Optical resonances in single microdroplets levitated in an ion trap

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We have studied resonant light scattering from a single micro-droplet and discussed the laser action of the droplet doped with dye molecules. Since photons confined inside the droplet correspond to electrons bound in an atom, such droplets are sometimes called photonic atoms.In our experiment, a single droplet of glycerol doped with dye molecules was levitated in an ion trap. The droplet was optically excited by a pump laser, and the emission from the droplet was observed through an optical spectrometer and a microscope. Since the droplet levitated in the ion trap is naturally shaped to an almost real sphere, some resonant modes of the light waves are very efficiently confined in the droplet and the comparison with theory can be made more rigorously compared to using solid spheres. The Q-value of the resonator is extremely high. This lowers the threshold for the lasing of the droplet.In order to investigate the characteristics of the lasing action, we have made the followingmeasurements :1) Dependence on the power of exciting laser2) Polarization properties3) Dependence on the concentration of dye molecules.From these measurements we have determined the modes of laser radiation and discussed the lasing mechanism.