Erbium luminescence imaging of infrared surface plasmon polaritons

We demonstrate a new technique to spatially map the propagation and damping of infrared surface plasmon polaritons (SPPs) on metal films using optically active erbium ions as a probe of the SPP field. The bound SPP mode propagating along the Ag/glass interface of a 96 nm thick Ag film on glass is excited by illuminating a subwavelength hole array in the metal with 1.49 µm light. By imaging the 1.53 µm photoluminescence of Er ions positioned in the glass at a distance of 60 nm from the Ag/glass interface in a confocal microscope, a SPP beam was observed to propagate along a broad stripe waveguide, with a characteristic propagation length of 76 µm. This technique provides a useful tool to study the characteristics of SPP modes at metal-dielectric interfaces in a wide range of geometries.