Search Results (2,349)

Ballistic para-aramid fabrics are widely used in personal protection and defense applications due to their high strength-to-weight ratio, thermal stability, and durability. This study investigates the influence of laser-based surface modification on graphene-modified Kevlar^® KM2-600 (600 dtex) fabrics, with a particular focus on surface morphology and topographical characteristics of para-aramid fabrics used in ballistic applications. The deposition of graphene onto para-aramid fibers introduces new opportunities for surface engineering, while laser processing enables localized and controlled modification of the fiber surface without compromising the integrity of the bulk material. In this work, graphene-modified Kevlar^® KM2-600 fabrics were subjected to controlled laser processing under various parameter settings, and the resulting surface modifications were systematically analyzed. Three-dimensional laser microscopy was employed to characterize surface morphology and roughness, providing detailed insight into laser-induced topographical changes. The results demonstrate that optimized laser processing enables controlled surface restructuring while avoiding severe thermal damage, particularly when appropriate mechanical stabilization and focal conditions are maintained. Under identical laser processing conditions (Matrix II, q = 3.65 × 10⁴ W/cm²), the mean arithmetic roughness increased from 4.57 ± 1.04 µm for the unmodified fabric to 5.54 ± 1.05 µm for the graphene-modified fabric, while the mean root mean square roughness increased from 5.76 ± 1.41 µm to 6.95 ± 1.39 µm. These findings contribute to an improved understanding of laser–graphene–aramid interactions and provide a foundation for future studies addressing the potential functional implications of surface modification in lightweight protective textiles. 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

Objectives: This study investigated whether visual field abnormalities are present in eyes with suspected nasal optic disc hypoplasia (NOH) by using fundus photography and optical coherence tomography (OCT). Methods: NOH was diagnosed using the following criteria: (1) small optic disc, (2) nasal optic disc pallor or optic disc margin irregularity, (3) wedge-shaped temporal visual field defects extending from Mariotte’s blind spot, and (4) reduced nasal circumpapillary retinal nerve fiber layer (cpRNFL) thickness. Eyes fulfilling criteria 1, 2, and 4 without visual field abnormalities were classified as pseudo-NOH (pNOH), whereas eyes without visual field or cpRNFL abnormalities were considered normal. Nasal cpRNFL thickness was measured using OCT, radial peripapillary capillary (RPC) density was assessed using OCT angiography (OCTA), visual field testing was performed, and optic disc blood flow velocity was evaluated using the mean blur rate (MBR) and laser speckle flowgraphy (LSFG). Results: Seven eyes with NOH, 13 eyes with pNOH, and 24 normal right eyes were included. Nasal cpRNFL thickness and MBR were significantly reduced in both the NOH and pNOH groups compared with the normal group, with no significant difference between the NOH and pNOH groups. Nasal RPC density was significantly lower in the NOH group than in both the pNOH and normal groups, and no significant difference was observed between the pNOH and normal groups. Conclusions: Even when NOH was suspected from fundus, LSFG, and OCT C-scan findings, visual field abnormalities were not consistently present. Differences in RPC density measured using OCTA may have contributed to this variability. This study examined whether suspected nasal optic disc hypoplasia (NOH) is always associated with visual field defects. Using fundus imaging, OCT, OCT angiography, and laser speckle flowgraphy, we compared eyes with NOH, pseudo-NOH, and normal eyes. Although structural changes such as reduced nasal nerve fiber layer thickness and decreased blood flow were observed in both NOH and pseudo-NOH, visual field abnormalities were not consistently present. Notably, reduced radial peripapillary capillary density was specific to NOH, suggesting that vascular differences may explain variability in visual function. These findings highlight the importance of multimodal imaging in NOH evaluation. Full article

