Equipment Enhancement for Femtosecond Pump-Probe Apparatus

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

This award is for additional instrumentation to expand the utility of the existing femtosecond pump-probe experimental setup in the Microscale Heat Transfer Laboratory. The current experiment utilizes the ultra-short (~190 fs) pulses from a passively mode locked Ti:Sapphire laser. This laser produces pulses with ~16 nJ/pulse at a repetition rate of 76 MHz. This facility has successfully been used over the past seven years in transient thermoreflectance experiments to make measurements of thermal transport in thin metallic films. It has also been used in transient thermotransmission experiments to study the fast carrier dynamics in thin film samples of hydrogenated amorphous silicon (a-Si:H) and similar alloys used in photovoltaic cells. More recently it has been used to attain sub-picosecond resolution of the transient reflectance of indium phosphide (InP) based films during hot carrier relaxation. These experiments have provided a better understanding of the thermophysical as well as optical and electronic properties of these thin film materials. The addition of the regenerative amplifier system to the current setup will produce ultrashort pulses of similar temporal and spectral characteristics, but with an increased pulse energy of more than two orders of magnitude and with a tunable repetition rate from single shot to ~300 kHz. This system, with the ability to provide high pulse energy (enabling studies of melting and of highly non-equilibrium systems) and a significantly reduced repetition rate (enabling studies on low thermal conductivity materials), will improve and enhance existing experiments while enabling new areas of research to be pursued. Advancements in the micro- and opto-electronics industries depend greatly on the development of thin film technology. This field has progressed rapidly with continued improvements in film growth and deposition techniques. While thin film technology has grown at a prodigious rate, our fundamental understanding of the dynamics of energy carriers in micro- and nanostructures has not kept pace. An improved understanding of excited carrier dynamics through these studies should prove beneficial for the optoelectronic, microelectronic, and photovoltaic industries, to name just a few.