Efficient Raman laser based on a CaF2 resonator

We report on an ultralow-threshold Raman laser based on a CaF2 whispering-gallery-mode resonator. The laser is demonstrated to have a conversion efficiency above 60%. The observed low lasing threshold is made possible by the ultrahigh optical quality factor of the cavity, which is on the order of Q = 10(10). The laser is fiber-compatible and is fabricated with a very simple technique. We also demonstrate a single-mode operation of the laser in a multimode cavity as well as a multimode operation of the laser in a single-mode cavity. (C) 2008 Optical Society of America.