Morphology-dependent resonances in radially inhomogeneous spheres

Abstract

Resonant frequencies and quality-factor (Q’s) of the morphology-dependent resonances of radially inhomogeneous spherical particles are computed with a Runge–Kutta method. In one type of inhomogeneity the refractive index of the sphere decreases smoothly from a core value of 1.5 to a value of 1.0(0.1)1.4 at the surface. The fraction of the radius over which the refractive index rolls off varies from 0.01 to 0.25. As the refractive index near the surface is decreased, the resonant frequencies shift to higher values and the Q’s decrease. Numerical results for modes with Q’s in the range of 500–1016 show that, when the change in refractive index occurs in only the outer few percent of the droplet radius, the change in the Q is less than 20%. Calculated resonant frequencies and Q’s simulating a refractive index that increases near the surface are also shown.