Center for Excitonics

Events

Probing Valance and Core Excitons in Molecules by Coherent Multidimensional Spectroscopy with Clasical and Quantum Light

September 20, 2011 at 3pm/36-428

Shaul Mukamel
University of California, Irvine

Abstract:
Multidimensional spectroscopic techniques which originated with NMR in the 1970’s have been extended over the past 18 years to the infrared and visible regimes. Novel extensions of these ideas to study excitons in the ultraviolet and the x-ray regimes, which make use of entangled photons, will be discussed. Two dimensional ultraviolet (2DUV) spectra of protein backbone and side chains are presented. The signals provide new insights into the protein structures, dynamics and functions. Simulated chirality-induced 2DUV spectra reveal characteristic patterns of protein secondary structures, and explore the structure and aggregation mechanism of amyloid fibrils which are associated with over 20 diseases related to protein misfolding. Signatures of aggregation propensity of peptides are identified. Energy- transfer and charge-separation pathways in the reaction center of photosystem II may be revealed by two-dimensional techniques in the visible. The excited state dynamics and relaxation of electrons and holes and their 2D signatures are simulated.

Time-domain experiments that employ sequences of attosecond x-ray pulses in order to probe electronic and nuclear dynamics in molecules are made possible by newly developed bright coherent ultrafast sources of soft and hard x-rays. By creating multiple core holes at selected atoms and controlled times it is possible to study the dynamics and correlations of valence electrons as they respond to these perturbations. Electron motions can thus be directly probed by detecting x-ray photons or photoelectrons. Two-dimensional stimulated x-ray resonant Raman spectra of core excitons are predicted. Novel 2D signals that make use of entangled photons will be presented. Entangled photons offer an unusual combination of bandwidths and temporal resolution not possible by classical beams. Contributions from different resonances can be selected by varying the parameters of the photon wave function. An assembly of non interacting atoms may become correlated upon interaction with entangled photons, and their density matrix can then show collective resonances. Possible experimental signatures of these effects are explored.

Bio:
Shaul Mukamel received his B.Sc degree in Chemical Physics in 1969 and his Ph.D. in 1976 both from Tel Aviv University. He served on the faculty of the Weizmann Institute and Rice University and in 1982 he joined the chemistry department of the University of Rochester and became a professor in 1985. In 2000 he became the Kenneth Mees Professor and in 2003 was appointed joint Professor of Physics. Since 2003 he serves on the faculty of UC Irvine as a Chancellor Professor of Chemistry.

Professor Mukamel’s group interests focus on the design of novel ultrafast multidimensional coherent optical spectroscopies for probing and controlling electronic and vibrational molecular dynamics in the condensed phase; Theoretical and computational studies and applications include attosecond nonlinear x-ray spectroscopy of molecules; Many-body theory of optical and photonic materials; a time dependent reduced density matrix framework for computing electronic excitations and nonlinear optical spectroscopy of conjugated polymers, molecular nanostructures, chromophore aggregates and semiconductor and solar cell nanoparticles; Folding and dynamical fluctuations in proteins and DNA; Long range electron transfer, energy funneling, and collective nonlinear optical response of biological light harvesting complexes; Photon statistics in single molecule spectroscopy; Nonlinear dynamics and fluctuations in quantum and classical optical response.

Mukamel is a Fellow of the American Physical Society and the Optical Society of America. He is the recipient of the Alfred P. Sloan, the Guggenheim, the Alexander von Humboldt Senior Scientist Award and the 2003 Lippincott award of the OSA.

VIDEO