Research articles

Re-absorption losses in luminescent solar concentrators cause concentration performances to be around ten times less than the ideal value. Researchers have now reduced re-absorption by forcing the emission in one region to be off-resonant with the other regions, achieving a two-fold enhancement in concentration performance over conventional devices.

Researchers demonstrate fast, single-qubit gates using a sequence of 13 ps pulses. Two vertically stacked InAs/GaAs quantum dots were coupled through coherent tunnelling and charged with controlled numbers of holes. The interaction between hole spins was investigated by Ramsey fringe experiments, showing a tunable interaction range of tens of gigahertz.

Surface-enhanced Raman sensors often rely on random chance for molecules to come near optical hotspots. Here, researchers use super-hydrophobic artificial surfaces and evaporation to direct molecules to plasmonic light-focusing structures. Molecules can be localized and detected even at attomolar concentrations.

Vortex–antivortex pairs in a polariton condensate are experimentally trapped and manipulated by a light beam in a semiconductor microcavity. Quantum hydrodynamical effects are observed and corroborated by time-dependent simulations.

Researchers report the preparation and storage of frequency-uncorrelated narrowband (5 MHz) entangled photons from a cavity-enhanced spontaneous parametric downconversion source. Electromagnetically induced transparency was implemented using ultraviolet pump pulses, and the violation of Bell's inequality was clearly observed for storage times of up to 200 ns.

Researchers demonstrate two-stage laser stabilization based on a combination of Fabry–Pérot and spectral-hole burning techniques. The laser was first pre-stabilized using Fabry–Pérot cavities and then modulated to address a spectral-hole pattern in Eu³⁺:Y₂SiO₅. Taking advantage of the low sensitivity of the spectral holes to environmental perturbations, the researchers obtained a fractional frequency stability of 6 × 10⁻¹⁶

Researchers report the first observation of the synchronous oscillation of electromagnetic modes in a cavity — known as mode-locking — in random lasers.

The authors demonstrate dynamic tuning of a photonic-crystal cavity by surface acoustic waves at frequencies exceeding 1.7 GHz. The tuning is claimed to preserve the quality factor and to be an order of magnitude faster than alternative approaches.

Researchers demonstrate all-optical light switching based on electromagnetically induced transparency at the single-photon level using a Coulomb crystal of ⁴⁰Ca⁺ ions enclosed in a moderately high-finesse linear cavity. Changes from essentially full transmission to full absorption for a single-photon probe field were achieved within unprecedentedly narrow windows of 47.5 ± 2.4 kHz.

Scientists demonstrate a low-cost technique for implementing arbitrarily designed surface morphologies directly into functional zinc oxide films. The researchers achieve conversion efficiencies of 10.1% when applying the films as transparent front electrodes in amorphous silicon solar cells.

Researchers have shown that imperfect quantum channels have a strong kind of synergy: there exist pairs of discrete, memoryless quantum channels that acquire positive quantum capacity when used together. Here the authors show that this superactivation phenomenon also occurs in the more realistic setting of optical channels with attenuation and Gaussian noise.

Researchers show that dispersed functionalized graphene can exhibit broadband nonlinear optical absorption at fluences well below the damage threshold. An optical energy-limiting onset benchmark of 10 mJ cm⁻² at a linear transmittance of 70% was obtained for nanosecond visible and near-infrared pulses. The findings shed light on the formation of practical thin films with broadband optical limiting characteristics.

Materials that exhibit strong reflectivity of hard X-rays at normal incidence are sought after for components such as hard-X-ray cavities, beamsplitters and delay lines. Here, researchers experimentally demonstrate hard-X-ray reflectivities of more than 99% from diamond crystals at near-normal incidence.

Based on CMOS-compatible spectral phase interferometry for direct electric-field reconstruction (SPIDER), researchers show that they are able to characterize both the amplitude and phase of ultrafast optical pulses with a time–bandwidth product of more than 100.

Scientists experimentally demonstrate a reconfigurable all-optical isolator based on the optical excitation of a gigahertz guided acoustic mode in a micrometre-sized photonic crystal fibre core. The work is expected to benefit advanced optical communications and all-optical signal-processing systems.

Researchers use extremely non-degenerate photon pairs to achieve two-photon absorption at levels 100-1,000 times that of degenerate two-photon absorption in direct-gap semiconductors. The technique enables the gated detection of sub-bandgap and sub-100-pJ mid-infrared radiation using large-bandgap detectors at room temperature.

Researchers demonstrate solution-processed light-emitting diodes based on a quantum-dot emissive layer between an organic hole-transport layer and an electron-transport layer of ZnO nanoparticles. The device achieves a luminance of 68,000 cd m⁻² and power efficiencies of up to 8.2 lm W⁻¹.

Theoretical analysis suggests that there exists an optical attractive force capable of “pulling” microparticles towards a light source. This backwards force is generated by using interference to optimize the scattering of light in the forwards direction.

Researchers have fired ultracold-atom Bose–Einstein condensates towards the submicrometre-featured potentials formed by the optical near-fields of surface plasmons. The strength and structural dependence of the optical near-fields were determined from the reflection of cold atoms. It is hoped that the work paves the way towards plasmonic guiding and the manipulation of cold atoms.

Researchers present a waveform synthesis scheme that coherently multiplexes the outputs from two broadband optical parametric chirped-pulse amplifiers. The technique provides control at the sub-cycle scale and generates high-energy ultrashort waveforms for use in strong-field physics experiments.