Two-photon fluorescence characterization of spiral plasmonic lenses as circular polarization analyzers

The spiral plasmonic lens is capable of focusing the left-hand and right-hand circular polarizations into spatially separated plasmonic fields caused by the geometric phase effect. Its function as a circular polarization analyzer has been studied analytically and numerically in a previous Letter [Opt. Lett. 34, 3047 (2009)]. Single Archimedes' spiral grooves with lateral sizes of approximately 4 lambda(spp) (similar to 2.8 mu m) were milled into a gold thin film by using a focused ion beam. The function of such a simple spiral plasmonic lens serving as a circular polarization analyzer was experimentally characterized with two-photon fluorescence microscopy. The circular polarization extinction ratio of the two-photon fluorescent signal is estimated to be larger than 200 for a detector diameter up to 0.3 lambda(spp) (C) 2010 Optical Society of America