Characterization of AN Isolated Cluster of Two Microparticles by Light Scattering, Using Morphological Resonances

Morphological resonances are detected in elastic and fluorescence excitation spectra from two-particle clusters isolated and oriented in an electrodynamic levitator trap. A new theoretical model, "The Parametric Barbell", is presented to explain the orientation of such a cluster due to the alternating gradient forces in the levitator-trap. Light scattering at 90^circ and perpendicular to the line of centers of the particles, with both states of polarization, shows that an independent particle model may be used in describing resonance positions and the shape of the spectrum, even though the particles may differ in size by less than 10nm. A new experimental approach, "Glare Spot Spectroscopy", is invented in order to decipher the individual particle attributes within a cluster. In endfire illumination the fluorescence excitation spectrum is missing a number of resonances that are seen with broadside illumination. It is believed that this may be due to the focusing of the light by the particle illuminated first into the second one and thus not coupling into the resonance modes of the particle in "shadow".