Month: April 2017

Lasing in curved geometry

A paper by Hong et al reports about lasing emission on modes sustained by local curvature.

The use of geometrical constraints opens many new perspectives in photonics and in fundamental studies of nonlinear waves. By implementing surface structures in vertical cavity surface emitting lasers as manifolds for curved space, we experimentally study the impacts of geometrical constraints on nonlinear wave localization. We observe localized waves pinned to the maximal curvature in an elliptical-ring, and confirm the reduction in the localization length of waves by measuring near and far field patterns, as well as the corresponding dispersion relation. Theoretically, analyses based on a dissipative model with a parabola curve give good agreement remarkably to experimental measurement on the transition from delocalized to localized waves. The introduction of curved geometry allows to control and design lasing modes in the nonlinear regime.

Quantum X Waves with Orbital Angular Momentum in Nonlinear Dispersive Media

Marco Ornigotti, Claudio Conti and Alex Szameit develop a rigorous theory of propagation invariant “X-wave” pulses with orbital angular momentum. These new photon states form and propagate in quadratic and cubic nonlinear media, and represent a novel tool for quantum information and entanglement. X-waves also allow a new 3D+1 representation of the propagation of light in nonlinear media as a spinning quantum fluid.

The graphene oxide contradictory effects against human pathogen

Valentina Palmieri et al review the hundreds of papers about the action of graphene against bacteria.

Standing out as the new wonder bidimensional material, graphene oxide (GO) has aroused an exceptional interest in biomedical research by holding promise for being the antibacterial of future. First, GO possesses a specific interaction with microorganisms combined with a mild toxicity for human cells. Additionally, its antibacterial action seems to be directed to multiple targets in pathogens, causing both membranes mechanical injury and oxidative stress. Lastly, compared to other carbon materials, GO has easy and low-cost processing and is environmentfriendly.
This remarkable specificity and multi-targeting antibacterial activity come at a time when antibiotic resistance represents the major health challenge. Unfortunately, a comprehensive framework to understand how to effectively utilize this material against microorganisms is still lacking. In the last decade, several groups tried to define the mechanisms of interaction between GO flakes and pathogens but conflicting results have been reported. This review is focused on all the contradictions of GO antimicrobial properties in solution. Flake size, incubation protocol,
time of exposure and species considered are examples of factors influencing results. These parameters will be summarized and analyzed with the aim of defining the causes of contradictions, to allow fast GO clinical application.