Continuous wave excitation two‐photon fluorescence microscopy exemplified with the 647‐nm ArKr laser line

Abstract

We report on efficient two‐photon fluorescence imaging in beam scanning microscopy by exciting UV dyes at the 647‐nm line of a continuous wave ArKr mixed gas laser. For a numerical aperture of 1.4 (oil), we used an illumination power of up to 210 mW at the sample. High‐resolution images were obtained for DAPI‐labelled cell nuclei within 4–60 s. Our method is a simple two‐photon alternative to UV confocal imaging with the potential of becoming a very useful feature of laser scanning microscopy.