Geraldine A. Kenney-Wallace

Multiple modulation spectroscopy at radiofrequencies for picosecond laser spectroscopy

Extension de la spectroscopie de modulation au domaine des radiofrequences qui conduit a une amelioration du rapport signal/bruit dans le cas ou w 1 (frequence du faisceau pompe)=w 2 (frequence du faisceau sonde)

Subpicosecond Laser Spectroscopy: Pulse Diagnostics and Molecular Dynamics in Liquids

The advent of picosecond (ps) [1,2] and more recently the first femtosecond (fs) [3] laser pulses now offers access to a time regime in simple liquids which approaches an interval corresponding perhaps to less than one hundred collisions. Yet, within this period, intermolecular potentials are sensitive to local density and configurational fluctuations, and the molecular dynamics to spatial correlations, which may persist over hundreds of collisions. This is the glimpse of memory in liquids. To what extent the early time behaviour of a molecular system at liquid densities can be adequately described by hydrodynamic models, developed from generalised Langevin equations, or by kinetically motivated models emphasizing collisional behaviour, has been a topic of considerable theoretical interest[4] in recent years and a long standing goal of our research in picosecond and nonlinear laser spectroscopy[5]. However, because the temporal profile of the laser pulse is often of finite width with respect to the time-evolution of the molecular response and its decay, the properties of the pump and probe laser pulses become a significant and even deterministic part of the problem when exploring such memory in liquids.

Generation And Amplification Of Ultrashort Laser Pulses And Applications To Electron Trapping In Amorphous Media

The dynamics of electron localization in amorphous media are of considerable interest to fundamental studies of electron transport as well as to applications in picosecond optoelectronics. Since efficient photoionization at 10-12 s usually requires at least Mwatt power densities, we describe two complementary routes to obtaining ultrafast, high power laser pulses. We first report some novel applications of the optical Kerr effect in CS2 for picosecond pulse generation in ruby and pulse gating on the femtosecond time scale, and then describe an amplified, subpicosecond, synchronously mode-locked tunable dye laser system. Recent results on photoionization and electron trapping in liquids and clusters are then discussed.

Picosecond reorientational dynamics of oppositely charged dye molecules. Correlation with the dielectric friction

The rotational reorientation times (τrot) of charged dyes have been measured in polar protic and aprotic solvents, using difference frequency modulation picosecond pump‐probe spectroscopy. The dielectric friction (DF) model has been shown to explain nonhydrodynamic behavior in alcohols and alcohol/water mixtures but is unsuccessful in predicting observed differences between the dye molecules in other solvent systems. These deviations are correlated with specific solvation interactions for cations in some solvents.