When a laser beam scatters from a microparticle whose shape deviates from t
hat of a sphere, a number of partial waves of the incident beam couple to a
given partial wave of the scattered and interior fields. As a result, part
ial-wave coupling caused by small surface irregularities of a liquid drople
t provides the mechanism for exciting low-radial-order morphology-dependent
resonances. (C) 1999 Optical Society of America.