Coherent spectroscopy of rare-earth-ion doped whispering-gallery mode   resonators
  We perform an investigation into the properties of Pr3+:Y2SiO5 whispering gallery mode resonators as a first step towards achieving the strong coupling regime of cavity QED with rare-earth-ion doped crystals. Direct measurement of cavity QED parameters are made using photon echoes, giving good agreement with theoretical predictions. By comparing the ions at the surface of the resonator to those in the center it is determined that the physical process of making the resonator does not negatively affect the properties of the ions. Coupling between the ions and resonator is analyzed through the observation of optical bistability and normal-mode splitting. 
D. L. McAuslan, D. Korystov, and J. J. Longdell
quant-ph cond-mat.other