Search Results (670)

This work presents a systematic methodology for generating bi-sinusoidal surface topographies with controlled and reproducible characteristics on Ti-6Al-4V using a progressive 1D–2D–3D framework. Such deterministic topographies are of interest for dental implants, where surface micro-texture can influence an early biological response and osseointegration. Single-pulse ablation thresholds were first determined to be 0.175 J/cm² at a 1031 nm wavelength using 306 fs pulses, with no polarization dependence. Studies were then carried out to identify fundamental ablation parameters, optimize scanning conditions for planar texturing, and extend the process to controlled three-dimensional surface architectures. During the 1D stage, increasing the fluence from 0.26 to 6.52 J/cm² enlarged the crater diameter from approximately 7 to 32 µm and increased the areal roughness Sa from 0.012 to 0.020 µm. With an increasing pulse number, the crater diameter continued to grow up to 25 pulses before stabilizing. Multi-pulse tests below the threshold showed that repeated exposures caused ablation, highlighting incubation and energy accumulation, with an incubation factor of S = 0.84. In the 2D stage, scanned irradiation was used to quantify how fluence and pulse overlap affect the ablated depth and areal roughness, with depth increasing linearly with the number of passes, and roughness strongly governed by overlap and fluence. Finally, 3D texturing combining x–y scanning with a z-axis focal adjustment enabled reproducible bi-sinusoidal topographies. Full article

Objectives: The VISUMAX 800 (Carl Zeiss Meditec) is the second-generation femtosecond laser for small incision lenticule extraction (SMILE), featuring faster pulse rates, automated cyclotorsion compensation (OcuLign), and automated centration (CentraLign) versus the VISUMAX 500. This systematic review and meta-analysis compared their clinical outcomes in myopia correction. Methods: Following PRISMA 2020 guidelines, we searched PubMed, EMBASE, and Web of Science through March 2026 for studies comparing the two platforms in myopia or myopic astigmatism with extractable data. Primary outcomes were predictability (SE ± 0.50 D) and astigmatism (CYL ≤ 0.50 D). Secondary outcomes included UDVA ≥ 20/20, safety (CDVA loss ≥ 1 line), R² values, surgically induced astigmatism, axis alignment (±5°), and higher-order aberrations. Risk of bias was assessed using the ROBINS-I tool for all included studies, as no randomized controlled trials were available. Publication bias was evaluated via funnel plots, Egger’s test, and Begg’s test, with appropriate caution noted regarding the limited number of studies. Sensitivity analysis used the leave-one-out method. Results: Nine studies (1672 eyes: 646 VISUMAX 800, 1026 VISUMAX 500) were included. For SE ± 0.50 D, the pooled risk ratio (RR) was 1.065 (95% CI: 0.997–1.137, p = 0.061) with substantial heterogeneity (I² = 64.7%, p = 0.004). For CYL ± 0.50 D (eight studies, 1585 eyes), the pooled RR was 1.022 (95% CI: 0.978–1.068, p = 0.333, I² = 51.7%). Astigmatism axis within ±5° significantly favored VISUMAX 800 (RR = 1.157, 95% CI: 1.071–1.250, p = 0.0002, I² = 0%). No statistically significant differences were observed for UDVA ≥ 20/20, safety, SEQ R², cylinder R², TIA, SIA, total HOAs, spherical aberration, or coma RMS. Publication bias tests showed no significant asymmetry for the primary outcomes, though these tests have limited power with fewer than 10 studies. ROBINS-I assessments classified most studies as having “serious” risk of bias due to their non-randomized designs. Conclusions: Both platforms yield comparable predictability, safety, and visual outcomes. VISUMAX 800 offers superior astigmatism axis alignment, likely due to automated compensation and centration. The borderline SE predictability warrants further randomized investigation Full article

We demonstrate an 80 MHz, 350 mW, 120 fs, 770 nm femtosecond laser based on a nonlinear compressed 1540 nm femtosecond fiber laser. The home-built 1540 nm fiber laser, delivering 80 MHz, 2.69 W, 269 fs laser pulses, was realized by employing spectral pre-modulation and pre-chirp management inside an Er/Yb co-doped fiber power amplifier. The subsequent nonlinear fiber pulse compression stage was utilized to further nonlinearly compress the pulse duration to 128 fs based on the Gaussian assumption. Detailed numerical simulation was also implemented to investigate the optical dynamics of the nonlinear compression process. Finally, a 0.5 mm thick fan-out periodically poled lithium niobate (PPLN) crystal was utilized to generate the frequency-doubled, 350 mW, 770 nm laser pulses with a 120 fs pulse duration based on the Gaussian assumption. Full article

