Two independent studies report new organic compounds that offer record rates of reverse intersystem crossing between triplet and singlet excited states. The result is sky-blue organic light-emitting diodes with improved efficiency, stability and reduced efficiency roll-off.

Photons in a nonlinear medium can repel or attract each other, resulting in strongly correlated quantum many-body states1,2. Typically, such correlated states of light arise from the extreme nonlinearity granted by quantum emitters that are strongly coupled to a photonic mode2,3. However, unavoidable dissipation (such as photon loss) blurs nonlinear quantum effects when such approaches are used. Here

The integration of diamond waveguide arrays into an aluminium nitride photonic platform offers hope for the realization of scalable chips for quantum information processing.

Gold atoms are stripped of 72 of their electrons to form nitrogen-like Au72+ ions inside extremely hot plasmas by irradiating gold foils and nanowires with highly relativistic femtosecond laser pulses.

Optical angular momentum-based photonic technologies demonstrate the key role of the optical spin–orbit interaction that usually refers to linear optical processes in spatially engineered optical materials1. Re-examining the basics of nonlinear optics of homogeneous crystals under circularly polarized light2,3, we report experiments on the enrichment of the spin–orbit angular momentum spectrum of paraxial

The increasingly prominent role of light in information processing makes optoelectronic devices a technology of fundamental importance. Coherent control of currents in semiconductors using synthesized optical waveforms provides a sensitive and robust means to transfer information from light to an electronic circuit. Currents driven by Gaussian laser beams are spatially uniform in direction, offering

Pseudo-magnetic fields generated in artificially strained lattices have enabled the emulation of exotic phenomena once thought to be exclusive to charged particles. However, they have so far failed to emulate the tunability of real magnetic fields because they are determined solely by the engineered strain configuration, rendering them fixed by design. Here, we unveil a universal mechanism to tune

Tunable sources of X-ray radiation are widely used for imaging and spectroscopy in fundamental science, medicine and industry. The growing demand for highly tunable, high-brightness laboratory-scale X-ray sources motivates research into new fundamental mechanisms of X-ray generation. Here, we demonstrate the ability of van der Waals materials to serve as a platform for tunable X-ray generation when

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Using topological singular points, the topological charge of photonic crystals in momentum space is successfully transferred to optical vortex beams in real space.

Modern communication systems rely on efficient quadrature amplitude modulation formats that encode information on both the amplitude and phase of an electromagnetic carrier. Coherent detection of such signals typically requires complex receivers that contain a continuous-wave local oscillator as a phase reference and a mixer circuit for spectral down-conversion. In optical communications, the so-called

The photovoltaics market has long been dominated by silicon, but further improvements of these solar cells require novel approaches. Now, triplet–triplet annihilation photon upconversion has been used to harvest photons from below the bandgap of silicon, extending the spectral response and potentially improving the efficiency of these cells.

Launching electrons to the centre of an optical field with a vortex phase profile via extreme-ultraviolet photoionization makes coherent imprinting of the spatial distribution of the vortex beam onto the electron wave packet possible.

Directly relating the complex second-harmonic-generation field to the second-order susceptibility tensor allows tomographic imaging of nonlinear optical contrast at high frame rates.

In this Review, we survey recent developments in the emerging field of high-speed variable-z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. Three-dimensional biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modification methods have made great

Exploration of the impact of synthetic material landscapes featuring tunable geometrical properties on physical processes is a research direction that is currently of great interest because of the outstanding phenomena that are continually being uncovered. Twistronics and the properties of wave excitations in moiré lattices are salient examples. Moiré patterns bridge the gap between aperiodic structures

The soft nature of metal halide perovskites makes them potentially applicable as flexible X-ray detectors. Here we report a structure of perovskite-filled membranes (PFMs) for highly sensitive, flexible and large-area X-ray detectors. PFMs with areas up to 400 cm2 are formed by infiltrating saturated perovskite solution through porous polymer membranes followed by hot lamination. The good connectivity

Jonathan P. Dowling, who died in June, was a pioneer in quantum optics and one of the founders of the US government’s research programme in quantum information.

Particle accelerators driven by laser-generated terahertz (THz) pulses promise unprecedented control over the energy–time phase space of particle bunches compared with conventional radiofrequency technology. Here we demonstrate acceleration of a relativistic electron beam in a THz-driven linear accelerator. Narrowband THz pulses were tuned to the phase-velocity-matched operating frequency of a rectangular

Ambitions to reach atomic resolution with light have been a major force in shaping nano-optics, whereby a central challenge is achieving highly localized optical fields. A promising approach employs plasmonic nanoantennas, but fluorescence quenching in the vicinity of metallic structures often imposes a strict limit on the attainable spatial resolution, and previous studies have reached only 8 nm resolution

