Guoping Lin,1,2 Rémi Henriet,1 Aurélien Coillet,1,3 Maxime Jacquot,1 Luca Furfaro,1 Gilles Cibiel,4 Laurent Larger,1 and Yanne K. Chembo1,5,*

1. FEMTO-ST Institute, Univ. Bourgogne Franche-Comté, CNRS, Optics Department, 15B Avenue des Montboucons, 25030 Besançon cedex, France
2. Currently at MOE Key Laboratory of Fundamental Quantities Measurement, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
3. Currently at Laboratoire Interdisciplinaire Carnot Bourgogne [CNRS UMR6303], Univ. Bourgogne-Franche-Comté, 9 Avenue A. Savary, 21078 Dijon, France
4. Centre National d’Etudes Spatiales (CNES), 18 Avenue Edouard Belin, F-31401 Toulouse, France
5. GeorgiaTech-CNRS Joint International Laboratory [UMI 2958], Atlanta Mirror Site, School of Electrical and Computer Engineering, 777 Atlantic Dr NW, Atlanta, Georgia 30332, USA

Abstract:
We present an experimental study of the variation of quality factor (Q-factor) of WGM resonators as a function of surface roughness. We consider mm-size whispering-gallery mode resonators manufactured with fluoride crystals, featuring Q-factors of the order of 1 billion at 1550 nm. The experimental procedure consists of repeated polishing steps, after which the surface roughness is evaluated using profilometry by white-light phase-shifting interferometry, while the Q-factors are determined using the cavity-ring-down method. This protocol permits us to establish an explicit curve linking the Q-factor of the disk-resonator to the surface roughness of the rim. We have performed measurements with four different crystals, namely, magnesium, calcium, strontium, and lithium fluoride. We have thereby found that the variations of Q-factor as a function of surface roughness is universal, in the sense that it is globally independent of the bulk material under consideration. We also discuss our experimental results in the light of theoretical estimates of surface scattering Q-factors already published in the literature.

https://doi.org/10.1364/OL.43.000495