Schroeder This award provides partial support for the development of a kilohertz laser system designed to provide the synchronized near infrared (~1.5eV) and ultraviolet (~10eV) femtosecond pulses suitable for time-resolved, two-photon, excited-state angle-resolved photoemission spectroscopy (ARPES). The development of the femtosecond radiation source will follow recent advances in chirped pulse amplification and harmonic generation schemes using all solid-state Ti:sapphire laser technology. Together with an available ARPES spectrometer, this radiation source will be used initially to determine the excited-state electronic structure of high-quality high-Tc superconductor single crystals by exploiting the dynamics of carriers photoexcited by the infrared pulse into the unoccupied states above the Fermi level. Determination of the excited state electronic structure of high-Tc cuprates should provide unique information relevant to our understanding of the superconducting mechanism in these materials. These measurements will be extended to twined crystals and thin films in order to study the effect of grain boundaries and defects on the electronic structure and density of states of high-Tc superconductors. The intrinsic temporal resolution provided by this ultrafast two-pulse measurement technique will be used to determine the effect of defects and grain boundaries on electron recombination rates through a comparison with the photoexcited carrier dynamics in single crystals. The further extension of this experimental technique to study the electronic properties of technologically relevant high-Tc superconducting wire materials is also planned.
The femtosecond radiation source will also be used to investigate the dynamics of single biological molecules with non-degenerate two-photon confocal fluorescence microscopy. The intent is to determine the feasibility of using this technique to study conformational fluctuations of single protein molecules and to monitor protein-induced DNA folding dynamics through high-resolution molecular tracking. Knowledge of the biophysics of molecular conformational fluctuations are fundamental to our understanding of protein and DNA folding dynamics, and hence, also the operation of enzymes.
In addition, future research is planned with this source of femtosecond laser pulses in several diverse fields; time-resolved THz spectroscopy of high-Tc superconductors, determination of the reaction mechanism of protochlorophyllide oxidoreductase, ultrafast spectroscopy of novel magnetic multilayer materials, coherent control of carrier dynamics in semiconductor heterostructures, and the time-resolved photodissociation of molecules. %%% ***
