Search Results (540)

Laser-induced breakdown in water-rich biological media results from the interplay between primary photoionization processes and avalanche amplification of free electrons. Understanding this competition is essential for predicting ablation thresholds under ultrashort-pulse irradiation. In this work, we develop an analytical rate-equation model for the buildup of electron density in water-like biological tissues. It combines photoionization and chromophore ionization into a single seed-generation term, while avalanche ionization is described through a cascade gain factor. This formulation provides a framework for describing cascade electron-impact ionization processes in liquid-like media under strong-field excitation. Our approach gives an analytical expression for the temporal evolution of electron density driven by a Gaussian laser pulse and makes it possible to separate the contributions of direct ionization of water and ionization of chromophore centers. The analytical results are compared with numerical simulations that include carrier diffusion, bimolecular recombination and trapping. The comparison clarifies the roles of seed formation and cascade amplification in the growth of the electron population. The predicted dependence of threshold fluence on pulse duration agrees well with experimental data reported for water-like tissues such as the corneal tissues at a wavelength of 800 nm. The model provides a simple analytical picture of ultrafast plasma formation and electron-driven energy deposition in water-like biological media. Full article

Ultrafast physical random bit generators (PRBGs) are essential components for modern applications in secure communication, quantum cryptography, encrypted optical fiber sensing and artificial intelligence. While optical chaos-based PRBGs offer high-speed capabilities, conventional systems often rely on discrete components that suffer from system complexity and environmental instability. This paper proposes and experimentally demonstrates a robust, integrated solution using a two-section mutual injection DFB laser. The device was fabricated using the reconstruction equivalent chirp (REC) technique, which provides precise control over grating phase variation while utilizing low-cost, high-volume fabrication methods. The laser sections, each measuring 450 μm in length, were designed with a free-running wavelength difference of 0.3 nm to ensure a flat optical spectrum and enhanced chaotic dynamics. By optimizing the bias currents, we achieved a chaos RF bandwidth of 20.1 GHz. Notably, the resulting chaotic signal lacks time-delayed signatures, which simplifies the randomness extraction process. To generate random bits, the chaotic waveform was sampled by an 8-bit analog-to-digital converter at 100 GSa/s. Following post-processing through delay-subtracting and the extraction of the four least significant bits (4-LSBs), we realized a total physical random bit rate of 400 Gb/s. The randomness of the generated sequence was successfully verified using the NIST SP 800-22 statistical test suite. This approach offers a compact, energy-efficient, and high-performance integrated chaotic source suitable for secure communication and high-performance computation. Full article

Microwave-assisted pyrolysis (MAP) has emerged as a revolutionary technology for converting solid waste into high-value hydrocarbons. However, conventional pyrolysis and traditional single-function catalysts often face an inevitable “performance trade-off” involving severe mass transfer resistance, poor microwave absorption, and rapid coking. This review systematically summarizes the recent evolution of catalyst design toward advanced multi-site composites. It highlights the synergistic mechanisms of integrating microwave-responsive cores, hierarchical pore networks, and metal-acid bifunctional sites to achieve ultrafast localized heat transfer, targeted bond cleavage, and in-situ coking suppression. Furthermore, this paper critically examines current bottlenecks in scaling MAP to industrial levels. To address these challenges, we discuss emerging solutions, including hydrogen-enriched co-pyrolysis, non-destructive in-situ regeneration, and the integration of machine learning frameworks for intelligent process optimization. Full article

Broadband antireflective surface technology constitutes a crucial technique in optoelectronic devices, playing a key role in reducing optical losses. Ultrafast laser processing provides a flexible route for fabricating micro-nano structures on metallic surfaces because it enables efficient fabrication, high spatial resolution, and minimal chemical consumption. This study uses a variable-angle scanning strategy to texture the copper surface, produce a series of antireflection arrayed micro-nano structures, and study the spectral reflectance characteristics of the copper surface. The results exhibit that 90° orthogonal scanning favors the formation of an arrayed microcone structure, which shows lower reflectance than the non-orthogonal scanning strategies in the 200–1300 nm band, with a minimum reflectance of 0.94%. The 60° and 45° cross-scanning based on the non-orthogonal strategy favors the formation of microcavity structures, and shows low reflectance in the 1300–2500 nm band, with the maximum reflectance remaining below 5%. Laser-induced periodic surface structures (LIPSS) are observed on the structures fabricated by all strategies. This work demonstrates that the scanning angle itself can be used to switch the dominant surface morphology and thereby tailor the spectral antireflection response, and lies in establishing a clear processing–structure–spectral response relationship for copper surfaces, which provides a designable route for wavelength-selective optical absorption in photothermal conversion, infrared detection, and sensing applications. Full article

