Search Results (656)

The growing demand for structural coloration methods that simultaneously exhibit an iridescent sheen effect and a base color on transparent substrates calls for a single-step fabrication procedure capable of periodic and localized modulation of thin-film structure. In this work, a composite thin-film structure consisting of aluminum nitride-aluminum (AlN-Al)-soda-lime glass substrate is designed, deposited, and subsequently processed using burst-mode femtosecond laser. By systematically varying the number of sub-pulses, the pulse-to-pulse distance, and the average laser power while maintaining a fixed single-sub-pulse energy (1 μJ), the precise control over thermal accumulation and surface protrusion morphology is achieved, resulting in a series of highly transparent structural colors with iridescent sheen effects. Reflectance spectra, transmittance data, confocal microscopy, scanning electron microscopy and coupled energy dispersive spectrometer analyses, and the finite-difference time-domain simulations reveal that the observed color variation originates from laser-induced air gaps between the Al and AlN layers, rather than from compositional changes, and that the resulting periodic surface protrusion structures govern the iridescent sheen effect. The proposed method enables large-scale patterning while preserving high transmittance, as demonstrated by the desired hue, saturation, and iridescent sheen. This burst-mode laser processing strategy offers a material- and production line-compatible route for realizing coupled interference- and diffraction-based structural colors, with promising applications in decorative purposes with anti-counterfeiting or encryption purposes, where both angle-independent base color and angle-dependent iridescent sheen effect are required. Full article

The interaction of femtosecond laser ultrashort pulses with carbon fiber-reinforced polymer (CFRP) based on epoxy resin modified with different ratios of copper hydroxyapatite (Cu-HAp) and calcium hydroxyapatite (Ca-HAp) was investigated. Ablation efficiency was examined for two CFRP groups containing 1 wt% and 5 wt% Cu-HAp in the epoxy matrix, and in both cases, the maximum ablation efficiency was obtained at a fluence of about 6.4–7.5 $\mathrm{J}/\mathrm{c}{\mathrm{m}}^2$. The corresponding energy-specific volumes were slightly higher for 1 wt% Cu-HAp (6.95 μm³/μJ) and lower for 5 wt% Cu-HAp (6.26 μm³/μJ), and at higher fluence, the ablation efficiency decreased smoothly, indicating a limited optimum fluence window for a given CFRP composition. A similar behaviour was observed for epoxy compounds containing 5 wt% total hydroxyapatite, both for Cu-HAp:Ca-HAp = 75:25 and 50:50 mixtures, which showed nearly identical maxima of energy-specific volume around 6.06 μm³/μJ at 6.4 $\mathrm{J}/\mathrm{c}{\mathrm{m}}^2$. Epoxy resin without carbon fibers, loaded with 1 wt% and 5 wt% Cu-HAp, exhibited higher energy-specific volumes of about 9–10 μm³/μJ and 9–13 μm³/μJ, respectively, at around 10 $\mathrm{J}/\mathrm{c}{\mathrm{m}}^2$, followed by a decay of ablation efficiency at higher fluence. Finally, cutting and milling experiments on CFRP demonstrated acceptable surface quality and processing rates under femtosecond laser irradiation, confirming realistic prospects for advanced CFRP fabrication using optimized ablation conditions. Full article

Metallic nanoantennas are promising structures for enhancing energy transfer in high-intensity laser–matter interactions, especially in nanoplasmonic-assisted fusion. Under ultrashort laser pulses, they generate strong localized fields, modify ionization dynamics, and significantly affect charge acceleration in dense media. In this work, we present a comprehensive particle-in-cell (PIC) study of gold nanoantennas of various geometries—dipoles, planar crosses, three-dimensional crosses, and Yagi-inspired planar structures—irradiated by near-infrared femtosecond pulses at intensities at a range of ~4 × 10¹⁷–4 × 10¹⁸ W/cm². The antenna structures are embedded in a dense hydrogen-rich medium, allowing us to follow electron emission, gold ionization, and proton acceleration self-consistently. Crossed and Yagi-type geometries exhibit more robust resonant behavior than dipoles, with higher field localization and greatly reduced sensitivity to incident polarization. The proton energies increase to ~200 keV at 4 × 10¹⁷ W/cm², and saturate around ~300 keV at a higher intensity >~4 × 10¹⁸ W/cm², dependent on the geometry. This happens largely due to a rapid loss of conduction electrons from the gold structures. Our results highlight Yagi-based and cross-based nanoantennas as promising resonant dopes for laser-driven energy coupling and point toward optimized multi-arm architectures for future nanofusion-target engineering applications. Full article

We extended self-similar amplification to a large-mode-area tapered Yb-doped fiber (LMA T-YDF) with longitudinally decreasing nonlinearity. The theoretical analysis and numerical simulation demonstrate that T-YDFs with different nonlinearity profiles can achieve self-similar evolution, which is confirmed by a self-similar amplifier that employs two kinds of T-YDFs. Further experimental study indicates that the T-YDF with a large core diameter at the thin end can achieve self-similar evolution across a wide range of pump powers and generate 51 W average power, 34 fs nearly transform-limited (TL) pulses with 32 dB gain. To the best of our knowledge, this is the first theoretical and experimental demonstration of self-similar amplification in T-YDFs. The high-gain feature of the T-YDF simplifies the laser system and can be used to build a compact all-fiber high-power femtosecond laser source. Full article

We report on a novel approach for the monitoring of tangential laser turning with ultrashort laser pulses. By using an ultra-sonic sensor consisting of a membrane-free optical microphone, the current state of the ablation process can be analyzed, potentially enabling a real-time automated regulation. With its high sensitivity, bandwidth, and sampling rate, it is an ideal tool for process monitoring. The material ablation caused by focused femtosecond laser pulses produces distinct sound waves, which can be detected by the optical microphone. The diameter reduction of a rotating cylindrical workpiece during the laser turning process with ultrashort laser pulses results in a variation in the acoustic emissions. From this, properties like the state of the machining progress can be inferred. 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

