Analytical Sciences

Photothermal Lensing Signal Enhancement by the Transient Absorption of Photoexcited States in Liquid Solutions

Akira HARATA   and Naonori YAMAGUCHI

Department of Molecular and Material Sciences, Graduate School of Engineering Sciences, Kyushu University, Kasugakoen 6-1, Kasuga, Fukuoka 816-8580, Japan

A two-color double-pulse excited photothermal lensing measurement was performed to investigate a signal enhancement owing to transient absorption by the excited states of solute molecules in liquid solutions. A colinear, mode-mismatched configuration with a continuous-wave probe laser at 633 nm was adapted with a focused pump pulse (6.9 ns, 355 nm) and a sequentially incident softly focused second-pump pulse (7.2 ns, 532 nm). The signal-intensity dependence on the energies of the pump and the second-pump pulses was measured for 1.0 muM solutions of 2,2'-p-phenylenebis(5-phenyloxazole) in 1-butanol and anthracene in ethanol. A signal enhancement was observed for both solutions. The signal intensity under certain conditions was one order higher than that expected from ground-state absorption. A discussion was made on determination of the absorption coefficient of the transient species and on the absorption saturation of the ground and excited states.

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