Search Results (4,379)

This work presents a novel high-speed random bit generation approach based on chaotic optical signals combined with a pseudo-random pulse amplitude modulation (PAM) sequence. Chaotic dynamics generated by a laser diode under optical feedback provide the physical entropy source. At the same time, the PAM signal is added as an amplitude-level transformation to enhance the statistical distribution of the digitized signal. Unlike conventional post-processing techniques such as least significant bit (LSB) extraction, which reduce the effective bit rate, the proposed method described in this article preserves the full 8-bit resolution of the analog-to-digital converter improving the distribution of amplitude levels. Experimental results show a significant improvement in compliance with the NIST SP 800-22 statistical test suite. The system operates at a sampling rate of 20 GSa/s, achieving a theoretical bit generation rate of 160 Gb/s. These results demonstrate that the proposed approach provides an alternative to conventional digital post-processing techniques while maintaining high throughput. Full article

We report on the generation and spectral shaping of ultrabroadband terahertz-to-infrared radiation (>119 THz) from air plasma excited by a conventional tightly focused femtosecond Ti:Sa laser pulse with a duration of 35 fs assisted by its second harmonic (SH). A controllable and large frequency detuning between the SH and blueshifted component of the fundamental spectrum was achieved by utilizing spectral broadening of the fundamental pulse under filamentation and adjusting the longitudinal separation of the two cascaded filaments. For convenience, the resulting ultrabroadband emission is divided into a low-frequency part (<30 THz), an intermediate-frequency part (~50 THz), and a high-frequency part (~100 THz) that can be optimized with the filaments’ longitudinal separation. We attribute such ultrabroadband THz radiation generation to the excitation of photocurrent from the nonlinear interaction of SH with both the field at the fundamental frequency and its blueshifted component acquired during filamentation. Theoretical calculations based on time-dependent Schrödinger equation, as well as the Maxwell–Schrödinger equation for spectral broadening dynamics, reproduced the spectral features as well as the distinct dependence of the low- and high-frequency THz components. Full article

We present a method to control broadband terahertz generation rapidly during the interaction of a strong laser field with a gas. To achieve it, we utilize a few-cycle double-pulse, which is a combination of two identically colored femtosecond fields with a time delay, as a driving laser field. By varying the laser delay, the magnitude of the amplitude of generated terahertz field changes drastically, making it suitable for use as a terahertz optical ultrafast switch, with an optical period of only a few femtoseconds from ON-OFF-ON and an enhancement ratio of 100. Furthermore, a change in time delay can alter the terahertz field waveform, easily generating terahertz electric fields with positive and negative polarity or any phase in the range of [0, 1.0$\pi$]. The strength of such terahertz source can be boosted by raising the laser wavelength. Our study will provide an effective approach for ultrafast terahertz modulation. Full article

The development of reproducible and stable plasmon-free substrates for surface-enhanced Raman scattering (SERS) is critical for practical applications in analytical chemistry. Transition metal dichalcogenides (TMDCs) have emerged as promising candidates due to their unique electronic properties, yet their performance is often constrained by the chemical inertness of their pristine basal planes. This work presents a systematic comparison of crystalline flakes and nanoparticles of tungsten diselenide (WSe₂) and tungsten ditelluride (WTe₂), prepared via liquid-phase ultrasonic exfoliation and non-equilibrium femtosecond pulsed laser ablation in liquid (PLAL), respectively. The results demonstrate that nanoparticle-based substrates consistently outperform their flake-based counterparts, achieving enhancement factors in the range of ${10}^4$. The superior performance of the nanoparticles is hypothesized to originate from the synthesis-induced defects and high-curvature regions in the nanoparticles shell which facilitates efficient, defect-mediated charge transfer between the substrate and the analyte. At the same time, the inner polycrystalline volume conserves the important characteristics of the bulk counterparts like excitons in semiconducting WSe₂ and broadband absorption in semimetallic WTe₂, which unblocks the tunable photothermal colloidal response. The study establishes morphology engineering through non-equilibrium synthesis as a powerful and generalizable strategy for designing high-performance, dual-function colloidal platforms, offering a pathway toward robust and reproducible analytical systems. Full article

