Research articles

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.

Nanfang Yu and colleagues show that plasmonics can be used to reduce the spread of laser beams. They demonstrate their technique using a quantum cascade laser, and show that by defining a metallic subwavelength slit and grating onto the facet of the laser, a beam divergence of 2.4 degrees can be achieved. The technique can potentially be used to collimate the beams from a variety of different lasers.

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.

Light is often thought of in terms of radial polarization, but longitudinal polarization is also possible, and it has some intriguing possibilities for particle acceleration. Binary optics, combined with a high-numerical-aperture lens, is a potential route to achieving light with this unusual property.

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.

A stack of silver nanorods could, according to calculations, be the answer to performing subwavelength colour imaging over far-field distances. The metallic nanolens is designed to operate in the visible wavelength range and by tapering the nanorods, image magnification is also shown to be feasible. If realized such a lens could be useful for imaging applications in the biomedical sciences and other fields.

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.

Incoherent optical spatial solitons are self-trapped beams with a multimodal structure that varies randomly in time. All incoherent solitons observed so far have been supported by nonlinearities with slow response times. Here, Segev and colleagues demonstrate such solitons in nonlinear media with fast (essentially instantaneous) response times and show that new physical features appear.

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.