Research articles

A terahertz quantum cascade laser that uses a grating etched into a double-metal waveguide to greatly improve the laser's performance is reported. The grating enhances the laser's optical power extraction and provides control over its emission wavelength and beam quality, yielding a single-mode beam that has a divergence of less than 10 degrees in both axes and a power of up to 15 mW.

By exploiting the nonlinearity of on-chip silicon nanowaveguides, a parametric temporal imaging system that can compress optical waveforms in time is demonstrated, enabling generation of complex and rapidly updatable ultrafast optical waveforms.

A handheld and battery-operated far-ultraviolet plane-emission device is demonstrated. The device has low current consumption and stable operation at an output power of 0.2 mW at 225 nm, and may be useful in photochemical and biotechnological applications such as photo catalysis, sterilization and the modification of chemical substances.

Radiation transfer on the nanoscale across gaps varying between 30 nm and 2.5 µm is investigated experimentally. The enhancement of heat transfer by evanescent wave contributions may pave the way for the design of sub-micrometre nanoscale heaters and radiators.

A streak camera for characterizing the ultrashort X-ray pulses produced by a free-electron laser is reported. The scheme has a single-shot capability, a resolution of a few femtoseconds and is expected to become a useful tool for X-ray metrology, including experiments involving time-resolved spectroscopy and imaging.

Maskless high-resolution patterning of structural colours is demonstrated using a new material called ‘M-Ink’. The period of the material is patterned magnetically and a photochemical process immobilizes the structure in a polymer network.

Quantum optical memory protocols are currently limited to storage times in the millisecond range. A quantum optical data storage protocol that extends the storage time by several orders of magnitude is proposed. The method introduces an optical locking technique to the resonant Raman optical echo approach.

An all-optical technique for cleaning and purifying crystals of congruent lithium niobate is demonstrated, whereby a moving light beam removes photoexcitable electrons from the illuminated region and thus improves the material's optical damage threshold. The benefits of the scheme are also demonstrated for both undoped and Fe-doped congruent lithium niobate.

Spectroscopy that combines the accuracy of a frequency comb with the ease of use of a tunable, external cavity diode laser is demonstrated, enabling precise dispersion measurements of microresonator modes.

All-optical wavelength routing based on optical gradient force in mechanically compliant spoked resonators is demonstrated over a wavelength range that is 3,000 times greater than the resonator linewidth. A switching time of less than 200 ns, a tuning efficiency of 309 GHz mW⁻¹ and 100% channel-quality preservation over the entire tuning range is achieved.

A triangular array of silicon nanostructures is experimentally demonstrated to function as an optical cloaking device, operating in the near-infrared at a wavelength of 1550 nm. This approach could, in principle, be extended to larger areas using fabrication techniques such as nanoimprinting.

Arbitrary phase control within a single photon wave packet is demonstrated and verified by two-photon quantum interference measurements. Combined with the previously demonstrated ability to control a single photon's amplitude, frequency and polarization, the phase shaping presented here allows for the complete control of single-photon wave packets.

Attractive and repulsive optical forces between coupled photonic waveguides are demonstrated – previously, only attractive forces had been observed. The sign of the force can be controlled by varying the relative phase between the guided modes. This effect could be used in planar light-force devices on a CMOS-compatible platform.

Applying external pressure to a sample molecule via the apex of a sharp nanotip allows tip-enhanced Raman imaging of molecules with a spatial resolution of 4 nm.

Airy beams have so far been generated by linear diffractive elements. Now, scientists show that they can also be created by a nonlinear process, opening the door to all-optical beam control and production at wavelengths unavailable by conventional methods.

Optical entanglement — a key requirement for many quantum communication protocols — is typically formed between two distinct beams, requiring repeated combination of complex resources, which becomes increasingly difficult as the number of entangled information channels increases. Here entanglement between two spatial modes within one beam is demonstrated.

Voltage-programmable liquid surface profiles with large amplitudes resulting from dielectrophoresis are demonstrated. The oil interface formed can be ultrastable and static, or rapidly switchable, as shown in the case of a modulated diffraction grating. The scheme provides the possibility for responsive and polarization-insensitive transmission and reflection devices, and for optical interfaces with arbitrary surface profiles.

The power-conversion efficiency of dye-sensitized solar cells is increased by 26% by using energy relay dyes. The scheme aids the absorption of high-energy photons that undergo Förster resonant energy transfer to a sensitizing dye, and may offer a viable pathway for developing more efficient dye-sensitized solar cells.

Opto-acoustic imaging of fluorescent proteins deep within living organisms (Drosophila melanogaster and zebrafish) is reported. The approach uses multiple wavelength illumination of the sample to generate ultrasound waves which are then detected and converted into images.

Precise control of single-photon states and multiphoton entanglement is demonstrated on-chip. Two- and four-photon entangled states have now been generated in a waveguide circuit and their interference tuned. These results open up adaptive and reconfigurable photonic quantum circuits not just for single photons, but for all quantum states of light.