Submissões Recentes
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Curved waveguide irradiated by femtosecond laser in Ag-doped GeO2–PbO glasses for photonic applications
2025 - FERNANDES, THIAGO V.; BORDON, CAMILA D.S.; WETTER, NIKLAUS U.; ROSSI, WAGNER de; KASSAB, LUCIANA R.P.
We demonstrate the fabrication of straight and curved dual waveguides in GeO2-PbO glasses embedded with silver nanoparticles using femtosecond laser inscription. This research includes evaluating beam quality, propagation loss, and polarization of the double-wall waveguides.
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Assessment of the surface characteristics of ISO 5832-1 stainless steel for biomaterial applications
20256 - PIERETTI, EURICO F.; PIAGGIO, DAVIDE; COSTA, ISOLDA
Marking techniques are employed to guarantee the identification and traceability of biomedical materials. This study investigated the impact of laser and mechanical marking processes on the tribological performance of ISO 5832-1 austenitic stainless steel (SS), specifically examining corrosion resistance, the coefficient of friction, and wear volume in ball-cratering wear tests. The laser marking was performed using a nanosecond Q-switched Nd:YAG laser. Cytotoxicity tests assessed the biocompatibility of the biomaterial. Non-marked surfaces were also evaluated for comparison. A phosphate-buffered saline solution (PBS) served as both the lubricant and corrosion medium. The surface finishing was analyzed using optical microscopy and scanning electron microscopy coupled with a field-emission gun (SEM-FEG), combined with an energy-dispersive X-ray spectrometer. The oxide film was examined through X-ray photoelectron spectroscopy (XPS). Wear tests lasted 10 min, with PBS drops applied every 10 s at 75 rpm; solid balls of AISI 316L stainless steel (SS) and polypropylene (PP), each 1 inch in diameter, were used as counter-bodies. Corrosion resistance was assessed using electrochemical methods. Results showed variations in roughness and microstructure due to laser marking. The tribological behaviour was influenced by the type of marking process, and the wear amount depended on the normal force and ball nature. None of the samples was considered cytotoxic, although laser-marked surfaces exhibited the lowest cellular viability among the tested surfaces and the lowest corrosion resistance.
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Characterization of a gelcast AISI 310 SS matrix composite reinforced by alumina and GNP particles
2025 - OLIVEIRA, LOUISE F.R.; ORTEGA, FERNANDO dos S.; MAGNABOSCO, RODRIGO; NEVES, MAURICIO D.M. das
Gelcasting is a versatile forming technique suitable for preparing composite materials with various powders, including metallic and ceramic particles, at any solids concentration. Despite its potential, the application of gelcasting to produce metal matrix composites reinforced with alumina and graphene remains limited. This study investigates the gelcasting of AISI 310 stainless steel composites reinforced with 1, 3, and 5 vol.% nanosized alumina and 0.5 vol.% graphene nanoplatelets (GNPs). Rheological behavior and particle interactions were analyzed to ensure uniform dispersion. Thermal analysis determined optimal sintering conditions, avoiding densification issues. Compression and microhardness tests revealed yield strengths of up to 285 MPa at room temperature (RT) and 140 MPa at 800 °C, exceeding ASTM A351/A351M-18e1 standards. Microstructural refinement and homogeneous alumina distribution were achieved, with 3 vol.% alumina providing the best performance. The gelcasting process proved effective for producing dense, mechanically robust composites at a low cost.
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Bayesian optimization of laser wakefield acceleration in the self-modulated regime (SM-LWFA) aiming to produce molybdenum-99 via photonuclear reactions
2025 - NUNES, B.S.; SANTOS, S.P.; NUNES, S.P.; BONTOIU, C.; ALVA-SANCHES, A.S.; SAMAD, R.E.; JUNIOR VIEIRA, N.D.; XIA, G.; RESTA-LOPEZ, J.; BONATTO, A.
While laser wakefield acceleration (LWFA) in the bubble regime demands ultra-short, high-peak-power laser pulses, operation in the self-modulated regime (SM-LWFA) works with more relaxed pulse conditions, albeit at the cost of lower beam quality. Modern laser systems can deliver few-terawatt pulses with tens of femtoseconds at kilohertz repetition rates. These systems are well-suited for developing SM-LWFA applications where high average energy and charge are prioritized over beam quality. Such beams could be used to generate high-energy bremsstrahlung photons, capable of triggering photonuclear reactions to produce radioisotopes like molybdenum-99. This isotope decays into technetium-99m, the most widely used medical radioisotope, with over 30 million applications worldwide per year. This work explores the use of Bayesian optimization to maximize the energy and charge of electron beams accelerated via SM-LWFA. Particle-in-cell (PIC) simulations model a 5 TW, ~60 fs-long (FWHM) Gaussian laser pulse, propagating through tailored hydrogen gas-density profiles. In these simulations, over multiple iterations, the algorithm optimizes a set of input parameters characterizing the gas-density profile and the laser focal position. Three distinct profiles, with lengths ranging from 200 to 400 μm and combining ramps and plateaus, were investigated. Optimal configurations produced electron beams with median energies ranging from 14 to 17 MeV and charges of 600 to 1300 pC, considering electrons with energies above 8 MeV. Preliminary estimates of molybdenum-99 yields for the optimal beams were obtained using their phase space data from PIC simulations as radiation sources in Monte Carlo simulations irradiating a tantalum-molybdenum target.