about the dyamics of the interaction and the saturation behaviour of the transition as a function of the different atomization environments. In simple cases, collisional mixing and ionization rate coefficients can also be evaluated. The measurements discussed here have been obtained with the following elements: Au, Hg, Mg, Na, Pb, Sr and Tl. It is shown that the analytical relevance of the information gained from the waveforms is particularly significant when two or more lasers (i.e., excitation steps) are used in the techniques of Laser Induced Fluoresence (LIF) and Laser Enhanced Ionization (LEI) in flames and electrothermal atomizers.