This article presents a structured spectral-stability assessment of an nJ-class ultrafast fiber laser generating femtosecond pulses with an approximate pulse duration of 115 fs, based on an ensemble of 61 consecutively acquired optical spectra. The study is motivated by the practical need to extract reliable short-sequence stability information from routine compact-spectrometer exports without requiring a separate pulse-diagnostic instrument at the initial assessment stage. For each spectrum, peak wavelength, centroid wavelength, FWHM bandwidth, integrated spectral area, correlation with the ensemble mean spectrum, and RMS deviation were calculated. Principal component analysis (PCA) was then applied to reduce the full spectral ensemble into a compact diagnostic space and to identify the dominant modes of residual spectral variation. The analyzed spectra yielded a peak wavelength of 775.31 ± 0.19 nm, a FWHM bandwidth of 7.95 ± 0.20 nm, an integrated spectral area of 10.43 ± 0.42 a.u.·nm, and a correlation with the mean spectrum of 0.99957 ± 0.00019, confirming a highly repeatable spectral envelope. PCA showed that PC1 and PC2 explained 66.50% and 12.60% of the variance, respectively, while PC3 contributed only 1.90%, indicating that the measured variability was weak and largely low-dimensional. These results demonstrate that consecutively exported optical spectra can provide a defensible and physically interpretable short-sequence stability assessment of ultrafast femtosecond fiber lasers, offering a practical route for routine monitoring, early-stage diagnostics, and future integration with simultaneous temporal and spectral characterization. Full article

A Q-switched pulsed laser based on a coupled 7-core Yb-doped fiber with a cavity based on a fiber Bragg grating array has been demonstrated with a maximum energy of microsecond pulses up to 15 μJ at a 1 kHz repetition rate. The lasing spectrum is hybridized so that the laser line maxima of each core are nearly the same, having a negligible spread relative to each other, which is much lower than the wavelength shifts between individual FBGs in the cores. At the same time, the generated power is nearly the same in all the cores. However, when increasing the power beyond the stimulated Raman scattering threshold, the supermodes are destroyed so that the spectra in the cores become increasingly different and less stable, and the output power is mainly concentrated in one of the cores, whereas the pulse shortens significantly to a sub-microsecond duration (300 ns), with damped oscillations appearing at the beginning. The new regimes we demonstrated of the multicore fiber laser are promising for creating powerful pulsed radiation sources with a narrow spectrum. Full article

Time-resolved visualization of local structural dynamics driven by external fields is essential for understanding structure–property relationships in functional materials and devices. Conventional ultrafast methods primarily capture femtosecond-to-picosecond photoinduced dynamics, yet they lack real-space access to spatially inhomogeneous processes occurring at their intrinsic mesoscopic timescales that govern material and device performance—particularly electrically driven processes that closely mimic actual device operating conditions. Here, we report a multifunctional ultrafast transmission electron microscopy (UTEM) platform targeting reversible structural dynamics spanning nanoseconds to microseconds under stroboscopic multi-field excitation. Our system employs photoelectron pulses generated by nanosecond UV laser illumination as the probe, alongside optical and electric pulses as pump excitation. A unified electronic synchronization scheme based on a high-speed photodiode and a digital delay generator enables precise timing control among the optical pump, electrical pump, and photoelectron pulses across the nanosecond-to-microsecond range. Using vanadium dioxide (${\mathrm{VO}}_2$) as a model system, we demonstrate a combined spatiotemporal resolution with measurable signals on the order of 10 nm–10 ns, allowing real-space mapping of spatially inhomogeneous dynamics. Electrical-pump experiments further reveal Joule-heating-induced non-uniform structural phase transitions and thermal-shock-excited megahertz-range mechanical oscillations. These results establish the developed multi-field UTEM platform as a practical tool for probing local structural dynamics in functional materials under optical and electrical excitation. Full article

