In this paper, we show for the first time that the lasing threshold and eventually the resonances intensity can be used for inferring changes of refractive index around a 15 μm dye doped polystyrene instead of the mode tracking procedure. The sensing mechanism relies on the spoiling of the resonator Q factor upon change of refractive index which eventually increases the lasing threshold. In addition to allow free space excitation and collection, alleviating the need for phase matched prism or fiber taper, this novel approach promises to reach lower detection limit by suppressing the need of high resolution spectral analysis of the whispering gallery mode spectra but instead relying on cost effective and highly sensitive intensity measurements.
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Alexandre François, Harald Schwefel, Tanya M. Monro, "Using the lasing threshold in whispering gallery mode resonators for refractive index sensing," Proc. SPIE 10518, Laser Resonators, Microresonators, and Beam Control XX, 105180V (16 February 2018);