Atomically strong light pulses can drive sub-optical-cycle dynamics. When the Rabi frequency—the rate of energy exchange between light and matter—exceeds the optical carrier frequency, fascinating non-perturbative strong-field phenomena emerge, such as high-harmonic generation and lightwave transport. Here, we explore a related novel subcycle regime of ultimately strong light–matter interaction without

Photons have fixed spin and unbounded orbital angular momentum (OAM). While the former is manifested in the polarization of light, the latter corresponds to the spatial phase distribution of its wavefront1. The distinctive way in which the photon spin dictates the electron motion upon light–matter interaction is the basis for numerous well-established spectroscopies. By contrast, imprinting OAM on

Among all the nonlinear effects stimulated Brillouin scattering offers the highest gain in solid materials and has demonstrated advanced photonics functionalities in waveguides. The large compressibility of gases suggests that stimulated Brillouin scattering may gain in efficiency with respect to condensed materials. Here, by using a gas-filled hollow-core fibre at high pressure, we achieve a strong

A spin-flip from a triplet to a singlet excited state, that is, reverse intersystem crossing (RISC), is an attractive route for improving light emission in organic light-emitting diodes, as shown by devices using thermally activated delayed fluorescence (TADF). However, device stability and efficiency roll-off remain challenging issues that originate from a slow RISC rate (kRISC). Here, we report a

Reverse intersystem crossing (RISC), originally considered forbidden in purely organic materials, has recently become possible by minimizing the energy gap between the lowest excited singlet state (S1) and lowest triplet state (T1) in thermally activated delayed fluorescence systems. However, direct spin-inversion from T1 to S1 is still inefficient when both states are of the same charge transfer (CT)

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Unidirectional and topological surface plasmon polaritons are currently attracting substantial interest and intense debate. Realistic material models and energy conservation considerations are essential to correctly understand extreme wave effects in non-reciprocal plasmonics, and to assess their potential for novel devices.

A correlation method that combines ultrasound and fluorescence enables imaging in strongly scattering environments.

A phase transition between disordered and quasi-ordered states, known as the Berezinskii–Kosterlitz–Thouless transition, has now been revealed in a two-dimensional photonic ‘fluid’. The interplay between phase singularities and coherence may lead to new vortex-based optical applications.

New methods to control how laser pulses propagate inside a plasma could signify the start of a global race to demonstrate truly high-energy compact particle accelerators.

The finding that hollow-core optical fibres can preserve the state of linearly polarized light over hundreds of metres with exceptional purity could benefit applications in sensing, gyroscopes and quantum optics.

Stripping heavy atoms in solid matter of most of their electrons requires the extreme conditions that exist in astrophysical plasmas, but are difficult to create in the laboratory1,2,3. Here we demonstrate solid-density gold plasmas with atoms stripped of up to 72 electrons (N-like Au72+) over large target depths. This record ionization is achieved by irradiating solid foils and near-solid-density

Recent technological advances in attosecond science hold the promise of tracking electronic processes at the shortest space and time scales. However, the necessary imaging methods combining attosecond temporal resolution with nanometre spatial resolution are currently lacking. Regular coherent diffractive imaging, based on the diffraction of quasi-monochromatic illumination by a sample, is inherently

Photochemical upconversion is a strategy for converting infrared light into more energetic, visible light, with potential applications ranging from biological imaging and drug delivery to photovoltaics and photocatalysis. Although systems have been developed for upconverting light from photon energies in the near-infrared, upconversion from below the silicon bandgap has been out of reach. Here, we

In addition to enhancing confinement, restricting optical systems to two dimensions gives rise to new photonic states, modified transport and distinct nonlinear effects. Here we explore these properties in combination and experimentally demonstrate a Berezinskii–Kosterlitz–Thouless phase transition in a nonlinear photonic lattice. In this topological transition, vortices are created in pairs and then

The availability of high-energy pulses with durations shorter than the period of their carrier frequency (sub-cycle) will reveal new regimes of strong-field light–matter interactions. Parametric waveform synthesis (that is, the coherent combination of carrier-envelope-phase-stable pulses that emerge from different optical parametric amplifiers) is a promising technology for the realization of tailored

Subluminal and superluminal light pulses have attracted considerable attention in recent decades1,2,3,4, opening perspectives in telecommunications, optical storage and fundamental physics5. Usually achieved in matter, superluminal propagation has also been demonstrated in vacuum with quasi-Bessel beams6,7 or spatio-temporal couplings8,9. Although, in the first case, the propagation was diffraction

Optical vortices, beams with spiral wavefronts and screw phase dislocations, have been attracting increasing interest in various fields. Here, we theoretically propose and experimentally realize an easy approach to generating optical vortices. We leverage the inherent momentum-space topological vortex-like response of polarization (strong polarization anisotropy) around bound states in the continuum

The development of high-performance near-infrared organic light-emitting diodes is hindered by strong non-radiative processes as governed by the energy gap law. Here, we show that exciton delocalization, which serves to decouple the exciton band from highly vibrational ladders in the S0 ground state, can bring substantial enhancements in the photoluminescence quantum yield of emitters, bypassing the

Using a photonic chip to generate the patterns of light needed for structured illumination microscopy could reduce the cost and complexity of super-resolution imaging.

