title: Four-wave mixing signals from beta-carotene and its n = 15 homologue.
abstract: The third-order nonlinear optical responses of beta-carotene and its homologue having a conjugation-double bond n = 15 have been investigated using sub-20 fs ultra-short optical pulses in order to clarify the dissipation processes of excess energy. Using the four-wave mixing spectroscopy, we observed a clear coherent oscillation with a period of a few tens of femtoseconds. The spectral density of these molecules was estimated that allowed the theoretical linear and nonlinear optical signals to be directly compared with the experimental data. Calculations based on the Brownian oscillator model were performed under the impulsive excitation limit. We show that the memory of the vibronic coherence generated upon the excitation into the S(2) state is lost via the relaxation process including the S(1) state. The vibronic decoherence lifetime of the system was estimated to be 1 ps, which is about 5 times larger than the life time of the S(2) state ( approximately 150 fs) determined in previous studies. The role of coherence and the efficient energy transfer in the light-harvesting antenna complexes are discussed.
authors.affiliation: Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi, Osaka, 558-8585, Japan. mitsuru@sci.osaka-cu.ac.jp
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Sugisaki
authors.forename: Masazumi
authors.initials: M
authors.lastname: Fujiwara
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Yanagi
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
mesh_terms: D013059:Spectrum Analysis, Raman; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D019207:beta Carotene