Letters

Metamaterials, based on split-ring resonators, for example, enable complete control over electromagnetic waves in terms of both the electric and magnetic vector components. Measuring the absolute extinction cross-section of a single split-ring resonator advances our understanding of these useful materials.

Here researchers report an integrated detection device for terahertz near-field imaging in which all the necessary detection components, that is, an aperture, a probe and a terahertz detector, are integrated on one cryogenically cooled, semiconductor chip. This scheme enables highly sensitive, high-resolution detection of the evanescent field and promises new capabilities for high-resolution terahertz imaging.

X-ray Fourier transform holography using free-electron lasers has the potential to enable nanoscale imaging on the timescale of atomic motion. A technique that dramatically increases the efficiency of this technique could move us a step towards such imaging.

Short-wavelength UV laser diodes are required for applications ranging from sensing, data storage and materials processing. Here, an electrically driven semiconductor laser that operates at 342.3 nm, the shortest wavelength so far, is reported. The device emits milliwatt-scale powers at room temperature when driven by pulsed current.

Frequency mixing the fundamental-and second-harmonic fields of an ultrafast laser in any one of a number of materials can generate radiation at terahertz frequencies. A better understanding of this process leads to a brighter source of light at these very useful wavelengths.

Free-electron lasers can produce powerful pulses of radiation at very short wavelengths, even in the hard-X-ray region. In general, however, they comprise facilities several kilometres in length. A 55-m-long laser could open up the technology to a broader range of researchers.

Several technologies have been invented as alternatives to the LCD, which transmits only a small portion of the backlight. Now researchers have come up with a display involving a telescopic pixel design, which can transmit 36% of the backlight. The eventual result could be large, bright displays that offer higher contrast at a low cost.

Xiang Zhang and colleagues from the University of California, Berkeley, propose a new approach for confining light on scales much smaller than the wavelength of light. Using hybrid waveguides that incorporate dielectric and plasmonic waveguiding techniques, they are able to confine surface plasmon polaritons very strongly over large distances. The advance could lead to truly nanoscale plasmonics and photonics.

Before the practical implementation of quantum information schemes, there is a need to reduce loss, both in terms of photons and the information they carry. A robust scheme now experimentally demonstrated tackles this problem using so-called decoherence-free subspace.

Extracting light from organic LEDs is difficult owing to the refractive index of the materials used, and the output efficiency is typically limited to around 15–20%. By embedding a grid with a low refractive index into the organic layers and using a microlens array researchers have now managed to increase this figure to 34%, representing an improvement by factor of 2.3 over a conventional device.

High-speed imaging gives us a fascinating insight into ultrafast changes in materials. By combining the speed of optical pulses and the short wavelength of X-ray pulses, imaging with 50-nm spatial and 10-ps temporal resolution is possible, with scope to go much further.

In a random laser, the conventional optical cavity is replaced by light scattering from many particles. The random arrangement of the particles makes it difficult to tune the lasing to a chosen wavelength. However, tuning is possible by controlling the size of the particles.

Determining the exact number of photons in a weak light pulse is an important requirement for many applications in quantum optics. Now, contrary to popular belief, Andrew Shields and colleagues have demonstrated that an avalanche-photodiode detector can perform the task.

A waveguide–integrated GeSi electro-absorption modulator on silicon with an ultra-low energy consumption of 50 fJ^–1bit is presented. Operating in the spectral range of 1539—1553 nm, the CMOS–compatible device has an active area of 30 µm² and is anticipated to be useful for future communication systems based on large–scale electronic–photonic integration on silicon.

Two-photon excitation is attractive for photodynamic therapy as it potentially allows deeper penetration within biological tissue and targeting with better precision. However, two-photon cross-sections of light-sensitive drugs are typically small, which has until now limited their practical utility. Now Anderson and colleagues have come up with a new family of light-sensitive drugs that are designed for efficient two-photon excitation. They demonstrate selective closure of blood vessels in mice using one of their new drugs.

The ‘spaser’ (surface plasmon amplification by stimulated emission of radiation) is a relatively new and exciting concept analogous to the laser. It involves amplifying specific surface plasmon modes using a nanoscale device. Zheludev and co-workers extend this concept by suggesting that metamaterials could be used to create a lasing spaser, that is, a spaser that can emit light with high spatial coherence.

Mode–locked fibre lasers enable high–power yet very stable optical frequency combs, paving the way towards higher resolution spectroscopy. The power scalability of such fibre–based systems opens the possibility of frequency combs operating with average powers in excess of 10 kW.

We report the experimental observation of one- and two-dimensional grating patterns formed in a disordered metal-nanoparticle layer by a single light pulse. The phenomenon is attributed to interference effects between the incident light and waveguided modes. Such self-patterning behaviour could be useful for the fabrication of complex nanostructures and advanced photonic devices.

Light absorbers are not 100% efficient, and it is a challenge to absorb light completely for any direction of incidence. Using nanostructured metal surfaces, de Abajo and colleagues show that such omnidirectional absorption is now possible, potentially leading to more efficient solar cells.

Optical-frequency antennas efficiently couple light into very small volumes. Introducing an important concept from radiofrequency antenna design, that of loading with so-called lumped circuit elements, may provide a way of tuning the frequency response of optical nanoantennas.