SURFACE-ENHANCED 2ND-HARMONIC DIFFRACTION - EXPERIMENTAL INVESTIGATION OF SELECTIVE ENHANCEMENT

Recent theoretical predictions demonstrating large enhancements of sec ond-harmonic diffraction through the control of surface harmonic compo sition when the surface-plasmon polariton (SPP) is excited on a corrug ated silver surface have been investigated experimentally for the spec ular order. Interpretation of the mechanism of enhancement in terms of a three-step selective scattering process involving only two spatial harmonics has been found to be justified. Fourier blaze holography, wh ich permits the phase- and amplitude-controlled superposition of multi ple harmonics in photoresist, has been used to fabricate the nanostruc tured, biperiodic gratings. Surfaces have been characterized by atomic force microscopy and Heitmann's method. As predicted, surfaces with o ptimized spatial frequency composition equal or exceed randomly rough surfaces in the enhancement of second-harmonic reflection relative to a flat silver surface. Enhancement produced by simultaneous excitation of counterpropagating SPP modes at the pump and second-harmonic frequ encies has also been detected by varying grating wave vector to tune t hrough a double resonance condition. Factors affecting the quantitativ e agreement between enhancement measurements and theoretical predictio ns are briefly discussed.