title: Barium fluoride whispering-gallery-mode disk-resonator with one billion quality-factor.
abstract: We demonstrate a monolithic optical whispering-gallery-mode resonator fabricated with barium fluoride (BaF₂) with an ultra-high quality (Q) factor above 10⁹ at 1550 nm, and measured with both the linewidth and cavity-ring-down methods. Vertical scanning optical profilometry shows that the root mean square surface roughness of 2 nm is achieved for our mm-size disk. To the best of our knowledge, we show for the first time that one billion Q-factor is achievable by precision polishing in relatively soft crystals with mohs hardness of 3. We show that complex thermo-optical dynamics can take place in these resonators. Beside usual applications in nonlinear optics and microwave photonics, high-energy particle scintillation detection utilizing monolithic BaF₂ resonators potentially becomes feasible.
authors.forename: Guoping
authors.initials: G
authors.lastname: Lin
authors.forename: Souleymane
authors.initials: S
authors.lastname: Diallo
authors.forename: Rémi
authors.initials: R
authors.lastname: Henriet
authors.forename: Maxime
authors.initials: M
authors.lastname: Jacquot
authors.forename: Yanne K
authors.initials: YK
authors.lastname: Chembo