The fluorescence of liquid micro spheres induced by laser irradiation

The fluorescence radiation of droplets rhodamine 6G solution in ethylene glycol is studied. The radiation of an argon ion laser was used for pumping. Our experiments show that amplification is taking place in whispering gallery modes (WGMʹs) of the micro spheres. The propagation of the pumping light in the micro spheres as well as the WGMʹs are discussed in the framework of geometrical optics. The dependence of the intensity of the fluorescence radiation on the position of the micro spheres as they fall through the pumping beam was studied. The temporal change of the fluorescence radiation during the falling of the micro spheres through a system of horizontal fringes obtained with a Michelson interferometer shows a saturation behavior. For droplet diameters of the order of tens of micrometers the fluorescence radiation is isotropical, whereas a diameter dependent anisotropy of fluorescence is observed for larger micro spheres.