Lasing of a Microsphere in Dye Solution

Lasing of micrometer-sized, nonluminescent, spherical particles dispersed in an aqueous solution of rhodamine B was demonstrated. The microspherical resonance field is composed of an evanescent field surrounding the sphere as well as a propagation component within the particle, so that the dye solution just outside of the spherical surface can function as a gain medium within an optical cavity. Periodical ripple structures were observed in the emission spectra, which agreed well with the Mie scattering theory. The lasing threshold was determined to be 7 mW for a 28 µm glass microsphere in 10-2 mol/l rhodamine B solution. The decrease in the lasing emission intensity caused by photodegradation can be suppressed by thermal diffusion of the dye molecules in the liquid solution.