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 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

Femtosecond laser processing has become a powerful approach for high-precision micro- and nanofabrication in transparent materials, owing to its ultrashort pulse duration and minimized thermal effects. However, the limited predictability of processing depth remains a major obstacle to practical applications. Here, we present a morphology prediction framework for femtosecond Bessel laser processing of ZnS that integrates plasma physics modeling with deep learning. Through combined experimental measurements and plasma physics simulations, the influence of laser pulse energy on electron density evolution and material removal depth is systematically investigated. The results reveal the dominant roles of multiphoton ionization, avalanche ionization, and free-electron dynamics in deep-volume processing, and demonstrate the strong sensitivity of the processing morphology to the plasma distribution. Conventional plasma models can accurately reproduce the ablation diameter, yet exhibit significant limitations in predicting the processing depth. We propose a physics data-based framework for femtosecond Bessel beam processing, which integrates a depth-residual regression network conditioned on the peak electron density distribution to effectively learn and compensate for systematic modeling errors in plasma-based simulations. This strategy leads to excellent agreement between predicted and experimental processing depths and three-dimensional morphologies under various energy conditions. The model achieves a mean absolute error (MAE) of 4.9 nm at the pixel level for 3D crater reconstruction. Under rigorous crater-grouped cross-validation with Leave-One-Group-Out evaluation, the model achieves a mean R² of 0.74 across 8 independent craters, demonstrating reliable generalization to unseen energy conditions. These results demonstrate that incorporating physical priors into data-driven learning provides an effective pathway to overcoming accuracy limitations in modeling complex laser–matter interactions. This approach offers a reliable tool for quantitative prediction and parameter optimization in deep femtosecond laser processing of transparent materials and enabling highly controllable and reproducible micro- and nanofabrication for advanced photonic and three-dimensional optical applications. Full article

As a key low-expansion material for high-end equipment such as aerospace and precision instruments, the surface quality of Invar alloy directly determines the operational performance of devices. To fill the research gap in the multi-parameter synergy and mechanism of Invar alloy laser polishing, this study performs polishing experiments on Invar alloy using a burst-mode femtosecond laser, with a repetition rate of 1 MHz and four sub-pulses per burst. The results indicate that energy density plays a dominant role in the polishing effect: with the increase in energy density, the surface roughness first decreases and then increases. A stable molten pool is formed under medium energy density (0.47–0.64 J/cm²), and under the optimal parameter conditions, the surface roughness is reduced to 394 ± 50 nm, representing a 52% reduction compared to the original surface (821 nm). Scanning speed and scanning pitch affect the polishing effect by synergistically regulating energy input: increasing scanning speed under high energy density can inhibit the rise in roughness, while a small scanning pitch can lower the threshold of optimal energy density. Amplitude spectrum analysis reveals that the medium-scale surface undulations are significantly improved after polishing. A four-layer Fully Connected Neural Network (FCNN) model is established to achieve high-precision prediction of polishing effects with a coefficient of determination R² = 0.92, which enables rapid prediction of unknown polishing parameter combinations and provides a new solution path for the optimization of polishing effects. This study clarifies the interaction mechanism between a burst-mode laser and Invar alloy, proposes an efficient ultra-precision polishing method for Invar alloy, and lays a theoretical foundation for its application in the field of high-end manufacturing. Full article

We demonstrate an all-polarization-maintaining (PM) mode-locked thulium-doped fiber laser operating in the net-normal-dispersion regime based on a figure-9 nonlinear amplifying loop mirror (NALM) configuration. A chirped fiber Bragg grating (CFBG) and a commercial PM dispersion-compensating fiber (PM-DCF) are incorporated into the figure-9 cavity, providing a large normal net dispersion and enabling stable dissipative-soliton mode-locking. Under stable dissipative-soliton operation, the laser delivers a maximum output power of 53.6 mW at a repetition rate of 12.31 MHz, corresponding to a pulse energy of 4.3 nJ. The output spectrum has a central wavelength of ~1952 nm with a 3 dB bandwidth of ~11 nm. The all-PM laser oscillator directly generates a fs pulse without extra-cavity compression, achieving a pulse duration of 545 fs at the CFBG arm. Moreover, stable fundamental mode-locking is verified by a high radio-frequency signal-to-noise ratio (SNR) exceeding 82 dB and a long-term root-mean-square (RMS) power fluctuation of 0.45% over two hours. To the best of our knowledge, this represents the highest output power generated from an all-PM-fiber figure-9 laser oscillator in the 2 μm band, alongside fs-pulse operation. This high-power, compact, stable and environment-insensitive fs-pulsed laser source shows great potential as an ideal seed for biomedical imaging and mid-infrared frequency combs. Full article

We have demonstrated a high-power, polarization-maintaining all-fiber amplifier operating at a repetition rate of 1 MHz. The seed laser is a Semiconductor Saturable Absorber Mirror (SESAM) mode-locked oscillator with an 18.1 nm full width in half-maximum (FWHM) spectrum. The pulse duration is stretched to 1.1 ns using temperature-controlled chirped fiber Bragg gratings (TCFBGs) and subsequently amplified in a 40 µm core Yb-doped fiber, achieving a maximum output power of 37 W. The amplified laser exhibits excellent beam quality with an M² factor of 1.04. The pulse duration is compressed to 207 fs in a single-grating compressor with 86% efficiency, yielding an average power of 32 W, a pulse energy of 32 µJ, and a peak power of 154.6 MW. This high-power all-fiber femtosecond laser is a promising source for scientific and industrial applications. Full article