Search Results (210)

(1) Background: A decrease in corneal hydration during refractive surgery is observed clinically as well as in laboratory settings, but the associated consequences are not yet fully understood. The purpose of this paper is to analyze the impact of the gain of ablation efficiency due to hydration changes during cornea refractive surgery. (2) Methods: We developed a simulation model to evaluate the influence of hydration changes on the ablation algorithms used in laser refractive surgery. The model simulates different physical effects of an entire surgical process, simulating the shot-by-shot ablation process based on a modeled beam profile. The model considers corneal hydration, as well as environmental humidity, along with the laser beam characteristics and ablative spot properties for evaluating any hydration changes and their effect on laser refractive surgery. (3) Results: Using pulse lists collected from actual treatments, we simulated the gain of efficiency during the ablation process. Ablation efficiency is increased due to dehydration effects during laser treatments. Longer treatments suffer larger dehydration effects and are more prone to overcorrections due to gain of efficiency than shorter treatments. (4) Conclusions: The improper use of a model that overestimates or underestimates the effects derived from the hydration dynamics during treatment may result in suboptimal refractive corrections. This model may contribute to improving emmetropization and the correction of ocular aberrations with improved laser parameters that can compensate for the changes in ablation efficiency due to hydration changes in the cornea. Full article

To address the poor thermal performance and low output efficiency of conventional solid-state microchip lasers, this study proposes and implements a bonded Nd:YAG/Cr⁴⁺:YAG laser based on fiber splitter pumping. Experimental results demonstrate that at a 4.02 mJ pump pulse energy and a 100 Hz repetition rate, the system achieves four linearly polarized output beams with an average pulse energy of 0.964 mJ, a repetition rate of 100 Hz, and an optical-to-optical conversion efficiency of 23.98%. The energy distribution ratios for the upper-left, lower-left, upper-right, and lower-right beams are 22.61%, 24.46%, 25.50%, and 27.43%, with pulse widths of 2.184 ns, 2.193 ns, 2.205 ns, and 2.211 ns, respectively. As the optical axis distance increases, the far-field spot pattern transitions from a single circular profile to four fully separated spots, where the lower-right beam exhibits beam quality factors of M_x² = 1.181 and M_y² = 1.289. Simulations at a 293.15 K coolant temperature and a 4.02 mJ pump energy reveal that split pumping reduces the volume-averaged temperature rise in Nd:YAG by 28.81% compared to single-beam pumping (2.57 K vs. 3.61 K), decreases the peak temperature rise by 66.15% (6.97 K vs. 20.59 K), and suppresses peak-to-peak temperature variation by 78.6% (1.34 K vs. 6.26 K). Compared with existing multi-beam generation methods, the fiber splitter approach offers integrated advantages—including compact size, low cost, high energy utilization, superior beam quality, and elevated damage thresholds—and thus shows promising potential for automotive multi-point ignition, multi-beam single-photon counting LiDAR, and laser-induced breakdown spectroscopy (LIBS) online analysis. Full article

In this work, we present a new partially coherent adjustable anomalous vortex laser beam (PCAAVLB) and introduce it into turbulent biological tissue. The equation of such PCAAVLB in turbulent biological tissue is obtained. By numerical analysis, the evolution of the intensity of such PCAAVLB in turbulent biological tissue is analyzed. It is found that the PCAAVLB in biological tissue can lose its ring shape and become a Gaussian beam, and a PCAAVLB with smaller topological charge $M$ or coherence length $\sigma$ will evolve into a Gaussian profile faster. The PCAAVLB in turbulent biological tissue with a smaller small-length-scale factor $l_0$ or larger fractal dimension $D$ will evolve into a Gaussian profile faster and have a larger intensity as z increases. The results may have potential applications in sensing under biological tissue environments and laser imaging in biology. Full article

The output energy of Laser Active Optical Systems (LAOSs), in which image brightness is amplified within the laser-active medium, is always higher than the input energy. This contrasts with conventional optical systems (OSs). As a result, a LAOS enables the creation of laser beams with tailored energy distribution across the aperture, making them ideal for material processing applications. This concept was first successfully implemented using metal vapor lasers as the gain medium. In these systems, material processing was achieved by using a laser beam that either carried the required energy profile or the image of the object itself. Later, other laser media were utilized for LAOSs, including barium vapor, strontium vapor, excimer XeCl lasers, and solid-state media. Additionally, during the development of these systems, several modifications were introduced. For example, Space-Time Light Modulators (STLMs) and CCD cameras were incorporated, along with the use of multipass amplifiers, disk-shaped or thin-disk (TD) solid-state laser amplifiers, and other advancements. These techniques have significantly expanded the range of power, energy, pulse durations, and operating wavelengths. Currently, TD laser amplifiers and STLMs based on Digital Light Processor (DLP) technology or Digital Micromirror Devices (DMDs) enhance the potential to develop LAOS devices for Subtractive and Additive Technologies (ST, AT), applicable in both macromachining (cutting, welding, drilling) and micro-nano processing. This review presents comparable characteristics and requirements for these various LAOS applications. Full article