This study investigates the influence of process parameters on dimensional accuracy and microhardness in fiber laser cutting of low-carbon steel. A full factorial design of experiments (DOE) with three factors—cutting speed, focal position, and assist gas pressure—was applied to evaluate their effects on dimensional deviations and microhardness in the heat-affected zone (HAZ). The results showed that focal position is the most significant factor affecting all evaluated dimensional responses, while cutting speed has a strong influence on circular and linear dimensions. The effect of assist gas pressure was found to be response-dependent, being insignificant for inner diameter deviation but significant for selected linear features and through interaction effects with focal position. Statistical analysis confirmed the presence of significant interaction effects between process parameters. Microhardness measurements revealed a substantial increase in hardness from the base material toward the cut edge, indicating microstructural transformations caused by rapid thermal cycles during laser cutting. While this increase in hardness may enhance wear resistance, it may also lead to increased brittleness and reduced toughness. The findings provide a detailed insight into the relationship between process parameters and dimensional accuracy, highlighting the importance of parameter optimization and interaction effects in contributing to improved quality of laser-cut components. Full article

High-power thulium-doped fiber lasers (TDFLs) operating near 2050 nm are of great interest for applications including atmospheric gas sensing and free-space optical communication owing to the favorable atmospheric transmission and the strong absorption bands of carbon dioxide (CO₂). Here, we report an all-fiber high-power TDFL based on a 793 nm-pumped master oscillator power amplifier (MOPA) architecture. The system comprises a custom-built linear-cavity seed laser and two amplification stages. With a maximum pump power of 818 W, the final amplifier delivers 501 W at 2050 nm with a slope efficiency of 51%. Stable operation is confirmed over two hours at full power, with an RMS power fluctuation of only 0.47%. The measured beam quality factors $M^2$ are 1.31 and 1.27 in the horizontal and vertical directions, respectively, indicating near-diffraction-limited performance. The demonstrated system combines high output power, excellent stability, and good beam quality, and thus provides a promising laser source for 2 μm high-performance applications. Full article

We present the integration of an automated polarization control system into a figure-eight fiber laser with the aim of self-tuning noise-like pulses (NLPs). The system optimizes polarization adjustments by using adaptive control and predictive neural networks (NNs), enhancing temporal and spectral behavior. This approach enables precise control over pulse characteristics, achieving an average output power of 275.25 mW (302.8 nJ) for signal emission at ~1567 nm; adjustable NLP envelope durations from 13 ns to 48 ns, corresponding to spectral widths from 50 to more than 200 nm; and the ability to increase in a controllable way the repetition frequency up to 100 times the fundamental frequency, which corresponds to 909 kHz, through cavity harmonic pulse generation. A multiparameter pulsed regime-seeking algorithm stabilizes high-energy NLPs in the fundamental or harmonic regime while predictive networks optimize the cavity response, and the process is completed in an average time of 11.5 s. The automated polarization control system enables high cavity harmonic pulse generation, as well as broadband supercontinuum (SC) spectrum with high flatness. Full article

Single-frequency fiber lasers (SFFLs) are essential for applications such as gravitational wave detection, high-precision spectroscopy, and inertial confinement fusion, requiring narrow linewidth, low noise, and high output power. Here, we present a comparative study of 1 μm waveband distributed Bragg reflector (DBR) SFFLs with varying cavity parameters. Numerically, we investigate the effects of key cavity parameters on laser performance by plotting contour maps of output power versus grating reflectivity and lasing wavelength. We also simulate intensity noise transfer functions from pump fluctuations. Increasing pump power shifts the relaxation oscillation peak to higher frequency and reduces its amplitude, which originates from the higher intracavity photon density that speeds up the damping of perturbations. Experimentally, we construct two lasers using 6.5 mm and 10.5 mm YDFs spliced between FBG pairs. These lasers employ low-reflectivity FBGs centered at 1053 nm and 1064 nm, with reflectivities of 74% and 55%, respectively. The corresponding maximum output powers are 29.7 mW and 197 mW. The 1053 nm SFFL exhibits a relative intensity noise (RIN) of −102 dBc/Hz at 2.07 MHz, a linewidth of 12.52 kHz, and a mode-hop-free tuning range of 0.64 nm. Although increasing the pump power suppresses the relaxation oscillation peak, it broadens the linewidth due to laser phase noise degradation caused by pump noise-induced temperature fluctuations in the gain fiber. For SFFLs, the output powers should be selected according to the specific application, as a higher output power inherently leads to a broader linewidth. These insights are essential for optimizing such lasers and underscore their strong potential for future applications. Full article

