Controlled Deformation and Raman Lasing in Microdroplets Standing on a Superhydrophobic Surface (original) (raw)
Related papers
2007
Abstract. Glycerol/water microdroplets take almost spherical shapes when standing on a superhydrophobic surface. Hence they are suitable to function as optical microcavities. Using Rhodamine B doped water microdroplets, large spectral tunability of the whispering gallery modes (WGMs)(> 5 nm) was observed. Tunability was achieved by evaporation/condensation in a current controlled mini humidity chamber. Experiments revealed a mechanism stabilizing the volume of these microdroplets with femtoliter resolution.
Raman lasing near 650 nm from pure water microdroplets on a superhydrophobic surface
Photonics and …, 2009
We demonstrate Raman lasing near 650 nm in pure water microdroplets located on a superhydrophobic surface. In the experiments, stationary, pure water microdroplets were prepared on a superhydrophobic surface and excited by a pulsed, frequencydoubled Nd:YAG laser at 532 nm. Intense laser emission was observed at frequencies corresponding to the whispering gallery mode resonances of the water microdroplets near 650 nm where Raman resonances due to OH-stretching bonds of water are located. Onoff behavior was observed during lasing and the average temporal inter-burst separation was determined from the time-dependent intensity traces. Our results can find applications in the development of novel organic light emitters for short-haul communication systems, and in the spectroscopic characterization of water microdroplets on a surface. #
Raman lasing near 630 nm from stationary glycerol-water microdroplets on a superhydrophobic surface
Optics Letters, 2007
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 m 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.
Controlled observation of nondegenerate cavity modes in a microdroplet on a superhydrophobic surface
We demonstrate controlled lifting of the azimuthal degeneracy of the whispering gallery modes (WGMs) of single glycerol–water microdroplets standing on a superhydrophobic surface by using a uniform electric field. A good agreement is observed between the measured spectral positions of the nondegenerate WGMs and predictions made for a prolate spheroid. Our results reveal fewer azimuthal modes than expected from an ideal spherical microdroplet due to the truncation by the surface. We use this difference to estimate the contact angles of the microdroplets.
Spectral tuning of liquid microdroplets standing on a superhydrophobic surface using electrowetting
Applied Physics Letters, 2008
Using electrowetting, we demonstrate reversible spectral tuning of the whispering gallery modes of glycerol/water microdroplets standing on a superhydrophobic surface by up to 4.7 nm at 400 V. Our results can inspire electrically tunable optical switches and filters based on microdroplets on a superhydrophobic surface. The sensitivity of the observed spectral drift to the contact angle can also be used to measure the contact angles of microdroplets on a superhydrophobic surface.
Journal of Materials Chemistry, 2011
Emission spectra from microdroplets doped with CdSe/ZnS quantum dots (QDs) have been recorded on superhydrophobic coatings (water contact angle > 170 ). Whispering gallery modes (WGMs) with Q-factors as high as 4.0 Â 10 3 were discernible. Excitation parameters for optimal microdroplet WGM response illumination and acquisition are also presented. Fluorescent QDs provide a robust WGM reporting mechanism under extreme continuous wave microdroplet excitation (465.5 mW) for periods greater than 15 minutes. In this format droplets could be optically tuned on demand using combinations of QDs. Ionic liquid QD-doped droplet emission was found to be spectrally stable: a >75% improvement in WGM blue-shift was recorded (due to droplet evaporation) compared to QD-doped glycerol/water droplet emission. Theoretical analysis of emission spectra confirmed the observed emission response curves correspond to Mie theory suggesting the droplets are extremely close to spherical on the surface. This versatile liquid resonator system has direct implications in high performance room-temperature laser development, telecommunications research and lab-on-a-chip based diagnostics. † Electronic supplementary information (ESI) available: Time dependent WGM emission analysis of glycerol/water and ionic liquid/water microdroplets. See
Journal of the Optical Society of America B, 2016
Optical whispering gallery modes (WGMs) were observed in elastic scattering spectra recorded from oil-in-water emulsion droplets in a microfluidic channel. Droplets with diameters ranging between 15 and 50 μm were trapped by optical tweezers near the tip of a single mode fiber that enabled the excitation of the WGMs using a tunable laser. Quality factors of the WGMs were observed to increase with droplet size. WGMs with quality factors of more than 10 4 were observed for droplets with diameters around 45 μm. In some cases, recorded WGMs drifted monotonically to the blue end of the spectrum due to droplet dissolution in the host liquid. Fluctuating spectral shifts to both blue and red ends of the spectrum were also observed. These were attributed to the presence of randomly diffusing particulate contaminants in the droplet liquid, indicating the potential of optically trapped droplet resonators for optical sensing applications.
Optics Communications, 2007
We report laser emission from single, stationary, Rhodamine B-doped glycerol/water microdroplets located on a superhydrophobic surface. In the experiments, a pulsed, frequency-doubled Nd:YAG laser operating at 532 nm was used as the excitation source. The microdroplets ranged in diameter from a few to 20 µm. Lasing was achieved in the red-shifted portion of the dye emission spectrum with threshold fluences as low as 750 J/cm 2 .
Applied Physics …, 2007
We demonstrate large spectral tuning of glycerol/water microdroplets standing on a superhydrophobic surface using the optical scattering force exerted by a 1064 nm Nd 3+ :YVO 4 solid-state laser. Spectral tuning up to 30 nm is presented in the whispering gallery modes as a result of the deformation of the microdroplets toward a truncated prolate spheroid geometry. Observed large spectral tuning is also reported to be highly reversible. This demonstration can inspire novel, largely tunable optical switches or filters based on liquid microdroplets kept in a sealed chamber.
Lasing action in microdroplets modulated by interfacial molecular forces
Advanced Photonics, 2021
Liquid droplets offer a great number of opportunities in biochemical and physical research studies in which droplet-based microlasers have come into play over the past decade. While the recent emergence of droplet lasers has demonstrated their powerful capabilities in amplifying subtle molecular changes inside the cavity, the optical interactions between droplet resonators and an interface remain unclear. We revealed the underlying mechanism of droplet lasers when interacting with a droplet-solid interface and explored its correlation with intermolecular forces. A vertically oriented oscillation mode-arc-like mode-was discovered, where the number of lasing modes and their Q-factors increase with the strength of interfacial hydrophobicity. Both experimental and theoretical results demonstrated that hydrophobicity characterized by contact angle and interfacial tension plays a significant role in the geometry of droplet cavity and laser mode characteristics. Finally, we demonstrated how tiny forces induced by proteins and peptides could strongly modulate the lasing output in droplet resonators. Our findings illustrate the potential of exploiting optical resonators to amplify intermolecular force changes, providing comprehensive insights into lasing actions modulated by interfaces and applications in biophysics.