Control of coherent vibronic oscillations in β‐carotene by ultrashort laser pulses

Abstract

AbstractThe nonlinear optical responses of carotenoids can be investigated by means of the four‐wave mixing (FWM) spectroscopy. Here we especially focus on the relationship among the pulse sequences, temporal separations between the pulses and the resulting coherent signals. In the transient grating configuration, coherent oscillations with a period of a few tens femtoseconds are clearly observed, which reflect nuclear motions in the ground state. Interestingly, it was found that the Raman inactive modes can be excited by properly controlling the temporal separation of the first and second excitation pulses. The amplitudes of these oscillations are more than three orders of magnitude stronger in comparison with the predicted values obtained by well‐established quantum mechanical calculations. We propose a model to explain our finding that takes the state mixing between S2 and Sx and the higher‐order interaction of the electron‐phonon coupling into consideration. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)