Direct welding of fused silica to pure titanium (Ti) foil using conventional methods faces significant challenges, such as poor interfacial wettability, insufficient joint strength, and the need for interlayers or surface pretreatments. Existing femtosecond (fs) laser welding techniques for these materials often require high-energy millijoule (mJ)-level pulses or alloy interlayers. Moreover, reports on direct microjoule (μJ)-level fs laser welding of Ti foil to fused silica remain scarce. This study successfully demonstrates a direct welding process for pure Ti foil and fused silica using μJ-level fs laser pulses under ambient conditions, achieving joints with a maximum shear strength of 9.19 MPa. Microstructural analysis revealed an elemental interdiffusion region at the weld interface, supported by mechanical interlocking effects. X-ray photoelectron spectroscopy (XPS) confirmed the occurrence of interfacial chemical reactions, forming titanium silicide (TiSi₂) and titanium oxide (TiO₂). Additionally, a 24 h water immersion test of a square sealed cavity revealed outstanding hermeticity, with no water ingress. This work provides a simple, efficient, and robust solution for high-strength, additive-free bonding of fused silica to Ti foil under low-energy processing conditions. Full article

L605 cobalt-based superalloy is a typical difficult-to-machine material because of its high strength, pronounced work hardening, and low thermal conductivity. To improve the microgroove machining performance of this alloy, a self-developed water-jet-guided laser (WJGL) system equipped with a multi-focus lens was employed, and single-factor experiments together with a Box–Behnken response surface design were conducted to investigate the effects of laser power, pulse frequency, water pressure, and feed speed on microgroove depth. The results showed that microgroove depth increased with laser power, decreased with pulse frequency and feed speed, and first increased and then decreased with water pressure. Analysis of variance demonstrated that the developed quadratic regression model was significant and fit the data well. A recommended parameter combination of 274.9 W laser power, 3334.9 Hz pulse frequency, 1.636 MPa water pressure, and 0.107 mm/s feed speed corresponded to a predicted microgroove depth of 621.2 μm. Validation experiments yielded an average microgroove depth of 600.2 μm, with a relative error of 3.4%, indicating that the model can be used for microgroove depth prediction and parameter selection in WJGL machining of L605 alloy and may provide guidance for future multi-objective optimization considering both machining quality and efficiency. 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

The laser-induced lift-off of functional surface layers is a key process in micro- and nano-fabrication; however, optimization criteria for maximizing the lifted-off area remain insufficiently defined. In analogy to the well-established theory of efficient laser ablation, where the maximum ablated volume per pulse is achieved at a peak fluence of $F_0^{\mathrm{o}\mathrm{p}\mathrm{t}}=e^2{F}_{\mathrm{t}\mathrm{h}}$, we develop a theoretical framework for efficient laser lift-off driven by Gaussian beams. The main highlight of this work is the derivation of a new analytical equation for the maximum delaminated area, enabling the straightforward determination of optimal processing conditions. By analytically describing the lift-off area as a function of peak fluence, beam radius, and focus position, we demonstrate that the maximum lifted-off area is achieved at a substantially lower optimal fluence, namely $F_0^{\mathrm{o}\mathrm{p}\mathrm{t}}=e^1{F}_{\mathrm{t}\mathrm{h}}$. Closed-form expressions for the optimal beam radius, maximal lift-off area, and optimal focus position are derived and validated by numerical modeling. The theory is applied to the picosecond laser lift-off of copper oxide from copper, showing excellent agreement between experimental observations and model predictions. The results reveal fundamental differences between ablation- and lift-off-dominated material removal and provide practical guidelines for maximizing process efficiency in laser-assisted delamination, selective coating removal, and surface functionalization. Full article

The effect of nanosecond laser modification on X165CrMoV12 tool steel before and after heat treatment was investigated. Three laser texturing modes were applied to the studied material, with the variables being the frequency used and the pulse energy: 50 kHz/pulse energy 0.9 mJ, 100 kHz/pulse energy 0.45 mJ, and 150 kHz/pulse energy 0.3 mJ. The other parameters of laser texturing were power—90%; speed—500 mm/s; hatching angle—0° (horizontal), +60°/−60° (or equivalent 120°), and +30°/−30° (or equivalent 150°); and Hatching Distance—0.02 mm. The surface laser modification process aims to obtain a homogeneous and adaptive surface relief optimizing the operational properties of the working surfaces of the parts under dry contact friction conditions. The influence of the used laser modification modes on the roughness class of the obtained surfaces, the structure of the formed modified surface and the friction coefficient was studied. The comparative analysis showed that the lowest roughness class (Ra—4.123 µm) was obtained when using an operating frequency of 50 kHz. The obtained friction coefficient values were lowest in the following sequence of processes: laser texturing and subsequent thermal treatment. The lowest friction coefficient (µ = 0.0041) was registered in the test bodies processed with a mode in which the operating frequency was 50 kHz and the pulse energy was 0.9 mJ, after which they were subjected to thermal treatment according to the used cycle. In this processing sequence, no diffusion-related defects (decarburization) were observed on the surface layer of the tested steel. Full article

