Articles in 2012

Scientists report that the photovoltaic effect and a photo-induced bolometric effect, rather than thermoelectric effects, dominate the photoresponse during a classic photoconductivity experiment in biased graphene. The findings shed light on the hot-electron-driven photoresponse in graphene and its energy loss pathway via phonons.

Researchers demonstrate that Bell's measure — a commonly used test of quantum nonlocality — can be used in classical optical schemes to separate incoherence associated with statistical fluctuations from incoherence based on correlation. This technique may be useful for quantum information applications such as classical optical coherence theory and optical signal processing.

Magnetic effects are fundamentally weak at optical frequencies. Now, by applying inhomogeneous strain in photonic band structures of a honeycomb lattice of waveguides, scientists show experimentally and theoretically that it is possible to induce a pseudomagnetic field at optical frequencies. The field yields 'photonic Landau levels', which suggests the possibility of achieving greater field enhancements and slow-light effects in aperiodic photonic crystal structures than those available in periodic structures.

Random lasing in the presence of nonlinearities and disordered gain media is still poorly understood. Researchers now present a semiclassical theory for multimode random lasing in the strongly scattering regime. They show that Anderson localization — a wave-interference effect — is not affected by the presence of nonlinearities, but instead suppresses interactions between simultaneously lasing modes.

A highly strained ultrathin membrane of MoS₂ could lead to the creation of a solar funnel, a new form of solar cell which absorbs a much broader range of the solar spectrum that a usual single junction device.

Chaotic behaviour is observed in the polarization of the output from a vertical-cavity surface emitting laser without the need for any external stimulus or feedback. The origin is nonlinear coupling between two elliptically polarized modes within the device.

Researchers experimentally demonstrate efficient nanofocusing in gap plasmon waveguides tapered in both transverse dimensions. Two-photon luminescence measurements show an intensity enhancement of 400 within a 14-by-80 nm² area at the tapers narrow end, with a transmittance of 74%.

Researchers use single-cycle THz pulses from an optical laser to extend streaking techniques of attosecond metrology to measure the temporal profile and arrival time of individual FEL pulses with ∼5 fs precision.

Video-rate imaging of various types of biological tissue is reported using stimulated Raman scattering microscopy. The label-free scheme offers molecular specificity and frame-by-frame wavelength tunability allowing the creation of 2D and 3D images of samples showing different constituents.

Researchers create high ionization states, up to Xe³⁶⁺, using 1.5 keV free-electron laser pulses. The higher than expected ionization may be due to transient resonance-enhanced absorption and the effect may play an important role in interactions of intense X-rays with high-Z elements and radiation damage.

Researchers propose a design of quantum communication based on directly transmitting quantum information in encoded form across a network. Involving no teleportation, the scheme does not require entangled links between nodes and long-lived quantum memories. It potentially provides higher communication rates than existing entanglement-based schemes.

By considering a resonator lattice in which the coupling constants between the resonators are harmonically modulated in time and by controlling the spatial distribution of the modulation phases, scientists introduce a scheme that can generate an effective magnetic field for photons, without the use of magneto-optical effects.

Researchers demonstrate the FERMI free-electron laser operating in the high-gain harmonic generation regime, allowing high stability, transverse and longitudinal coherence and polarization control.

By time-sharing optical forces, researchers show that it is possible to adapt the shape of a trapping potential to the shape of an elongated helical bacterium. This approach allows the bacterium to be held and stably oriented for several minutes, which will aid investigations into the nanomechanics of single wall-less bacteria reacting to external stimuli.

Researchers experimentally demonstrate an upconversion system for field-deployable mid-infrared spectral imaging. The system provides a room-temperature dark noise of 0.2 photons per spatial element per second — a billion times below the dark noise level of cryogenically cooled cameras — and a quantum efficiency of 20%.

Carrier multiplication is a carrier-relaxation process that results in the generation of multiple electron–hole pairs after the absorption of a single photon. Researchers have now studied the role of nanoparticle interplay on the carrier-multiplication dynamics of two interacting silicon nanocrystals for photovoltaic applications.

Frequency stabilization in a high-finesse optical cavity is limited fundamentally by thermal-noise-induced cavity length fluctuations. Scientists have now developed a single-crystal silicon system that offers a fractional frequency instability of 1 × 10⁻¹⁶ at short timescales and supports a laser linewidth of less than 40 mHz at 1.5 µm.

Researchers show that Förster resonance energy transfer between two different dyes makes it possible to realize an efficient and stable laser for applications in biophotonics.

Lasing in a hard-X-ray free-electron laser is typically seeded from noise due to the self-amplification of spontaneous emission, which limits temporal coherence and spectral characteristics. Researchers now demonstrate self-seeding using X-rays from the first half of the magnetic undulator to seed the second half via a diamond-based monochromator at ångström wavelengths.

Optical fibres heavily doped with alumina are shown to exhibit an exceptionally low Brillouin gain coefficient and an athermal Brillouin frequency response. Such fibres could prove useful for applications that employ fibre sensing or require high-power fibre laser systems.