Some characteristics of a droplet whispering-gallery-mode laser

We report lasing characteristics of 40-60-microm-diameter Rhodamine 590/water solution droplets pumped by a 20-nsec-duration Q-switched laser. The Rhodamine/water solution provides a useful model system for studying the properties of oscillators based on whispering-gallery-wave spherical cavities. The low threshold for lasing, 10(4) W/cm(2) for 10(-4) M solutions, is consistent with particle size and a cavity Q factor of 10(4). Portions of the droplet lase purely in transverse electric (TE) modes, while other portions contain both TE and lower-Q transverse magnetic modes. In the far field, the lasing droplet approximates a coherent point source emitting in all directions.