Second-harmonic generation with surface plasmons from a silvered quartz grating

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Abstract
We report a theoretical and experimental study of enhanced optical second-harmonic generation (SHG) due to grating excitation of surface plasmons in a noncentrosymmetric crystal. The interface is formed by ion etching a grating of 1200 lines per mm with a groove depth of 270 Å into an x-cut quartz crystal and evaporating an opaque silver overlayer. Radiation from a Nd-doped yttrium aluminum garnet laser is incident on the quartz-silver grating through the quartz crystal and diffracted SHG in the n=+1, 0, and -1 modes is observed in reflection. At the incident angle for surface-plasmon excitation the diffracted SHG in the n=+1 mode is enhanced by 4 orders of magnitude relative to the specular nonresonant SHG in the x-cut quartz crystal. Nonlinear reflectance ratios are calculated by using the reduced Rayleigh equations. A grating profile function that is 95% sinusoidal with a 5% mixture of the third spatial harmonic yields calculated nonlinear reflectances which agree with the observed peak resonance values to within 25% for all three diffracted orders. These results demonstrate that the Rayleigh method may be used to accurately predict the enhancement of SHG due to diffractive coupling of surface plasmons in noncentrosymmetric crystals.