title: Magnification in excess of 100-times of the microscopic photothermal lensing signal from solute molecules by two-color excitation with continuous-wave lasers.
abstract: A microscopic photothermal lensing measurement under two-color continuous-wave laser excitation was performed to investigate a signal enhancement owing to the transient absorption by photoexcited solute molecules in liquid solutions. An intensity-modulated 409 nm laser beam and an un-modulated 532 nm laser beam were used for excitation, and a 670 nm probe beam was used for detecting the modulation amplitude of thermal lensing signals generated with a microscopic objective lens focusing laser beams into a capillary flow cell of 0.1 mm optical path length. The amplitude of the modulated signal increased as the power of the un-modulated laser beam increased, and a 143-times magnification was observed for an iso-propanol solution of naphthacene having 4.6 x 10(-4) absorbance at 409 nm and a negligible absorbance at 532 nm. A four-level model explaining the signal enhancement is proposed, and an important role of the transient absorption by photoexcited molecules is discussed.
authors.affiliation: Department of Molecular and Material Sciences, Graduate School of Engineering Sciences, Kyushu University, Kasugakoen 6-1, Kasuga, Fukuoka 816-8580, Japan. harata@mm.kyushu-u.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Harata
authors.forename: Kenji
authors.initials: K
authors.lastname: Fukushima
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Hatano