The formation and size evolution of gas-phase nanoparticles (NPs) in laser ablation inductively coupled plasma mass spectrometry critically influence aerosol transport, plasma ionization efficiency, and ultimately analytical accuracy. Nevertheless, burst-mode laser ablation, as an efficient and versatile strategy for controlling gas-phase NP size, remains insufficiently explored. Here, we combine experimental investigations and theoretical analysis to elucidate the mechanisms of gas-phase nanoparticle formation and size control by tuning the interpulse interval in burst-mode femtosecond (fs) laser ablation. The mean nanoparticle size exhibits a non-monotonic dependence on interpulse spacing, decreasing with a narrowing size distribution as the interval increases from 0 to 300 ps, and then increasing with distribution broadening at longer delays up to 1000 ps, closely correlating with ablation-crater depth. A characteristic transition at ~300 ps is identified, where both nanoparticle size and crater depth reach a minimum, revealing a critical timescale in pulse–plume–surface interactions. Simulations show that the interpulse interval governs the redistribution of laser energy between the surface and plume, driving a transition from surface-dominated ablation to plume-dominated absorption and partial recovery of surface coupling. This delay-dependent framework provides a unified explanation for nanoparticle formation, where particle size is determined by the competition between plume-mediated fragmentation and surface-driven material supply, and offers a basis for tailoring NP size distributions via temporal pulse shaping. Full article

Ultrafast fiber lasers operating near 2 μm have emerged as a critical platform for advancing mid-infrared photonics due to their narrow pulse durations, high peak powers, and broad tunability. These sources exploit the rich energy-level structures of Tm³⁺ and Ho³⁺ doped fibers and reside within an atmospheric transmission window, enabling applications spanning nonlinear microscopy, precision micromachining, optical frequency metrology, biophotonics, and free-space optical communication. Recent progress in low-loss fiber fabrication, dispersion-engineered cavity design, and mode-locking technologies has significantly expanded the performance boundaries of 2 μm ultrafast fiber lasers. This review systematically examines the underlying pulse-formation mechanisms and categorizes state-of-the-art mode-locking approaches. Representative laser architectures are compared with respect to pulse duration, energy scalability, repetition-rate enhancement, spectral characteristics, and environmental stability. Key application pathways in high-resolution spectroscopy, biomedical diagnostics, and mid-IR supercontinuum generation are highlighted. Finally, the remaining challenges and prospective research directions are discussed to inform the development of next-generation ultrafast photonic sources in the 2 μm band. Full article

To suppress the Secondary Electron Yield (SEY) of Al₂O₃ ceramic surfaces for accelerator ceramic windows, a synergistic strategy integrating TiN film deposition and laser surface texturing was developed. TiN films were first deposited on Al₂O₃ substrates by pulsed DC magnetron sputtering, and the sputtering power was optimized through systematic characterization of the film morphology and chemical states, with 300 W identified as the optimal deposition condition. Laser surface texturing was then introduced to construct micro-structured Al₂O₃ surfaces with different geometrical features. Among the investigated laser powers, the 12 W-treated surface exhibited the most developed surface morphology and the highest roughness, indicating the most favorable topography for electron trapping. SEY measurements showed that the maximum SEY decreased from 8.2 for the as-received Al₂O₃ to 5.5 after deposition of a 10 nm TiN film, and was further reduced to 2.1, 1.0, and 1.7 for the textured TiN/Al₂O₃ surfaces prepared at 6, 12, and 18 W, respectively, with the best suppression for the 12 W textured TiN/Al₂O₃. The enhanced performance is attributed to the synergistic effect of low-SEY TiN surface chemistry and geometrical electron trapping induced by laser texturing. This work provides an effective route for constructing low-SEY Al₂O₃ ceramic surfaces for beam-window-related applications. Full article

