Reviews & Analysis

Accurate frequency measurements of a narrow optical clock transition in ¹⁷¹Yb atoms trapped in an optical lattice establish this system as a serious contender in the quest to develop increasingly accurate atomic clocks.

Could hexagonal boron nitride turn out to be the answer for a practical and compact source of deep-ultraviolet light? Although initial results are promising, the challenge for the future is in improving the fabrication technology.

High-resolution microscopy, lithography and materials analysis all look set to benefit from the emergence of compact and efficient table-top soft-X-ray lasers.

Semiconductor nanowires, by definition, typically have cross-sectional dimensions that can be tuned from 2–200 nm, with lengths spanning from hundreds of nanometres to millimetres. These subwavelength structures represent a new class of semiconductor materials for investigating light generation, propagation, detection, amplification and modulation. After more than a decade of research, nanowires can now be synthesized and assembled with specific compositions, heterojunctions and architectures. This has led to a host of nanowire photonic devices including photodetectors, chemical and gas sensors, waveguides, LEDs, microcavity lasers, solar cells and nonlinear optical converters. A fully integrated photonic platform using nanowire building blocks promises advanced functionalities at dimensions compatible with on-chip technologies.

A spectroscopic method that combines the accuracy of optical frequency combs with the rapid tuning of an external-cavity diode laser opens the door to fast, broadband spectral characterization.

A new idea for 'freezing-out' unwanted losses in an atomic memory could make it possible to store light pulses on-chip for several minutes, increasing the capability of optical quantum computing.

Solar cell technology and optical information storage could be the first applications to benefit from plasmonics.

The polarization of terahertz pulses emitted from a laser-generated plasma can be rotated at will by changing the relative delay between ultrashort red and blue excitation pulses. The result is a fast and convenient method of polarization control.

New insights into the behaviour of radiative heat transfer at the nanoscale have now been made, thanks to highly precise measurements made using scanning probe microscopy.

The need for reliable mass-produced photonic crystal devices and the exciting potential of nanoscale optomechanics were both highlights of a recent meeting on integrated photonics in Hawaii, USA.

Photoacoustic tomography (PAT) is probably the fastest-growing area of biomedical imaging technology, owing to its capacity for high-resolution sensing of rich optical contrast in vivo at depths beyond the optical transport mean free path (∼1 mm in human skin). Existing high-resolution optical imaging technologies, such as confocal microscopy and two-photon microscopy, have had a fundamental impact on biomedicine but cannot reach the penetration depths of PAT. By utilizing low ultrasonic scattering, PAT indirectly improves tissue transparency up to 1000-fold and consequently enables deeply penetrating functional and molecular imaging at high spatial resolution. Furthermore, PAT promises in vivo imaging at multiple length-scales; it can image subcellular organelles to organs with the same contrast origin — an important application in multiscale systems biology research.

The demonstration of all-optical switching by confining light and cold rubidium atoms in a hollow-core photonic band-gap fibre may help bring the goal of single-photon switching closer to reality.

The successful control of the phase of light within a single photon wavepacket paves the way to a range of applications in quantum information science.

Researchers at Nichia Corporation have demonstrated green InGaN-based lasers grown on c-plane sapphire, with lifetimes capable of supporting commercial applications.

The tenth anniversary of the optical frequency comb, an enormously important tool in metrology, was celebrated at this year's CLEO/IQEC conference in Baltimore.

The demonstration of Airy beam generation and all-optical control by quasi-phase matched nonlinear crystals looks set to help these unique beams realize their exciting potential in applications.