Volume 7 Issue 9, September 2013

The development of innovative tools and techniques is vital for improving research capabilities and opening up new research directions in the terahertz regime. Terahertz sources and plasmonics are just two examples of current exciting advances.

Advances in theoretical nano-optics provide new insights into how nanoscale modification of spontaneous emission can be realized.

The abundance of unique effects found at the nanoscale offers advantages for electronics. Now, complex heterostructures of metal clusters grown on a carbon-dot support exhibit interactive plasmonic activity that enhances the performances of LEDs and solar cells.

The generation of light pulses with programmable waveforms opens up exciting new avenues for coherent control. Researchers in Japan have now introduced a way to tailor the polarization state of custom-shaped terahertz pulses at the push of a button.

This article provides an overview and illustrative examples of how the electric and magnetic fields of intense terahertz transients can be used to resonantly, and even nonresonantly, control matter and light. It discusses the fundamental interaction mechanisms of intense terahertz radiation with matter.

This article reviews state-of-the-art engineering of the spectral and spatial emission properties of terahertz quantum cascade lasers by focusing on three key factors: photonic structures for extracting and confining light in a cavity, an upconversion technique based on nonlinear intracavity mixing and a frequency stabilisation technique based on femtosecond-laser combs.

Recent progress on terahertz-emission devices based on the high-temperature superconductor Bi₂Sr₂CaCu₂O_8+δ is reviewed. The emission mechanism is explained as a result of collective resonant modes in a stack of intrinsic Josephson junctions. Remarkable features of the linewidth, tunability, the optimum bias condition and the thermal influence are discussed.

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.

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.

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.

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.

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.

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.

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.

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.

A sensor based on an array of piezoelectric ZnO nanowires on a light-emitting GaN substrate can generate high-resolution images of pressure distributions. Zhong Lin Wang tells Nature Photonics that it could lead to superior touch interfaces for electronic devices.

This Focus Issue describes the interaction mechanism between terahertz radiation and matter. Topics covered include terahertz sources, on- and off-resonant control using intense terahertz pulses, quantum cascade lasers, superconducting terahertz emitters and terahertz plasmonics.