Two-photon fluorescence surface wave microscopy

This paper demonstrates the principle of two-photon surface wave microscopy with a view to applications on biological samples. We describe a modified scanning optical microscope, which uses specially prepared coverslips. These coverslips are designed to support the propagation of surface waves capable of large field enhancements. We also discuss the beam conditioning necessary to ensure efficient use of the available illumination. Two-photon surface wave fluorescent excitation is demonstrated on fluorescent nanospheres, demonstrating a point spread function width of ≈220 nm at an illumination wavelength of 925 nm. The potential of non-linear surface wave excitation for both fluorescence and harmonic imaging microscopy is discussed.