Nonclassical polarization effects in fluorescence emission spectra from microdroplets

We report a pronounced nonclassical polarization effect on the shape of fluorescence emission spectra from isolated microdroplets containing a dilute solution of soluble fluors or a dilute layer of surfactant fluors. We see different spectral shapes for 90 degrees scattering when comparing between I-VV, I-VH, I-HH, I-HV. However, we measure the largest difference in spectral shape in the surfactant case, with the incident polarization directed toward the detector (I-HV vs I-HH). Imaging reveals that the emission in this case principally arises from two distinct regions near the surface of the droplet, which are diametrically opposed and along the axis of the incident laser beam. The effect appears to be the direct result of coupling between molecular emission moments and electromagnetic modes of the droplet. It is not the molecule which radiates but the molecule microvessel. Directional emission is sensitive to the polarization of the electromagnetic mode which is stimulated by the coupling. (C) 1999 American Institute of Physics. [S0021-9606(99)70647-1].