High Energy Physics Seminars

Exciting Whispering Gallery Modes in solid & liquid micro-cavities using sub-micron size tapered fibers.

by Ms. Meenakshi Gaira (DHEP, TIFR)

Thursday, May 16, 2019 from to (Asia/Kolkata)
at TIFR, Mumbai ( AG-66 )
Whispering Gallery modes (WGMs) in optics are the eigenmodes of circular cavities (like micro-spheres, micro-disks, etc.) which get excited when a light beam gets trapped due to continuous total internal reflections and after orbiting the cavity, it returns to its starting point in phase. Due to their high Quality factor (Q) and confinement of enhanced field in very small mode volume, such systems are ideally suited for non-linear optics, opto-mechanics, cavity QED and bio-chemical sensing. I will present our experimental set up for efficiently exciting and detecting WGMs of Q > 107 in silica micro-spheres and Q > 108 in silicone oil micro-drops of sizes 30 to 300 microns, using tapered fibers of sub-micron waist sizes. I will discuss the hysteretic thermal broadening of WGM resonances in silica micro-spheres due to high power density inside the micro-cavities. I will subsequently present our observations of WGMs in liquid drops of silicone oil and glycerol. These drops are time-dependent micro-cavities with thermal oscillations and constantly varying evaporation and condensation rate. I will explain the fast scanning ring-down technique to determine the Q factor of liquid drops, as the standard technique of measuring the linewidths of resonance dips doesn't work due to thermal oscillations of drops. The measured optical Q can be used to determine an upper limit of the absorption coefficient of high transmission liquids, in particular the liquids with very very low/negligible absorption ( < 10-4 cm-1) in the visible range. Also, high Q optical WGMs in liquids drops (Q > ~108) can excite acoustic modes (frequencies > 1 MHz) by radiation pressure. Due to their high Q and high power density, optical WGMs in liquid micro-drops can pave the way for understanding dynamics of liquid drops with better precision.