Coherent sum and frequency difference generation in microparticle composites

Abstract

We examine coherent sum and difference frequency generation in two-component media composed of dilute suspensions of metallic or n-type semiconductor microspheres embedded in a passive dielectric host. If one or both of the incident laser beam frequencies is near the surface dipole resonance, the Frohlich mode is excited and the medium exhibits an enhanced response. Enhancement of the sum or difference frequency wave is also possible if this frequency coincides with the surface quadrupole resonance of the microsphere. It is shown that a coherent second-order response is possible only if the symmetry of the system is reduced, which requires two laser beams in a noncollinear configuration. Detailed calculations are presented for the macroscopic response of the individual particles as well as the macroscopic electrodynamics of the composite as a whole. Results for the perturbed electron density and drift velocity as well as the laser-induced microparticle quadrupole moment are displayed. Expressions for the intensity, polarization, and angular dependence of the coherent sum and difference frequency radiation are given.