Imaging with and without time resolution using femtosecond laser pulses

Femtosecond laser pulses were applied to four-wave mixing (FWM) microscopy with lateral resolution and to image one-dimensional ballistic electron transport in gold films with time resolution. The FWM microscope was illuminated with synchronized pulses from a Ti:sapphire laser and an optical parametric oscillator (OPO). The OPO was set up as part of the thesis and delivered an average power of about 60 mW tunable from 1 micron to 1.3 microns at pulse durations between 100 fs and 200 fs. The FWM microscope was designed to detect the long wavelength signal (infrared stimulated parametric emission, IR SPE) to probe electronic resonances of target molecules. A polarization sensitive detection scheme was applied to suppress the nonresonant background. The SPE signal proved to be insensitive to photo-bleaching, which is an inherent limiting factor in fluorescence microscopy. The FWM microscope was also applied to determine the real and imaginary part of the third-order susceptibilities of various dyes and solvents. Time-resolved fs pump-probe measurements were performed on thin Au films to image ballistic electron transport in these films. Damped oscillations in the transient reflectivity signals were observed, and are attributed to anisotropic ballistic electron motion and back-scattering at the film boundaries. A theoretical model based on a modified Fermi-liquid theory can explain the observed oscillation periods as a result of ballistic transport in directions determined by the actual shape of the Fermi surface of Au.