Optical second-harmonic generation with grating-coupled surface plasmons from a quartz-silver-quartz grating structure

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Abstract
We report a theoretical and experimental study of enhanced optical second-harmonic generation (SHG) due to grating excitation of coupled surface-plasmon modes from a thin silver grating bounded by two quartz crystals. The two interfaces are formed by ion-etching a grating of 1200 lines/mm with a groove depth of 27 nm into an x-cut quartz crystal, evaporating a thin silver overlayer, and optically contacting a second quartz crystal to the other grating surface with an index-matching liquid. Using incident radiation from a neodymium-doped yttrium aluminum garnet laser, we observe diffracted SHG in the n=1, 0, and -1 modes. Resonances in the SHG due to excitation of the fundamental long-range and short-range surface plasmon modes are studied. Also the resonance due to phase matching of the fundamental short-range and harmonic long-range modes is detected. This layered grating structure permits separation of the contributions of the coupled mode to the SHG from each of the two interfaces. Nonlinear reflectance ratios calculated by using the reduced Rayleigh equations show good agreement with all the experimental results, except in the thinnest silver films in which scattering of the long-range mode is important.