Crystalline MgF2 whispering gallery mode resonators for enhanced bulk index sensitivity
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We report on experiments on refractrometric sensing with crystalline Whispering Gallery Mode (WGM) resonators made of magnesium fluoride, which has a refractive index that is only slightly larger than that of water (Δn ≈ 0.05). The resulting evanescent field of a WGM resonator placed in an aqueous environment penetrates therefore deep into the surrounding medium, which makes it a promising candidate for sensing applications. We measured a bulk index sensitivity of 1.09 nm/RIU (refractive index unit) in a resonator with a radius of R = 2.91 mm and intrinsic Q-factors of more than 108 in aqueous environments. Furthermore, we describe the fabrication process of crystalline WGM resonators.
KeywordsRefractive Index European Physical Journal Special Topic Polarization Beam Splitter Whispering Gallery Mode Refractive Index Contrast
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