Surface scattering and opto-mechanical effects in droplet microresonators
Authors: Giorgini A., Avino S., Malara P., De Natale P., Gagliardi G.
Autors Affiliation: Consiglio Nazionale Delle Ricerche, Istituto Nazionale di Ottica (INO), Via Campi Flegrei, 34, Comprensorio A. Olivetti Pozzuoli (Naples), 80078, Italy; Consiglio Nazionale Delle Ricerche, Istituto Nazionale di Ottica (INO), Largo E. Fermi 6, Firenze, 50125, Italy
Abstract: Optical whispering-gallery modes (WGMs) have been extensively investigated in solid micro-cavities of various geometries and materials demonstrating impressive quality (Q) factors. The peculiarity of WGMs supported by such solid structures is that they can be excited via evanescent-wave coupling while resonant light travels along closed paths at the boundary between the surface of the resonator and the surrounding environment. Here, we use micro-cavities made directly from small, vertically-suspended liquid droplets realizing excitation of their whispering-gallery modes by free-space laser beams and demonstrating laser-frequency locking on corresponding optical resonances with various liquids for sensing applications. From direct cavity photon lifetime measurements, we show intrinsic optical Q-factors > 107 for highly-transparent liquid polymers in the visible, that may be limited by scattering due to thermal-induced surface distortions and residual optical absorption. On the other hand, the interaction between light and mechanical motion is also investigated in these droplets. Based on our recent experimental results, liquid microresonators exhibit interesting properties that potentially allow for optical stimulation of mechanical vibrations.
KeyWords: Drops; Laser beams; Laser excitation; Laser mode locking; Laser resonators; Light absorption; Liquids; Locks (fasteners); Microcavities; Q factor measurement; Quantum optics; Surface scattering; Vibrations (mechanical), Capillary wave; Laser frequency; Liquid droplets; Micro resonators; Optical stimulation; Sensing applications; Surrounding environment; Transparent liquids, Whispering gallery modes