University of Connecticut

Events Calendar

UConn Physics Colloquium

Friday, September 22, 2017
3:30pm – 4:30pm

Storrs Campus
Physics Building, Room PB-38

Prof. Shaul Mukamel, University of California, Irvine

Ultrafast Multidimensional Spectroscopy of Molecules with x-ray pulses and Quantum Light

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.

REFERENCES

[1] J. Biggs, D. Healion, Y. Zhang, and S. Mukamel, Ann Rev Phys Chem, 64, 101-127 (2013).

[2] M. Kowalewski, K. Bennett, K. Dorfman, and S. Mukamel, Phys. Rev. Lett. 115, 193003 (2015).

[3] M. Kowalewski, K. Bennett, and S. Mukamel, Structural Dynamics, 4,054101 (2017)

[4] K. E. Dorfman, F. Schlawin, and S. Mukamel, Rev. Mod. Phys. 88, 045008 (2016)

Contact:

Prof. Nora Berrah

Physics Department (primary), UConn Master Calendar

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