Search Results (494)

Conventional wavefront sensors face challenges when detecting frequency-domain information. In this study, we developed a high-precision, and fast multi-spectral wavefront detection technique based on neural networks. Using an etalon and a diffractive optical element for spectral encoding, the measured pulses were spatially dispersed onto the sub-apertures of the Shack-Hartmann wavefront sensor (SHWFS). We employed a neural network model as the decoder to synchronously calculate the multi-spectral wavefront aberrations. Numerical simulation results demonstrate that the average calculation time is 21.38 ms, with a root mean squared (RMS) wavefront residual error of approximately 0.010 μm for 4-wavelength, 21st-order Zernike coefficients. By comparison, the conventional modal-based algorithm achieves an average calculation time of 102.98 ms and wavefront residuals of 0.090 μm. Remarkably, for 10-wavelength analysis, traditional centroid algorithms fail; this approach maintains high simulation accuracy with the RMS wavefront residual error below 0.016 μm. The proposed approach significantly enhances the measurement capabilities of SHWFS in multi-spectral and single-shot wavefront detection, particularly for single-shot spatio-temporal characterization in ultra-intense and ultra-short laser systems. Full article

This work aims to maximize the Hawking emission temperature arising in the optical analog model of the event horizon of an astrophysical black hole. A weak probe wave interacts with an intense ultrashort optical pulse via the Kerr effect in a photonic crystal fiber. This interaction causes the probe wave to experience an effective spacetime geometry characterized by the presence of an optical event horizon, where the analogous Hawking radiation effect arises. Here we refer to the simulated or classical version of the analog of Hawking radiation. This study considers four distinct types of photonic crystal fibers with anomalous dispersion curves that allow for maximizing the effect. Our first three numerical simulations indicate that a Hawking emission temperature of up to 361 K can be achieved with a photonic crystal fiber with two zero-dispersion wavelengths, while the emission temperature values in the original investigation are lower than 244 K. And in the fourth, we can see that we have a configuration in which the temperature can be improved up to 1027 K. Moreover, these results also emphasize the feasibility of using analog models to test the quantum effects of gravity, such as Hawking radiation produced by typical black holes, whose magnitude is far below the temperature of the cosmic microwave background (2.7 K). Full article

Kerr nonlinear effect extremely impacts both the spectral and the temporal evolutions of ultrashort pulses, although it is challenging to tailor over a broadened spectral region. In this work, we propose an on-chip Si₃N₄-organic hybrid waveguide with sophisticated non-monotonic nonlinear coefficient γ(ω). A chirp-free pulse can be broadened or compressed at different peak powers in the normal dispersion range. The impact of the second-order Kerr nonlinearity with respect to frequency can overbalance that of dispersion. This new method deepens the understanding of the high-order nonlinear effects and help exploit innovative nonlinearity-engineered on-chip platforms for pulse shaping in the immediate future. Full article

The paper uses the model of the coupled Boltzmann transport equations, numerically modeled using the lattice Boltzmann method, which describes the impact of an ultra-short laser on thin metal surfaces. The main reason for using this method is the need to create an appropriate model on a very small scale, both in terms of space and time. In the present study, a three-dimensional model is used, for which, in the case of optimization or identification tasks, the characteristics of the obtained numerical solution are quite different from those of other numerical methods and models. The proposed and numerically implemented task of identifying parameters characterizing the laser pulse, such as the power of the stationary laser source, the laser-beam absorptivity coefficient, and the radius of the laser beam, appropriately illustrates the problem. The problem has also been solved for ideal deterministic (no noise) and randomly disturbed (with noise) values of measured temperatures. Three different optimization algorithms are used to solve the inverse task. Several variants of the identification tasks, differing in terms of the number of temperature measurement points, are solved. The results and effectiveness of the identification tasks are compared for the best solution, as well as the statistical measures. Full article

