Tracking Ultrafast Energy Flow in Molecules Using Broadly Tunable Few-Optical-Cycle Pulses

Many (bio) molecules, following light absorption, undergo ultrafast nonradiative decay processes, taking place over timescales of tens to hundreds of femtoseconds. Ultrafast optical spectroscopy allows tracking in real time this energy flow using broadly tunable few-optical-cycle light pulses. Optical parametric amplifiers, thanks to their broad and tunable gain bandwidths, are powerful tools for the generation of such pulses. This paper first reviews our work on broadband optical parametric ampli- fiers, which led to the demonstration of few-optical-cycle sub-10-fs pulses continuously tunable from the visible (500 nm) to the near-IR (2 μm). We then present selected examples of applications to ultrafast spectroscopy of molecules, such as isomerization of rhodopsin, carotenoid–bacteriochlorophyll energy transfer in light-harvesting complexes, and polymer–fullerene electron transfer in blends for organic photovoltaics.