Photon avalanche is a distinctive optical nonlinear phenomenon observed in lanthanide-doped nanocrystals, which holds great potential for super-resolution imaging, ultrasensitive optical sensing, and multiphysics field detection.However, further enhancement of nonlinearity in photon avalanche nanomaterials remains challenging.Researchers from the National University of Singapore, Xiamen University, A*STAR in Singapore, and the National University of Singapore Suzhou Research Institute, have developed a very promising approach to amplifying the optical nonlinearity of photon-avalanche nanoparticles.They induced local crystal field distortions by modulating the internal sublattice structure inside the lanthanide-doped nanocrystals.This approach enhanced cross-relaxation between ions, while the engineered 27 nm nanocrystals enabled super-resolution imaging with a lateral resolution of 33 nm and an axial resolution of 80 nm using singlebeam scanning microscopy, surpassing previous photon avalanche-based imaging techniques.Moreover, 176 nm nanodiscs exhibited an amplified optical nonlinearity exceeding 500, with this extreme nonlinearity effectively making the nanoparticles appear smaller than their physical dimensions during optical imaging, thus offering a pathway to overcome the traditional resolution limits imposed by probe dimensions.

Increased micro- and nanoplastic (MNP) pollution poses significant health risks, yet the mechanisms of their accumulation and effects on absorptive tissues remain poorly understood. Addressing this knowledge gap requires tractable models coupled to dynamic live cell imaging methods, enabling multi-parameter single cell analysis. We report a new method combining adult stem cell-derived small intestinal organoid cultures with live fluorescence lifetime imaging microscopy (FLIM) to study MNP interactions with gut epithelium. To facilitate this, we optimized live imaging of porcine and mouse small intestinal organoids with an ‘apical-out’ topology. Subsequently, we produced a set of pristine MNPs based on PMMA and PS (<200 nm, doped with deep-red fluorescent dye) and evaluated their interaction with organoids displaying controlled epithelial polarity. We found that nanoparticles interacted differently with apical and basal membranes of the organoids and showed a species-specific pattern of cellular uptake. Using a phasor analysis approach, we demonstrate improved sensitivity of FLIM over conventional intensity-based microscopy. The resulting ‘fluorescence lifetime barcoding’ enabled distinguishing of different types of MNP and their interaction sites within organoids. Finally, we studied short (1 day)- and long (3 day)-term exposure effects of PMMA and PS-based MNPs on mitochondrial function, total cell energy budget and epithelial inflammation. We found that even pristine MNPs could disrupt chemokine production and mitochondrial membrane potential in intestinal epithelial cells. The presented FLIM approach will advance the study of MNP toxicity, their biological impacts on gastrointestinal tissue and enable the tracing of other fluorescent nanoparticles in live organoid and 3D ex vivo systems.

Solar thermoelectric generators (STEGs) have recently gained increasing attention. However, their widespread adoption has been limited due to the lack of high-efficiency thermoelectric materials and compact heat sinks for effective heat dissipation. To address these issues, we develop a spectral engineering and thermal management strategy that significantly increases STEG power generation by 15 times with only a 25% increase in weight. At the hot side, we transform a regular tungsten (W) to a selective solar absorber (W-SSA) through a femtosecond (fs)-laser processing technique, which enhances the solar absorption while minimizing the IR emissivity, obtaining >80% absorption efficiency at elevated temperatures. We also design a greenhouse chamber for W-SSA and achieved >40% reduction in convective heat loss. At the cold side, we apply the fs laser processing to transform a regular aluminum (Al) to a super-high-capacity micro-structured heat dissipator (μ-dissipator), which improves the cold-side heat dissipation through both radiation and convection, achieving twice the cooling performance of a regular Al heat dissipator. These spectral engineering and thermal management increase the temperature difference across the STEG, resulting in a substantial increase in output power. The high-efficiency STEG can find a wide range of applications, such as wireless sensor networks, wearable electronics, and medical sensors.

High-power single-frequency fiber lasers with diffraction-limited spots are indispensable for a wide range of photonic applications and are particularly in advanced detection and sensing technologies. However, the simultaneous achievement of kilowatt-level output power and diffraction-limited beam quality has remained elusive in all reported single-frequency fiber laser systems to date, primarily due to limitations imposed by the stimulated Brillouin scattering (SBS) effect and transverse mode instability (TMI) effect. In this study, we demonstrate the design and manufacturing of an ultra-low numerical aperture (NA) functional Yb-doped fiber featuring a bat-type refractive index distribution, specifically engineered for single-frequency laser amplification. In the fabrication, we implemented multiple chelate gas filling and particle deposition iterations, leading to an active fiber with a bat-type refractive index distribution. The unique capabilities of this large mode area and high-order modes leakage fiber (HOMLF) were demonstrated by stably amplifying the single-frequency laser with more than one kilowatt output power and near single mode beam quality (Mx2 = 1.10, Mx2 = 1.18) for the first time. This fiber design advances the leap forward in single-frequency fiber lasers, which could contribute as a novel and efficient laser amplification technique for the next generation of gravitational wave detection systems.

