Accurate Low Complexity Quadrature Angular Diversity Aperture Receiver for Visible Light Positioning.

Despite the many potential applications of an accurate indoor positioning system (IPS), no universal, readily available system exists. Much of the IPS research to date has been based on the use of radio transmitters as positioning beacons. Visible light positioning (VLP) instead uses LED lights as beacons.

Emerging nanophotonic biosensor technologies for virus detection.

Highly infectious viral diseases are a serious threat to mankind as they can spread rapidly among the community, possibly even leading to the loss of many lives. Early diagnosis of a viral disease not only increases the chance of quick recovery, but also helps prevent the spread of infections. There is thus an urgent need for accurate, ultrasensitive, rapid, and affordable diagnostic techniques to test large volumes of the population to track and thereby control the spread of viral diseases, as evidenced during the COVID-19 and other viral pandemics.

Germanium Nanosheets with Dirac Characteristics as a Saturable Absorber for Ultrafast Pulse Generation.

Bulk germanium as a group-IV photonic material has been widely studied due to its relatively large refractive index and broadband and low propagation loss from near-infrared to mid-infrared. Inspired by the research of graphene, the 2D counterpart of bulk germanium, germanene, has been discovered and the characteristics of Dirac electrons have been observed. However, the optical properties of germanene still remain elusive.

Oxidation of Monolayer WS in Ambient Is a Photoinduced Process.

We have studied the ambient air oxidation of chemical vapor deposition (CVD) grown monolayers of the semiconducting transition metal dichalcogenide (S-TMD) WS using optical microscopy, laser scanning confocal microscopy (LSCM), photoluminescence (PL) spectroscopy, and atomic force microscopy (AFM). Monolayer WS exposed to ambient conditions in the presence of light (typical laboratory ambient light for weeks or typical PL spectroscopy map) exhibits damage due to oxidation which can be detected with the LSCM and AFM, though may not be evident in conventional optical microscopy due to poorer contrast and resolution. Additionally, this oxidation was not random and was correlated with "high-symmetry" high intensity edges and red-shifted areas in the PL spectroscopy map, areas thought to contain a higher concentration of sulfur vacancies.

Evolution of large-scale flow from turbulence in a two-dimensional superfluid.

Nonequilibrium interacting systems can evolve to exhibit large-scale structure and order. In two-dimensional turbulent flow, the seemingly random swirling motion of a fluid can evolve toward persistent large-scale vortices. To explain such behavior, Lars Onsager proposed a statistical hydrodynamic model based on quantized vortices.

Vortex Thermometry for Turbulent Two-Dimensional Fluids.

We introduce a new method of statistical analysis to characterize the dynamics of turbulent fluids in two dimensions. We establish that, in equilibrium, the vortex distributions can be uniquely connected to the temperature of the vortex gas, and we apply this vortex thermometry to characterize simulations of decaying superfluid turbulence. We confirm the hypothesis of vortex evaporative heating leading to Onsager vortices proposed in Phys.

High efficiency, low cost holographic optical elements for ultracold atom trapping.

We demonstrate a method of creating high efficiency, high fidelity, holographic optical elements for the generation of complex optical fields, in a low cost photopolymer, Bayfol HX. The desired optical field profile is generated by a spatial light modulator and written into an optically addressable photopolymer as a volume hologram. We demonstrate the utility of this approach by trapping a Bose-Einstein condensate of rubidium-87 atoms in the nodal plane of an HG mode generated by one of these holographic optical elements.

Optical vortex knots - one photon at a time.

Feynman described the double slit experiment as "a phenomenon which is impossible, absolutely impossible, to explain in any classical way and which has in it the heart of quantum mechanics". The double-slit experiment, performed one photon at a time, dramatically demonstrates the particle-wave duality of quantum objects by generating a fringe pattern corresponding to the interference of light (a wave phenomenon) from two slits, even when there is only one photon (a particle) at a time passing through the apparatus. The particle-wave duality of light should also apply to complex three dimensional optical fields formed by multi-path interference, however, this has not been demonstrated.

Emergence of order from turbulence in an isolated planar superfluid.

We study the relaxation dynamics of an isolated zero temperature quasi-two-dimensional superfluid Bose-Einstein condensate that is imprinted with a spatially random distribution of quantum vortices. Following a period of vortex annihilation the remaining vortices self-organize into two macroscopic coherent "Onsager vortex" clusters that are stable indefinitely--despite the absence of driving or external dissipation in the dynamics. We demonstrate that this occurs due to a novel physical mechanism--the evaporative heating of the vortices--that results in a negative-temperature phase transition in the vortex degrees of freedom.

Surface acoustic waves for on-demand production of picoliter droplets and particle encapsulation.

