Abstract: Multi-photon excitation fluorescence microscopy is carried out by focusing an excitation beam by an objective lens onto a specimen and collecting the multi-photon fluorescence light emitted from the specimen to the objective lens and directing the fluorescent light on an optical path to a detector. Fluorescent light emissions from the specimen collected by a condenser lens on the opposite side of the specimen from the objective lens are directed to a dichoic mirror, which reflects the light photons back into the condenser lens and thence into and through the objective lens where they are directed on an optical path to the detector. Significantly increased fluorescent photon collection efficiency is obtained as well as improved image intensity of the detected fluorescent light.