Stimulated emission into optical whispering modes of a spherical sample of Ca${\mathrm{F}}_2$: ${\mathrm{Sm}}^{++}$ has been observed. Light produced by the stimulated emission is radiated tangentially form each point on the surface of the sphere. The experimental results have been interpreted in terms of the electromagnetic analog of the Rayleigh theory of the whispering gallery.

• Received 16 August 1961

DOI:https://doi.org/10.1103/PhysRev.124.1807