title: Two-photon resonances in femtosecond time-resolved four-wave mixing spectroscopy: beta-carotene.
abstract: Femtosecond time-resolved pump-degenerate four-wave mixing (pump-DFWM) spectroscopy has been used to study the ultrafast dynamics of beta-carotene involving several electronic and vibrational states. An initial pump pulse, resonant with the S(0)-to-S(2) transition, excites the molecular system and a DFWM process, resonant with the S(1)-to-S(n) transition, is used to probe the relaxation pathways. The transient shows a peculiar decay behavior, which is due to the contributions of resonant DFWM signal of the excited S(1) state, nonresonant DFWM signal of the ground S(0) state and vibrational hot S(0)* state, and the two-photon resonant DFWM signal of the ground S(0) state. We have used a kinetic model including all the signal contributions to successfully fit the transient. The time constants extracted are in very good agreement with the known values for beta-carotene. For comparison, a two-pulse pump-probe experiment was performed measuring the transient absorption at the wavelength of the DFWM experiment.
authors: Center of Functional Materials and Nanomolecular Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany.
authors: V
authors: V
authors: Namboodiri
authors: M
authors: M
authors: Namboodiri
authors: G
authors: G
authors: Flachenecker
authors: A
authors: A
authors: Materny
mesh_terms: D007700:Kinetics; D056004:Molecular Dynamics Simulation; D017785:Photons; D013057:Spectrum Analysis / Q000379:methods*; D013997:Time Factors; D014732:Vibration; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D019207:beta Carotene