Search Results (254)

The 795 nm wavelength corresponds to the D1 transition of rubidium atoms and is widely used in atomic optical pumping, atomic clocks, magnetometers, and precision spectroscopy. For compact free-space collimation, beam shaping, and efficient fiber coupling, edge-emitting semiconductor lasers with reduced fast-axis (vertical) divergence are highly desirable, yet low-divergence designs at 795 nm remain limited. Here, we propose and demonstrate low-divergence photonic-crystal epitaxy (LD–PC) for 795 nm edge-emitting lasers. By engineering a periodic n-side photonic-crystal stack to place the fundamental vertical mode near the photonic band edge, the vertical mode is expanded while maintaining effective modal discrimination. Narrow-ridge Fabry–Pérot lasers based on GaAsP/AlGaAs single-quantum-well epitaxy were fabricated and characterized. The optimized LD–PC device (3 μm ridge width, 1 mm cavity length) delivers 227 mW at 200 mA with a threshold current of 23 mA, a slope efficiency of 1.28 W/A, and a peak wall-plug efficiency of 55% under continuous-wave operation at 25 °C. The measured far-field divergences (FWHMs) are 7.16° and 18.83° in the lateral and vertical directions, respectively, corresponding to a reduction in the vertical divergence from >40° in the reference structure to <20° with LD–PC. These results validate photonic-crystal epitaxy as an effective route toward compact, high-performance, low-divergence 795 nm semiconductor laser sources for rubidium-based atomic systems. Full article

This paper demonstrates a C-band continuously tunable mode-locked fiber laser based on a carbon nanotube saturable absorber (CNT-SA) and a commercial broadband tunable filter. The laser operates in the C-band with a continuous tuning range of 37.3 nm from 1532.6 nm to 1569.9 nm. The erbium-doped fiber (EDF) has a wide gain range, enabling the laser to achieve ultrafast mode-locking. Meanwhile, the tunable filter offers a broad wavelength selection range. This continuously tunable mode-locked fiber laser features a simple structure and a broad operating wavelength range, making it highly suitable for applications in optical communication, sensing, and laser processing. Full article

We report on sub-50 fs pulse generation from a diode-pumped mode-locked laser based on an ytterbium-doped monoclinic potassium yttrium double tungstate crystal operating in the 1 μm spectral region. Pumping by a low-power, spatially single-mode, fiber-coupled laser diode at 976 nm, a maximum continuous-wave output power of 433 mW at 1066.1 nm was obtained. Using a quartz-based intracavity Lyot filter, an exceptionally broad continuous-wavelength tuning range of 98 nm was achieved. In the mode-locked regime, the diode-pumped Yb:KY(WO₄)₂ laser delivered soliton pulses as short as 46 fs at a central wavelength of 1069.2 nm by employing a SEmiconductor Saturable Absorber Mirror. To the best of our knowledge, these results represent the broadest continuous-wave tuning range and the shortest pulse duration ever reported for lasers based on ytterbium-doped monoclinic double tungstate crystals. Full article

Thermally grown amorphous SiO₂ (a-SiO₂) on Si is widely used in microfluidic and biointerface devices, where surface charge governs capillary flows. We used amplitude-modulation Kelvin probe force microscopy (AM-KPFM) in air to test whether low-power visible light modulates a-SiO₂ surface potential and to derive mathematical charging-discharging models. Single-point contact potential difference (CPD) was recorded on ~0.6 µm p-type a-SiO₂ on p-type monocrystalline Si during repeated illumination cycles with continuous-wave diode lasers at 405, 505, and 685 nm delivered by optical fiber. The 405 and 505 nm wavelengths produced reproducible negative CPD shifts with steady-state values of ~−28 mV and ~−16 mV, while 685 nm stayed within noise (±2.5 mV). The 405 nm response followed bi-exponential kinetics with fast (tens of seconds) and slow (hundreds of seconds) components dominated by the slow process; after switch-off, CPD relaxed only from ~−28 to ~−23 mV over ~10³ s, indicating retention for ≥10³–10⁴ s. The 505 nm charging trace fit a single slower xponential, whereas discharging could not be fit robustly. These results demonstrate wavelength-dependent optical tuning of a-SiO₂ surface potential and provide compact kinetic descriptors for comparing charging, discharging, and retention. Full article