Changing the topography of electrodes by ultrafast laser ablation has shown great potential in enhancing electrochemical performance in lithium-ion batteries. The generation of microstructured channels within the electrodes creates shorter pathways for lithium-ion diffusion and mitigates strain from volume expansion during electrochemical cycling. The topography modification enables faster charging, improved rate capability, and the potential to combine high-power and high-energy properties. In this study, we present a preliminary exploration of this approach for sodium-ion battery technology, focusing on the impact of laser-generated channels on hard carbon electrodes in sodium-metal half-cells. The performance was analyzed by employing different conditions, including different electrolytes, separators, and electrodes with varying compaction degrees. To identify key factors contributing to rate capability improvements, we conducted a comparative analysis of laser-structured and unstructured electrodes using methods including scanning electron microscopy, laser-induced breakdown spectroscopy, and electrochemical cycling. Despite being based on a limited sample size, the data reveal promising trends and serve as a basis for further optimization. Our findings suggest that laser structuring can enhance rate capability, particularly under conditions of limited electrolyte wetting or increased electrode density. This highlights the potential of laser structuring to optimize electrode design for next-generation sodium-ion batteries and other post-lithium technologies. Full article

We conducted a comprehensive experimental investigation of dual-wavelength switching of 1560 nm, 75 fs pulses (referred to as signal) driven by 1030 nm, 270 fs pulses (referred to as control) using two dual-core fibers with high refractive index contrast and different levels of asymmetry. The study explores the influence of fiber length, control pulse energy, and control-signal pulse delay on switching performance. For the fiber with higher dual-core asymmetry, we achieved an exceptional switching contrast of 41.6 dB at a 14 mm fiber length, exhibiting a homogeneous character within the spectral range of 1450–1650 nm. In contrast, the study of the weaker dual-core asymmetry fiber revealed a maximum switching contrast of 10.7 dB at a 22 mm fiber length, albeit under lower control pulse energy. These observations confirm that the switching mechanism is based on the nonlinear balancing of dual-core asymmetry, wherein the control pulse induces an enhancement of the effective refractive index in the fast fiber core, facilitating the switching of the signal pulse. This work demonstrates high switching contrasts with only a 0.4–0.6 nJ control pulse energy requirement, providing experimental confirmation of a previously reported theoretical model. For the first time, the dual-wavelength switching performance of dual-core fibers with varying levels of asymmetry is compared. The results reveal key directions for the further development of dual-core fibers in view of their potential applications. Full article

The control of mechanical effects, such as shock waves, induced by ultrashort laser pulses in water is crucial for applications in biomedicine and material processing. However, optimizing these effects requires a detailed understanding of how laser parameters, particularly pulse duration, influence the underlying energy deposition mechanisms. This study systematically investigates the dependence of shock wave amplitude on fluence (up to 10 J/cm²) and pulse duration (200 fs to 10 ps) of near-infrared laser pulses under tight focusing conditions (Numerical aperture NA = 0.42), using a combined experimental and numerical approach based on the dynamical rate equation model. Our key finding is that the shock wave amplitude is governed by the total kinetic energy of the electrons in the laser-induced plasma, leading to a distinct maximum at approximately 5 ps (confidence interval: 4.5–5.5 ps) and saturation at fluences ~7 J/cm². This optimum arises from a balance between the increasing effectiveness of avalanche ionization for longer pulses and the competing effects of electron recombination and reduced photoionization efficiency. Consequently, these results identify a practical parameter window—pulse durations of 4–6 ps at moderate fluences—for optimizing laser-induced mechanical effects in applications such as laser surgery in aqueous media. Full article

Carbon-fiber-reinforced plastic (CFRP) machining by ultrashort-pulse lasers promises high precision but is limited due to the heterogeneous epoxy–carbon fiber structure, which creates heat-affected zones and variable kerf quality. This work investigates synthesized copper hydroxyphosphate as a laser-absorbing additive to improve femtosecond (1030 nm) laser ablation of CFRP. Copper hydroxyphosphate particles were synthesized hydrothermally and incorporated into an epoxy matrix to produce single-ply CFRP laminates. Square patterns (0.5 × 0.5 mm) were ablated with a pulse energy of 0.5–16 μJ. Then, ablated volumes were profiled and materials characterized by SEM and EDS. In neat epoxy the copper additive reduced optimum ablation efficiency and decreased penetration depth, while producing smoother, less porous surfaces. In contrast, CFRP with copper hydroxyphosphate showed increased efficiency and higher penetration depth. SEM and EDS analyses indicate more uniform matrix removal and retention of resin residues on fibers. These results suggest that copper hydroxyphosphate acts as a local energy absorber that trades volumetric removal for improved surface quality in epoxy and enhances uniformity and process stability in CFRP femtosecond laser machining. Full article

