Resonance light scattering from microspheres on substrates

Abstract

In a recent investigation, Hill et al. show that the wavelengths of sharp structural resonances in the fluorescence emission from single dielectric microspheres resting on glass and metallic substrates are the same as those for unsupported microspheres.1 The objective in the present study was to obtain resonance light-scattering (RLS) spectra from an ensemble of nonfluorescing dielectric microspheres. The incident light from a dye laser was swept continuously through a range of wavelengths, and the intensity of the elastically scattered light at 90° was recorded as a function of wavelength. The resultant RLS spectrum was then compared to Mie-scattering computer calculations for unsupported microspheres, averaged over a diameter distribution. Three different types of substrate were used: ultrablack-coated metal; black glass; and clear glass. For polystyrene microspheres on the ultrablack-coated metal substrate, the experimental RLS spectra were in good agreement with Mie-scattering calculations for unsupported dielectric microspheres. This was true regardless of the tilt angle of the substrate relative to the incident and scattered light fields as long as the scattering angle was not changed. However, for microspheres on the black- and clear-glass substrates, the match with Mie calculations was not so good; in particular, the RLS patterns changed appreciably as the substrates were tilted. This is most likely due to the light reflected from the glass substrates which was not present with the highly absorbing ultrablack-coated metal substrate.