Pollen allergies represent a growing public health concern that necessitates enhancements to the network of instruments and modeling calculations in order to facilitate a more profound comprehension of pollen transportation. The Beenose instrument quantifies the light scattered by particles that traverse a laser beam at four angles. This methodology enables the differentiation of pollen particles from other particulate matter, predominantly mineral and carbonaceous in nature, thereby facilitating the retrieval of pollen concentrations. The Beenose instrument has been installed on the tourist balloon known as “Ballon de Paris” in a large park situated in the southwest of Paris, France. The measurement period is from April to November 2024, coinciding with the pollen seasons of trees and grasses. The balloon conducts numerous flights per day, reaching an altitude of 150 m when weather conditions are conducive, which occurs approximately 58% of the time during this period. The data are averaged to produce vertical profiles with a resolution of 30 m. Concentrations of the substance decrease with altitude, although a secondary layer is observed in spring. This phenomenon may be attributed to the presence of emissions from a proximate forest situated at a higher altitude. The average decrease in concentration of 11 ± 8% per 10 m is consistent with the findings of previous studies. The long-term implementation of Beenose measurements on this tourist balloon is intended to enhance the precision of the results and facilitate the differentiation of the various parameters that can influence the vertical transportation of pollen. Full article

Wide-beam laser direct energy deposition (LDED) has been widely used due to its superior deposition efficiency. To achieve optimal laser-powder coupling, this technique typically employs rectangular powder nozzles. This study establishes a simulation model to systematically investigate the powder flow field characteristics of rectangular symmetric nozzles. Through parametric analysis of powder feeding rate, carrier gas flow rate, and shielding gas flow rate, the effects on powder stream convergence behavior are quantitatively evaluated to maximize powder utilization efficiency. Key findings reveal that, while the powder focal plane position is predominantly determined by nozzle geometry, powder feeding parameters exhibit negligible influence on flow field intersections. The resulting powder spot demonstrates a rectangular profile slightly exceeding the laser spot dimensions, and the powder concentration exhibits a distinctive flat-top distribution along the laser’s slow axis, contrasting with a Gaussian distribution along the scanning direction. Experimental validation through powder collection tests confirms strong agreement with the simulation results. Furthermore, a mathematical model was developed to accurately describe the powder concentration distribution at the focal plane. These findings provide fundamental theoretical guidance for optimizing powder feeding systems in wide-beam LDED applications. Full article

This study experimentally demonstrates transverse symmetry breaking—a mechanism governing laser planar trapping—and distinguishes its unique role from related phenomena such as the lateral Goos–Hänchen shift and angular deviations. While the latter effects describe positional or angular beam displacements at interfaces, transverse symmetry breaking fundamentally alters the beam’s spatial symmetry, enabling unprecedented control over its intensity and phase profiles. Empirical results exhibit exceptional agreement with a recently proposed theoretical model, validating its predictive capability. Crucially, our findings highlight transverse symmetry breaking as a critical tool for tailoring beam profiles, advancing applications in optical trapping, structured light systems, and photonic device engineering, where symmetry manipulation unlocks new degrees of freedom in light–matter interactions. Full article

