title: Solute migration caused by excited state absorptions.
abstract: Using the Z-scan technique, we find that migration of chloroaluminum phthalocyanine in liquid ethanol can be induced by the absorption of a 19 ps laser pulse with energy exceeding a threshold but not by that of a 2.8 ns pulse depositing more energy at the solute molecules. Considering each solute molecule as an oscillator confined within a potential well, we explain, in accordance with the five-energy-band model, that solute molecules excited by a 19 ps pulse retain more translational excess energy to overcome the potential well barrier compared with those excited by a 2.8 ns pulse of equal energy. Therefore, they are more likely to migrate out of the laser beam center, weakening the solution's absorption that we detect in the Z-scan measurements. Furthermore, we theoretically infer that the 19 ps pulse-induced solute migration tends to be nonquasistatic and experimentally verify that it cannot be attributed to the Soret effect, a quasistatic process.
authors.affiliation: Department of Physics, National Chung Cheng University, Min-Hsiung, Chia-Yi 621, Taiwan.
authors.forename: Che-Kai
authors.initials: CK
authors.lastname: Chang
authors.forename: Yi-Ci
authors.initials: YC
authors.lastname: Li
authors.forename: Chen-Wei
authors.initials: CW
authors.lastname: Chen
authors.forename: Li-Shu
authors.initials: LS
authors.lastname: Lee
authors.forename: Jaw-Luen
authors.initials: JL
authors.lastname: Tang
authors.forename: Chi-Chen
authors.initials: CC
authors.lastname: Wang
authors.forename: Chang-Chi
authors.initials: CC
authors.lastname: Leu
authors.forename: Tai-Huei
authors.initials: TH
authors.lastname: Wei
authors.forename: Tzer-Hsiang
authors.initials: TH
authors.lastname: Huang
authors.forename: Yinglin
authors.initials: Y
authors.lastname: Song