We report on two-photon fluorescence excitation (TPE) action cross sections for five widely used molecular fluorophores. Measurements were performed by use of ultrashort (∼100-fs) Ti:sapphire pulsed excitation over the range 690–960 nm. TPE spectra were obtained by comparison with a fluorescein calibration standard. Large cross sections were found for the cyanine reagent Cy 3 (∼140 GM) and for Rhodamine 6G (∼150 GM), both at 700 nm [1 GM = 10<sup>−50</sup> (cm<sup>4</sup> s)/photon]. Several fluorophores show interesting and desirable blue shifts with respect to twice the one-photon absorption wavelength. Fluorophore fluorescence intensities showed no significant departure (∓4%) from quadratic illumination power dependence, indicating genuine two-photon processes. Implications of these measurements for two-photon laser-scanning microscopy are discussed.
© 1998 Optical Society of America
(170.2520) Medical optics and biotechnology : Fluorescence microscopy
(190.1900) Nonlinear optics : Diagnostic applications of nonlinear optics
(190.4180) Nonlinear optics : Multiphoton processes
Marius A. Albota, Chris Xu, and Watt W. Webb, "Two-Photon Fluorescence Excitation Cross Sections of Biomolecular Probes from 690 to 960 nm," Appl. Opt. 37, 7352-7356 (1998)