Photosynthetic light-harvesting by carotenoids: detection of an intermediate excited state

This paper studies all-trans-/spl beta/-carotene in cyclohexane solution, excited by 15-fs blue pulses (510 nm), resonant with the S/sub 0/ /spl rarr/ S/sub 2/ transition. The temporal evolution of differential transmission is probed using sub-10-fs visible pulses (500-700 nm) and 12-fs near-IR pulses (820-1020 nm). Pump and probe pulses are derived from two independent non-collinear optical parametric amplifiers.