Excitation localization principle for whispering-gallery wave microcavities

Summary form only given.Theory predicts that a tightly focused Gaussian light beam passing outside but near a spherical or cylindrical microcavity will preferentially excite specific cavity resonances depending on its distance to the cavity center. This has been called the localization principle. In effect, this is a restatement of conservation of angular momentum with ray momentum being proportional to the index of refraction multiplied by the radial position of the peak of the mode. We discuss experimental tests of the theory using two types of microcavitis: spherical liquid droplets and cylindrical glass fibers. Both cavity types displayed excellent agreement with theory. Localization was measured by monitoring the ability of the beam to generate stimulated Raman scattering (SRS).