Very low threshold whispering-gallery-mode microsphere laser

Abstract

We report on the realization of a whispering-gallery-mode laser based on neodymium-doped silica microspheres. Absorbed pump powers at threshold are as low as 200 nW. The linear variation of the threshold with the loss factor of the cavity mode has also been observed. We discuss the potential of this system as a permanent microlaser operating with a few active ions at liquid-helium temperature.