Title：Femtosecond pump-probe spectroscopy: why not try strong pulses?

Speaker: Maxim F. Gelin (Technische Universität München)

Time: Fridday, March 3, 15:00

Venue: Room 213, PhysicsBuilding, Wushan Campus

Abstract：Pump-probe spectroscopy is one of the key techniques in the arsenal of femtosecond molecular spectroscopy. The pump pulse excites molecular system, the probe pulse interrogates it, and the signal is recorded as a function of the time delay between the pump and probe pulses. Traditionally, femtosecond pump-probe spectroscopy is performed with weak pulses. The well-established method of the analysis of such signals is based on third-order perturbation theory in the light-matter interaction.

    The idea of strong-field pump-probe spectroscopy is to induce additional (beyond the third order) responses of the molecular system. By varying the strength and/or the duration of the pump pulse, a highly non-equilibrium vibrational wave packets can be created in the electronic ground state and excited electronic states. After the pump pulse is over, the system evolves according to its field-free dynamics until it is probed by another (strong) probe pulse.

    In the present talk, the non-perturbative theory of femtosecond pump-probe spectroscopy is outlined. By explicit calculations of pump-probe responses of selected model systems and by simulations of selected experiments, we show that strong pulses can be applied to enhance weak transitions, to provide time resolution beyond the pulse duration, to manipulate electronic & vibrational coherences, and to enhance the visibility of vibrational wave packets. It can be concluded that strong-pulse (nonperturbative) pump-probe spectroscopy allows us to extract more information from complex material systems than is accessible with weak pulses.

    1.  M. F. Gelin, Jayachander B. Rao, M. Nest, and W. Domcke. Domain of validity of the perturbative approach to femtosecond optical spectroscopy. J. Chem. Phys. 139, 224107 (2013).

    2.  M. F. Gelin, D. Egorova, and W. Domcke. Strong-pump strong-probe spectroscopy: effects of higher excited electronic states. Phys. Chem. Chem. Phys. 15, 8119-8131 (2013).

    3.  M. F. Gelin, D. Egorova, and W. Domcke. Strong and Long Makes Short: Strong-Pump Strong-Probe Spectroscopy. J. Phys. Chem. Lett. 2, 114-119 (2011).

    4.  M. F. Gelin, A. K. Belyaev, and W. Domcke. Pump-probe spectroscopy with strong pulses as a tool to enhance weak electronic transitions. Phys. Rev. A 87, 063416 (2013).

    5.  J. B. Rao, M. F. Gelin, and W. Domcke. Resonant Femtosecond Stimulated Raman Spectra: Theory and Simulations. J. Phys. Chem. A 120, 3286-3295 (2016).

About the speaker: Maxim F. Gelin received his PhD from the institute of physics of the national academy of science of Belarus in 1995. In 2002-2003, he got Alexander von Humboldt fellowship and moved to the Technical University of Munich (Germany). In 2004-2007, he worked as a research scientist at the university of Maryland in College Park (USA). In 2008, he returned to the Technical University of Munich, where he works as a senior research scientist at the position provided by the DFG Cluster of excellence Munich Advanced Photonics (MAP). Maxim F. Gelin is an expert in theoretical femtosecond nonlinear spectroscopy and nonequilibrium statistical mechanics.