Optical Coupling of Mie Particles Adsorbed on a Whispering Gallery   Resonator
  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. 
F. Vollmer, H. C. Ren, S. Arnold and A. Libchaber