title: Two-Photon Fluorescence Excitation Cross Sections of Biomolecular Probes from 690 to 960 nm.
abstract: 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(-50) (cm(4) 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.
authors.forename: M A
authors.initials: MA
authors.lastname: Albota
authors.forename: C
authors.initials: C
authors.lastname: Xu
authors.forename: W W
authors.initials: WW
authors.lastname: Webb