Dielectric whispering-gallery-mode (WGM) resonators can confine light via total internal reflection. Small perturbations in the local environment usually lead to a frequency shift of the resonator modes directly proportional to the polarizability of the perturbation. Here, we report experimental observations and a theoretical model of strong frequency shifts that can be opposite and even exceed the contribution of the perturbations' polarizability [1]. We also report on a new, independent way of calibrating the prism distance based on Newton’s rings [2] and report on results from ultra-low threshold lasing from a titanium doped sapphire WGM resonator, showing that lasing as well as linewidth narrowing is possible [3].
[1] F. Azeem, …, and H.G.L. Schwefel, Opt. Lett. 46, 2477(2021).
[2] J. T. Christensen, …, and H. G. L. Schwefel, arXiv:2208.00667(2022).
[3] F. Azeem, …, and H.G.L. Schwefel, Adv. Optical Materials 10, 2102137(2022).
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