Observation of whispering gallery modes in nanocrystalline diamond microdisks

Abstract

Nanocrystalline diamond microdisks have been fabricated and characterized. The process conditions were chosen to ensure smooth and vertical sidewalls. Focused ion beam milling was used to create ultrasmooth sidewalls. Whispering gallery modes were observed near the nitrogen-vacancy center emission wavelength $\left(637\mathrm{nm}\right)$ by photoluminescence and near $\sim 1550\mathrm{nm}$ by evanescent fiber coupling. The cavity quality factors $\left(Q\right)$ are about 100 in both experiments. The $Q$ ’s for these disks were calculated to be as high as ${10}^5$ by three-dimensional finite-difference time-domain simulations. The authors believe the $Q$ ’s to be limited by absorption and scattering within the nanocrystalline cavity material.