Measuring optical loss in yttrium orthosilicate using a whispering gallery mode resonator

The fabrication of a yttrium orthosilicate (YSO) whispering gallery mode (WGM) resonator is described, displaying quality ( Q )-factors as high as 1.1 × 10 9 . An overview of the experimental setup is presented including the procedure for spatial and spectral characterisation of the WGMs. We consider the optical losses present in such a resonator and what steps were taken in order to minimise these losses. The surface scattering in such a resonator is considered and we show that in the wavelength range of 1.5 μ m, the Q -factor is not limited by scattering losses for the case in which surface inhomogeneities are weakly correlated. The high Q -factors we demonstrate have implications for rare earth ion dopant based quantum technologies because YSO is an important host material for these applications.