Abstract

The internal intensity has a standing wave pattern where a sphere [with index of refraction n(ω) and size parameter ka > 1, where a is the radius and k = 2π/λ] is illuminated by a plane wave at specific wavelengths λ, which correspond to the morphology-dependent resonances (MDR's) of the sphere. The MDR's can provide high Q optical feedback for the internally generated fluorescent, Raman, and Brillouin waves. The standing-wave distribution of MDR's can be decomposed into two counterpropagating guided waves with specific phase velocity and radial distribution. We have calculated the phase velocity of the MDR's ${\text{V}}_{n,l}{}^{\text{MDR}}$ as a function of the angular mode number n and the radial mode order l. The ${\text{V}}_{n,l}{}^{\text{MDR}}\to \text{c}/\text{n}(\omega )$ for MDR's with small l values because the internal intensity distribution is confined in the sphere. The ${\text{V}}_{n,l}{}^{\text{MDR}}\to \text{c}$ for MDR's with large l values because the internal intensity distribution extends into the surrounding air. The coherence length between the pumping wave on a MDR with n,l and the resultant wave with n′,l′ has been calculated. The effects of phase matching and spatial overlap of MDR's are demonstrated with four-wave mixing experiments.

© 1990 Optical Society of America