Abstract

Metallic microparticles are endowed with electronic transitions, in particular plasmon modes, that can be resonantly excited by visible laser radiation. Once these modes have been excited, they will amplify the laser electric field in the vicinity of the microparticle. This feature of microparticle electrodynamics has been utilized as an efficient mechanism for a variety of nonlinear optical processes, such as frequency mixing, phase conjugation, and beam combination. Furthermore, the electronic nature of these excitations ensures fast optical responses, typically of the order of picoseconds. We present experimental data and theoretical calculations of two-beam coupling in metallic microparticle suspensions which suggest that efficient beam combination is achievable with such media. The specific mechanism responsible for this optical nonlinearity is the electron quantum pressure that is localized near the microparticle’s surface. On physical grounds it follows that the smaller the microparticle, the greater the quantum pressure. Since the optical nonlinearity depends strongly on the particle volume, a plot of the optical susceptibilities vs particle size will exhibit a maximum at specific particle sizes. For two-beam coupling the optimum particle size is predicted to be near 30 Å.

© 1991 Optical Society of America