High-entropy MAX (HE-MAX) phases represent a new class of layered ceramics that combine the multi-principal-element chemistry of high-entropy materials with intrinsic damage tolerance, electrical conductivity, and multifunctionality of conventional MAX phases. Despite their promise, the synthesis of HE-MAX phases remains fundamentally constrained by sluggish multicomponent diffusion, narrow thermodynamic stability windows, and strong competition from thermodynamically favored binary and ternary carbides, borides, and nitrides. These challenges are further exacerbated by the volatility of A-site elements under near-equilibrium processing conditions. This review positions self-propagating high-temperature synthesis (SHS) as an energy-efficient, non-equilibrium processing route capable of stabilizing selected entropy-driven MAX chemistries through ultrafast thermal excursions and rapid quenching. A unified thermodynamic–kinetic framework is developed to elucidate the interplay among reaction enthalpy, configurational entropy, combustion wave sustainability, and phase evolution in HE-MAX systems. Predictions of thermochemical adiabatic temperature are systematically correlated with experimental SHS studies to delineate phase stability boundaries, stoichiometric sensitivity, and the roles of diluents and transient liquid formation. Finally, practical design principles for scalable SHS synthesis of HE-MAX phases are outlined, alongside strategies for their selective exfoliation into high-entropy MXenes and a critical assessment of their emerging functional applications. Full article

Surface protection and functional modification of aircraft-certified aluminum alloys are essential for corrosion resistance, durability, and long-term airworthiness. At the same time, increasingly restrictive environmental regulations motivate the development of alternatives to legacy wet-chemical surface treatments. This study presents an integrated assessment of ultrafast femtosecond laser surface texturing as a surface functionalization approach for Aluminum 6061 alloys within an aerospace manufacturing and sustainability context. Ultrashort-pulse laser processing enables controlled micro- and nano-scale surface topographical modification with limited thermal impact, allowing adjustment of wettability and surface functionality while preserving bulk material integrity. As a dry and contactless process, femtosecond laser treatment eliminates the use of hazardous chemicals, reduces consumable inputs, and generates minimal secondary waste. A streamlined cradle-to-gate life cycle assessment conducted in accordance with ISO 14040/14044 indicates a lower global-warming potential per functional unit compared with conventional surface treatments, including anodization, plasma-assisted coatings, and organic coating systems. Complementary qualitative analyses addressing environmental health and safety, supply-chain risk, and ESG alignment indicate potential advantages related to occupational safety, regulatory compliance, waste management, and end-of-life recyclability. The investigation is performed on planar Aluminum 6061 reference surfaces with a treated area of 25 mm², providing a controlled laboratory-scale basis for analyzing process behavior, functional surface modification, and associated environmental metrics. Within this defined scope, the results support further evaluation of femtosecond laser surface texturing as a surface engineering option for future aerospace manufacturing. Full article

Understanding the rapid non-isothermal crystallization behavior of polymers is crucial for tailoring and optimizing their performance. However, conventional techniques are limited in achieving rapid heating and cooling rates, which hinders in-depth investigation of the crystallization kinetics of fast-crystallizing polymers. In this study, a high-scan-rate MEMS thermopile DSC chip is employed to systematically investigate the non-isothermal crystallization kinetics of polyamide 66 (PA66) under rapid temperature variations. The results show that PA66 forms a lamellar α phase under slow cooling (1 °C/s) and a cauliflower-like γ phase under rapid cooling (300 °C/s), and becomes completely amorphous under ultrafast cooling (quenching). Furthermore, the technique enables quantitative analysis of the cold crystallization kinetics of fully amorphous PA66 during rapid heating. The results indicate that PA66 exhibits a higher apparent activation energy for homogeneous nucleation cold crystallization at low heating rates (≤10 °C/s), reaching 172.3 kJ·mol⁻¹, which is approximately 3.2 times that at high heating rates (≥25 °C/s). The results of this study demonstrate that the developed fast-scanning chip-based DSC provides a powerful tool for analyzing the processing heating and cooling rate conditions of rapidly crystallizing polymers. Full article