Femtosecond laser surface texturing offers a promising route to tailor the functionality of bio-based wood coatings, yet the interplay between coating composition and laser processing remains poorly understood. In this study, bio-based epoxy coatings with eventual micronized wax additives were textured using a femtosecond laser to investigate the effects of laser processing parameters on pattern formation and resulting hydrophobicity. The epoxy coatings containing PE, PE/PTFE, HDPE, and rice bran waxes at 1, 5, and 7 wt.-% were characterized in terms of morphology, roughness, wettability, and chemical stability, followed by systematic variation of pulse repetition rate and laser power. The results reveal that the ablation threshold strongly depends on intrinsic coating properties. Ablation resistance increases with surface roughness and wax melting enthalpy, reflecting the role of phase transition energy in laser–matter interaction. The wax-filled coatings exhibit a transition from melting-dominated behavior at low energy input to ablation-dominated behavior at a higher energy. Laser texturing enhances hydrophobicity in parallel with theoretical values calculated from the Cassie–Baxter wetting model, with the highest hydrophobicity achieved for coatings combining intrinsic hydrophobicity and stable pattern formation. Chemical analysis confirms limited degradation of the epoxy matrix without significant carbonization, while wax additives provide partial thermal shielding. Overall, this work demonstrates clear options for tailoring surface morphology and wettability of hydrophobic polymer coatings through controlled femtosecond laser processing. Full article

This study investigates the process optimization and predictive modeling of femtosecond laser precision milling for commercial poly(methyl methacrylate) (PMMA) slices, with emphasis on surface roughness R_a and milling depth h. Three-dimensional surface morphology was measured using a laser confocal microscope, and the measurement methods for R_a and h were defined based on stable regions of interest and reference-plane correction. The effects of pulse energy, scanning line speed, scanning line spacing and pulse repetition frequency on milling quality were systematically analyzed. The results show that pulse energy and repetition frequency promoted material removal and increased milling depth, whereas scanning line speed and scanning line spacing reduced milling depth by decreasing the effective energy deposition per unit area. Surface roughness was influenced by both energy input and scanning uniformity, showing non-monotonic responses to scanning line speed and scanning line spacing. Quadratic response surface models were established using the Box–Behnken design. The ANOVA results indicate that both the R_a and h models were statistically significant, with R² values of 0.9970 and 0.9982, respectively. The validation results show that the average relative errors of the R_a and h models were 6.51% and 2.62%, respectively. These results demonstrate that the proposed models can effectively predict femtosecond laser milling quality and provide guidance for parameter selection and surface-quality control of commercial PMMA slices. Full article

We investigate the formation of surface periodic structures during ablation of a 20 nm aluminum film on a glass substrate by high-power terahertz pulses. Using subpicosecond pulses in the 0.5–3 THz range with a field strength of 15 MV/cm (fluence 0.3 J/cm²) generated in a DSTMS crystal pumped by a femtosecond Cr:Forsterite laser, we observe discrete growth of cone-shaped damage channels with a period of 20 µm at an energy density below the single pulse ablation threshold ($F_a\approx 0.15$ J/cm²). The channel length increases from pulse to pulse (for 8, 20, and 100 pulses) due to local current density enhancement at the channel tip. This enhancement scales inversely with the square root of the tip radius and reaches an order of magnitude. Surface morphology analysis reveals a thermomechanical mechanism governing film destruction. The observed self-organized periodic structures, whose orientation is strictly perpendicular to the THz electric field, hold promise for functional devices in the terahertz band, such as polarizers, near-field sensors, and spatially selective absorbers, provided the formation process can be regulated. Full article

