|M.Sc Student||Kher-Alden Jacob|
|Subject||Photonic Hyperfine-Structure Induced by a Lab|
Levitating in Air
|Department||Department of Mechanical Engineering||Supervisor||Professor Tal Carmon|
|Full Thesis text|
In this research we experimentally demonstrate, for the first time, activating a liquid micro-droplet as a fiber coupled resonator while it's levitating in air. Our levitating droplet resonator exhibits record values of optical enhancement as well as the highest degeneracy ever reported.
Optical traps were first used for activating optical resonances in droplets in 1977 by Ashkin, by tuning the frequency of the laser beam of the trap. An upward motion of the drop indicated that the laser frequency was near resonance. In fact, this was the first demonstration of micro resonator droplets. Droplets then continued to serve as the major and only micro cavity platform, until solids took the lead. Yet and unlike current solid-based technology, droplets represents several properties unique to the liquid-phase of matter:
1. Droplets allow optically interrogating, exciting, and cooling capillary waves.
2. Micro droplets can host an acoustic-breath, and WGM modes (The only works where acoustic resonances are reported in micro droplets).
3. Light circulating in droplets generates fluidic vortices.
4. Modes mapping in micro droplets allowing crossing between resonances.
In 2015 WGM resonators were activated in trapped droplets by using optical tweezers in aquatic environment. Light was evanescently coupled to the trapped droplet using a tapered fiber and Q-factor of 12∙106 was measured.
In our experiment we are activating WGM in droplet resonators while they are levitating in air. There are several advantages to a droplet levitating in air:
1. The fluid-air large index contrast allows reducing the resonator size without suffering loss of radiation that tunnels through the resonator. This result in an improvement in the optical finesse of the droplet.
2. As nothing is in touch with the cavity, its cleanness is improved, which further improves finesse.
This reduction of optical loss and size allowed measuring a high Q-factor of 1.34∙109, 10 million finesse, and together with the small volume of our droplet (25 µm diameter), gave us a Q/V of 2.5∙107 (µm)-3, which is the highest values reported in any micro-resonator.
Trapping the resonator in air and not connecting it to mechanical supports also reduces the losses of the acoustic- and capillary-energy of the resonator (support losses), which is important for investigating acoustic and capillary waves in liquid resonators.
Furthermore, the droplet is uniquely almost perfectly spherical, this high symmetry suggests the highest degree of degeneracy for its modes. Such a high degree of degeneracy is generally referred to as hyperfine in atomic physics. Similarly, our perfectly spherical resonators serve as hyperfine photonic devices as theoretically predicted, Yet, this is the first time that an almost perfectly spherical resonator is reported. In more details, a perfectly spherical droplet can serve as a new type of sensor where an analyte will break the resonator symmetry to split its super degenerated modes. Our hyperfine cavities may present a new paradigm, with highest degeneracy and narrowest lines - to be split by minute measurable.