Excitation of surface-plasmon polaritons by a focused laser beam

A method is reported for exciting surface-plasmon polaritons with a focused laser beam as the excitation probe. We calculate the electric-field intensity distribution on a silver surface that is due to the excited surface-plasmon polaritons. We find that polaritons are locally excited over an area that approximates the spot size of the focused beam. We also find that the field distribution is strongly influenced by polarization of the incident light. Our theoretical findings are experimentally confirmed by measuring the scattered light that is produced when a microsphere is scanned (from the air side) across a silver surface that is being probed for surface-plasmon polaritons.