Scientific Results

Liquid droplet microresonators

Year: 2019

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, Na 80078, Italy; Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica (INO), Largo E. Fermi 6, Firenze, 50125, Italy

Abstract: We provide here an overview of passive optical micro-cavities made of droplets in the liquid phase. We focus on resonators that are naturally created and suspended under gravity thanks to interfacial forces, illustrating simple ways to excite whispering-gallery modes in various slow-evaporation liquids using free-space optics. Similar to solid resonators, frequency locking of near-infrared and visible lasers to resonant modes is performed exploiting either phase-sensitive detection of the leakage cavity field or multiple interference between whispering-gallery modes in the scattered light. As opposed to conventional micro-cavity sensors, each droplet acts simultaneously as the sensor and the sample, whereby the internal light can detect dissolved compounds and particles. Optical quality factors up to 107–108 are observed in liquid-polymer droplets through photon lifetime measurements. First attempts in using single water droplets are also reported. These achievements point out their huge potential for direct spectroscopy and bio-chemical sensing in liquid environments. Finally, the first experiments of cavity optomechanics with surface acoustic waves in nanolitre droplets are presented. The possibility to perform studies of viscous-elastic properties points to a new paradigm: a droplet device as an opto-fluid-mechanics laboratory on table-top scale under controlled environmental conditions.

Journal/Review: SENSORS

Volume: 19 (3)      Pages from: 473-1  to: 473-20

More Information: This research was funded by Italian Ministry for Education and Research (MIUR) grant PON 01_01525 “MONICA” and by Regione Campania FESR 2007–2013 grant “BERSAGLI”.The authors acknowledge technical support by Gianluca Notarialewith project.
KeyWords: Acoustic surface wave devices; Acoustic waves; Chemical sensors; Drops; Infrared devices; Laser excitation; Light; Light measurement; Liquids; Locks (fasteners); Microcavities; Optical resonators; Optomechanics; Q factor measurement; Spectroscopy, Cavity optomechanics; Cavity ring down spectroscopies; Environmental conditions; Free spaces; Optical Q; Optical quality factor; Phase sensitive detection; Surface acoustic waves; Whispering gallery modes
DOI: 10.3390/s19030473

Citations: 3
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