Letters in 2011

Materials that exhibit strong reflectivity of hard X-rays at normal incidence are sought after for components such as hard-X-ray cavities, beamsplitters and delay lines. Here, researchers experimentally demonstrate hard-X-ray reflectivities of more than 99% from diamond crystals at near-normal incidence.

Based on CMOS-compatible spectral phase interferometry for direct electric-field reconstruction (SPIDER), researchers show that they are able to characterize both the amplitude and phase of ultrafast optical pulses with a time–bandwidth product of more than 100.

Theoretical analysis suggests that there exists an optical attractive force capable of “pulling” microparticles towards a light source. This backwards force is generated by using interference to optimize the scattering of light in the forwards direction.

Researchers present a waveform synthesis scheme that coherently multiplexes the outputs from two broadband optical parametric chirped-pulse amplifiers. The technique provides control at the sub-cycle scale and generates high-energy ultrashort waveforms for use in strong-field physics experiments.

Researchers show that thin films containing HgTe quantum dots with diameters of around 10 nm exhibit a photoresponse in the mid-infrared that extends to wavelengths as long as 5 µm. Such films could become the basis of a new form of low-cost mid-infrared photodetector.

Scientists demonstrate that strong single-cycle terahertz pulses can switch off interlayer superconductivity in a cuprate superconductor while leaving in-plane superconductivity unaltered. The effect may prove useful for studying and controlling the behaviour of future ultrafast nanoelectronics.

Researchers demonstrate a microwave generator based on a high-Q optical resonator and a frequency comb functioning as an optical-to-microwave divider. They generate 10 GHz electrical signals with a fractional frequency instability of ≤8 × 10⁻¹⁶ at 1 s.

Researchers report a colloidal quantum-dot solar cell that features two junctions, each designed to absorb and convert different spectral bands of light within the solar spectrum. The device offers a power conversion efficiency of 4.2% and an open circuit voltage of 1.06 V.

Poor coherence resulting from long exposure times is a problem for many coherent diffractive X-ray imaging schemes. Here, researchers show that coherent diffractive imaging using a broadband source can achieve a 60-fold reduction in exposure time.

Growing a group III–V quantum dot laser directly on a group IV substrate could provide silicon photonics with a convenient new form of laser source for use in optoelectronic circuitry.

Scientists demonstrate living biological lasers by pumping cells containing green fluorescent protein in a highly reflective microcavity. The researchers also investigate the thresholds and modes of their cellular lasers.

Scientists study the coupling, guiding and polarizing of electromagnetic waves in graphene and demonstrate a graphene-based fibre polarizer that exhibits a transverse-electric-pass polarization at an extinction ratio of up to ∼27 dB in the telecommunications band.

Researchers demonstrate active control over the spatial distributions of surface plasmon electromagnetic fields by using a digital spatial light modulator to manipulate the phase of the waves. Digital addressing of surface plasmons, which avoids the use of slow mechanical components, is hoped to enable new directions for imaging, sensing and data storage.

Using transformation optics, researchers predict that birefringent dielectrics can be engineered to control both polarizations of light independently. They also show that structures can be designed to allow light to pass through as if the birefringence did not exist at all.

By controlling the group velocity dispersion of a microresonator through proper shape design, scientists generate a comb whose central frequency can be tuned throughout the transparency window of the microresonator host material.

Scientists couple the zero-phonon line of individual nitrogen-vacancy centres to the modes of microring resonators fabricated in single-crystal diamond using standard semiconductor techniques, paving ways towards integrated diamond photonics.

Researchers demonstrate continuous-wave lasing from a quantum dot photonic crystal nanocavity at temperatures of up to 150 K. The achieved lasing thresholds of 181 nA (at 50 K) and 287 nA (at 150 K) are record-lows for any type of electrically pumped laser.

Researchers cancel out the Dick effect through a synchronous frequency comparison between two optical lattice clocks based on ⁸⁷Sr and ⁸⁸Sr atoms. This scheme achieves an Allan standard deviation of around 10⁻¹⁷, which represents a significant advantage when using a large number (2,000) of atoms in an optical clock.

Using a tapered two-wire transmission line, researchers experimentally focus mid-infrared energy to a nanoscale confined spot with a diameter of 60 nm at the taper apex.

Experimental investigation of the reverse-Doppler shift of electromagnetic waves has previously been restricted to the microwave regime. Here, direct confirmation of the Doppler effect is reported at the infrared wavelength of 10.6 µm using a moving photonic crystal exhibiting a negative refractive index.