29,469 research outputs found
A Self-Assembled Microlensing Rotational Probe
A technique to measure microscopic rotational motion is presented.
When a small fluorescent polystyrene microsphere is attached to a larger
polystyrene microsphere, the larger sphere acts as a lens for the smaller
microsphere and provides an optical signal that is a strong function of the
azimuthal angle. We demonstrate the technique by measuring the rotational
diffusion constant of the microsphere in solutions of varying viscosity and
discuss the feasibility of using this probe to measure rotational motion of
biological systems.Comment: 3 pages with 2 figures (eps format). Paper has been submitted to
Applied Physics Letter
Observation and characterization of mode splitting in microsphere resonators in aquatic environment
Whispering gallery mode (WGM) optical resonators utilizing resonance shift
(RS) and mode splitting (MS) techniques have emerged as highly sensitive
platforms for label-free detection of nano-scale objects. RS method has been
demonstrated in various resonators in air and liquid. MS in microsphere
resonators has not been achieved in aqueous environment up to date, despite its
demonstration in microtoroid resonators. Here, we demonstrate scatterer-induced
MS of WGMs in microsphere resonators in water. We determine the size range of
particles that induces MS in a microsphere in water as a function of resonator
mode volume and quality factor. The results are confirmed by the experimental
observations.Comment: 4 Pages, 5 Figures, 13 Reference
A spatial refractive index sensor using whispering gallery modes in an optically trapped microsphere
We propose the use of an optically trapped, dye doped polystyrene microsphere
for spatial probing of the refractive index at any position in a fluid. We
demonstrate the use of the dye embedded in the microsphere as an internal
broadband excitation source, thus eliminating the need for a tunable excitation
source. We measured the full width at half maximum of the TE and TM resonances,
and their frequency spacing as a function of the refractive index of the
immersion fluid. From these relations we obtained an absolute sensitivity of
5e-4 in local refractive index, even when the exact size of the microsphere was
not a priori known.Comment: 3 pages, 3 figure
Recoiling DNA Molecule: Simulation & Experiment
Single molecule DNA experiments often generate data from force versus
extension measurements involving the tethering of a microsphere to one end of a
single DNA molecule while the other is attached to a substrate. We show that
the persistence length of single DNA molecules can also be measured based on
the recoil dynamics of these DNA-microsphere complexes if appropriate
corrections are made to the friction coefficient of the microsphere in the
vicinity of the substrate. Comparison between computer simulated recoil curves,
generated from the corresponding Langevin equation, and experimental recoils is
used to assure the validity of data analysis.Comment: 14 pages (single column preprint), 7 figures. Major changes: data
analysis method improved; dna-ethidium bromide results removed (dna-ethidium
bromide protocol affected microspheres and coverglass behavior
All-Optical Nanopositioning of High-Q Silica Microspheres
A tunable, all-optical, coupling method has been realized for a
high-\textit{Q} silica microsphere and an optical waveguide. By means of a
novel optical nanopositioning method, induced thermal expansion of an
asymmetric microsphere stem for laser powers up to 171~mW has been observed and
used to fine tune the microsphere-waveguide coupling. Microcavity displacements
ranging from (0.612~~0.13) -- (1.5 0.13) m and nanometer scale
sensitivities varying from (2.81 0.08) -- (7.39 0.17) nm/mW, with
an apparent linear dependency of coupling distance on stem laser heating, were
obtained. Using this method, the coupling was altered such that different
coupling regimes could be explored for particular samples. This tunable
coupling method, in principle, could be incorporated into lab-on-a-chip
microresonator systems, photonic molecule systems, and other nanopositioning
frameworks.Comment: 6pages,4figure
Development of 3D PCL microsphere/TiO\u3csub\u3e2\u3c/sub\u3e nanotube composite scaffolds for bone tissue engineering
In this research, the three dimensional porous scaffolds made of a polycaprolactone (PCL) microsphere/TiO2 nanotube (TNT) composite was fabricated and evaluated for potential bone substitute applications. We used a microsphere sintering method to produce three dimensional PCL microsphere/TNT composite scaffolds. The mechanical properties of composite scaffolds were regulated by varying parameters, such as sintering time, microsphere diameter range size and PCL/TNT ratio. The obtained results ascertained that the PCL/TNT (0.5 wt%) scaffold sintered at 60 °C for 90 min had the most optimal mechanical properties and an appropriate pore structure for bone tissue engineering applications. The average pore size and total porosity percentage increased after increasing the microsphere diameter range for PCL and PCL/TNT (0.5 wt%) scaffolds. The degradation rate was relatively high in PCL/TNT (0.5 wt%) composites compared to pure PCL when the samples were placed in the simulated body fluid (SBF) for 6 weeks. Also, the compressive strength and modulus of PCL and PCL/TNT (0.5 wt%) composite scaffolds decreased during the 6 weeks of storage in SBF. MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) assay and alkaline phosphates (ALP) activity results demonstrated that a generally increasing trend in cell viability was observed for PCL/TNT (0.5 wt%) scaffold sintered at 60 °C for 90 min compared to the control group. Eventually, the quantitative RT-PCR data provided the evidence that the PCL scaffold containing TiO2 nanotube constitutes a good substrate for cell differentiation leading to ECM mineralization
Highly efficient hybrid fiber taper coupled microsphere laser
A novel hybrid fiber taper is proposed and demonstrated as the coupler in a microsphere laser system. The pump wave and the laser emission, respectively, are more efficiently coupled to and from the sphere modes with this taper structure. A 980-nm pumped erbium–ytterbium codoped phosphate microsphere laser is demonstrated in the 1550-nm band. As much as 112 µW of single-frequency laser output power was measured, with a differential quantum efficiency of 12%
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