Cylindrical Microcavity Laser Based on the Evanescent-Wave-Coupled Gain

Abstract

A microcavity laser based on the gain only in the evanescent field region of whispering gallery modes has been demonstrated. A cylindrical microcavity of $125\mu \mathrm{m}$ diam was surrounded by rhodamine $6G$ dye molecules in an ethanol solution of lower refractive index such that whispering gallery modes of the microcavity underwent laser oscillation when the dye molecules in the evanescent field region outside the cavity were excited by a second harmonic of a Nd:YAG laser. For particular pumping spots, single-mode laser oscillation of a transverse magnetic mode was observed at about 600 nm with associated cavity $Q$ of $3\times {10}^7$.