11.12.18, Dr. Maxim Gelin "Femtosecond optical spectroscopy from the point of view of a theoretican"

Nonlinear femtosecond optical spectroscopy comprises a family of techniques such as fluorescence up-conversion, pump-probe, transient grating, photon echo, coherent anti-Stokes-Raman scattering, etc. These techniques differ in the number, ordering, and phase-matching directions of the pulses involved and in the specific information they deliver on the material system under study.

I will present my personal perspective on the development of nonlinear femtosecond spectroscopy from the point of view of a theoretician. Focusing on transient absorption pump-probe spectroscopy and three-pulse photon-echo two-dimensional (2D) spectroscopy, I will clarify the information content of these techniques and demonstrate how the dynamics of the material system under study can be uncovered from measured time- and frequency resolved signals.

Finally, I will discuss a possibility of applying these techniques in the strong-field regime (beyond the third order in system-field interaction). By explicit calculations of responses of selected model systems and by simulations of selected experiments, I will show that strong pulses can be used to enhance weak transitions, to provide time resolution beyond the pulse duration, to manipulate electronic & vibrational coherences, to get rid of electronic dephasing, and to visualize vibrational wave packets.