Semiconductor lasers have been widely employed in chaos-based information processing due to their ability to generate enhanced chaotic bandwidths. In this study, we investigate broadband polarization chaos in optically injected QD spin-VCSELs and their ability to act as high-speed physical entropy sources for random number generation (RNG). We achieve chaotic bandwidths approaching 50 GHz per polarization mode using elliptical injection. With optimized conditions and post-processing, we demonstrate RNG at rates of up to 240 Gb/s. The quality of the generated random sequences is evaluated using multiple statistical metrics, including entropy estimation based on the NIST SP800-90B framework, uniqueness analysis using Hamming distance, and bias assessment through autocorrelation and histogram analysis. In addition, the influence of different polarization injection schemes on randomness is examined using the NIST SP800-22 statistical test suite. These results highlight the potential of QD spin-VCSELs as compact and ultrafast sources for RNG in secure communication systems. Full article

Microchannel plate gated framing camera is commonly used in inertial confinement fusion diagnostics. However, it is a vacuum electronic device with bulkiness and non-single-line-of-sight imaging. To reduce the size of the camera and achieve a single line of sight image, a CMOS image sensor composed of a pixel unit and a readout circuit is presented to form the framing camera. The CMOS image sensor has a 32 × 32 × 4 pixel array with ultrashort shutter-time and four-frame imaging. The pixel array and analog to digital converter (ADC) readout circuit are designed using a standard 0.18 μm CMOS process. The pixel array includes 5T structured pixel units, a voltage-controlled delay, a clock tree and the row decoding scan circuits. A temporal resolution of 65 ps for the pixel circuit is achieved. The ADC readout circuit is composed of a counter, a comparator, a ramp generator and a register, which operates at a sampling frequency of 24.41 kS/s. An effective number of bits of 11.3, a spurious free dynamic range (SFDR) of 73.4 dB, and a signal-to-noise ratio (SNR) of 70.0 dB for the ADC are achieved. The CMOS image sensor will provide a novel and important imaging method for the field of ultrafast science. Full article

Background and Objectives: After undergoing a Fontan operation, children with single-ventricle physiology are at a risk of neurodevelopmental impairment; data from the Korean population are scarce. We characterized the neurocognitive profiles of early school-aged Fontan patients and evaluated the feasibility of a sedation-free ultrafast brain magnetic resonance imaging (MRI) protocol for volumetric analysis. Methods: This prospective study screened 25 children who had undergone Fontan surgery and were in grades 1–3 (8–11 years of age) in 2023. After excluding children with a history of seizure, epilepsy, or brain infarction, 11 participants underwent standardized neurocognitive evaluation. Among them, four with extreme full-scale intelligence quotient (FSIQ) underwent 3T sedation-free ultrafast brain MRI (total scan time, 3 min 22 s), including volumetry-capable three-dimensional T1-weighted imaging. Six age-matched children served as controls. MRI volumetric analysis was exploratory and limited to a small subset of Fontan participants (n = 4), restricting statistical power and generalizability. Between-group comparisons were performed using Welch’s t-test, with Hedges’ g calculated as the effect size. Results: Mean FSIQ was 85.2 ± 24.3, with 36% patients with <85 FSIQ. Working memory (64%) and processing speed (55%) were most frequently impaired. Cerebellar volumes were lower in Fontan patients than in controls, although these differences were not statistically significant (left: 59.74 ± 8.86 vs. 72.26 ± 6.92 mL; right: 60.63 ± 7.70 vs. 71.54 ± 7.01 mL; very large effect sizes). Hippocampal volumes tended to be lower, and cerebellar volume showed a positive but non-significant correlation with processing speed. White matter hyperintensities and microbleeds were observed in two patients, both with impaired processing speed. Conclusions: School-aged Fontan patients exhibited selective deficits in working memory and processing speed, while exploratory MRI analysis suggested lower cerebellar volumes in the Fontan group. The ultrafast sedation-free MRI protocol proved feasible for volumetric assessment and, when combined with neurocognitive assessments, may support future milestone-based surveillance and early intervention for at-risk children. Full article