We present a broadband and polarization-insensitive unidirectional imager that operates at the visible part of the spectrum, where image formation occurs in one direction, while in the opposite direction, it is blocked. This approach is enabled by deep learning-driven diffractive optical design with wafer-scale nano-fabrication using high-purity fused silica to ensure optical transparency and thermal stability. Our design achieves unidirectional imaging across three visible wavelengths (covering red, green, and blue parts of the spectrum), and we experimentally validated this broadband unidirectional imager by creating high-fidelity images in the forward direction and generating weak, distorted output patterns in the backward direction, in alignment with our numerical simulations. This work demonstrates wafer-scale production of diffractive optical processors, featuring 16 levels of nanoscale phase features distributed across two axially aligned diffractive layers for visible unidirectional imaging. This approach facilitates mass-scale production of ~0.5 billion nanoscale phase features per wafer, supporting high-throughput manufacturing of hundreds to thousands of multi-layer diffractive processors suitable for large apertures and parallel processing of multiple tasks. Beyond broadband unidirectional imaging in the visible spectrum, this study establishes a pathway for artificial-intelligence-enabled diffractive optics with versatile applications, signaling a new era in optical device functionality with industrial-level, massively scalable fabrication.

Twisted bilayer photonic crystals introduce a twist between two stacked photonic crystal slabs, enabling strong modulation of their electromagnetic properties. The change in the twist angle strongly influences the resonant frequencies and available propagating diffraction orders with applications including sensing, lasing, slow light or wavefront engineering. In this work, we design and analyze twisted bilayer crystals capable of steering light in a direction controlled by the twist angle. To achieve beam steering, the device efficiently routes input power into a single, twist-dependent, transmitted diffraction order. The outgoing light then follows the orientation of this diffraction order, externally controlled by the twist angle. Our study shows, using systematic exploration of the design space, how the device resembles blazed gratings by effectively canceling the undesired diffraction orders. The optimized devices exhibit a shared slant dependent on the selected diffraction order and that proves robust to the twist angle. Our analysis is supported by a classical blazing model and a data-oriented statistical analysis. The data-oriented approach is steered by high-efficiency heuristic optimization method, which enabled the design of optimized devices demonstrating an efficiency above 90% across twist angles ranging from 0 to 30° for both TE and TM polarizations. Extending the optimization to include left- and right-handed polarizations yields overall accuracy nearing 90% when averaged across the entire 0 to 60° control range. Finally, with the identification of the blazing effect in this initially black box structure, we show one can consider simpler design for a first prototype.

Structured illumination microscopy (SIM) has emerged as a promising super-resolution fluorescence imaging technique, offering diverse configurations and computational strategies to mitigate phototoxicity during real-time imaging of biological specimens. Traditional efforts to enhance system frame rates have concentrated on processing algorithms, like rolling reconstruction or reduced frame reconstruction, or on investments in costly sCMOS cameras with accelerated row readout rates. In this article, we introduce an approach to elevate SIM frame rates and region of interest (ROI) coverage at the hardware level, without necessitating an upsurge in camera expenses or intricate algorithms. Here, parallel acquisition-readout SIM (PAR-SIM) achieves the highest imaging speed for fluorescence imaging at currently available detector sensitivity. By using the full frame-width of the detector through synchronizing the pattern generation and image exposure-readout process, we have achieved a fundamentally stupendous information spatial-temporal flux of 132.9 MPixels · s−1, 9.6-fold that of the latest techniques, with the lowest SNR of −2.11 dB and 100 nm resolution. PAR-SIM demonstrates its proficiency in successfully reconstructing diverse cellular organelles in dual excitations, even under conditions of low signal due to ultra-short exposure times. Notably, mitochondrial dynamic tubulation and ongoing membrane fusion processes have been captured in live COS-7 cell, recorded with PAR-SIM at an impressive 408 Hz. We posit that this novel parallel exposure-readout mode not only augments SIM pattern modulation for superior frame rates but also holds the potential to benefit other complex imaging systems with a strategic controlling approach.

Understanding the solid target dynamics resulting from the interaction with an ultrashort laser pulse is a challenging fundamental multi-physics problem involving atomic and solid-state physics, plasma physics, and laser physics. Knowledge of the initial interplay of the underlying processes is essential to many applications ranging from low-power laser regimes like laser-induced ablation to high-power laser regimes like laser-driven ion acceleration. Accessing the properties of the so-called pre-plasma formed as the laser pulse’s rising edge ionizes the target is complicated from the theoretical and experimental point of view, and many aspects of this laser-induced transition from solid to overdense plasma over picosecond timescales are still open questions. On the one hand, laser-driven ion acceleration requires precise control of the pre-plasma because the efficiency of the acceleration process crucially depends on the target properties at the arrival of the relativistic intensity peak of the pulse. On the other hand, efficient laser ablation requires, for example, preventing the so-called “plasma shielding”. By capturing the dynamics of the initial stage of the interaction, we report on a detailed visualization of the pre-plasma formation and evolution. Nanometer-thin diamond-like carbon foils are shown to transition from solid to plasma during the laser rising edge with intensities < 1016 W/cm². Single-shot near-infrared probe transmission measurements evidence sub-picosecond dynamics of an expanding plasma with densities above 1023 cm−3 (about 100 times the critical plasma density). The complementarity of a solid-state interaction model and kinetic plasma description provides deep insight into the interplay of initial ionization, collisions, and expansion.

An ultra-simple and miniaturized spectrometer using an arbitrarily shaped pinhole as diffraction element reconstructs a broadband spectrum from the information of diffraction of monochromatic radiation by clever computational reconstruction algorithms. This circumvents complex calibration procedures and paves the way to cost-effective on-chip spectrometers combining fast acquisition without significant loss in spectral resolution.

A type of multifunctional erbium (Er3+) and ytterbium (Yb3+) codoped NaY(WO4)2 phosphors, with simultaneous photon upconversion, photon quantum cutting, and luminescence ratiometric temperature sensing abilities, have been developed, opening up new possibilities for high-performance silicon solar cells.