Convenient Method of Micrometer-Scale Excitation of Propagating Surface Plasmons by a Focused Laser Beam

Surface plasmons (SPs) excited on microscopic areas are desired in a variety of applications, including SP microscopy and (bio)sensing. We present an optical method of excitation of SPs using a dry, medium-magnification microscope objective and a diffraction grating. SPs are excited by focusing laser light into a diffraction-limited spot on the grating. We demonstrate that the excitation of SPs is manifested by dark arcs in the light cone reflected from the focus. The behavior of the arcs with respect to the spatial distribution of refractive index in the vicinity of the focal spot is explored.