Risk of Airborne COVID-19 Transmission While Performing Humphrey Visual Field Testing.

PRECIS: Designing and demonstrating an experiment that shows the risk of airborne transmission of COVID-19 between patients having visual fields analyzed is low. PURPOSE: The aim was to investigate the possibility of airborne transmission of COVID-19 during Humphrey visual field testing in a real-world scenario. METHODS: A particle counter was placed within the bowl of Humphrey visual field analyzer (HFA) before and after turning on the machine to ascertain the effect of the air current produced by the ventilation system on aerosols. A second experiment was run where the particle counter was placed in the bowl and recorded particulates, in the air, as a 24-2 SITA standard was performed by a mock patient and then again immediately after the patient had moved away. We measured aerosol particle counts sized ≤0.3 µm, >0.3≤0.5 µm, >0.5≤1 µm, >1≤2.5 µm, >2.5≤5 µm, and >5≤10 µm. RESULTS: Particulates of all sizes were shown to be significantly reduced within the bowl after turning the machine on, demonstrating that the air current produced by the HFA pushes air out of the bowl and it cannot stagnate. There was no significant difference in measurement of aerosol while there was a patient performing the test and immediately after they had moved away, suggesting that aerosols breathed out by the patient are not able to remain in suspension in the bowl because of the ventilation current. CONCLUSION: There is no significant difference between aerosol count in the bowl of a HFA before, during and after testing. This suggests the risk of airborne transmission of COVID-19 is low between subsequent patients. This is in keeping with manufacturer's guidance on Humphrey visual field testing.

Aerosol generation during phacoemulsification in live patient cataract surgery environment.

PURPOSE: To investigate whether phacoemulsification is an aerosol-generating procedure in a live patient environment. SETTING: New Hayesbank Ophthalmology Services, Kent, United Kingdom. DESIGN: In vivo experimental human eyes study. METHODS: Aerosol particle counts sized 0.3 µm or lesser, more than 0.3 to 0.5 µm or lesser, more than 0.5 to 1 µm or lesser, more than 1 to 2.5 µm or lesser, more than 2.5 to 5 µm or lesser, and more than 5 to 10 µm or lesser were measured during elective phacoemulsification surgery of 25 eyes. The baseline particle count in the operating theater was measured on 2 separate days to assess for fluctuation. Then, 5 readings each during prephacoemulsification and phacoemulsification of all eyes were measured. The difference in aerosol generation during prephacoemulsification and phacoemulsification was also measured with the use of the mobile laminar air flow (LAF) machine. Finally, aerosol generation during phacoemulsification was measured using 2% hydroxypropyl methylcellulose (HPMC). RESULTS: There was no statistically significant difference in measurement of aerosol between the baseline measurements on both days and between each patient's prephacoemulsification and phacoemulsification stages of surgery. The LAF system showed statistically significant reduction in particles size of 0.3 µm or lesser, more than 0.3 to 0.5 µm or lesser, more than 0.5 to 1 µm or lesser, more than 1 to 2.5 µm or lesser, more than 2.5 to 5 µm or lesser, and more than 5 to 10 µm during phacoemulsification compared with that during prephacoemulsification (P value .00 for all particle sizes, t test). The use of 2% HPMC did not show any statistically significant reduction in particle measurements. CONCLUSIONS: Aerosol particles sized less than 10 µm are not produced during phacoemulsification of human crystalline lens in a live patient setting. The use of a mobile LAF machine significantly reduced the number of particles sized 10 µm or lesser within the surgical field.

Mn2+/Yb3+ Codoped CsPbCl3 Perovskite Nanocrystals with Triple-Wavelength Emission for Luminescent Solar Concentrators.

Doping metal ions into lead halide perovskite nanocrystals (NCs) has attracted great attention over the past few years due to the emergence of novel properties relevant to optoelectronic applications. Here, the synthesis of Mn2+/Yb3+ codoped CsPbCl3 NCs through a hot-injection technique is reported. The resulting NCs show a unique triple-wavelength emission covering ultraviolet/blue, visible, and near-infrared regions. By optimizing the dopant concentrations, the total photoluminescence quantum yield (PL QY) of the codoped NCs can reach ≈125.3% due to quantum cutting effects. Mechanism studies reveal the efficient energy transfer processes from host NCs to Mn2+ and Yb3+ dopant ions, as well as a possible inter-dopant energy transfer from Mn2+ to Yb3+ ion centers. Owing to the high PL QYs and minimal reabsorption loss, the codoped perovskite NCs are demonstrated to be used as efficient emitters in luminescent solar concentrators, with greatly enhanced external optical efficiency compared to that of using solely Mn2+ doped CsPbCl3 NCs. This study presents a new model system for enriching doping chemistry studies and future applications of perovskite NCs.