Transverse mode instability (TMI) in high-power ytterbium-doped double-clad fiber lasers is widely interpreted as being a consequence of a thermo-optic nonlinear phenomenon driven by stimulated thermal Rayleigh scattering. This work presents a coupled optical–thermal model for a continuous-wave forward-pumped (${\lambda }_p=976\mathrm{nm}$) fiber amplifier emitting at ${\lambda }_s=1064\mathrm{nm}$ over an optimal length of 12 m. The formulation explicitly resolves the three radial regions of a double-clad fiber, avoiding single-clad approximations. Modal fields are computed using the weakly guiding approximation (WGA) in the core combined with the semi-WGA at the cladding interfaces, enabling accurate calculation of higher-order modes of penetration into the inner cladding and of the transverse eigenvalues $U_{01}$ and $U_{mn}$ relevant to TMI. Within this framework, the nonlinear stimulated thermal Rayleigh scattering coupling coefficient is evaluated, including gain saturation and the thermal eigenmodes of the multi-layer geometry. The results show that the inner cladding modifies both the optical and thermal mode structures, altering the optical–thermal overlap between ${\mathrm{LP}}_{01}$ and higher-order modes and changing the effective strength of STRS, directly influencing the predicted TMI threshold. The proposed formulation provides a quantitative and physically consistent tool for analyzing thermo–optic dynamics in Yb-double-clad fiber amplifiers and supports the design of next-generation high-power fiber lasers with improved modal stability. Full article

Microplastics (<5 mm) are an increasing concern for environmental and human health, continuously detected in ecosystems worldwide and a variety of human tissues. While health effects remain unclear, experimental studies on microplastic particles have suggested adverse outcomes. Microplastic fibers, which shed from everyday items, are more toxic than particles and twice as prevalent, yet remain understudied. Microplastic studies vary widely and use various extraction techniques, with few validating recovery accuracy. These limited recovery studies primarily examine particles, raising concerns about the true abundance of microfibers. This study establishes baseline recovery rates of polyethylene terephthalate (PET) and polypropylene (PP) microfibers of varying lengths from formalin-fixed human cadaveric lung tissue. Following enzymatic and oxidative digestion, PET microfibers showed a recovery rate of 47%, while 87% of PP microfibers was recovered. Chemical alterations were assessed using laser direct infrared (LDIR) spectroscopy; optical microscopy and scanning electron microscopy (SEM) evaluated physical changes post-digestion. These findings provide insights into microfiber recovery, highlight potential over- and underestimations, and characterize the chemical and physical behavior of fibers within human tissue studies. Establishing accurate recovery methods is essential for advancing microfiber toxicology research and assessing potential health risks. Full article

Background: Endoscopic kidney-sparing surgery (eKSS) is increasingly adopted for the management of selected patients with upper tract urothelial carcinoma (UTUC). Laser energy is central to tumor ablation during eKSS; however, multiple laser platforms with distinct physical and thermal properties are currently available, and their comparative oncological and safety profiles remain poorly defined. This systematic review aims to summarize the available evidence on oncological outcomes and perioperative complications associated with laser-based endoscopic treatment of UTUC and to explore potential differences according to laser technology. Methods: A systematic literature search identified 25 eligible studies published between 1997 and 2024, including 1344 patients treated with laser-assisted eKSS. All included studies were non-randomized, predominantly retrospective, and characterized by moderate-to-serious risk of bias. Holmium:YAG, Thulium:YAG (thu:YAG, continuous-wave and pulsed), thulium fiber laser (TFL), Neodimio:YAG (Nd:YAG), diode lasers, and combination platforms were reported. Results: Ipsilateral upper tract recurrence was common across all laser categories, with weighted proportions ranging approximately from 27% to 52% and substantial inter-study heterogeneity. Progression and conversion to radical nephroureterectomy (RNU) were relatively infrequent overall, with numerically weighted proportions observed in thu:YAG-based cohorts. Major complications (Clavien–Dindo ≥ III) were rare across all laser technologies, although a trend toward a higher weighted proportions was observed in Ho:YAG- and Nd:YAG-based series. Minor complications were more frequently reported and highly heterogeneous. Conclusions: Available evidence supporting laser selection in endoscopic kidney-sparing management of UTUC is limited and largely descriptive. Thulium:YAG and TFL platforms seem to demonstrate encouraging trends toward lower progression and conversion to-radical-nephroureterectomy rates; however, these findings are derived from heterogeneous, non-comparative studies with limited follow-up. No standard laser platform can currently be recommended over others based on existing data. Prospective, comparative, and methodologically robust studies are required to determine whether laser technologies confer clinically meaningful advantages in oncological control or safety for UTUC treated with eKSS. Full article