The Mpemba effect refers to the counterintuitive situation in which a system initially farther from equilibrium can relax faster than one that starts closer to it. In quantum systems, the effect is enriched by the presence of coherent dynamics, dissipation, and metastable manifolds associated with long-lived Liouvillian modes. Here we demonstrate a giant Mpemba effect in open quantum systems, where relaxation can be either hyper-accelerated or dramatically slowed depending on the initial state. We focus on weakly-coupled particle-conserving bosonic networks, each of which independently relaxes rapidly to a unique stationary state. When a weak coherent interaction is introduced, the composite system typically develops slow metastable modes and a hierarchy of relaxation timescales. We show that by tailoring the interaction Hamiltonian, these slow modes can be effectively suppressed for a broad class of initial states satisfying a minimal global requirement, enabling ultrafast relaxation even when the system starts far from equilibrium. Conversely, other initial states—sometimes arbitrarily close to the stationary state—may remain trapped in the metastable manifold and decay anomalously slowly. This mechanism provides a general route to engineer giant Mpemba effects, offering new possibilities for controlling dissipative dynamics, accelerating state preparation, and manipulating relaxation processes in complex quantum devices. Full article

Quantum beams-including X-rays, synchrotron radiation, electrons, neutrons, ions, and ultrafast photon sources-are indispensable tools for probing the structure, dynamics, and electronic properties of matter. The excitation time scale ${\tau }_{exc}$ is defined operationally as the characteristic temporal interval governing externally imposed energy deposition events within the interaction volume, such as pulse duration, bunch spacing, or beam dwell time. Interpretation of beam–matter interactions has traditionally relied on steady-state or quasi-equilibrium assumptions, implicitly presuming that intrinsic material relaxation processes can accommodate externally imposed excitation. Recent advances in high-brightness synchrotron sources, X-ray free-electron lasers (XFELs), and pulsed electron beams increasingly operate in regimes where this assumption is strained, and systematic nonequilibrium effects, radiation damage, and irreversible transformations are reported even under routine experimental conditions. This work examines the role of time-scale mismatch between beam-driven energy deposition and intrinsic material relaxation as a governing constraint in beam–matter interactions. Analyzing the hierarchy of excitation, electronic relaxation, phonon coupling, and thermal diffusion time scales, the analysis introduces a dimensionless mismatch parameter $\mathsf{\Lambda }={\displaystyle \frac{{\tau }_{rel}}{{\tau }_{exc}}}$, which quantifies the competition between externally imposed excitation and intrinsic relaxation processes in beam–matter interactions. The resulting framework provides a unified physical interpretation of beam-induced damage, signal distortion, dose dependence, and nonlinear response across quantum beam modalities, framing these effects as consequences of forced nonequilibrium dynamics rather than technique-specific artifacts. Full article

Large-sized, room-temperature ultrafast scintillator single crystals are highly demanded for fast timing applications such as time of flight–positron emission tomography, high-speed medical imaging, and pulse heavy-ray detection. Sub-nanosecond scintillation was discovered in 16 mm sized CsPbCl₃Br_x single crystals in our previous research. In this work, the crystal size of CsPbCl₃Br_0.03 was enlarged to 2 inches (50.8 mm). Meanwhile, by precisely optimizing the vertical Bridgman growth process, we further increased the concentration of Br dopant to realize even faster scintillation decay. In this study, we conducted a series of tests on the grown crystals, including temperature-dependent photoluminescence tests, alpha particle excitation tests, X-ray imaging tests, etc. Via the strategy of the incorporation of Br₂, Br dopant introduces highly efficient fast recombination centers in perovskite CsPbCl₃Br_0.03 crystals, resulting in an unprecedently fast scintillation decay time of 303 ps under ²⁴¹Am α-particle excitation, which is significantly shorter than that of the pure CsPbCl₃ and all other perovskites by at least two orders of magnitude. Benefiting from the excellent optical transparency and high crystalline quality of the CsPbCl₃Br_0.03 crystal, an X-ray spatial resolution of up to 20 lp/mm is achieved. These results further demonstrate the great potential of large-sized CsPbCl₃Br_x single crystals for fast timing applications. Full article

This paper demonstrates a C-band continuously tunable mode-locked fiber laser based on a carbon nanotube saturable absorber (CNT-SA) and a commercial broadband tunable filter. The laser operates in the C-band with a continuous tuning range of 37.3 nm from 1532.6 nm to 1569.9 nm. The erbium-doped fiber (EDF) has a wide gain range, enabling the laser to achieve ultrafast mode-locking. Meanwhile, the tunable filter offers a broad wavelength selection range. This continuously tunable mode-locked fiber laser features a simple structure and a broad operating wavelength range, making it highly suitable for applications in optical communication, sensing, and laser processing. Full article