title: Development of a total internal reflection ultrafast transient lens method for studying molecular dynamics on an interface.
abstract: We have developed the total internal reflection ultrafast transient lens (TIR-UTL) method to detect nonradiative chemical processes at interfaces and surfaces with subpicosecond time resolution. In the TIR-UTL measurements, the evanescent field of a pump beam irradiated under the TIR condition generates a refractive index change. The refractive index change is attributed to changes of the molecular electronic state, of density by molecular orientation/structure change, and of temperature by vibrational relaxation processes. The refractive index change is detected as a change of the power intensity of the probe beam adjusted coaxially with the pump beam. At first, we discuss a theoretical principle of a coaxial configuration in the TIR-UTL measurement. This configuration has an advantage of versatility over the established TIR configuration. Then, we evaluate time resolution of TIR-UTL and obtain a value of less than 400 fs. We measure the ultrafast molecular dynamics of the cationic chromophore Auramine O (AuO) at a silica/water interface. Two slow time constants originating from AuO adsorbed on the silica surface are detected by TIR-UTL. These are attributed to AuO, whose twisting motion is strongly hindered by adsorption on a silica surface.
authors.affiliation: Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5-401 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Sugimoto
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Hirose
authors.forename: Hiroharu
authors.initials: H
authors.lastname: Yui
authors.forename: Tsuguo
authors.initials: T
authors.lastname: Sawada