Hi-Q whispering gallery mode resonators in nonlinear crystals

We report on the progress of developing nonlinear crystal-based whispering gallery mode resonators, which are circular cavities that support long-lived optical modes along their inside surface via total internal reflection. We have been refining our optical polishing techniques to produce lithium niobate ($LiNbO_3$) disks of $<1cm$ in diameter and $1mm$ in height. We have also been optimizing the process of coupling light into whispering gallery modes using frustrated total internal reflection from a rutile prism. In a $LiNbO_3$ disk with free spectral range of 5.1 $GHz$ coupled to a frequency-scanned diode laser centered around $\lambda = 795nm$, we achieved a quality factor on the order of $Q = 10^7$. This Q-factor is limited by the quality of polish on the surface, which we estimate to be $20$/$5$ scratch/dig. However, this is sufficiently high to support our goal of low-threshold non-critically phase-matched frequency conversion at near-infrared wavelengths.