Continuous Wave Diode Laser Induced Two-Photon Fluorescence Excitation of Three Calcium Indicators

Abstract
Continuous wave (CW) diode laser induced two-photon fluorescence spectra have been measured for calcium indicators of Indo-1, Oregon-green, and Fluo-3. The near 2.0 log-log power-dependence of fluorescence intensity versus incident laser power indicates that the fluorescence from these three calcium indicators was excited by two-photon absorption process of 809-nm laser light. Calcium-dependent emission spectra of Indo-1 and Oregon-green for two-photon excitation under wavelength of 809-nm have also been measured.