A. L. Demirel

Simple largely tunable optical microcavity

The authors demonstrate more than 9nm tunability of the whispering gallery modes (WGMs) of rhodamine B doped water microdroplets resting on a superhydrophobic surface. Tunability was achieved by controlling the size of the microdroplets in a current controlled mini humidity chamber. WGMs were observed with quality factors of more than 8000 when kept stable. The sensitivity of the resonances to the size and shape of the microdroplet reveals opportunities for the use of this technique as a probe to characterize superhydrophobic surfaces and investigate liquid-solid surfaces.

Raman lasing near 630 nm from stationary glycerol-water microdroplets on a superhydrophobic surface

We demonstrate, for the first time to our knowledge, Raman lasing from stationary microdroplets on a superhydrophobic surface. In the experiments, glycerol-water microdroplets with radii in the 11-15 microm range were pumped at 532 nm with a pulsed, frequency-doubled Nd:YAG laser. Two distinct operation regimes of the microdroplets were observed: cavity-enhanced Raman scattering and Raman lasing. In the latter case, the Raman lasing signal was higher than the background by more than 30 dB. Investigation of the Raman spectra of various glycerol-water mixtures indicates that lasing occurs within the glycerol Raman band. Raman lasing was not sustained; rather, oscillation would occur in temporally separated bursts. Increasing the rate of convective cooling by nitrogen purging improved the lasing performance and reduced the average interburst separation from 2.3 to 0.4 s.

Volume stabilization of single, dye-doped water microdroplets with femtoliter resolution

A self-control mechanism that stabilizes the size of Rhodamine B-doped water microdroplets standing on a superhydrophobic surface is demonstrated. The mechanism relies on the interplay between the condensation rate that was kept constant and the evaporation rate induced by laser excitation, which critically depends on the size of the microdroplets. The radii of individual water microdroplets (>5 μm) stayed within a few nanometers during long time periods (up to 455 s). By blocking the laser excitation for 500 ms, the stable volume of individual microdroplets was shown to change stepwise.

Enhanced radiative energy transfer in single glycerol/water microdroplets on a superhydrophobic surface

Up to 10 times enhancement in the energy transfer rate from donor to acceptor molecules is demonstrated at wavelengths resonant with a whispering gallery mode of a glycerol/water microdroplet standing on a superhydrophobic surface.

Laser Emission from Single, Dye-Doped Microdroplets Situated on a Superhydrophobic Surface

Optical microcavities are attractive in developing ultralow threshold lasers which hold a great promise for applications in optical communications systems and fundamental studies in cavity quantum electrodynamics. Up to date laser emission has been observed from various different optical microcavities: Microdisks, microspheres, micropillars, photonic crystal defect microcavities, and microdroplets flying in air. Here we report the observation of laser emission from single, stationary, dye-doped microdroplets situated on a superhydrophobic surface. In contrast to the previous demonstrations on microdroplets flying in air, the technique we use allows for the analysis of laser emission from a particular microdroplet over prolonged periods.

Erratum: “Simple largely tunable optical microcavity [Appl. Phys. Lett. 89, 081118 (2006)]

We have determined a calibration error in the diameter measurements reported in Ref. 1. The diameter of the microdroplet discussed in Fig. 2 a is corrected to 8 μm. Data points reported in Fig. 3 are also changed as a result of this correction. Figure 3 is now corrected to Fig. 1 in this erratum where the dashed line represents the expected dependence for ideal water microspheres in air. From this figure, it is no longer possible to conclude that there is a considerable deviation between the observed free spectral ranges FSRs and those predicted from ideal water microspheres. Hence we retract the statement that the deviation of the shape of a microdroplet standing on a superhydrophobic surface from an ideal microsphere leads to a difference between the measured FSRs and those predicted from ideal water microspheres in air. All other conclusions drawn in Ref. 1 remain unaffected by this correction.