Degenerate four-wave mixing in composites containing small metallic particles

Abstract

Composite materials containing small metal particles exhibit third-order nonlinearities of the same magnitude as found in composites containing CdS x Se1– x microcrystals. For metal particles the largest nonlinearities occur in the vicinity of the surface plasmon resonance. For the work reported here gold microparticles were embedded in a gelatin matrix to study degenerate four-wave mixing (DFWM) in both bulk and thin-film forms. The gelatin has a higher index of refraction (1.55) than most glasses and low propagation losses making it suitable for waveguide studies. The gelatin was spin coated in aqueous solution with the water later removed by baking. Thin-film thicknesses were ~1 μm. The metal particle concentration was adjusted to optimize the conjugate signal relative to absorption losses. Guided wave propagation loss ranged from 2 to 6 dB/cm. The DFWM reflectivity was measured as a function of the pump intensity at frequencies near the plasmon resonance. The plasmon resonance was found from absorbance spectra obtained with a spectrophotometer. Metal particle sizes were determined using a scanning electron microscope. Reflectivity data and fabrication procedures are presented as well as a comparison to other composite materials.