Free-space coupled, ultralow-threshold Raman lasing from a silica microcavity

We report Raman lasing in a slightly deformed silica microcavity using an efficient free-space coupling technique, with an absorbed pump threshold as low as 100 mu W in the 1550 nm wavelength band. This ultralow threshold originates from the ultrahigh quality factors of whispering gallery modes, exceeding 10 8, even though the microcavity is deformed from a circular symmetry. Furthermore, the threshold of free-space coupled Raman lasing is experimentally demonstrated to show a strict inverse square dependence on the intrinsic quality factor of the cavity mode, which agrees well with the theoretical prediction. (C) 2013 AIP Publishing LLC.