Spectral tuning of liquid microdroplets standing on a superhydrophobic surface by using a focused infrared laser or electrowetting

Abstract

Optik mikrokovuklar ışığın küçük hacimler içinde hapsolmasını sağlar. Optik mikrokovuklarteorik ve deneysel araştırmalarda kullanılmak için tercih edilen sistemlerdir. Boşlukkuantum elektrodinamiğinde, optoelektonik alanında ve biyolojik algılamada sıklıkla kullanılırlar.Değişik tiplerde optik mikrokovuk şekilleri gösterilmişdir. Fabry-Perot çınlaçları,mikroküreler, mikrodamlacıklar ve mikrotoroidler bu tiplerin bazılarıdır.

Optical microcavities provide confinement of light into small volumes. They are favorablesystems to use both for theoretical and experimental research areas. They are widely used incavity quantum electrodynamics (CQED), optoelectronic, and biological sensing. Differenttypes of optical microcavities have been demonstrated. Some types of them are fabry-perotresonators, microspheres, microdroplets, microtoroids.Liquid microdroplets standing on a superhydrophobic surface can also provide a threedimensional confinement for light. The use of superhydrophobic surfaces is very efficientand costless way to protect the sphericity and provide the position stabilization of liquidmicrodroplets. The whispering gallery modes (WGMs) of liquid microdroplets can havehigh quality factors due to the large contact angle. The liquid nature of the microdropletsprovides large spectral tuning which can not be obtained by using solid microcavities. Thelarge spectral tuning ofWGMs of liquid microdroplets can be obtained by the size change byusing evaporation/condensation kinetics or the shape deformation by using electrowetting.In this thesis, first we demonstrate the large spectral tuning of a water-glycerol microdropletstanding on a superhydrophobic surface by local heating experimentally by opticalspectroscopy and computationally using a lumped system formulation of the mass and heattransfer between the microdroplet and the chamber. The water-glycerol system is not fullyreversible mainly due to glycerol content of the microdroplet. Some hysteresis effects dueto whispering-gallery mode resonances are also observed in this system. Second, we obtaina fully reversible spectral tuning by using a highly soluble and nonvolatile inorganic saltinstead of the glycerol content of the microdroplet. The self-stability and optical bistabilityare observed using NaCl-water microdroplet standing on superhydrophobic surface. Finally,we demonstrate reversible spectral tuning of the whispering gallery modes of glycerol-watermicrodroplets using electrowetting. We are able to obtain 4.7 nm spectral tuning at 400 V.The techniques for large spectral tuning can inspire novel largely tunable microdropletbasedcomponents required for optical communications systems.They can be used in cavity quantum electrodynamics, and in characterizing liquid aerosols on surface. Also the spectraltuning with electrowetting can be used in measuring the contact angles of microdropletsstanding on superhydrophobic surface. The self-stability of liquid microdroplets can providestable experimental conditions for ultrahigh resolution spectroscopy of microdroplets. Opticalbistability observed in photothermal tuning cycle can be used as a microdroplet-basedoptical memory device.