Benign ferroelastic twin boundaries in halide perovskites for charge carrier transport and recombination.

Grain boundaries have been established to impact charge transport, recombination and thus the power conversion efficiency of metal halide perovskite thin film solar cells. As a special category of grain boundaries, ferroelastic twin boundaries have been recently discovered to exist in both CH3NH3PbI3 thin films and single crystals. However, their impact on the carrier transport and recombination in perovskites remains unexplored. Here, using the scanning photocurrent microscopy, we find that twin boundaries have negligible influence on the carrier transport across them. Photoluminescence (PL) imaging and the spatial-resolved PL intensity and lifetime scanning confirm the electronically benign nature of the twin boundaries, in striking contrast to regular grain boundaries which block the carrier transport and behave as the non-radiative recombination centers. Finally, the twin-boundary areas are found still easier to degrade than grain interior.

Anisotropic bianchi V cosmological model in Scale Covariant Theory of Gravitation with a time-variable deceleration parameter.

In this paper we solve the field equations for Scale covariant theory of gravitation which was introduced by Caunato et al. [1], for Bianchi V line element in the presence of perfect fluid medium. Here the deceleration parameter is considered to be time dependent which gives the average scale factor a ( t ) = [ sinh ⁡ ( ß t ) ] 1 / n , where n and ß are positive constants. This value of average scale factor is the key expression for solving the field equations. Using the recent observational value of q 0 = - 0.52 - 0.04 + 0.08 and H 0 = 69.2 ± 1.2 derived from BAO/CMB and H(z) data by Santos et al. (2016) [46], we have evaluated three different pairs of ( n , ß ) . We observe that the model represents a phase transition from early deceleration to a present accelerating phase for a particular choice of the pair ( n = 2 , ß = 92.75 ) . Applying some recently developed diagnostic tools like jerk parameter and statefinders, we find that the derived model is exactly in accordance with standard ΛCDM model. Along with these, many physical, geometric and kinematic properties of the model are thoroughly studied and found consistent with recent observations.

Bright magnetic dipole radiation from two-dimensional lead-halide perovskites.

Light-matter interactions in semiconductors are uniformly treated within the electric dipole approximation; multipolar interactions are considered "forbidden." We experimentally demonstrate that this approximation inadequately describes light emission in two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs), solution processable semiconductors with promising optoelectronic properties. By exploiting the highly oriented crystal structure, we use energy-momentum spectroscopies to demonstrate that an exciton-like sideband in 2D HOIPs exhibits a multipolar radiation pattern with highly directed emission. Electromagnetic and quantum-mechanical analyses indicate that this emission originates from an out-of-plane magnetic dipole transition arising from the 2D character of electronic states. Symmetry arguments and temperature-dependent measurements suggest a dynamic symmetry-breaking mechanism that is active over a broad temperature range. These results challenge the paradigm of electric dipole-dominated light-matter interactions in optoelectronic materials, provide new perspectives on the origins of unexpected sideband emission in HOIPs, and tease the possibility of metamaterial-like scattering phenomena at the quantum-mechanical level.

Yb- and Mn-Doped Lead-Free Double Perovskite Cs2AgBiX6 (X = Cl-, Br-) Nanocrystals.

