As a result of their ability to amplify input light, ultra-high quality factor (Q) whispering gallery mode optical resonators fabricated from silica have demonstrated extremely low threshold nonlinear behaviors (eg FWM, Raman). However, while the cavity Q may reduce the threshold, it is not able to improve the efficiency. By coating optical resonators with gold nanorods functionalized with small molecule coatings or magnetic nanoparticles, we are able to increase the nonlinearity of the material system and demonstrate an efficient frequency comb generator in the near-IR. Additional nonlinear behaviors, e.g. Anti-Stokes/Stokes generation, are also observed with low thresholds.
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