Microscopic water-in-oil droplets are a versatile chemical and biological platform whose dimensions result in short reaction times and require minuscule amounts of reagent. Methods exist for the production of droplets, though the vast majority are only able to do so in continuous flows, restricting the ability to independently control reactions of individual droplets, a prerequisite for programmable digital microfluidics. Here we present a novel method to produce individual picoliter-scale droplets on-demand using surface acoustic waves (SAW).

Partial-transfer absorption imaging: a versatile technique for optimal imaging of ultracold gases.

Partial-transfer absorption imaging is a tool that enables optimal imaging of atomic clouds for a wide range of optical depths. In contrast to standard absorption imaging, the technique can be minimally destructive and can be used to obtain multiple successive images of the same sample. The technique involves transferring a small fraction of the sample from an initial internal atomic state to an auxiliary state and subsequently imaging that fraction absorptively on a cycling transition.

Tunable optical tweezers for wavelength-dependent measurements.

Optical trapping forces depend on the difference between the trap wavelength and the extinction resonances of trapped particles. This leads to a wavelength-dependent trapping force, which should allow for the optimization of optical tweezers systems, simply by choosing the best trapping wavelength for a given application. Here we present an optical tweezer system with wavelength tunability, for the study of resonance effects.

Detection of heteroplasmic mitochondrial DNA in single mitochondria.

Background: Mitochondrial DNA (mtDNA) genome mutations can lead to energy and respiratory-related disorders like myoclonic epilepsy with ragged red fiber disease (MERRF), mitochondrial myopathy, encephalopathy, lactic acidosis and stroke (MELAS) syndrome, and Leber's hereditary optic neuropathy (LHON). It is not well understood what effect the distribution of mutated mtDNA throughout the mitochondrial matrix has on the development of mitochondrial-based disorders. Insight into this complex sub-cellular heterogeneity may further our understanding of the development of mitochondria-related diseases.

Shaped nondiffracting beams.

We demonstrate that nondiffracting beams can be generated with an arbitrary transverse shape. In particular, we show that the azimuthal complex modulation of the angular spectra of Helmholtz-Gauss wave fields constitutes a degree of freedom sufficient to tailor nondiffracting beams with an intensity pattern of choice.

Generation and mixing of subfemtoliter aqueous droplets on demand.

We describe a novel method of generating monodisperse subfemtoliter aqueous droplets on demand by means of piezoelectric injection. Droplets with volumes down to 200 aL are generated by this technique. The droplets are injected into a low refractive index perfluorocarbon so that they can be optically trapped.

Antimicrobial photodynamic action on dentin using a light-emitting diode light source.

Objective: The aim of this study was the evaluation of two different photosensitizers activated by red light emitted by light-emitting diodes (LEDs) in the decontamination of carious bovine dentin.

Materials And Methods: Fifteen bovine incisors were used to obtain dentin samples which were immersed in brain-heart infusion culture medium supplemented with 1% glucose, 2% sucrose, and 1% young primary culture of Lactobacillus acidophilus 10(8) CFU/mL and Streptococcus mutans 10(8) CFU/mL for caries induction. Three different concentrations of the Photogem solution, a hematoporphyrin derivative (1, 2, and 3 mg/mL) and two different concentrations of toluidine blue O (TBO), a basic dye (0.

Green fluorescent protein in inertially injected aqueous nanodroplets.

We inertially inject and study the contents of optically trappable aqueous nanodroplets (hydrosomes) emulsified in a perfluorinated matrix. A new piezoelectric actuated device for production of single hydrosomes on demand is introduced. Hydrosomes containing enhanced green fluorescent protein (EGFP) were injected, optically trapped, and held at the focus of an excitation laser in a confocal microscope, and single-molecule photobleaching events were observed.

Stable and robust polymer nanotubes stretched from polymersomes.

We create long polymer nanotubes by directly pulling on the membrane of polymersomes using either optical tweezers or a micropipette. The polymersomes are composed of amphiphilic diblock copolymers, and the nanotubes formed have an aqueous core connected to the aqueous interior of the polymersome. We stabilize the pulled nanotubes by subsequent chemical cross-linking.

Directed growth of pure phosphatidylcholine nanotubes in microfluidic channels.

The morphology of self-assembled phospholipid membranes (e.g., micelles, vesicles, rods, tubes, etc.

Real-time measurement of spontaneous antigen-antibody dissociation.

We report observations in real time of thermally driven adhesion and dissociation between a monoclonal IgE antibody and its specific antigen N-epsilon-2,4-dinitrophenyl-L-lysine. Both molecules were attached to the surfaces of different polystyrene microspheres trapped by optical tweezers. Monitoring spontaneous successive attachment and detachment events allowed a direct determination of the reaction-limited detachment rate k(off) for a single bond and also for multiple bonds.