Lead-free double perovskite nanocrystals (NCs) have emerged as a new category of materials that hold the potential for overcoming the instability and toxicity issues of lead-based counterparts. Doping chemistry represents a unique avenue toward tuning and optimizing the intrinsic optical and electronic properties of semiconductor materials. In this study, we report the first example of doping Yb3+ ions into lead-free double perovskite Cs2AgBiX6 (X = Cl-, Br-) NCs via a hot injection method. The doping of Yb3+ endows the double perovskite NCs with a newly emerged near-infrared emission band (sensitized from the NC hosts) in addition to their intrinsic trap-related visible photoluminescence. By controlling the Yb-doping concentration, the dual emission profiles and photon relaxation dynamics of the double perovskite NCs can be systematically tuned. Furthermore, we have successfully inserted divalent Mn2+ ions in Cs2AgBiCl6 NCs and observed emergence of dopant emission. Our work illustrates an effective and facile route toward modifying and optimizing optical properties of double perovskite Cs2AgBiX6 (X = Cl-, Br-) NCs with an indirect bandgap nature, which can broaden a range of their potential applications in optoelectronic devices.

Probing the Combined Electromagnetic Local Density of Optical States with Quantum Emitters Supporting Strong Electric and Magnetic Transitions.

We experimentally demonstrate that the radiative decay rate of a quantum emitter is determined by the combined electric and magnetic local density of optical states (LDOS). A Drexhage-style experiment was performed for two distinct quantum emitters, divalent nickel ions in magnesium oxide and trivalent erbium ions in yttrium oxide, which both support nearly equal mixtures of isotropic electric dipole and magnetic dipole transitions. The disappearance of lifetime oscillations as a function of emitter-interface separation distance confirms that the electromagnetic LDOS refers to the total mode density, and thus similar to thermal emission, these unique electronic emitters effectively excite all polarizations and orientations of the electromagnetic field.

Comparative analysis of imaging configurations and objectives for Fourier microscopy.

Fourier microscopy is becoming an increasingly important tool for the analysis of optical nanostructures and quantum emitters. However, achieving quantitative Fourier space measurements requires a thorough understanding of the impact of aberrations introduced by optical microscopes that have been optimized for conventional real-space imaging. Here we present a detailed framework for analyzing the performance of microscope objectives for several common Fourier imaging configurations. To this end, we model objectives from Nikon, Olympus, and Zeiss using parameters that were inferred from patent literature and confirmed, where possible, by physical disassembly. We then examine the aberrations most relevant to Fourier microscopy, including the alignment tolerances of apodization factors for different objective classes, the effect of magnification on the modulation transfer function, and vignetting-induced reductions of the effective numerical aperture for wide-field measurements. Based on this analysis, we identify an optimal objective class and imaging configuration for Fourier microscopy. In addition, the Zemax files for the objectives and setups used in this analysis have been made publicly available as a resource for future studies.

Dynamic control of light emission faster than the lifetime limit using VO2 phase-change.

Modulation is a cornerstone of optical communication, and as such, governs the overall speed of data transmission. Currently, the two main strategies for modulating light are direct modulation of the excited emitter population (for example, using semiconductor lasers) and external optical modulation (for example, using Mach-Zehnder interferometers or ring resonators). However, recent advances in nanophotonics offer an alternative approach to control spontaneous emission through modifications to the local density of optical states. Here, by leveraging the phase-change of a vanadium dioxide nanolayer, we demonstrate broadband all-optical direct modulation of 1.5 µm emission from trivalent erbium ions more than three orders of magnitude faster than their excited state lifetime. This proof-of-concept demonstration shows how integration with phase-change materials can transform widespread phosphorescent materials into high-speed optical sources that can be integrated in monolithic nanoscale devices for both free-space and on-chip communication.

Reusable Inorganic Templates for Electrostatic Self-Assembly of Individual Quantum Dots, Nanodiamonds, and Lanthanide-Doped Nanoparticles.

In this paper, we present an electrostatic self-assembly method for the controlled placement of individual nanoparticle emitters based on reusable inorganic templates. This method can be used to integrate quantum emitters into nanophotonic structures over macroscopic areas and is applicable to a variety of patterning materials and emitter systems. By utilizing surface-charge-mediated self-assembly, highly ordered arrays of nanoparticle emitters were created. To illustrate the broad applicability of this technique, we demonstrate self-assembly using colloidal quantum dots (QD), nitrogen vacancy (NV) centers in diamond nanoparticles, and lanthanide-doped upconversion nanoparticles (UCNP). Placement of single QDs and NV centers was confirmed by performing photon antibunching measurements using a Hanbury-Brown Twiss setup. In addition, template reusability was demonstrated through daily redeposition experiments over a one month period.

Wide-angle energy-momentum spectroscopy.