Optical clocks held at slightly different heights provide a stringent test of general relativity comparable to space experiments and open new opportunities for clock-based geophysical sensing.

A particular class of focused, pulsed light beams can propagate self-similarly in free space at a fixed group velocity. Now, scientists present a law of refraction that determines how the group velocity of these beams changes as they refract at an interface between two materials.

By utilizing exciton resonances in atomically thick semiconductors, researchers have now demonstrated the ultimate downscaling of optical lenses and reported on their efficacious electrical tunability.

Refraction at the interface between two materials is fundamental to the interaction of light with photonic devices and to the propagation of light through the atmosphere at large1. Underpinning the traditional rules for the refraction of an optical field is the tacit presumption of the separability of its spatial and temporal degrees of freedom. We show here that endowing a pulsed beam with precise

Thermal noise is ubiquitous in microscopic systems and high-precision measurements. The control of thermal noise would reveal quantum regimes1 and enable fundamental physics searches2. Recently, nonlinearity in microresonators has enabled laser devices such as Kerr microresonator soliton frequency combs3. Soliton microcombs explore nonlinear dynamics and enable optical synthesizers4, optical clockwork5

In integrated photonics, specific wavelengths such as 1,550 nm are preferred due to low-loss transmission and the availability of optical gain in this spectral region. For chip-based photodetectors, two-dimensional materials bear scientifically and technologically relevant properties such as electrostatic tunability and strong light–matter interactions. However, no efficient photodetector in the telecommunication

Philip Warren Anderson is one of the founding fathers of modern condensed-matter physics. With his death on 29 March 2020, we have lost one of the most influential physicists of the twentieth century.

The contractility of cardiac cells is a key parameter that describes the biomechanical characteristics of the beating heart, but functional monitoring of three-dimensional cardiac tissue with single-cell resolution remains a major challenge. Here, we introduce microscopic whispering-gallery-mode lasers into cardiac cells to realize all-optical recording of transient cardiac contraction profiles with

Small-twist-angle (<2°) bilayer graphene has received extraordinary attention recently due to its exciting physical properties1,2,3,4,5,6,7,8,9,10,11. Compared with monolayer graphene, the Brillouin zone folding in twisted bilayer graphene (TBG) leads to the formation of a superlattice bandgap and substantial modification to the density of states4,6,7,12,13. However, these emerging properties have

III–nitride light-emitting diodes (LEDs) are the backbone of ubiquitous lighting and display applications. Imparting directional emission is an essential requirement for many LED implementations. Although optical packaging1, nanopatterning2,3 and surface roughening4 techniques can enhance LED extraction, directing the emitted light requires bulky optical components. Optical metasurfaces provide precise

Second-harmonic generation microscopy is a valuable label-free modality for imaging non-centrosymmetric structures and has important biomedical applications from live-cell imaging to cancer diagnosis. Conventional second-harmonic generation microscopy measures intensity signals that originate from tightly focused laser beams, preventing researchers from solving the scattering inverse problem for second-order

Research activities in the areas of X-ray imaging and ultraviolet sterilization illustrate how photonics is helping to combat the threat of COVID-19.

Asymmetric forward and backward transmission through photonic structures can be achieved via optical nonlinearities, but existing systems have typically used slow thermo-optic effects. A new resonator design has now enabled low-loss, non-reciprocal pulse routing based on the Kerr nonlinearity in integrated silicon waveguides.

Advanced computational imaging techniques have the potential to extract neural activity patterns from scattered data without reconstructing images.

A monolithic chip-scale ring laser gyroscope based on both Brillouin and Sagnac effects provides a sensitivity sufficient to measure sinusoidal rotations with an amplitude as small as 5 degrees per hour, thus enabling the first on-chip Earth rotation measurement.

Ultrashort pulse generation hinges on the careful management of dispersion. Traditionally, this has exclusively involved second-order dispersion, with higher-order dispersion treated as a nuisance to be minimized. Here, we show that this higher-order dispersion can be strategically leveraged to access an uncharted regime of ultrafast laser operation. In particular, our mode-locked laser—with an intracavity

The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Sensitive photodetectors that operate at a wavelength of 2 μm are required for applications in sensing and imaging but state-of-the-art devices are severely limited by high dark current density (Jdark). The narrow-bandgap materials required for mid-infrared (2–5 µm) detection are plagued by carrier recombination and band-to-band tunnelling; as a result, detectors must be operated at cryogenic temperatures

Fluorescence imaging is indispensable to biomedical research, and yet it remains challenging to image through dynamic scattering samples. Techniques that combine ultrasound and light as exemplified by ultrasound-assisted wavefront shaping have enabled fluorescence imaging through scattering media. However, the translation of these techniques into in vivo applications has been hindered by the lack of