Letters in 2009

Radiation transfer on the nanoscale across gaps varying between 30 nm and 2.5 µm is investigated experimentally. The enhancement of heat transfer by evanescent wave contributions may pave the way for the design of sub-micrometre nanoscale heaters and radiators.

Quantum optical memory protocols are currently limited to storage times in the millisecond range. A quantum optical data storage protocol that extends the storage time by several orders of magnitude is proposed. The method introduces an optical locking technique to the resonant Raman optical echo approach.

An all-optical technique for cleaning and purifying crystals of congruent lithium niobate is demonstrated, whereby a moving light beam removes photoexcitable electrons from the illuminated region and thus improves the material's optical damage threshold. The benefits of the scheme are also demonstrated for both undoped and Fe-doped congruent lithium niobate.

A triangular array of silicon nanostructures is experimentally demonstrated to function as an optical cloaking device, operating in the near-infrared at a wavelength of 1550 nm. This approach could, in principle, be extended to larger areas using fabrication techniques such as nanoimprinting.

Arbitrary phase control within a single photon wave packet is demonstrated and verified by two-photon quantum interference measurements. Combined with the previously demonstrated ability to control a single photon's amplitude, frequency and polarization, the phase shaping presented here allows for the complete control of single-photon wave packets.

Attractive and repulsive optical forces between coupled photonic waveguides are demonstrated – previously, only attractive forces had been observed. The sign of the force can be controlled by varying the relative phase between the guided modes. This effect could be used in planar light-force devices on a CMOS-compatible platform.

Applying external pressure to a sample molecule via the apex of a sharp nanotip allows tip-enhanced Raman imaging of molecules with a spatial resolution of 4 nm.

Airy beams have so far been generated by linear diffractive elements. Now, scientists show that they can also be created by a nonlinear process, opening the door to all-optical beam control and production at wavelengths unavailable by conventional methods.

Optical entanglement — a key requirement for many quantum communication protocols — is typically formed between two distinct beams, requiring repeated combination of complex resources, which becomes increasingly difficult as the number of entangled information channels increases. Here entanglement between two spatial modes within one beam is demonstrated.

Voltage-programmable liquid surface profiles with large amplitudes resulting from dielectrophoresis are demonstrated. The oil interface formed can be ultrastable and static, or rapidly switchable, as shown in the case of a modulated diffraction grating. The scheme provides the possibility for responsive and polarization-insensitive transmission and reflection devices, and for optical interfaces with arbitrary surface profiles.

A small angular deviation of the law of reflection has been previously predicted for a light beam, and is a consequence of the angular dependence of the reflectivity. Experimental proof of such a deviation at near-infrared wavelengths is now reported.

Near-infrared imaging with solution-processed organic–inorganic hybrid photodiodes is demonstrated for the first time. The hybrid bulk-heterojunction photodiodes contain PbS nanocrystalline quantum dots as sensitizers for the detection of light of up to 1.8 µm in wavelength, have a minimum lifetime of one year, and external quantum efficiencies of up to 51%.

Whether the electromagnetic fields in random lasers are localized or extended is a topic of ongoing debate. Now, the localization of modes in micro-structured ZnO powder is experimentally determined and lasing from both kinds of modes (localized and extended) shown to exist simultaneously.

Evolution of the infrared near-fields of progressively loaded gap antennas is probed using near-field microscopy. The amplitude and phase is shown to be controlled by the antenna loading and the changes can be understood within the framework of circuit theory.

Electrical detection and characterization of gap plasmons is achieved by means of an integrated metal–semiconductor–metal photodetector. Integration of electro–optical components in metallic waveguides may lead to active high-bandwidth on-chip nano-optical circuits.

The use of slow light for enhancing a nonlinear optical process in a two-dimensional silicon photonic-crystal waveguide is demonstrated. More specifically, green emission by third-harmonic generation is obtained, highlighting yet another functionality of silicon photonics chips.

Imaging through a nonlinear medium can be difficult because signals distort as they propagate through it owing to intensity-dependent phase changes. Here, digital reconstruction of optical spatial beams propagating in a nonlinear medium is presented, which could help the understanding of coupled-wave dynamics and suggest new image-processing techniques.

A silicon–organic hybrid slot waveguide with a strong optical nonlinearity is demonstrated to perform ultrafast all-optical demultiplexing of high-bit-rate data streams. The approach could form the basis of compact high-speed optical processing units for future communication networks.

Based on a far-field fluorescence-based optical super-resolution scheme – stimulated emission depletion microscopy – scientists resolve densely packed individual fluorescent colour centres inside crystals with a far-field spatial resolution of 5.8 nm without photobleaching. The approach will support future studies of solid-state single-photon sources and quantum optics.

The effect of a tiny gap in a metal substrate on incident terahertz radiation in the regime where the gap's dimensions are smaller than the metal's skin-depth are investigated. The results and theoretical analysis show that the gap acts as a capacitor charged by light-induced currents, and dramatically enhances the local electric field.