Harmonic generation from metal nanoparticle arrays

Metal nanoparticle arrays have optical coherence properties that are predicted to have interesting consequences for optical harmonic generation. We have prepared planar arrays of non-spherically symmetric silver-nanoparticle clusters using a combination of focused ion-beam lithography and pulsed laser deposition. The 150-fs amplified pulses of a Ti:sapphire laser were incident on the array, which was mounted on the rotatable sample stage of a dark-field confocal microscope; this arrangement permits the elimination of virtually all optical background so that the scattered harmonic signal from the array is easily detectable. We describe experiments designed to test a recent theoretical prediction [1] to the effect that the nanoparticle array should produce phase-matched second harmonics like those generated by bulk media without a center of inversion symmetry, and that the harmonic- generation efficiency should scale inversely as the square of the nanoparticle size.[1] N. I. Zheludev and , J. Opt. A: Pure Appl. Opt. 6 (2004) 26-28.