The extincion efficiency of transparent spheres with a radial gradient
of refractive index irradiated by electromagnetic plane waves was obt
ained by using the finely stratified sphere model [L. Kae, P. Massoli,
Appl. Opt. 33 (1994) 501-511]. The extinction efficiency of gradient-
index microspheres and location changes of morphology-dependent resona
nces on the Mie extinction efficiency curves are discussed.