Radial polarization induced surface plasmon virtual probe for two-photon fluorescence microscopy.

Surface plasmons excited by a focused femtosecond radially polarized beam on a metal surface form a standing wave pattern with a sharp peak that can be used as a "virtual probe" for surface plasmon microscopy. The rotational symmetry of radially polarized light effectively provides the TM polarization required for coupling to the surface plasmons while the short pulse nature of the probe allows for nonlinear processes to be studied.