Optical harmonic generation from periodically arrayed hexagonal structure of silver nanoparticles.

: A self-assembled method was successfully exploited to fabricate a close-packed hexagonal structure of nano-silver clusters by deposition of silver films on polystyrene micro-spheres in conjunction with lift-off the micro spheres. An enhancement of the optical second-harmonic susceptibility was observed from these periodically arrayed silver particles with an intensity of several folds larger than that is generated from a uniform silver-film of the same thickness. The quasi-phase matching condition contributed from the Bragg wave vectors of the periodically arrayed silver nano-particles can satisfactorily express this enhancement.