http://hdl.handle.net/10366/133237 Sat, 09 May 2026 15:14:54 GMT 2026-05-09T15:14:54Z http://hdl.handle.net/10366/171245 [EN]In this Letter we report the demonstration of the first cyan Pr-based waveguide laser, fabricated inscribing depressed-cladding waveguides in Pr:Ba(Y0.8Lu0.2)2F8 by direct femtosecond laser writing. With an optimized waveguide geometry for the monoclinic crystal matrix, we demonstrate lasing at 495 nm, observing a maximum output power of 22 mW and a maximum slope efficiency of 7% in a compact 6 mm-long laser cavity. These values are comparable with those reported in the literature for solid-state devices based on bulk crystals. Incidentally, this is also the first, to our knowledge, demonstration of a waveguide visible laser based on a monoclinic crystal matrix. Sat, 01 Nov 2025 00:00:00 GMT http://hdl.handle.net/10366/171245 2025-11-01T00:00:00Z http://hdl.handle.net/10366/171244 [EN]Ultrafast-laser inscription enables the fabrication of three-dimensional photonic microstructures in laser-active dielectric crystals, yet the interplay between geometry and laser-induced refractive-index changes remains insufficiently quantified. We investigate depressed-cladding waveguides written in a uniaxial Er3+:LiYF4 fluoride crystal using spatially resolved confocal luminescence and Raman spectroscopy with sub-micrometric resolution. The measurements reveal partial amorphization within the irradiated zones, as well as a complex distribution of local stress fields—compressive within the cladding and tensile at the periphery of the core. These stress patterns, and the associated refractive-index modifications, are found to be highly sensitive to the cladding geometry. From the spectroscopic analysis, we estimate a maximum compressive stress of 1 GPa and a refractive-index change of −2.6 × 10−3 for the e-wave within the damage tracks. Complementary differential interference contrast (Nomarski) microscopy yields quantitative maps of stress-induced birefringence, on the order of 10−6—well below the intrinsic birefringence of LiYF4 and therefore not detrimental to the polarization properties of laser waveguides. Based on these findings, we provide design guidelines for optimizing mid-infrared waveguide structures. Sun, 01 Mar 2026 00:00:00 GMT http://hdl.handle.net/10366/171244 2026-03-01T00:00:00Z http://hdl.handle.net/10366/171243 [EN]In this work we present the power scaling of diode-pumped waveguide lasers fabricated in a Pr:LiLuF4 crystal by direct femtosecond writing. We demonstrated a maximum output power of 360 mW at 604 nm, 420 mW at 721 nm, and 55 mW at 523 nm. Moreover, we demonstrated what we believe to be the first operation of a waveguide laser at 545 nm. In the end, we achieved stable lasing at 604 nm with an extraction of 96%, demonstrating the high gain achievable in waveguide devices. Sat, 01 Feb 2025 00:00:00 GMT http://hdl.handle.net/10366/171243 2025-02-01T00:00:00Z http://hdl.handle.net/10366/170600 [EN]Cemented carbides exhibit an outstanding performance as materials for tools and components. As applications of these materials become more and more challenging, complex tool geometries are often needed to suit the extreme requirements. Within this context, Additive Manufacturing (AM) has emerged as a popular option, as they combine a group of processing techniques involving layer-by-layer printing. In general, AMed samples are expected to exhibit characteristics linked to the layer-by-layer wise shaping route; and hence, a dependence of the mechanical properties on layer directionality may come out. It is then the main objective of this study to investigate, document and understand the fracture behavior of WC-12wt.Co samples fabricated via binder jetting printing (BJT), as a function of layer assemblage orientation. In doing so, specimens corresponding to four combinations of two printing directions and two testing configurations were studied. Use of samples micronotched by means of ultrashort pulsed laser ablation allowed to conclude that, similar to microstructure and hardness, fracture toughness of BJT cemented carbides exhibits an isotropic behavior. However, this is not the case for flexural strength, property for which a strong dependence on the relative orientation of layer assemblage is assessed. In this regard, higher strength and wider data dispersion are attained as loading is applied perpendicular to planes containing layer interfaces, as compared to the parallel case. Similar characteristic strength levels together with relatively lower Weibull modulii, as compared to conventionally manufactured WC-Co grades with similar microstructures, are determined. Extensive and detailed fractographic inspection of broken surfaces allows to conclude that specific location, orientation and distribution of flaws intrinsic to layer interfaces as well as printing route followed, depending on testing