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"Tracking Primary Processes in Biomolecules with Tunable Few-Cycle Pulses"

Relatore: Giulio Cerullo- Dipartimento di Fisica, Politecnico Di Milano
Note: Seminario di Dipartimento

Aula Newton
28 Novembre 2012 ore 16.30

Many light-induced processes in organic molecules, such as energy relaxation, energy/charge transfer and conformational changes, occur on ultrafast timescales, ranging from 10-14 to 10-13 s. The speed of such elementary processes is intimately linked to their efficiency, making ultrafast optical spectroscopy an invaluable tool for their investigation. Pump-probe spectroscopy requires both short pulses, in order to observe fast dynamics, and broad frequency tunability, to excite a system on resonance and probe optical transitions occurring at different frequencies. Optical parametric amplifiers (OPAs) are ideal tools for such experiments, because they provide frequency tunability and support broad gain bandwidths, enabling the generation of very short pulses. In this talk we will describe a state of the art system, based on two synchronized OPAs, providing sub-10-fs temporal resolution over a very broad spectral range, from 400 nm to 2 ým. After reviewing the pulse generation techniques and the system performance, we will present selected examples of applications to the study of ultrafast processes, such as: energy transfer in photosynthetic light harvesting complexes, electron relaxation dynamics in carbon nanotubes and graphene, isomerization of rhodopsin.