In Ref. 1 we have demonstrated large spectral tuning in the whispering gallery modes of glycerol/water microdroplets standing on a superhydrophobic surface upon exposure to a 1064 nm laser beam focused to approximately the center of the microdroplet. At the time when the manuscript was written, the spectral tuning mechanism was interpreted to rely on the optical scattering force. Our recent experiments have revealed an error in this interpretation. In our recent experiments we have been able to

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... analyze microdroplets in the reverse geometry while kept in a sealed chamber ͑Fig. 1͒. In this geometry, the optical scattering force is expected to cause a deformation towards an oblate spheroid, leading to an increase in the equatorial radius of the microdroplet. However, our experiments revealed a decrease in the equatorial radius, similar to the observations made in Ref. 1. In addition to that, the fact that the degeneracy of the whispering gallery modes with the same angular momentum was not lifted with increased laser power ͑apparent in the resolution limited peaks in Fig. 3 of Ref. 1͒, suggests that the spherical symmetry was well preserved during spectral tuning. Furthermore, our calculations considering the magnitude of the optical scattering force and the surface tension of the liquid microdroplet revealed the expected deformation due to the optical scattering force to be too small. These findings indicate laser induced evaporation of the microdroplet as the source of the spectral tuning mechanism. Constant infrared laser illumination leads to the evaporation of the water content of individual microdroplets until a new equilibrium is established with the sealed chamber. At the new equilibrium point, the microdroplet has a smaller mole fraction of water, and it is warmer than the sealed chamber. When the laser illumination is turned off, the temperature of the microdroplet becomes equal to the temperature of the sealed chamber, and the mole fraction of water recovers to its equilibrium value. Using the results of the detailed analysis done in Ref. 2, we have calculated the expected change in the equilibrium mole fraction of water in a microdroplet in response to a change in its temperature ͑Fig. 2͒. We have found that a 10°C increase in the microdroplet's temperature will lead to 38% reduction in its equilibrium volume under an atmosphere with 90% relative humidity. Considering the absorption of water and glycerol 3 at 1064 nm, these calculation compare well with our observations. We note that all our experimental findings remain unaffected by this error in the interpretation. 1