Light emission is defined by its distribution in energy, momentum, and polarization. Here, we demonstrate a method that resolves these distributions by means of wide-angle energy-momentum spectroscopy. Specifically, we image the back focal plane of a microscope objective through a Wollaston prism to obtain polarized Fourier-space momentum distributions, and disperse these two-dimensional radiation patterns through an imaging spectrograph without an entrance slit. The resulting measurements represent a convolution of individual radiation patterns at adjacent wavelengths, which can be readily deconvolved using any well-defined basis for light emission. As an illustrative example, we use this technique with the multipole basis to quantify the intrinsic emission rates for electric and magnetic dipole transitions in europium-doped yttrium oxide (Eu³âº:Y2O3) and chromium-doped magnesium oxide (Cr³âº:MgO). Once extracted, these rates allow us to reconstruct the full, polarized, two-dimensional radiation patterns at each wavelength.

Surface phonon-polariton enhanced optical forces in silicon carbide nanostructures.

The enhanced optical forces induced by surface phonon-polariton (SPhP) modes are investigated in different silicon carbide (SiC) nanostructures. Specifically, we calculate optical forces using the Maxwell stress tensor for three different geometries: spherical particles, slab waveguides, and rectangular waveguides. We show that SPhP modes in SiC can produce very large forces, more than one order of magnitude larger than the surface plasmon-polariton (SPP) forces in analogous metal nanostructures. The material and geometric basis for these large optical forces are examined in terms of dispersive permittivity, separation distance, and operating wavelength.

Time-resolved energy-momentum spectroscopy of electric and magnetic dipole transitions in Cr3+:MgO.

Due to the recent interest in magnetic light-matter interactions, the magnetic dipole (MD) transitions in lanthanide ions have been studied for potential applications in nano-optics. Similar to lanthanide ions, transition-metal ions also exhibit strong MD emission at room temperature, but their prominent MD zero-phonon lines are often accompanied by significant electric dipole (ED) sideband emission. Here, we extend energy-momentum spectroscopy to time-resolved measurements, and use this technique to quantify the ED and MD contributions to light emission from trivalent chromium doped magnesium oxide (Cr(3+):MgO). This allows us to differentiate the MD (2)E → (4)A2 zero-phonon line from phonon-assisted (2)E → (4)A2 and (4)T2 → (4)A2 ED sidebands. We also demonstrate how the relative intensities of the sharp MD zero-phonon line and the broad ED sidebands can be used as a qualitative measure of the MD and ED local density of optical states.

Direct modulation of lanthanide emission at sub-lifetime scales.

The long lifetime of lanthanide emitters can present a challenge for conventional pump-based modulation schemes, where the maximum switching speed is limited by the decay time of the excited state. However, spontaneous emission can also be controlled through the local optical environment. Here, we demonstrate a direct modulation scheme enabled by dynamic control of the local density of optical states (LDOS). Specifically, we exploit the LDOS differences between electric and magnetic dipole transitions near a metal mirror and demonstrate that rapid nanometer-scale mirror displacements can modulate the emission spectra of trivalent europium ions within their excited state lifetime. The dynamic LDOS modulation presented here can be readily extended to faster optical modulation schemes and applied to other long-lived emitters to control the direction, polarization, and spectrum of spontaneous emission at sublifetime scales.

Orientation of luminescent excitons in layered nanomaterials.

In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties. Directional optical properties can be exploited to enhance the performance of optoelectronic devices, optomechanical actuators and metamaterials. In layered materials, optical anisotropies may result from in-plane and out-of-plane dipoles associated with intra- and interlayer excitations, respectively. Here, we resolve the orientation of luminescent excitons and isolate photoluminescence signatures arising from distinct intra- and interlayer optical transitions. Combining analytical calculations with energy- and momentum-resolved spectroscopy, we distinguish between in-plane and out-of-plane oriented excitons in materials with weak or strong interlayer coupling-MoS2 and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), respectively. We demonstrate that photoluminescence from MoS2 mono-, bi- and trilayers originates solely from in-plane excitons, whereas PTCDA supports distinct in-plane and out-of-plane exciton species with different spectra, dipole strengths and temporal dynamics. The insights provided by this work are important for understanding fundamental excitonic properties in nanomaterials and designing optical systems that efficiently excite and collect light from exciton species with different orientations.