Crystalline MgF2 whispering gallery mode resonators for enhanced bulk index sensitivityR. Zeltner, F. Sedlmeir, G. Leuchs and H.G.L SchwefelEur. Phys. J. Special Topics, 223 10 (2014) 1989-1994DOI: https://doi.org/10.1140/epjst/e2014-02241-8