Sub-10 fs time resolved study of excited state relaxation in /spl beta/-carotene

Summary form only given. Carotenoids are a widespread class of natural pigments with a number of important functions in biological systems. In their light-harvesting role, carotenoids absorb light in the blue-green region and transfer energy to the bacterio-chlorophyll with efficiency close to 1. In our experiments photoexcitation with broad band sub-1o fs pulses from an optical parametric amplifier populates the second excited singlet state (S2). Interrogating the excited molecules with a second, delayed probe pulse, in the usual pump-probe configuration we are able to directly monitor the dynamic Stokes shift of stimulated emission from S2, taking place in about 40 fs, and internal conversion to S1.