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The method used to deduce the spectral density distribution of intermolecular and intramolecular (vibrational) degrees of freedom in the liquid state from optical heterodyne detected optical (Raman-induced) Kerr effect (OHD-RIKE) measurements is reexamined within a multimode Brownian oscillator model. The ramifications of nonlinear coupling of the nuclear degrees of freedom to the medium polarizability are explored for discrimination between "homogeneous" and "inhomogeneous" contributions to the vibrational spectral density. Under physically reasonable assumptions, an estimation of the homogeneous contribution to the vibrational line shape can be made from the OHD-RIKE observable (if nonlinear coupling is nonnegligible). The model is developed generally, and calculations are applied specifically to temperature-dependent OHD-RIKE measurements of liquid water. The results indicate that the line broadening in the low-frequency vibrational distribution due to the hydrogen-bonded network structure of liquid water is mostly inhomogeneous, with an effective homogeneous relaxation time of 350 fs at 24°C.

Heterogeneous electron transfer involves the coupling of a dense manifold of highly delocalized electronic levels of the solid state to a discrete molecular state as well as an abrupt change in phase in the reaction coordinate. These features make this problem unique relative to homogeneous solution phase or gas phase reaction mechanisms which involve coupling between discrete states within a uniform medium. Recent advances in time domain optical methods are discussed in the context of studying interfacial charge transfer processes at single crystal semiconductor surfaces as a means to probe the primary processes governing heterogeneous electron transfer. Two distinct boundary conditions are discussed: charge injection into a semiconductor from an adsorbate and charge emission from a semiconductor to an acceptor. The reaction dynamics are investigated using a combination of nonlinear spectroscopies with an emphasis on mapping the electron transport and transfer and investigating the role of nuclear vs electronic relaxation mechanisms in the bamer crossing dynamics. A fundamental understanding at this level seeks to determine the criteria for fully optimizing charge separation at surfaces.

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A diode-pumped Yb:YAG laser with a novel end-pumped zigzag slab architecture has been developed. This architecture provides uniform transverse pump profiles, conduction cooling of the laser crystal, mechanical robustness, and ready scalability to higher powers. At room temperature the laser emits 415 W of cw power with 30% optical conversion efficiency. An image-inverting stable resonator permits a high-brightness output of 252 W with linear polarization and an average M(2) beam quality of 1.45. Q-switched pulse energies of as much as 20 mJ and average Q-switched powers of as much as 150 W were obtained while M(2) was maintained at <1.5.