Observation of Whispering-Gallery Modes in a Diamond Microsphere

We demonstrate a Type Ib diamond (nitrogen impurity of >5 ppm) microsphere whispering-gallery mode resonator in the near-infrared wavelengths between 1426.10 nm and 1427.42 nm in the 90 degrees elastic-light-scattering for both transverse magnetic (TM) and transverse electric (TE) polarizations. The highest measured whispering-gallery mode quality-factor is in the order of 10(4), and the mode spacing is 0.332 nm both for TM and TE polarizations. The coupling of the continuous-wave tunable infrared excitation laser to the diamond microsphere is achieved by a single-mode silica optical-fiber half-coupler. Such a diamond resonator can further be used as stable optical-frequency-comb generating or lasing microcavities by exploiting the nitrogen-vacancy centers present within the diamond.