Mid-infrared ultra-high-Q resonators based on fluoride crystalline materials.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 27869119.
- Also identified by DOI 10.1038/ncomms13383 and PMC identifier 5121327.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The unavailability of highly transparent materials in the mid-infrared has been the main limitation in the development of ultra-sensitive molecular sensors or cavity-based spectroscopy applications. Whispering gallery mode microresonators have attained ultra-high-quality (Q) factor resonances in the near-infrared and visible. Here we report ultra-high Q factors in the mid-infrared using polished alkaline earth metal fluoride crystals. Using an uncoated chalcogenide tapered fibre as a high-ideality coupler in the mid-infrared, we study via cavity ringdown technique the losses of BaF<sub>2</sub>, CaF<sub>2</sub>, MgF<sub>2</sub> and SrF<sub>2</sub> microresonators. We show that MgF<sub>2</sub> is limited by multiphonon absorption by studying the temperature dependence of the Q factor. In contrast, in SrF<sub>2</sub> and BaF<sub>2</sub> the lower multiphonon absorption leads to ultra-high Q factors at 4.5 μm. These values correspond to an optical finesse of , the highest value achieved for any type of mid-infrared resonator to date.