Mid-infrared supermirrors with finesse exceeding 400 000

• Published in: Nature communications Vol. 14; no. 1; p. 7846
• Main Authors: Truong, Gar-Wing, Perner, Lukas W., Bailey, D. Michelle, Winkler, Georg, Cataño-Lopez, Seth B., Wittwer, Valentin J., Südmeyer, Thomas, Nguyen, Catherine, Follman, David, Fleisher, Adam J., Heckl, Oliver H., Cole, Garrett D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06-12-2023; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 639/301/1019; 639/624/1107/527/2257; 639/624/399; Absorption; Cavity ringdown; Coatings; Electric fields; Environmental science; Gas analysis; Gas sensors; Humanities and Social Sciences; Interference; Molecular beam epitaxy; multidisciplinary; Near infrared radiation; Science; Science (multidisciplinary); Single crystals; Spectroscopy; Spectrum analysis; Substrates; Trace gases
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-43367-z

For trace gas sensing and precision spectroscopy, optical cavities incorporating low-loss mirrors are indispensable for path length and optical intensity enhancement. Optical interference coatings in the visible and near-infrared (NIR) spectral regions have achieved total optical losses below 2 parts per million (ppm), enabling a cavity finesse in excess of 1 million. However, such advancements have been lacking in the mid-infrared (MIR), despite substantial scientific interest. Here, we demonstrate a significant breakthrough in high-performance MIR mirrors, reporting substrate-transferred single-crystal interference coatings capable of cavity finesse values from 200 000 to 400 000 near 4.5 µm, with excess optical losses (scatter and absorption) below 5 ppm. In a first proof-of-concept demonstration, we achieve the lowest noise-equivalent absorption in a linear cavity ring-down spectrometer normalized by cavity length. This substantial improvement in performance will unlock a rich variety of MIR applications for atmospheric transport and environmental sciences, detection of fugitive emissions, process gas monitoring, breath-gas analysis, and verification of biogenic fuels and plastics.
The researchers showcase all-crystalline and hybrid mid-infrared supermirrors with the lowest optical losses ever demonstrated in this wavelength range, representing an unprecedented improvement over any existing mirrors made with any production technology.