Controlled coupling of counterpropagating whispering-gallery modes by a single Rayleigh scatterer: a classical problem in a quantum optical light.

We present experiments where a single subwavelength scatterer is used to examine and control the backscattering induced coupling between counterpropagating high-Q modes of a microsphere resonator. Our measurements reveal the standing wave character of the resulting symmetric and antisymmetric eigenmodes, their unbalanced intensity distributions, and the coherent nature of their coupling. We discuss our findings and the underlying classical physics in the framework common to quantum optics and provide a particularly intuitive explanation of the central processes.

Stimulated effects in one-photon resonant interferometric four-wave mixing with incoherent light.

The interferometric four-wave mixing technique with broadband light is extended to measurements of population relaxation. For what is believed to be the first time, the population relaxation rate in the presence of a pump field is measured. It is shown that stimulated emission can significantly affect the results when one is dealing with resonant transient wave mixing, and, consequently, in most cases stimulated processes should be taken into account.