We report on an ultralow-threshold Raman laser based on a 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 . 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.
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