Tungsten carbide and cobalt cutting tools require low surface roughness to improve cutting performance by reducing the wear from machining friction. While this is achieved by conventional manufacturing processes (pressing and sintering, grinding), with additive manufacturing processes it is more difficult (layer height, printing strategy). Since less costly and more sustainable solutions (without lubricants) are being studied as alternatives to conventional processes, a complementary technology (laser ablation) is suggested for the additive manufacturing of green WC-10Co. In this study, material extrusion (MEX) was used to produce green WC-10Co 3D objects, followed by laser ablation (50 W ytterbium fiber laser, 800–1100 nm wavelength) on their surface. Different laser strategies and parameters (power, speed, frequency, distance between lines, number of passages) were tested to find the most suitable. Most combinations were excluded by initial visual inspection, while the best ones were measured with a contact and non-contact profilometer. Further analysis was made on the composition and microstructure (with techniques such as Raman spectroscopy, scanning electron microscope, x-ray diffraction, and hardness indentation) to study what the interaction with the laser changed on the surface. Results show that with a combination of 50 W laser power, 1000 mm/s laser speed, 2000 kHz laser frequency, 0.1 mm distance between lines and three laser passages, it was possible to achieve a surface roughness of 0.6 µm (Sa) for the sintered WC-10Co, produced by MEX. No η-phase and graphite were detected, as well as microporosity and fissures. 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

Background/Objectives: In lingual frenectomy/frenotomy surgeries, thermal surgical instruments are commonly used because of their hemostatic effect, precise cutting, and lack of need for sutures. However, the effects of tissue heating on the biological repair process remain under investigation. This study aimed to evaluate the thermal and histological effects of a surgical lingual frenulum incisions performed with high-power diode lasers at 450 nm (blue) and 980 nm (infrared), compared with a surgical scissor incision (control group). Methods: The experimental project was conducted in two phases: first, an ex vivo experiment on porcine tongues using different surgical instruments, with different parameters, with thermal variations recorded using infrared thermography; and second, an in vivo phase using the instruments previously determined in the ex vivo phase. Results: Results demonstrated minimal tissue heating in the control group. There was a thermal elevation with the laser instruments, particularly with the 980 nm and 450 nm diode lasers; however, the 450 nm laser showed a high initial temperature increase, but exhibited faster tissue cooling. Thermal and histological analyses performed immediately after the procedure and on the seventh postoperative day showed clinically similar tissue repair across groups, with less disorganization of collagen fiber bundles on day seven in the group treated with the 450 nm laser. Conclusions: In conclusion, both diode lasers can be safely employed for lingual frenulum incision when appropriate parameters are used; however, further clinical studies are warranted to establish safe and effective parameters. Full article

Background/Objectives: Recently, a 6.3 Fr single-use flexible ureteroscope (f-URS) was introduced to the market. The purpose of this pilot study is to present our experience with it during Endoscopic Combined Intrarenal Surgery (ECIRS) and to compare its performance with the conventional 7.5 Fr scope. Methods: For percutaneous access, renal puncture was performed in a nonpapillary approach. Regarding retrograde access, for the first group, a 7.5 Fr single-use f-URS was used, while for the second group, a 6.3 Fr single-use f-URS was utilized. Lithotripsy was primarily performed in an antegrade manner, using the Lithoclast Trilogy^®. In cases where stones could not be reached with a nephroscope, retrograde lithotripsy was performed with either a Holmium:YAG laser or a Thulium Fiber Laser. Results: In total, 45 patients were included. Of these, 23 patients underwent ECIRS with the 6.3 Fr f-URS and 22 with the 7.5 Fr f-URS. The mean operative time, fluoroscopy time and lasing time were 59.5 ± 5.6 min, 139.7 ± 14.2 s and 18.4 ± 2.7 min in the 6.3 Fr group and 57.1 ± 3.9 min, 133.8 ± 29.7 s and 18.6 ± 1.9 min in the 7.5 Fr group, respectively. Two patients in the 6.3 Fr group and three patients in the 7.5 Fr group experienced Grade II complications. Stone-free rates were 91.3% in the 6.3 Fr group versus 86.4% in the 7.5 Fr group. Conclusions: The use of a 6.3 Fr f-URS during ECIRS is potentially a feasible, safe and efficient approach. Both the 6.3 Fr and 7.5 Fr scopes were associated with comparable outcomes during ECIRS. Additional studies are needed so as to draw safer conclusions. Full article

