Articles in 2013

The use of a thin layer of zinc oxide nanoparticles as an electron-transport layer allows flexible perovskite solar cells to be fabricated with a power conversion efficiency as high as 15.7%.

Temporal dissipative solitons are observed in a nonlinear, high-finesse, optical microresonator driven by a continuous-wave laser. This approach enables ultrashort pulses to be generated in spectral regimes lacking broadband laser gain media and saturable absorbers, making it potentially useful for applications in broadband spectroscopy, telecommunications, astronomy and low-phase-noise microwave generation.

An optical-field-driven streak camera for the temporal characterization (with potentially attosecond resolution) of ultrashort free-electron pulses at 25 keV is demonstrated. It involves intersecting an electron beam and a laser beam at a thin metal mirror.

Little is known about triplet excitons in semiconducting single-walled nanotubes, despite their importance in various applications. The pump–probe and spin-sensitive photoluminescence of such nanotubes is studied, and the quantum yield of triplet formation, triplet lifetime and triplet exciton size are found to be 5 ± 2%, 30 ± 10 µs and 0.65 nm, respectively.

The use of Raman spectroscopy for high-resolution optical imaging is severely limited by the inherent weakness of the Raman effect. Now, a giant resonant Raman effect is demonstrated from J-aggregated dye molecules encapsulated in single-walled carbon nanotubes, and it is used to realize multispectral Raman imaging.

Perpendicular photoswitching of the polarization plane of the output second-harmonic light is observed in a chiral spin-crossover assembly based on an iron-octacyanoniobate magnet. This photoswitching can be reversed by irradiating with blue or red light. It originates from alternate photoswitching between the crystallographic and magnetic contributions to second-harmonic generation.

An approach is demonstrated that allows the optical transmission matrix to be noninvasively measured over a large volume inside complex samples using a standard photoacoustic imaging set-up. This approach opens the way towards deep-tissue imaging and light delivery utilizing endogenous optical contrast.

A seeded free-electron laser with a two-stage harmonic upshift configuration provided tunable and coherent soft-X-ray pulses. The configuration produced single-transverse-mode, narrow-spectral-bandwidth femtosecond pulses with energies of several tens of microjoules and a low pulse-to-pulse wavelength jitter at wavelengths of 10.8 nm and below.

Topological edge states of light are observed in a two-dimensional array of coupled optical ring resonators, which induce a virtual magnetic field for photons using silicon-on-insulator technology. The edge states are experimentally demonstrated to be robust against intrinsic and introduced disorder, which is a hallmark of topological order.

Transparent polymer solar cells are demonstrated that can transmit 30% of visible light and operate with a power conversion efficiency of 5.6%. The cells employ photonic crystals to trap ultraviolet and infrared light.

Polymer hydrogel patches that are capable of supporting living cells and guiding light are used to perform in-vivo optical sensing and therapy in living mice. Tasks performed include toxicity testing and glucose regulation.

Silver and silicon nitride metamaterial structures with dielectric permittivities close to zero are demonstrated at visible wavelengths. In such materials, the optical phase advance during propagation can be very small.

The self-organization of many laser modes in phase and frequency realized by minimizing radiation losses in a cavity enables the complex wavefront required to focus light scattered by turbid samples to be generated on sub-microsecond timescales without employing electronic feedback, spatial light modulators or phase-conjugation crystals.

Tamm states on subwavelength, reconfigurable plasmonic crystals are studied in the terahertz regime. By introducing an independently controlled plasmonic defect, an electromagnetically induced transparency phenomenon is revealed.

By utilizing a microstructured optical waveguide around a microsphere, an optical anlogue of the effects of gravity on the motion of light rays is demonstrated. Both far-field gravitational-lensing effects and the critical phenomenon that occurs close to the photon sphere of astrophysical objects under hydrostatic equilibrium are experimentally demonstrated.

A stretchable polymer LED is fabricated that is capable of emitting light when subjected to strains as large as 120%. A prototype 5 × 5 pixel monochrome display based on an array of these LEDs is demonstrated.

An array of piezoelectric nanowire LEDs with a pixel density of 6,350 dpi is capable of mapping two-dimensional pressure distributions with a spatial resolution of 2.7 micrometres. Pressure alters the light emissions from the LEDs, which are then imaged. Possible applications include artificial skin, robotics and touchpads.

The long-standing problem of determining the classical communication capacities of Gaussian bosonic channels is addressed by determining upper and lower bounds for the classical capacities of important active and passive bosonic channels. The results apply to any bosonic thermal-noise channel, including electromagnetic signaling at any frequency.

New designs of donor polymers yield organic solar cells with fill factors approaching 80%, significantly higher than those of conventional cells. This enhanced performance is attributed to the close-packed and highly ordered structure of the polymers PTPD3T and PBT13T, which leads to efficient charge extraction and suppressed recombination.

A terahertz pulse shaper based on optical rectification is proposed. The polarization of the terahertz pulses depends on the polarization selection rules for the rectification process in a GaP crystal. The terahertz pulse shaper can arbitrarily control the chirality, phase, pulse duration and frequency of circularly polarized few-cycle terahertz pulses.