Marine atmospheric boundary-layer height (MABLH) is crucial for ocean heat, momentum, and substance transfer, affecting ocean circulation, climate, and ecosystems. Due to the unique geographical location of the South China Sea (SCS), coupled with its complex atmospheric environment and sparse ground-based observation stations, accurately determining the MABLH remains challenging. Coherent Doppler wind lidar (CDWL), as a laser-based active remote sensing technology, provides high-resolution wind profiling by transmitting pulsed laser beams and analyzing backscattered signals from atmospheric aerosols. In this study, we developed a stacking optimal ensemble model (SOEM) to estimate MABLH in the vicinity of the site by integrating CDWL measurements from a representative SCS site with ERA5 (fifth-generation reanalysis dataset from the European Centre for Medium-Range Weather Forecasts) data from December 2019 to May 2021. Based on the categorization of the total cloud cover data into weather conditions such as clear/slightly cloudy, cloudy/transitional, and overcast/rainy, the SOEM demonstrates enhanced performance with an average mean absolute percentage error of 3.7%, significantly lower than the planetary boundary-layer-height products of ERA5. The SOEM outperformed random forest, extreme gradient boosting, and histogram-based gradient boosting models, achieving a robustness coefficient ($R^2$) of 0.95 and the lowest mean absolute error of 32 m under the clear/slightly cloudy condition. The validation conducted in the coastal city of Qingdao further confirmed the superiority of the SOEM in resolving meteorological heterogeneity. The predictions of the SOEM aligned well with CDWL observations during Typhoon Sinlaku (2020), capturing dynamic disturbances in MABLH. Overall, the SOEM provides a precise approach for estimating convective boundary-layer height, supporting marine meteorology, onshore wind power, and coastal protection applications. Full article

Lattice structures offer the possibility to obtain lightweight components with additional functionalities, improving their shock absorption and thermal exchange properties. Recently, a body-centered cubic (BCC) lattice structure has been used to fabricate metal lattice sandwich panels (MLSPs) for aerospace applications. MLSPs are made of two external skins and a lattice core and can be produced thanks to laser powder bed fusion technology (LPBF), which is characterized by its superior printing accuracy with respect to other additive manufacturing processes for metals. Since few studies can be found in the literature on Ti-6Al-4V MLSPs, further work is needed to evaluate the mechanical response of these panels. Moreover, due to their design complexity and to avoid a costly experimental campaign, numerical simulation could be used to encourage the industrial application of these structures. In this paper, different cell configurations were printed and tested in compression to study the influence of the cell’s geometrical parameters, i.e., the cell size and beam radius, on the mechanical response of MLSPs. Numerical simulations of the LPBF of these geometries were also carried out to understand how the residual stresses can be varied by varying the cell configuration. A geometrical evaluation was carried out to quantitatively express the influence of the beam radius and cell size on the resulting volume fraction, which strongly influences the mechanical behavior and residual stress profiles of MLSPs. From the analysis, we found that the C2-R0.35 sample resulted in the configuration with the highest compressive strength, while C3-R0.25 showed the lowest and most uniform residual stress profile. Full article

Shaping or splitting of a Gaussian beam is often desired to optimise laser–material interactions, improving throughput and quality. This can be achieved holographically using liquid crystal-on-silicon spatial light modulators (LC-SLMs). Until recently, maximum exposure has been limited to circa 120 W average power with a Gaussian profile, restricting potential applications due to the non-linear (NL) phase response of the liquid crystal above this threshold. In this study, we present experimental tests of a new SLM device, demonstrating high first-order diffraction efficiency of η = 0.98 ± 0.01 at 300 W average power and a phase range Δφ > 2π at P = 383 W, an exceptional performance. The numerically calculated device temperature response with power closely matches that measured, supporting the higher power-handling capability. Surface modification of mild steel and molybdenum up to P = 350 W exposure is demonstrated when employing a single-mode (SM) fibre laser source. Exposure on mild steel with a vortex beam (m = +6) displays numerous ringed regions with varying micro-structures and clear elemental separation created by the radial heat flow. On molybdenum, with multi-spot Gaussian exposure, both MoO₃ films and recrystallisation rings were observed, exposure-dependent. The step change in device capability will accelerate new applications for this LC-SLM in both subtractive and additive manufacturing. Full article

We report on fabricating planoconcave lenses using a picosecond 355 nm wavelength laser and a CO₂ laser. We also report the fabrication of the planoconvex microlens array on fused silica by patterned micromachining using a picosecond laser and reshaping using a CO₂ laser. We report results on the surface morphology, profile, roughness, optical transmission efficiency, and laser beam profile of transmitted light passing through the microlens. We demonstrate laser fabrication of planoconcave lenses on infrared transmitting material sapphire. Furthermore, we present the results of an experimental and simulation comparative performance study of planoconcave microlenses obtained by individual picosecond and CO₂ lasers. Full article

To address the demand for laser beam-shaping techniques, we developed a one-step exposure process based on moving-mask lithography for the fabrication of a continuous-surface diffractive optical element (DOE) for laser beam shaping. The fabrication process is described in detail, and the influence of key parameters, such as pre-baking conditions, exposure gaps, development conditions, and post-baking conditions, of the lithography process on the microstructure profile of the DOE is analyzed. The reliability of the preparation method was verified through optical performance experiments. The speckle contrast, uniformity, and diffraction efficiency of the prepared linear beam-shaping element are 4.2%, 97.3%, and 87%. Full article

