Speaker
Description
Pump-probe ellipsometry has the ability to capture many essential aspects of a material's excited states and their dynamics, e.g. relaxation, recombination and scattering rates, carrier temperatures, bandgap renormalization, and band-filling effects. Quantitative analyses of selected of these aspects are carried out in the community with increasing success. With access to electronic structure calculations it is also possible to form a reasonably comprehensive picture of charge carrier dynamics from observed transient ellipsometry spectra.
However, in trying to fit models in which the transient dielectric function is derived from underlying charge carrier dynamics, we regularly encounter challenges. These are on the one hand technicalities like parameter correlations and badly conditioned Hessians of the cost function or likelihood, but also seemingly more fundamental inconsistencies between the assumed models and the processes underlying the real measurement data, especially as occupations of excited states approach conditions of population inversion.
In this talk we present, based on pump-probe ellipsometry measurements of different semiconductors, doped glasses and metals, how these difficulties present themselves, and how we may tackle them with numerical techniques, additional information from other experiments, and careful treatment of artifacts arising from the use of short pulses.