  We present an experimental observation on particles adsorbed to a whispering
gallery mode (WGM) optical resonator produced from a glass sphere of about 100
micro meter in radius. For spherical adsorbates of radius about 100 nm, we find
a striking nonlinear dependence of the induced wavelength shift on the adsorbed
particle density, whereas for Rayleigh particles with dimensions much smaller
than the infrared wavelength the dependence is linear with particle density. An
explanation of the anamalous effect based on optical coupling between
meso-optic adsorbates is suggested.
