Discriminating between Coherent and Incoherent Light with Planar Metamaterials

Planar metamaterials represent a powerful paradigm of optical engineering, which enables one to control the flow of light across structured material interfaces in the absence of high-order diffraction modes. We report on a discovery that planar metamaterials of a certain type, formed by nanopatterned metal films, respond differently to spatially coherent and incoherent light, enabling robust speckle-free discrimination between different degrees of light coherence. The effect has no direct analogue in natural optical materials and may find applications in nanoscale metadevices enhancing imaging, vision, detection, communication, and metrology.

In-depth analysis of chloride treatments for thin-film CdTe solar cells

CdTe thin-film solar cells are now the main industrially established alternative to silicon-based photovoltaics. These cells remain reliant on the so-called chloride activation step in order to achieve high conversion efficiencies. Here, by comparison of effective and ineffective chloride treatments, we show the main role of the chloride process to be the modification of grain boundaries through chlorine accumulation, which leads an increase in the carrier lifetime. It is also demonstrated that while improvements in fill factor and short circuit current may be achieved through use of the ineffective chlorides, or indeed simple air annealing, voltage improvement is linked directly to chlorine incorporation at the grain boundaries. This suggests that focus on improved or more controlled grain boundary treatments may provide a route to achieving higher cell voltages and thus efficiencies.

Linear wave dynamics explains observations attributed to dark solitons in a polariton quantum fluid

We investigate the propagation and scattering of polaritons in a planar GaAs microcavity in the linear regime under resonant excitation. The propagation of the coherent polariton wave across an extended defect creates phase and intensity patterns with identical qualitative features previously attributed to dark and half-dark solitons of polaritons. We demonstrate that these features are observed for negligible nonlinearity (i.e., polariton-polariton interaction) and are, therefore, not sufficient to identify dark and half-dark solitons. A linear model based on the Maxwell equations is shown to reproduce the experimental observations.