A 1319 nm, single-frequency, two-stage partially end-pumped slab (Innoslab) amplifier with high output power and excellent beam quality was reported. A 3 W, quasi-continuous wave pulsed, single-frequency all-fiber seed laser was amplified to a maximum average power of 154.0 W with a magnification of ~51.3 and overall optical-to-optical efficiency up to 12.0%. The output pulse width was 132.6 μs at a repetition rate of 500 Hz. The beam quality factors of M² were 1.4 and 1.3 in the horizontal and vertical directions, respectively. The power stability at the maximum output power was 0.43% (RMS) in 10 min. Higher output power and optical-to-optical efficiency could be achieved through optimizing mode matching between the pump beam and the seed laser beam. Full article

This study investigates laser transmission welding of 30% glass fiber-reinforced polybutylene terephthalate (PBT-GF30). Injection-molded plates were used as base material, from which specimens were prepared, welded, and experimentally tested. The influence of key process parameters, including laser power, beam size, and scanning speed, on weld quality was systematically evaluated through an iterative optimization approach. An optimized parameter set (400 W laser power, reduced beam size, and increased scanning speed) enabled stable and repeatable weld formation with minimal thermal degradation. Experimental results were further supported by finite element analysis, showing good agreement between numerical and experimental data. The findings confirm the feasibility of laser welding for PBT-GF30 and its potential for aerospace applications requiring precision, weight reduction, and structural reliability. Full article

Tube boilers are extensively employed in oil and gas refineries, as well as in petroleum, energy, and power generation industries, where they serve critical functions in local steam-generation units and combined-cycle gas turbine (CCGT) plants. However, these boilers are prone to defects arising from waterside corrosion (e.g., thinning of U-bend tubes), fireside corrosion, and material degradation caused by stress or creeping. Among these issues, wall thinning of tube bends is particularly severe, as it results in localized metal loss, reduced structural integrity, and an elevated risk of tube rupture or failure under high-temperature and high-pressure operating conditions. Such failures can significantly compromise boiler safety and efficiency, potentially leading to forced outages, costly unplanned repairs, or catastrophic damage if not detected in time. The current condition-monitoring policy for U-bends relies on scheduled preventive maintenance and unscheduled corrective interventions. In practice, this involves randomly checking approximately 10–20% of the tubes through spot scanning, partial scanning, or full scanning, with repairs typically carried out only after an undetected failure occurs. Such maintenance strategies generally require plant shutdowns, making the process time-consuming, labor-intensive, and ultimately not cost-effective. This paper reviews existing solutions, technologies, and research addressing the problem, and introduces femtosecond laser micromachined fiber optic sensors as a transformative approach for real-time monitoring of wall thickness reduction in U-bend boiler tubes, thereby opening pathways for further research. Full article

This paper addresses the chromatic aberration and off-axis collimation issues in the laser–lens–fiber coupling system by proposing a chromatic aberration-corrected Meta-lens design based on a particle swarm optimization algorithm and structural interleaving method. By establishing an optimization model that includes wavelength-dependent phase factors, achromatic performance with a focal length standard deviation of less than 0.4 μm is achieved in the 1260–1360 nm band. Innovatively, the structural interleaving technique is adopted to integrate multiple different phase distributions into a single meta-surface, keeping the coupling efficiency fluctuation within 8% over a ±1 μm off-axis displacement range. The research results demonstrate that this method effectively solves the phase quantization and dispersion matching challenges of large-scale meta-lens, achieving a phase matching efficiency of 95.2%, providing a feasible path for the engineering application of highly robust meta-lens in high-precision optical systems. Full article