High-order multiphoton excitation processes are becoming a reality for fluorescence imaging and phototherapy treatment because they afford minimization of scattered light losses and a reduction of unwanted linear absorption in the living organism transparency window, making them less susceptible to photodamage, while improving the irradiation penetration depth and spatial resolution. We report the four-photon-excited fluorescence emission of (7-benzothiazol-2-yl-9, -didecylfluoren-2-yl)-diphenylamine in hexane and its four-photon absorption cross section ς<sub>4</sub>′ = 8.1 × 10<sup>−109</sup> cm<sup>8</sup> s<sup>3</sup> photon<sup>−3</sup> for the transition S<sub>0</sub> → S<sub>1</sub> when excited at 1600 nm with a tunable optical parametric generator (OPG) pumped by picosecond laser pulses. When pumped at 1200 nm, three-photon absorption was observed, corresponding to the same transition.
© 2004 Optical Society of America
(160.2540) Materials : Fluorescent and luminescent materials
(190.4180) Nonlinear optics : Multiphoton processes
(300.2530) Spectroscopy : Fluorescence, laser-induced
(300.6410) Spectroscopy : Spectroscopy, multiphoton
Florencio E. Hernández, Kevin D. Belfield, Ion Cohanoschi, Mihaela Balu, and Katherine J. Schafer, "Three- and Four-Photon Absorption of a Multiphoton Absorbing Fluorescent Probe," Appl. Opt. 43, 5394-5398 (2004)