Nature Photonics最新文献

Optical information processing and computing can potentially offer enhanced performance, scalability and energy efficiency. However, achieving nonlinearity—a critical component of computation—remains challenging in the optical domain. Here we introduce a design that leverages a multiple-scattering cavity to passively induce optical nonlinear random mapping with a continuous-wave laser at a low power. Each scattering event effectively mixes information from different areas of a spatial light modulator, resulting in a highly nonlinear mapping between the input data and output pattern. We demonstrate that our design retains vital information even when the readout dimensionality is reduced, thereby enabling optical data compression. This capability allows our optical platforms to offer efficient optical information processing solutions across applications. We demonstrate our design’s efficacy across tasks, including classification, image reconstruction, keypoint detection and object detection, all of which are achieved through optical data compression combined with a digital decoder. In particular, high performance at extreme compression ratios is observed in real-time pedestrian detection. Our findings open pathways for novel algorithms and unconventional architectural designs for optical computing.

Chirality conferral is fundamental for understanding the origin of life, and it is of direct importance for synthesizing new pharmaceuticals in the face of growing antibiotic resistance. Human-made, self-assembling nanostructures replicate the biological chirality conferral processes utilizing covalent and non-covalent bonds. However, chirality conferral from one form of matter to another via electromagnetic fields is more subtle and less explored. Here we report chirality conferral between gold nanohelices and achiral molecules (crystal violet). This conferral enables the experimental observation of a physical effect predicted in 1979—hyper-Raman optical activity. To benefit from Fermi’s golden rule, the chirality conferral system was designed as doubly resonant, with the nanohelices and molecules resonating at the fundamental frequency and at the second-harmonic, respectively. We provide a theoretical framework for our results that expands the original mathematical formalism to include surface-enhanced hyper-Raman scattering and the chirality conferral process. Our results demonstrate that field-driven chirality conferral mechanisms are opening up entire fields of research, as exemplified by the discovery of a physical phenomenon.

Deep neural networks have achieved remarkable breakthroughs by leveraging multiple layers of data processing to extract hidden representations, albeit at the cost of large electronic computing power. To enhance energy efficiency and speed, the optical implementation of neural networks aims to harness the advantages of optical bandwidth and the energy efficiency of optical interconnections. In the absence of low-power optical nonlinearities, the challenge in the implementation of multilayer optical networks lies in realizing multiple optical layers without resorting to electronic components. Here we present a novel framework that uses multiple scattering, and which is capable of synthesizing programmable linear and nonlinear transformations concurrently at low optical power by leveraging the nonlinear relationship between the scattering potential, represented by data, and the scattered field. Theoretical and experimental investigations show that repeating the data by multiple scattering enables nonlinear optical computing with low-power continuous-wave light. Moreover, we empirically find that scaling of this optical framework follows a power law.

Halide perovskites have shown great potential for X-ray detection in medical imaging and product inspection applications. However, the ion migration in perovskites causes large noise and baseline drift, deteriorating the X-ray detection and imaging performance. Here we adopt the atmosphere-controlled edge-defined film-fed growth (EFG) method to grow high-quality shape-controlled CsPbBr₃ single crystals (SCs) in an Ar and HBr mixed atmosphere. Compared with the vertical Bridgman (VB)-CsPbBr₃ SCs, the EFG-CsPbBr₃ SCs show a much lower trap density, a higher resistivity (1.61 × 10¹⁰ Ω cm) and a larger ion migration activation energy (0.378 eV), decreasing the leakage current and baseline drift. An X-ray detector based on EFG-CsPbBr₃ SCs hence exhibits outstanding balanced performance, with a negligible dark-current drift of 1.68 × 10⁻⁹ μA cm⁻¹ s⁻¹ V⁻¹, an incredibly low detection limit of 10.81 nGy_air s⁻¹ and a sensitivity of 46,180 μC Gy_air⁻¹ cm⁻² under a high electric field of 5,000 V cm⁻¹. Furthermore, the detector maintains a stable response for 30 days. Our work provides an effective strategy to improve lead-halide perovskite SCs for high-performance X-ray detection and imaging.

Designing next-generation light-harvesting devices requires a detailed understanding of the transport of photoexcited charge carriers. The record-breaking efficiencies of metal halide perovskite solar cells have been linked to effective charge-carrier diffusion, yet the exact nature of charge-carrier out-of-plane transport remains notoriously difficult to explain. The characteristic spatial inhomogeneity of perovskite films with nanograins and crystallographic disorder calls for the simultaneous and hitherto elusive in situ resolution of the chemical composition, the structural phase and the ultrafast dynamics of the local out-of-plane transport. Here we simultaneously probe the intrinsic out-of-plane charge-carrier diffusion and the nanoscale morphology by pushing depth-sensitive terahertz near-field nanospectroscopy to extreme subcycle timescales. In films of the organic–inorganic metal halide perovskite FA_0.83Cs_0.17Pb(I_1−xCl_x)₃ (where FA is formamidinium), domains of the cubic α-phase are clearly distinguished from the trigonal δ-phase and PbI₂ nano-islands. By analysing deep-subcycle time shifts of the scattered terahertz waveform after photoexcitation, we access the vertical charge-carrier dynamics within single grains. At all of the measured locations, despite topographic irregularities, diffusion is surprisingly homogeneous on the 100 nm scale, although it varies between mesoscopic regions. Linking in situ carrier transport with nanoscale morphology and chemical composition could introduce a paradigm shift for the analysis and optimization of next-generation optoelectronics that are based on nanocrystalline materials.

Plasma wakefield accelerators use tabletop equipment to produce relativistic femtosecond electron bunches. Optical and X-ray diagnostics have established that their charge concentrates within a micrometre-sized volume, but its sub-micrometre internal distribution, which critically influences gain in free-electron lasers or particle yield in colliders, has proven elusive to characterize. Here, by simultaneously imaging different wavelengths of coherent optical transition radiation that a laser-wakefield-accelerated electron bunch generates when exiting a metal foil, we reveal the structure of the coherently radiating component of bunch charge. The key features of the images are shown to uniquely correlate with how plasma electrons injected into the wake: by a plasma-density discontinuity, by ionizing high-Z gas-target dopants or by uncontrolled laser–plasma dynamics. With additional input from the electron spectra, spatially averaged coherent optical transition radiation spectra and particle-in-cell simulations, we reconstruct coherent three-dimensional charge structures. The results demonstrate an essential metrology for next-generation compact X-ray free-electron lasers driven by plasma-based accelerators.