Giant enhancement of sum-frequency yield by surface-plasmon excitation

We show experimentally that the radiation generated in infrared-visible sum-frequency mixing at an air-silver interface can be greatly enhanced when the visible input beam excites a surface plasmon-polariton at the interface. With either a prism or a grating used to couple the visible radiation with the surface polariton, the sum-frequency-generation yield is observed to be enhanced by a factor of 10(2) for the prism and 10(4) for the grating for counterpropagating infrared and visible input beams. The result for the prism configuration can be simply understood in terms of the field enhancement associated with the surface polariton excited by the visible input beam. For the grating configuration there is an additional effect in that the nonlinear polarization at the sum frequency can also couple with a surface polariton. As a result the effective interaction length of the sum-frequency-mixing process is sizably increased. The experimental results are in good agreement with estimates based on this model. (C) 1999 Optical Society of America [S0740-3224(99)01907-4].