Second-harmonic generation from a silver grating with surface plasmons

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Abstract
We have studied both experimentally and theoretically enhanced optical second-harmonic generation (SHG) from a silver grating due to surface-plasmon excitation with a Nd-glass laser. Reduced Rayleigh equations are employed to calculate the enhancement of the diffracted SHG over that reflected from a smooth surface. Using a grating of 1200 lines/mm with an effective groove depth of 220 Å we observe diffracted SHG in the n = −1, 0, and +1 orders. For the n = −1 order we measure an enhancement factor of 7000, which is the largest reported. By assuming a grating profile function that is 97% sinusoidal with a 3% admixture of the third spatial harmonic, we obtain a calculated enhancement factor that agrees with experiment to within 25% for all three diffracted orders. The n = +1 diffracted intensity is particularly sensitive to the existence of a spatial third-harmonic Fourier component in the grating profile. These results demonstrate that the Rayleigh method may be used to predict accurately the enhancement of SHG due to diffractive coupling to surface plasmons.