Reviews & Analysis

Exquisitely low-loss optical resonators have thus far remained discrete. Monolithic integration of waveguides with silica resonators that have Q factors >100 million charts a path toward incorporating these devices in photonic circuits.

High-order harmonics in the extreme-ultraviolet regime can be produced and a stable waveform-locked attosecond pulse can be formed when quartz is excited by a strong short-pulsed laser, providing a robust path towards attosecond photonics.

In the quest for nanoscopy with super-resolution, consensus from the imaging community is that super-resolution is not always needed and that scientists should choose an imaging technique based on their specific application.

The polarization state of isolated attosecond pulses generated by high-order harmonic generation can now be manipulated at will. The development opens the door for a multitude of ultrafast experiments to investigate chiral media.

Optical trapping of metal nanoparticles with conventional ‘tweezers’ can be challenging due to absorption and heating. Now, an opto-thermoelectric trapping approach that exploits heating has been demonstrated.

Observing ultrafast transient dynamics in optics is a challenging task. Two teams in Europe have now independently developed ‘optical oscilloscopes’ that can capture both amplitude and phase information of ultrafast optical signals. Their schemes yield new insights into the nonlinear physics that takes place inside optical fibres.

The observation of terahertz nonlinearities in graphene and quantum wells and the emission of terahertz waves from water show that terahertz science is still a fertile area of research that is full of surprises.

Reflected light is often unwanted, causing interference, and reducing transmitted power. Controlling the non-local response of a material can lead to anti-reflection coatings with impressive properties.

With the availability of high-intensity terahertz free-electron lasers, surprisingly large multiphoton absorptions in a phosphorus atom doped in a silicon crystal have been obtained, providing the possibility of a hydrogen-like system in silicon photonics and quantum information devices.

Phosphors often suffer luminescence quenching at elevated temperatures. Now, thermal quenching can be combated with surface phonon-assisted energy transfer, enabling the luminescence of ultrasmall upconversion nanophosphors to be dramatically enhanced.

This Review describes how non-fullerene electron acceptor materials are bringing improvements in the power conversion efficiency and stability of organic solar cells.

Irradiating arrays of metal nanowires with intense femtosecond laser pulses produces high-brightness picosecond X-ray pulses. By specifically tailoring the plasma properties, up to 20% conversion efficiency of optical light into X-rays can be achieved.

Implementing non-reciprocal elements with a bandwidth comparable to optical frequencies is a challenge in integrated photonics. Now, a phonon pump has been used to achieve optical non-reciprocity over a large bandwidth.

The study of the complex, unstable dynamics of lasers is not just of scientific value but is also creating new opportunities for making secure lidar and generating high-frequency microwave signals.

The ability to switch fluorophores on and off is key to performing super-resolution nanoscopy. To date, all switching schemes have been based on an incoherent response to the laser field. Now, a nanoscope that uses on–off coherent switching of quantum dots has been demonstrated.

Metasurfaces can in principle provide a versatile platform for optical functionalities, but in practice designing and fabricating them to specifications can be difficult. Now, the realization of metasurfaces with engineered disorder allows for versatile optical components that combine the best features of periodic and random systems.