Nature Photonics最新文献

Atomic and molecular structure inversion symmetry breaking in naturally occurring crystals dictate their physical properties including nonlinear optical (NLO) effects, piezo- or ferroelectricity, and non-reciprocal charge transport behaviour. With metamaterials composed of nanoscale building blocks (that is, meta-atoms), the spatial inversion symmetry violation on planar surfaces leads to spin-controlled photonics as well as NLO metasurfaces. Synthetically, low-symmetry 3D metacrystals can be synthesized, but NLO behaviour has not been identified so far (for example, harmonic generations). Herein we show how DNA-mediated assembly of octahedron-shaped plasmonic gold nanocrystals can be used to design and deliberately synthesize non-centrosymmetric and centrosymmetric colloidal crystals. Importantly, while the centrosymmetric structures do not exhibit substantial second-harmonic generation, the non-centrosymmetric crystals do—a consequence of the asymmetric distribution of localized electric fields in plasmonic hotspots. Moreover, this non-centrosymmetric NLO metacrystal represents a 3D NLO metamaterial being developed via a bottom-up approach, exhibiting a maximum second-harmonic generation conversion efficiency of 10⁻⁹ to surpass the efficiencies observed in the majority of plasmonic 2D metasurfaces. Finally, the DNA-loading density on the particle building blocks can be used to toggle between the centrosymmetric and non-centrosymmetric phases.

Considerable efforts are being made to advance inverted (p–i–n) perovskite solar cells (PSCs). Several passivation and insulation strategies have effectively been applied to reduce non-radiative recombination, a notorious issue for PSCs. Consequently, the performance of inverted PSCs has begun to rival those of regular (n–i–p) PSCs, with power conversion efficiency (PCE) values above 26%. The efficiency of tandem solar cells containing an inverted PSC as a subcell has also grown rapidly, reaching >33%. This Review discusses the origin of non-radiative recombinations in PSCs and recent progress in reducing them. We review how innovative device configurations, perovskite composition and interfacial engineering contribute to the high efficiency and long-term operational stability of inverted PSCs. We aim to provide readers with important insights into materials chemistry, physical processing and device configurations to further improve perovskite-based photovoltaics.

Processing information in the optical domain promises advantages in both speed and energy efficiency over existing digital hardware for a variety of emerging applications in artificial intelligence and machine learning. A typical approach to photonic processing is to multiply a rapidly changing optical input vector with a matrix of fixed optical weights. However, encoding these weights on-chip using an array of photonic memory cells is currently limited by a wide range of material- and device-level issues, such as the programming speed, extinction ratio and endurance, among others. Here we propose a new approach to encoding optical weights for in-memory photonic computing using magneto-optic memory cells comprising heterogeneously integrated cerium-substituted yttrium iron garnet (Ce:YIG) on silicon micro-ring resonators. We show that leveraging the non-reciprocal phase shift in such magneto-optic materials offers several key advantages over existing architectures, providing a fast (1 ns), efficient (143 fJ per bit) and robust (2.4 billion programming cycles) platform for on-chip optical processing.

Measuring transient optical fields is pivotal not only for understanding ultrafast phenomena but also for the quantitative detection of various molecular species in a sample. Here we demonstrate near-petahertz electric field detection of a few femtosecond pulses with 200 attosecond temporal resolution and subfemtojoule detection sensitivity. By field-resolved detection of the impulsively excited molecules in the liquid phase, termed femtosecond fieldoscopy, we demonstrate temporal isolation of the response of the target molecules from those of the environment and the excitation pulse. In a proof-of-concept analysis of aqueous and liquid samples, we demonstrate field-sensitive detection of combination bands of 4.13 μmol ethanol for the first time. This method expands the scope of aqueous sample analysis to higher detection sensitivity and dynamic range, while the simultaneous direct measurements of phase and intensity information pave the path towards high-resolution biological spectro-microscopy.

Optical imaging through scattering media is important in a variety of fields ranging from microscopy to autonomous vehicles. Although advanced wavefront shaping techniques have offered several breakthroughs in the past decade, current techniques still require a known guide star and a high-resolution spatial light modulator or a very large number of measurements and are limited in their correction field of view. Here we introduce a guide-star-free, non-invasive approach that can correct more than 190,000 scattered modes using only 25 incoherently compounded, holographically measured, scattered light fields, obtained under unknown random illuminations. This is achieved by computationally emulating an image-guided wavefront shaping experiment, where several virtual spatial light modulators are simultaneously optimized to maximize the reconstructed image quality. Our method shifts the burden from the physical hardware to a digital, naturally parallelizable computational optimization, leveraging state-of-the-art automatic differentiation tools. We demonstrate the flexibility and generality of this framework by applying it to imaging through various complex samples and imaging modalities, including epi-illumination, anisoplanatic multi-conjugate correction of highly scattering layers, lensless endoscopy in multicore fibres and acousto-optic tomography. The presented approach offers high versatility, effectiveness and generality for fast, non-invasive imaging in diverse applications.