B. M. Chernobrod

Electron transfer in the inverted region: Adiabatic suppression and relaxation hindrance of the reaction rate

Kramers’s model is applied to an electron transfer reaction in the inverted region. The reaction rate is considered at different values of the coupling matrix element and the damping, which is a measure of the interaction of the reaction coordinate with the other, nonreactive degrees of freedom of the system. The coupling characterizes overlap of the electron orbits of the donor and acceptor. It is shown that at the low/high damping the reaction rate is controlled by the slowest of the two rates. One is the thermally averaged transition rate (the reaction rate in the intermediate damping regime) and another one is the rate controlled by the energy/spatial diffusion. We demonstrate that the reaction rate as a function of the electron coupling shows a striking difference from the normal region case. The rate passes via maximum and decreases exponentially with the increase of the coupling.

PUMP-PROBE SPECTROSCOPY OF H-BONDS AS THE LEVEL-CROSSING PROBLEM

Saturation of the H-bond absorption spectra by a strong laser field is described as a level-crossing problem with diffusional motion along the reaction coordinate. The stationary populations of the ground and excited vibronic states were found, assuming that the light induced transitions between them occur only at the point of exact resonance and the nonradiative decay of the upper state is uniform. The stationary distributions in both states are also obtained and shown to be Gaussian at slow vibrational relaxation, but essentially distorted when relaxation is faster than diffusion. The absorption spectra of the weak probe light in the frame of two-level and three-level models are calculated, which show either loss or gain in different spectral regions. The existence of bleaching and superabsorption branches in corresponding transmission spectra are confirmed.

PUMP-PROBE SPECTROSCOPY OF H-BONDS : SATURATION KINETICS AND SPECTRAL TRANSFORMATION DURING AND AFTER PUMPING

The saturation kinetics of the H-bond absorption spectra in a strong laser field is described as a level-crossing problem with diffusional motion along the reaction coordinate. The full analogy with kinetics and rate of electron transfer reactions is emphasized when vibrational relaxation to the ground state is negligible. In this case, the transition rate saturates with a field strength reaching the diffusional regime limited by the friction in the ground or excited state. Taking vibrational relaxation into consideration changes qualitatively the kinetics of approaching the stationary level populations and absorption of pumping light. The fast relaxation results in significant desaturation of the light induced transitions and a shortening of the transient time. The absorption spectra of the weak probe light in the context of two-level and three-level models show either loss or gain in the red wing, as well as bleaching and superabsorption in the corresponding transmission spectra. The time evolution of t...

Coherent scattering for efficient near field microscopy

Summary form only given. A large class of near-field optical microscopes employ tapered Al coated single mode optical fibers which form a subwavelength aperture at their ends. Better spatial resolution had been achieved at IBM by an apertureless scheme in which a sharp nanosize probe of an AFM device was externally illuminated and the amplitude of the scattered light was interferometrically measured in the far-field zone.