Arsenopyrite (FeAsS) is an important sulfide that holds gold in orogenic systems. Its arsenic content is often used as a proxy for gold fertility. However, arsenopyrite from the Um Rus gold deposit in Egypt’s Central Eastern Desert shows a complicated gold distribution that makes simple Au-As correlations hard to make. Integrated electron microprobe analysis (EMPA), laser ablation ICP-MS, and principal component analysis (PCA) reveal three unique textural and geochemical domains. Fine-grained arsenopyrite inclusions within pyrite aggregates (28–31 at% As) are devoid of detectable gold; PCA elucidates 84% of their variance through Fe–S versus Co-As substitution (PC1: 61.8%) and Pb-decoupled variability (PC2: 22.2%), suggesting crystallization from a Co-rich, Au-poor fluid. On the other hand, coarse oscillatory-zoned arsenopyrite can hold up to 6154 ppm of invisible gold. This is because of a moderate Au-As substitution (R = 0.41063, p = 0.08074) that was overprinted by a separate Au-Ag-Sb-Te hydrothermal pulse (Au–Ag: R = 0.97762; Au–Sb: R = 0.97608). PCA finds four parts (72.8% variance): Ag-Cu-As associations (PC1: 25.1%), Te versus Bi-Au signatures (PC2: 17.8%), Fe–S stoichiometry (PC3: 17.1%), and an Au versus Pb-decoupled event (PC4: 12.9%). This shows that minerals formed in more than one stage. Irregular As-rich overgrowths, containing ≤950 ppm gold and lacking significant Au–As correlation (R = −0.14011, p = 0.56726), show PCA (74.3% variance) that highlights S-As contrasts (PC1: 25.2%), Co-Ni enrichment (PC2: 18.8%), Cu-Fe-Ni associations (PC3: 16.2%), and a late Au-decoupled event (PC4: 14.2%), indicating barren recrystallization. These results show that just adding arsenic is not a good way to tell if gold is fertile. The highest amounts of invisible gold, on the other hand, are found in oscillatory-zoned domains with Ag-Sb-Te signatures. This research highlights the importance of combining PCA, geochemistry, and microtextures to differentiate auriferous from barren arsenopyrite, thereby enhancing exploration methodologies for structurally intricate orogenic gold systems. Full article

Diode-pumped alkali vapor lasers (DPALs) offer high quantum efficiency, low thermal loading, excellent beam quality, and emission wavelengths matched to important application scenarios. Extending DPALs toward pulsed regimes is of particular interest for applications such as lidar, free-space optical communication, and precision material processing, where high peak power and flexible temporal control are required. This review surveys the key technologies underlying DPAL systems and summarizes the progress in pulsed-generation approaches. The pulsed techniques reported to date are systematically reviewed, including pump modulation, intracavity modulation, cavity dumping, and mode-locking, together with a comparison of their performance. The current status indicates that pulsed DPALs remain at an early stage, with limitations in parameter space exploration and performance scaling. Future developments are expected along several directions, including further exploration of mode-locked DPALs, burst-mode pulse generation for structured temporal output, power scaling through MOPA architectures, and spectral extension via nonlinear frequency conversion. These directions collectively define the pathway toward high-performance pulsed DPAL systems. Full article

This study elucidates the critical role of pulse repetition frequency (PRF) in optimizing laser inhibition of Microcystis aeruginosa. Using a 355 nm laser (20 ns pulse width, 5 W average power) at 20–65 kHz, 50 kHz is identified as the optimal parameter, achieving 70.6% growth suppression by day 6 (p < 0.001) and reducing cell viability to 28.0 ± 1.6% by day 5 (p < 0.001). Photosynthetic analysis reveals severe PSII dysfunction with Fᵥ/Fₘ of 0.028, representing 91% inhibition (p < 0.001). Biochemical assays demonstrate peak reactive oxygen species generation at 1.59 (p < 0.001) and progressive lipid peroxidation with MDA of 45 nmol/L protein. Transmission electron microscopy and Evans Blue staining corroborate the complete thylakoid disintegration in abundant cells after laser treatment at 50 kHz. These findings establish PRF-dependent photothermal–photomechanical synergy as a deterministic mechanism for efficient, chemical-free algal control. Full article