Evanescent-field-induced two-photon fluorescence: Excitation of macroscopic areas of planar waveguides

Two-photon excitation (TPE) of fluorescence is a powerful tool for separating a faintly emitted fluorescence signal from background excitation noise. Until now TPE has only been accomplished for very small excitation areas of a few square micrometre dimensions since they are readily available in the focal zone of high-power lasers. In this paper we demonstrate, to our knowledge for the first time, two-photon excited fluorescence with planar thin-film waveguide structures of macroscopic excitation areas of the order of square millimetres to square centimetres. Based upon our results, it can be envisaged that the new combination of planar waveguide technology with TPE will become a powerful tool for macroscopic surface-iteraction studies. It can also open the way for further improving the sensitivity of biosensing platforms like genomic and proteomic microarrays based upon planar waveguides.