This article investigates fiber coupling techniques for low numerical aperture 808 nm semiconductor lasers. A coupling optical system combining fast-axis/slow-axis collimators (FAC/SAC) with a focusing lens was designed, achieving efficient coupling through high-precision optical integration packaging. First, a high-power GaAs-based 808 nm semiconductor laser chip was designed and fabricated. Its thermal performance and operational stability were enhanced by optimizing packaging materials and structures. The coupling system employs a fast-axis collimating lens, slow-axis collimating lens, and aspheric focusing lens to shape the beam and focus it into a 200 μm/0.12 NA fiber. Experimental results show that the developed coupling module achieves the threshold current of 1.2 A at 298 K, the continuous output power of 9.59 W, with the slope efficiency of 1.1 W/A, a coupling efficiency of 95%, the maximum output numerical aperture of 0.116, the wavelength temperature drift coefficient of approximately 0.2 nm/°C, and the peak brightness of 0.72 MW/cm²·sr. This study validates the feasibility and superiority of the FAC/SAC combined with focusing lens approach for low-NA fiber coupling. It provides theoretical and practical foundations for fiber coupling in high-brightness, high-power laser systems, offering promising applications in solid-state laser pumping, enhancing system integration, and enabling long-distance, high-brightness transmission. Full article

Laser slicing of 4H-SiC wafers offers high efficiency and minimal material loss. While nanosecond lasers are the preferred light source, simultaneously achieving high output power, excellent beam quality (M² < 1.3), and broad operational tunability remains an outstanding challenge. This study developed a highly efficient nanosecond laser source using hybrid fiber and solid-state multi-stage amplification architecture. With excellent beam quality (M² < 1.3), it achieves the highest output power, widest continuously tunable pulse width range, and broadest repetition rate range currently reported for 4H-SiC laser slicing. This advancement is poised to advance the continued development of 4H-SiC slicing technology. Full article

Excimer Laser Coronary Atherectomy (ELCA) has re-emerged as a valuable adjunctive modality in percutaneous coronary intervention (PCI), particularly in the context of increasingly complex coronary anatomy and rising procedural expectations. By delivering pulsed ultraviolet energy at 308 nm through flexible fiber-optic catheters, ELCA enables precise photochemical, photothermal, and photomechanical ablation of atherosclerotic, fibrotic, calcified, and thrombotic tissue while minimizing thermal injury to surrounding structures. Recent technical refinements, simplified catheter designs, and improved safety profiles have enhanced its feasibility and utility across a range of challenging lesion subsets. This review summarizes the fundamental principles underlying excimer laser–tissue interaction, discusses available equipment and key procedural considerations, and examines the expanding clinical evidence supporting ELCA in contemporary practice. Data from observational studies and multicenter registries suggest that ELCA may enhance device crossability, restore coronary flow, and reduce distal embolization in thrombus-rich lesions, particularly during primary PCI. In device-uncrossable lesions, ELCA facilitates plaque modification and improves procedural success, including in chronic total occlusions. Furthermore, ELCA—especially when performed with simultaneous contrast injection—has demonstrated efficacy in treating stent underexpansion refractory to high-pressure balloon dilation, improving minimal stent area and enabling optimal post-dilatation. As lesion complexity continues to increase, ELCA is gaining recognition as an important tool within the interventional armamentarium. While generally safe in experienced hands, ELCA carries a risk of procedural complications that must be carefully considered. Ongoing investigations are expected to further define its optimal use and reinforce its relevance in modern interventional cardiology. Full article

This work presents a combined numerical and experimental investigation into the laser machining of aluminum alloy Al 1050 H14 using a high-power Continuous Wave (CW) fiber laser. Advanced three-dimensional, coupled thermal–structural Finite Element Method (FEM) simulations are developed to model key laser–material interaction processes, including laser-induced plastic deformation, laser etching, and engraving. Cases for both static single-shot and dynamic linear scanning laser beams are investigated. The developed numerical models incorporate a Gaussian heat source and the Johnson–Cook constitutive model to capture elastoplastic, damage, and thermal effects. The simulation results, which provide detailed insights into temperature gradients, displacement fields, and stress–strain evolution, are rigorously validated against experimental data. The experiments are conducted on an integrated setup comprising a 2 kW TRUMPF CW fiber laser hosted on a 3-axis CNC milling machine, with diagnostics including thermal imaging, thermocouples, white-light interferometry, and strain gauges. The strong agreement between simulations and measurements confirms the predictive capability of the developed FEM framework. Overall, this research establishes a reliable computational approach for optimizing laser parameters, such as power, dwell time, and scanning speed, to achieve precise control in metal surface treatment and modification applications. Full article

