Abstract of the Talk:
Multidimensional spectroscopy uses sequences of optical pulses to study dynamical processes in complex molecules through correlation plots involving several time delay periods. Extensions of these techniques to the x-ray regime will be discussed. Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses and the atomic selectivity of core X-ray excitations offer a uniquely high spatial and temporal resolution. Stimulated Raman detection of an X-ray probe may be used to monitor the phase and dynamics of the nonequilibrium valence electronic state wavepackets created by e.g. photoexcitation, photoionization and Auger processes. Conical intersections (CoIn) dominate the pathways and outcomes of virtually all photophysical and photochemical molecular processes. Despite extensive experimental and theoretical effort CoIns have not been directly observed yet and the experimental evidence is being inferred from fast reaction rates and some vibrational signatures. Novel ultrafast X ray probes for these processes will be presented. Short X-ray pulses can directly detect the passage through a CoIn with the adequate temporal and spectral sensitivity. The technique is based on a coherent stimulated Raman process that employs a composite femtosecond/attosecond X-ray pulse to directly detect the electronic coherences (rather than populations) that are generated as the system passes through the CoIn. New imaging techniques based on x-ray diffraction from electronic coherence in conical intersections will be presented. Quantum light opens up new avenues for spectroscopy by utilizing parameters of the quantum state of light as novel control knobs and through the variation of photon statistics by coupling to matter. Utilizing the quantum nature of light in nonlinear spectroscopy will be discussed. Entangled-photon pairs are not subjected to the classical Fourier limitations on the joint temporal and spectral resolution. Strong coupling of molecules to the vacuum field of micro cavities can modify the potential energy surfaces thereby manipulating the photophysical and photochemical reaction pathways.
Biography of the Speaker:
Shaul Mukamel is a Distinguished Professor of Chemistry and of Physics and Astronomy at UC Irvine and a member of the National Academy of Science. He received his Ph.D. degree from Tel Aviv University and served on the faculty at Rice University, the Weizmann Institute, and the University of Rochester. His research focuses on the design of ultrafast multidimensional coherent optical spectroscopies in molecules which span from the infrared to the X-ray spectral regimes and are used for probing and controlling electronic and vibrational molecular dynamics in the condensed phase. His theoretical and computational work shows how to employ these techniques to study energy and electron transfer in photosynthetic complexes, excitons in semiconductor nanostructures, and the secondary structure of proteins. His recent effort includes attosecond X-ray spectroscopy, utilizing the quantum nature of optical fields and photon entanglement to achieve temporal and spectral resolutions not possible with classical light, and nonlinear spectroscopy of nonadiabatic dynamics at concial intersections of molecules dressed by photons in microcavities. He is the author of over 900 publications and the textbook Principles of Nonlinear Optical Spectroscopy (1995), which paved the way for the field of multidimensional spectroscopy. His recent awards include the Ahmed Zewail ACS Award in Ultrafast Science and Technology, the Coblentz Society ABB Sponsored Bomem-Michelson Award, the William F. Meggers Award of OSA, and senior Humboldt and FRIAS fellowships.