Research articles

Gradientless light fields are shown to exert pulling forces on arbitrary objects in purely passive dielectric media. These forces arise from amplification of the photon linear momentum when light is scattered from one dielectric to another with a higher refractive index. They can manipulate objects over macroscopic distances along dielectric interfaces.

Off-resonant femtosecond magnetization dynamics are observed after applying an ultra-intense, phase-stable terahertz laser field to ferromagnetic cobalt films. The laser's phase and field-strength characteristics are directly imprinted onto the magnetization response. The off-resonant magnetization removes the speed limitation caused by the cooling process, providing new opportunities for ultrafast data storage.

An array of piezoelectric nanowire LEDs with a pixel density of 6,350 dpi is capable of mapping two-dimensional pressure distributions with a spatial resolution of 2.7 micrometres. Pressure alters the light emissions from the LEDs, which are then imaged. Possible applications include artificial skin, robotics and touchpads.

The long-standing problem of determining the classical communication capacities of Gaussian bosonic channels is addressed by determining upper and lower bounds for the classical capacities of important active and passive bosonic channels. The results apply to any bosonic thermal-noise channel, including electromagnetic signaling at any frequency.

New designs of donor polymers yield organic solar cells with fill factors approaching 80%, significantly higher than those of conventional cells. This enhanced performance is attributed to the close-packed and highly ordered structure of the polymers PTPD3T and PBT13T, which leads to efficient charge extraction and suppressed recombination.

A terahertz pulse shaper based on optical rectification is proposed. The polarization of the terahertz pulses depends on the polarization selection rules for the rectification process in a GaP crystal. The terahertz pulse shaper can arbitrarily control the chirality, phase, pulse duration and frequency of circularly polarized few-cycle terahertz pulses.

A miniature spectrometer has been developed that employs light scattering in a photonic chip with a random structure. It generates wavelength-dependent speckle patterns, which are detected and analysed to recover the spectrum of the input signal. It has a resolution of 0.75 nm in the 1,500 nm wavelength region.

The rotational Doppler frequency shift is observed for a circularly polarized lightwave propagating through a gas of synchronously spinning molecules by using a linearly polarized pulsed laser beam to align diatomic molecules and a linearly polarized pulse to induce concerted unidirectional rotation.

Ultrathin sheets of polymer LEDs that emit light even when being crumpled or stretched have been realized. The 2-μm-thick devices emit red or orange light with a sufficiently high brightness for indoor applications, and they could prove useful for integration with textiles.

A wide-field, high-resolution imaging scheme that offers enhanced depth of field is demonstrated. The approach relies on stitching together time-multiplexed images in Fourier space.

The coupling of surface plasmons and excitons in organic materials can improve the performance of organic optoelectronic devices. Carbon-dot-supported silver nanoparticles have now been used to improve the efficiency of polymer light-emitting diodes and polymer solar cells.

An organic field effect transistor featuring the chiral molecule helicene acts as a photodetector that is able to distinguish between left- and right-handed circularly polarized light.

Squeezed states of light have been experimentally demonstrated to improve the performance of the Laser Interferometer Gravitational-wave Observatory (LIGO) in astrophysically relevant frequency regions. This enhanced performance may help to reach the sensitivity required for detecting gravitational waves.

By employing monocrystalline semiconductor materials as high-quality optical coatings, the long-standing challenge of minimizing the optical phase noise produced by Brownian motion in a multilayer has been overcome. A thermally limited noise floor consistent with a tenfold reduction in mechanical damping relative to that in the best dielectric multilayers is achieved.

Nonlinear optics can overcome the diffraction limit through the presence and interaction of many photons. Abbe's diffraction theory is now generalized to include spatial nonlinearity, and wave mixing is treated as a self-induced structured illumination, thereby allowing a standard imaging system to be nonlinearly enhanced beyond its conventional limits.

An ultrafast terahertz (THz) scanning tunnelling microscope (STM) with subpicosecond time resolution and nanometre spatial resolution has been developed. THz pulses are coupled to the metal tip of a commercial STM and THz-pulse-induced tunnelling is observed in the STM. The THz-STM can directly image ultrafast carrier capture by a single InAs nanodot.

Artificially reducing the effective dimensionality of carbon nanotubes from one to zero dimensions increases the luminescence quantum yield of excitons confined in zero-dimensional-like states to ∼18%, which is over one order of magnitude larger than that of intrinsic one-dimensional excitons (∼1%). This finding will help realize future nanoscale photonic devices.

Spatially coherent 11.45 nm radiation is produced by outcoupling the harmonics of cavity-enhanced nonlinearly compressed pulses from a Yb-based laser through a pierced cavity mirror. This technique may lead to high-photon-flux ultrashort-pulse extreme-ultraviolet sources for use in a wide range of applications.

An all-optical photonic streaking measurement is demonstrated that provides direct experimental access to individual attosecond pulses. The effects of non-adiabatic electron dynamics and plasma formation on the generated attosecond pulse train are directly observed when the pulse train is applied to harmonic generation in gases.

A highly efficient method is demonstrated for detecting individual photons scattering from short-lived transitions in single trapped ions. An entangled state is used to amplify the tiny momentum kick an ion receives on scattering a photon. Cat-state spectroscopy has an 18-fold higher measurement sensitivity than the direct detection method.