Large spectral tuning of a water–glycerol microdroplet by a focused laser: characterization and modeling

Abstract

Large spectral tuning of a water-glycerol microdroplet standing on a superhydrophobic surface by local heating with a focused infrared laser is studied both experimentally by optical spectroscopy and computationally using a lumped system formulation of the mass and heat transfer between the microdroplet and the chamber. The effects of optical scattering force, chamber humidity, size of microdroplet and laser power on the tuning mechanism are examined. The reversibility of the tuning mechanism is also studied. In spite of its negligibly small volatility compared to that of water, irreversibility is found to be mainly caused by evaporation of glycerol. It is also found that reversibility increases dramatically with the relative water and glycerol humidities, and spectral tuning can be made almost fully reversible when the chamber is saturated with glycerol vapor and the relative water humidity approaches unity. Some hysteresis effects are observed, especially in large microdroplets, and this behavior is attributed to the whisperinggallery mode resonances in laser absorption. The time response of the tuning mechanism is also analyzed both experimentally and computationally. The technique presented can find applications in optical communication systems, and can be used in fundamental studies in cavity quantum electrodynamics and in characterizing liquid aerosols on a surface.

Size-change and deposition of conventional and composite cigarette smoke particles during inhalation in a subject-specific airway model

“…(18a) was obtained from Tu & Ray (2005) and Eq. (18b) from Kiraz et al (2008). Both simulated and measured results show that the size and water content of a droplet increase rapidly when the water vapor in the surrounding gas phase increases.…”

Photothermal Tuning and Size Locking of Salt-Water Microdroplets on a Superhydrophobic Surface

“…Figure 1 a considers on-axis illumination, i.e., the beam is focused at the center of the microdroplet. WGMs are therefore not excited in this configuration; only low quality oscillations corresponding to Fabry-Perot resonance modes are observed (Kiraz et al 2008). This experimental configuration allows for almost linear and reversible size tuning of the microdroplets and is used for the photothermal tuning spectroscopy experiments described in Section 4.…”

“…We have recently demonstrated that photothermal tuning can be used in large, almost reversible spectral tuning of the whispering gallery modes (WGMs) of liquid microdroplets (Kiraz et al 2008. We have also demonstrated that a hysteretic behavior can be observed in a photothermal tuning cycle when the infrared laser is focused near the rim of the microdroplet, enabling bistable operation ).…”

“…A lumped system model which assumes that all of the variables of the saltwater microdroplet and the chamber are uniform throughout their whole respective volumes is used for photothermal tuning (Kiraz et al 2008. The rate of change of the number of moles of water (N A ) in the microdroplet is given as (Ray et al 1989),…”

Near-infrared Laser-induced Temperature Elevation in Optically-trapped Aqueous Droplets in Air

“…Experimental studies on local heating in the focus of an optical trap have been hitherto reported for various systems. [6][7][8][9][10][11][12][13][14][15][16][17][18] However, the number of the reports on estimation of the amount of heat generation through absorption of a photon energy by single optically-trapped water droplets in air is still limited. [14][15][16][17][18] In order to achieve the quantitative measurement of temperature elevation of opticallytrapped water droplets in air, we employed a 1064-nm laser beam as a heating light source.…”