We propose an external-cavity laser that combines wide tunability with narrow linewidth. The design utilizes a low-loss Si₃N₄ waveguide and a thermally tuned cascaded triple-ring resonator to enable continuous wavelength tuning. The numerical simulations indicate that the proposed laser exhibits a tuning range of 64 nm with a sub-kHz linewidth, an SMSR of more than 80 dB, an output power of 24 mW and a linewidth of 193 Hz at 1550 nm. Furthermore, we perform comparative system-level simulations using QPSK and 16QAM coherent optical fiber links at 50 Gbaud over 100 km. Under identical conditions, when the laser linewidth is reduced from 1 MHz level to 193 Hz, the BER of 16QAM decreases from 1.5 × 10⁻³ to 5.3 × 10⁻⁵. These results indicate that a narrow linewidth effectively mitigates phase noise degradation in high-order modulation formats. With its narrow linewidth, wide tuning range, high SMSR, and high output power, this laser serves as a promising on-chip light source for high-resolution sensing and coherent optical communications. Full article

Background and Objectives: This prospective case series evaluated a treatment strategy in endodontic-periodontal lesions resulting from concurrent pulpal and periodontal infections. These present significant management challenges, particularly when they exhibit resistance to standard treatment modalities. Persistent microbial biofilms in regions like dentinal tubules and lateral canals can make it hard for healing to happen, even with good endodontic and periodontal care. Diode lasers have antibacterial and photobiomodulatory effects, but they are most often used as single-stage disinfection techniques. This pilot study evaluated a multi-stage diode laser protocol designed to enhance healing outcomes in refractory endo-perio lesions that had not responded to conventional treatment. Materials and Methods: Twelve patients (aged 20–60 years) with chronic endo-perio lesions, referred after unsuccessful earlier treatment, were treated utilizing a sequential diode laser regimen: Phase 1—Endodontic disinfection: Following canal instrumentation (0.75 W, pulsed mode, frequency 15 Hz, 200 μm fiber, 15 J dosage/20 s) using a 976 nm diode laser. Phase 2—Periodontal disinfection: Following SRP, intra-pocket (0.75 W, pulsed mode, frequency 15 Hz, 300 μm fiber, 3.75 J dosage/5 s) using a 976 nm diode laser; Phase 3—Post treatment photobiomodulation: After periodontal and endodontic therapy, photobiomodulation was applied using a 650 nm diode laser intra-pocket and in the periapical region (25 mW, continuous mode, 1.5 J dosage) to reduce postoperative inflammation and stimulate healing. Clinical parameters—probing depth (PD), bleeding on probing (BOP), and mobility—along with radiographic bone fill were recorded at baseline and after 6 months. Results: All twelve cases showed measurable within-patient improvements over the six-month follow-up. Median probing depth decreased from 7.6 mm to 6.0 mm, and median bleeding on probing declined from 0.9 to 0.3. Radiographically, partial bone fill was observed in all cases, with a median value of 58.3 percent. Postoperative pain decreased progressively over the first 24 h, with patients reporting mild discomfort by 24 h. No adverse events were recorded. Conclusions: Within the limitations of this small, uncontrolled pilot study, the multi-stage diode laser protocol was associated with clinical and radiographic improvements and low postoperative discomfort in refractory endo-perio lesions. These preliminary findings suggest that such a protocol may serve as a useful adjunct to conventional therapy. Larger, controlled studies are required to confirm these outcomes and determine long-term efficacy. Full article

We experimentally and through simulations demonstrate a passively mode-locked fiber laser based on nonlinear polarization rotation, which generates the evolution from h-shaped pulses to GHz harmonic trains. When the polarization angle is continuously changed, the h-shaped pulse sequentially evolves into multiple pulses, bunched solitons, and harmonic pulses. The maximum order of harmonic trains obtained in experiments is 120, corresponding to the repetition frequency of 1.03996 GHz. The coupled Ginzburg-Landau equation and two-time-scale approach to gain is provided to characterize the laser physics. The fast and slow evolution of gain contributes to the stabilization and length of one soliton pattern, respectively. The proposed fiber laser is cost effective and easy to implement, providing a potential way to study soliton dynamics in depth. Full article

We demonstrate a 1.5 μm methane-filled hollow-core fiber (HCF) amplifier that delivers 7.1 W of narrow-linewidth (<0.1 nm), near-diffraction-limited (M² < 1.2) pulsed Raman output. The system is pumped by a 1064 nm pulsed fiber laser and amplifies a 1543 nm continuous-wave seed via stimulated Raman scattering in methane. Using a 45-m HCF, we systematically investigated the influence of seed injection on key laser characteristics, covering the spectral profile, power scaling, and beam properties. This work provides an effective strategy for realizing high-performance fiber lasers in the 1.5 μm band. Full article