The linear and third-order nonlinear optical (NLO) properties of a water-soluble perylenediimide derivative, N,N′-di(2-(trimethylammonium iodide) ethylene) perylenediimide (TAIPDI), doped with semiconductor nanoparticles (NPs), were systematically investigated under femtosecond laser excitation. ZnO and TiO₂ NPs were synthesized using a pulsed laser ablation technique. Nanocomposite systems were prepared by incorporating different concentrations of ZnO and TiO₂ NPs into the TAIPDI dye solution. The optical properties were characterized using UV–visible absorption spectroscopy together with open- and closed-aperture Z-scan measurements at 800 nm. Linear absorption measurements revealed concentration-dependent modifications in the optical band gap, indicating electronic interaction between the dye molecules and the semiconductor NPs. Open-aperture Z-scan results demonstrated strong nonlinear absorption (NLA) behavior dominated by two-photon absorption and excited-state absorption processes. Closed-aperture measurements showed a negative nonlinear refractive (NLR) index, corresponding to self-defocusing behavior. Both the NLA coefficient and the NLR index increased with increasing NP concentration, resulting in a significant enhancement of the third-order nonlinear susceptibility of the nanocomposite systems. In addition, optical limiting measurements revealed a pronounced reduction in the limiting threshold with increasing nanoparticle concentration, demonstrating improved laser attenuation capability. These findings indicate that ZnO@TAIPDI and TiO₂@TAIPDI nanocomposites are promising candidates for applications in optical limiting, all-optical switching, and advanced photonic devices. Full article

Ultra-High Molecular Weight Polyethylene (UHMWPE), the standard base material in ski manufacturing, offers excellent gliding performance but exhibits limited mechanical and scratch resistance on hard and icy snow conditions. In this work, stainless steel is proposed as a mechanically robust alternative, and its inherently higher friction against snow is addressed through surface engineering. The snow friction behavior of 301H stainless steel surfaces decorated with fishbone-like microstructures combined with Laser-Induced Periodic Surface Structures (LIPSSs) was investigated using a custom-built snow tribometer. Several pattern designs, with different pitch distances and depths, were engraved using femtosecond laser pulse irradiation. We conducted morphological, physical, and chemical investigations through microscopy, static contact angle measurements, and X-ray Photoelectron Spectroscopy analyses. Results indicate that the gliding performance is not directly related to the modifications in surface chemistry and wetting behavior of the samples but is affected by the geometry and orientation with respect to the sliding direction of the specific micro- and nano-features. Overall, we achieved friction coefficient values comparable to those found in UHMWPE with a fast and economically sustainable single-step laser-texturing process. This approach allows the industrial up-scaling of the fishbone-texture design to real-size alpine ski prototypes. Full article

Miniature plasma lenses capable of withstanding high laser intensities could provide compact focusing elements for a variety of laser-plasma applications. In particular, they offer a simple route to increase ignitor beam intensity in fast ignition targets while remaining compatible with the geometric constraints of cone-in-target configurations. We report an experimental proof-of-concept demonstration of such a lens using a Ti:Sa femtosecond laser system. The lens is generated by a nanosecond laser pulse incident on a foil aperture, producing an expanding plasma with a transient radial density gradient that focuses a delayed femtosecond pulse. The resulting plasma lens focal spot is reduced to a few microns $⟨D_{\mathrm{FWHM}}⟩\approx 5.5$ $\mathsf{\mu }$m. After accounting for transmitted energy contained within the FWHM contour, the effective intensity enhancement was estimated to be ${\displaystyle \frac{I_{\mathrm{PL}}}{I_0}}\approx 47\pm 15$. Full article

To address the critical challenges of edge chipping and poor processing quality in sapphire precision dicing, this paper proposes a femtosecond laser filamentation-guided dicing technology. By systematically investigating the influence of pulse overlap rate, energy, and scan counts on damage evolution, the physical differences between 343 nm UV and 515 nm visible lasers in suppressing plasma shielding and breaking through processing saturation limits are revealed. The results indicate that an extremely high pulse overlap rate (>98%) significantly inhibits lateral energy dissipation and drives the efficient propagation of the filament deep along the optical axis; furthermore, the 343 nm laser demonstrates superior removal rates and localisation compared to the 515 nm laser. Using super-resolution imaging, the precision cleavage cross-section is clearly categorised into four evolutionary stages: general ablation, filament ablation, transition, and mechanical cleavage. To mitigate morphological degradation induced by multiple scans, a sacrificial-layer-assisted strategy is innovatively proposed to achieve spatial damage transfer and in situ self-polishing, effectively eliminating longitudinal damage striations and residual stress-induced hackles. Finally, taper-free, high-precision separation of 1 mm × 450 μm micro-units is successfully achieved on a 220-μm-thick sapphire wafer. This technology not only achieves ultra-low-loss dicing but also establishes a highly efficient, contamination-free in situ characterisation paradigm for buried structures in hard and brittle materials. Full article

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