Abstract
We report the observation of enhanced optical second-harmonic generation in transmission that is due to excitation of the fundamental long-range surface-plasmon mode on both surfaces of a thin silver film bounded by a nonlinear X-cut quartz crystal and an index-matched liquid. The coherent harmonic generation that is observed leaving the polished side face of the nonlinear crystal is 3 orders of magnitude larger than that generated from a Z-cut quartz crystal in a Maker experiment.