Ultrafast dynamics of all-trans-β-carotene explored by resonant and nonresonant photoexcitations -: art. no. 213601

Excitation energy dependence of transmittance change has been investigated in beta-carotene. The signal induced by nonresonant excitation is ascribed to the ac Stark effect and the two-photon absorption of the excitation and probe pulses in three-level systems. The ultrafast response following resonant excitation is assigned to the two-photon absorption and the transient absorption of the photogenerated S-2(1 B-1(u)+) state with a lifetime of 150 fs. The long-debated S-2-S-1 relaxation in beta-carotene can be explained by a two-state model (S-2,S-1) without involving any intermediate states.