This study is a comprehensive experimental and computational investigation into high-resolution laser beam diagnostics, combining classical statistical techniques, numerical image processing, and machine learning-based predictive modeling. A dataset of 50 sequential beam profile images was collected from a femtosecond fiber laser operating at a central wavelength of 780 nm with a pulse duration of approximately 125 fs. These images were analyzed to extract spatial and temporal beam characteristics, including centroid displacement, Full Width at Half Maximum (FWHM), ellipticity ratio, and an asymmetry index. All parameters were derived using intensity-weighted algorithms and directional cross-sectional analysis to ensure accurate and consistent quantification of the beam’s dynamic behavior. Linear regression models were applied to horizontal and vertical intensity distributions to assess long-term beam stability. The resulting predictive trends revealed a systematic drift in beam centroid position, most notably along the vertical axis, and a gradual broadening of the horizontal FWHM. The modeling further showed that vertical intensity increased over time while horizontal intensity displayed a slight decline, reinforcing the presence of axis-specific fluctuations. These effects are attributed to minor optical misalignments or thermally induced variations in the beam path. By integrating deterministic analysis with data-driven forecasting, this methodology offers a robust framework for real-time beam quality evaluation. It enhances sensitivity to subtle distortions and supports the future development of automated, self-correcting laser systems. The results underscore the critical role of continuous, high-resolution monitoring in maintaining beam stability and alignment precision in femtosecond laser applications. Full article

Ultrafast laser systems, implemented at the ELI-NP, require exceptional beam quality and spatial stability due to their femtosecond pulse durations and extremely high peak powers. This work presents a diagnostic and computational framework for analyzing the ELI-NP Front-End beam characteristics, where spatial coherence and precise pulse shaping are essential for reliable amplification and experimental consistency. The methodology integrates classical beam diagnostics with image processing and machine learning tools to evaluate anomalies based on high-resolution beam profile images. We use centroid tracking to monitor pointing fluctuations, statistical intensity analysis to detect energy instabilities, and Sobel-based edge detection to evaluate beam sharpness and extract structural features from the beam image. Geometric parameters such as ellipticity, roundness, and symmetry indicators are extracted and examined over time. The system applies an unsupervised Isolation Forest algorithm to detect subtle or short-lived anomalies, identifying irregularities without relying on predefined thresholds. These diagnostics are supported by visual plots and statistical summaries, offering a clear picture of the beam’s behavior under real operating conditions. Results confirm that this integrated approach effectively captures major and minor beam instabilities, making it a practical tool for continuous monitoring and performance optimization in ultrafast laser systems. Full article

Laser alloying was used to form metal matrix composite layers strengthened by WC particles. The process parameters were selected in such a way that there was no complete melting of the WC particles. Four different laser beam powers (from 0.65 kW to 1.3 kW) were used, generating different temperature distributions during processing. The temperature across the laser track axis was determined according to the mathematical model proposed by Ashby and Esterling. All layers produced contained unmelted WC particles in an aluminum-based matrix. The depth of the WC-Al composite layers strongly depended on the applied laser beam power. The lowest thickness of 198 ± 36 µm was measured for the layer produced at a laser beam power of 0.65 kW. A twofold increase in power P was the reason for obtaining a thickness th_AZ = 387 ± 21 µm. The power of the laser beam also affected the percentage of the substrate material (7075 alloy) in the molten pool during the laser processing. As a result, the highest amount of substrate material was obtained for the WC-Al composite layer produced using the highest laser beam power P = 1.3 kW. Simultaneously, this layer was characterized by the lowest percentage of tungsten carbide particles in this layer. The temperature profile along the axis of the laser track and also the maximum temperature reached confirmed the difference in the bonding between the reinforcing WC particles and the metal matrix. For P = 0.65 kW, too low a temperature was reached for the tungsten carbide particles to overmelt, resulting in poor bonding to the metallic matrix in the layer. Moreover, the layer showed serious defects such as discontinuity, porosity, and cracks. As a result, the WC-Al composite layer produced at the lowest laser beam power was characterized by a wear resistance lower (I_mw = 6.094 mg/cm²/h) than the 7075 alloy without surface layer (I_mw = 5.288 mg/cm²). The highest wear resistance was characteristic of the 7075 alloy laser alloyed with a laser beam power equal to 1.17 kW (I_mw = 2.475 mg/cm²/h). This layer showed satisfactory quality and adhesion to the substrate material. Full article