Automatic mode-locking is a crucial approach for achieving ultrashort pulses in fiber lasers. Here, a random search algorithm was developed, and an automatic mode-locked laser was constructed. Numerical simulations of an automatic mode-locked Yb-doped fiber laser were conducted, and both continuous-wave, as well as mode-locked pulse states, were successfully obtained. The laser utilized a squeezer-type electrically controlled polarization controller to adjust the mode-locking states and enabled the controllable output of 532.71 fs dissipative solitons and 23.87 ps noise-like pulses, with search times of 14.19 s and 2.37 s, respectively. The center wavelengths were 1034 nm and 1038 nm, with signal-to-noise ratios of 63.1 dBm and 51.2 dBm, respectively. This work effectively addresses the polarization state drift caused by temperature and vibration, enhancing the laser’s environmental adaptability through adaptive monitoring. Full article

Ultrashort pulsed laser annealing is an efficient technique for crystallizing amorphous semiconductors with the possibility to obtain polycrystalline films at low temperatures, below the melting point, through non-thermal processes. Here, a multilayer structure consisting of alternating amorphous silicon and germanium films was annealed by mid-infrared (1500 nm) ultrashort (70 fs) laser pulses under single-shot and multi-shot irradiation conditions. We investigate selective crystallization of ultrathin (3.5 nm) a-Ge non-hydrogenated films, which are promising for the generation of highly photostable nanodots. Based on Raman spectroscopy analysis, we demonstrate that, in contrast to thicker (above 10 nm) Ge films, explosive stress-induced crystallization is suppressed in such ultrathin systems and proceeds via thermal melting. This is likely due to the islet structure of ultrathin films, which results in the formation of nanopores at the Si-Ge interface and reduces stress confinement during ultrashort laser heating. Full article

The combination of polypyrrole (PPy) with graphene has attracted extensive attention as a nonlinear optical material with various optoelectronic applications. Here, we describe the development of PPy nanoplates prepared using a simple spin-coating method. The appropriate volume of the dropped PPy solution was determined to be 50 drops by comparing the surface morphologies, chain structures, elementary compositions, and optical properties of PPy saturable absorbers (SAs). The hybrid PPy/graphene heterostructure SA was obtained using the wet transfer process of a graphene layer. This approach led to significant improvements in optical properties, including a ~7.2% increase in linear optical absorption, a 2.5-fold increase in modulation depth, and a third decrease in saturable intensity at 1550 nm due to the additional optical absorption and the π-π interaction between PPy nanoplates and the graphene layer. By inserting the PPy/graphene heterostructure SA into the passively mode-locked fiber laser cavity, 1559 nm ultrashort laser pulses were generated, with an average output power of 1.24 mW, a 815 fs pulse width, and a repetition frequency of 3.26 MHz. Our experimental results demonstrate that the prepared PPy SA has excellent nonlinear optical characteristics, providing a new opportunity for the generation of ultrashort laser pulses. Full article

Microfluidic device prototyping demands rapid, cost-effective, and high-precision mould fabrication, yet ultrashort pulsed laser structuring of polymer inserts remains underexplored. This study presents a novel method for fabricating microfluidic mould inserts using femtosecond (fs) laser ablation of polyimide (PI) films, achieving high precision from design to prototype. PI films (250 µm) were structured using a 355 nm fs laser (300 fs, 500 kHz, 0.95 J/cm²) in a photochemically dominated ablation regime and bonded to reusable steel plates. Injection moulding trials with cyclic olefin copolymer (COC) and polymethyl methacrylate (PMMA) were conducted with diverse designs, including concentration gradient generators (CGG), organ-on-chip (OOC) with 20 µm bridges, and double emulsion droplet generators (DEDG) with 100–500 µm channels, ensuring robustness across complex geometries. The method achieved near 1:1 replication (errors < 2%, microchannel height tolerances < 1%, Sa = 0.02 µm in channels, 0.26 µm in laser-structured areas), machining times under 2 h, and mould durability over 100 cycles without significant deterioration. The PI’s heat-retarding effect mimicked variothermal moulding, ensuring complete micro-penetration without specialised equipment. By reducing material costs using PI films and reusable steel plates, enabling rapid iterations within hours, and supporting industry-compatible prototyping, this approach lowers barriers for small-scale labs. It enables rapid prototyping of diagnostic lab-on-chip devices and supports decentralised manufacturing for biomedical, chemical, and environmental applications, offering a versatile, cost-effective tool for early-stage development. Full article

