Excitation energy dependence of transmittance change has been investigated in β-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 S2(1Bu+1) state with a lifetime of 150fs. The long-debated S2-S1 relaxation in β-carotene can be explained by a two-state model (S2,S1) without involving any intermediate states.
ASJC Scopus subject areas
- Physics and Astronomy(all)