In this study, we examine the characteristics of laser-induced periodic surface structures (LIPSSs) fabricated on N-doped 4H-SiC (N-SiC) and high-purity 4H-SiC (HP-SiC) crystals using femtosecond–picosecond lasers. The effects of various laser parameters on the orientation, size, and morphology of the LIPSS are systematically investigated. The results reveal that, under identical laser irradiation conditions, the area of LIPSS on both N-SiC and HP-SiC increases linearly with the number of pulses, with N-SiC exhibiting a higher growth coefficient. Furthermore, analysis of differences in photothermal weak absorption and electric field modulation during the LIPSS fabrication process indicates that distinct SiC crystals yield varied LIPSS formation outcomes. This work not only elucidates the underlying physical mechanisms governing LIPSS formation on different silicon carbide crystal surfaces but also provides valuable guidance for precisely controlling the size and orientation of LIPSS regions on various 4H-SiC substrates. Full article

Glass, as an amorphous material with excellent optical transparency and chemical stability, plays an irreplaceable role in modern engineering and technology fields such as semiconductor manufacturing and micro-electro-mechanical systems (MEMS). For example, borosilicate glass, with a coefficient of thermal expansion (CTE) that is close to having good thermal shock resistance and chemical stability, can be applied to MEMS packaging and aerospace fields. SiO₂ glass exhibits excellent thermal stability, extremely low optical absorption, and high light transmittance, while also possessing strong chemical stability and extremely low dielectric loss. It is widely used in semiconductors, photolithography, and micro-optical devices. However, the stress sensitivity of traditional mechanical joints and the poor weather resistance of adhesive bonding make conventional methods unsuitable for glass joining. Welding technology, with its advantages of high joint strength, structural integrity, and scalability for mass production, has emerged as a key approach for precision glass joining. In the field of glass welding, technologies such as glass brazing, ultrasonic welding, anodic bonding, and laser welding are being widely studied and applied. With the advancement of laser technology, laser welding has emerged as a key solution to overcoming the bottlenecks of conventional processes. This paper, along with the application cases for these technologies, includes an in-depth study of common issues in glass welding, such as residual stress management and interface compatibility design, as well as prospects for the future development of glass welding technology. Full article

Noise interference and multipath effects in complex marine environments seriously constrain the performance of hydroacoustic positioning systems. Traditional millisecond-level signal application and processing methods are widely used in existing research; however, it is difficult to meet the requirements of centimeter-level positioning accuracy in marine engineering. To address this problem, this study proposes a hydroacoustic positioning method based on a short baseline system for the cooperative reception of multi-channel signals. The method adopts ultra-short pulse signals with microsecond pulse width, and significantly improves the system signal-to-noise ratio and anti-interference capability through multi-channel signal alignment and coherent superposition techniques; meanwhile, a joint energy gradient-phase detection algorithm is designed, which solves the instability problem of the traditional cross-correlation algorithm in the detection of ultra-short pulse signals through the identification of signal stability intervals and accurate phase estimation. Simulation verification shows that the 8-hydrophone × 4-channel configuration can achieve 36.06% signal-to-noise gain under harsh environmental conditions (−10 dB), and the performance of the joint energy gradient-phase detection algorithm is improved by about 19.1% compared with the traditional method in an integrated manner. Marine tests further validate the engineering practicability of the method, with an average SNR gain of 2.27 dB achieved for multi-channel signal reception, and the TDOA estimation stability of the new algorithm is up to 32.0% higher than that of the conventional method, which highlights the significant advantages of the proposed method in complex marine environments. The results show that the proposed method can effectively mitigate the noise interference and multipath effects in complex marine environments, significantly improve the accuracy and stability of hydroacoustic positioning, and provide reliable technical support for centimeter-level accuracy applications in marine engineering. Full article