configuration, are key factors for defining strength level and dispersion in each case. Tue, 01 Apr 2025 00:00:00 GMT http://hdl.handle.net/10366/170600 2025-04-01T00:00:00Z http://hdl.handle.net/10366/170599 [EN]WC-Co cemented carbides, commonly known as hardmetals, are composite materials constituted by hard ceramic particles embedded in a ductile metal matrix. Due to their unique microstructural assemblage, these materials exhibit excellent combinations of hardness, strength, and toughness, consolidating them as a first choice for tools, structural and wear components. During recent decades, extensive research and technological advancements have driven the development of alternative cemented carbide grades, where traditionally used WC or Co are partially or entirely replaced. Within this context, hardmetals containing a third γ-phase (mixed cubic carbides) represent an interesting alternative. However, accurate evaluation of their fracture toughness remains a significant issue, especially as conventional methods using either indentation or precracking approaches are limited by either restricted implementation of fracture mechanics analysis or testing challenges. Within this context, this study proposes, implements, and validates the use of a novel laser-micronotching methodology to evaluate the fracture toughness of a γ-phase containing cemented carbide grade. For comparison purposes, the investigation also includes assessment of such a property by means of two other well-established testing methodologies. Moreover, similar experimental work was conducted in a plain WC-Co system with similar microstructural features. It is shown that machining of a through-thickness micronotch by means of ultra-short pulsed laser ablation is a reliable and efficient method for fracture toughness evaluation of γ-phase containing hardmetals. The main reason behind this is its capability for providing a precise and reproducible micronotch, with minimal thermal damage, that finally acts as a real through-thickness crack for which a stress-intensity factor is well-defined under flexural testing. Furthermore, toughness values obtained are in satisfactory agreement with those determined using precracked specimens with machined large notches and/or indentation techniques. Sat, 01 Mar 2025 00:00:00 GMT http://hdl.handle.net/10366/170599 2025-03-01T00:00:00Z http://hdl.handle.net/10366/170597 [EN]An effective post-compression scheme requires a good compression system to generate the desired ultrashort pulse. In this work, we demonstrate that a compressor based on a pair of grisms, with an additional piece of dispersive glass, is able to shorten pulses coming from an all-bulk multipass cell post-compression setup to temporal profiles very close to the transform limited one. This proposal paves the way for the design of compressors, not based on chirped mirrors, with excellent performance. Sat, 01 Mar 2025 00:00:00 GMT http://hdl.handle.net/10366/170597 2025-03-01T00:00:00Z http://hdl.handle.net/10366/170595 [EN]We present a detailed numerical study of ultrashort pulse compression using a three-stage hybrid all-bulk multipass cell scheme. By operating in the enhanced frequency chirp regime, we achieve the compression of pulses from around 180 fs to 4 fs pulse duration (a total compression factor above 45), with side lobes contributing with intensity values lower than 0.3 % of the peak intensity. Optimal conditions for the enhanced frequency chirp regime propagation have been identified, enabling smooth spectral broadening and high-quality temporal profiles. The first two stages are based on bulk multipass cells to achieve a controlled spectral broadening, while the third stage consists of a thin plate to reach the spectral broadening needed for few cycle pulses without leaving the enhanced frequency chirp regime. Thu, 01 May 2025 00:00:00 GMT http://hdl.handle.net/10366/170595 2025-05-01T00:00:00Z http://hdl.handle.net/10366/170575 [EN]Wavefront reconstruction is a critical component in various optical systems, including adaptive optics, interferometry, and phase contrast imaging. Traditional reconstruction methods often employ either the Cartesian (pixel) basis or the Zernike polynomial basis. While the Cartesian basis is adept at capturing high-frequency features, it is susceptible to overfitting and inefficiencies due to the high number of degrees of freedom. The Zernike basis efficiently represents common optical aberrations but struggles with complex or non-standard wavefronts such as optical vortices, Bessel beams, or wavefronts with sharp discontinuities. This paper introduces a novel approach to wavefront reconstruction using an over-complete phase dictionary combined with sparse representation techniques. By constructing a dictionary that includes a diverse set of basis functions-ranging from Zernike polynomials to specialized functions representing optical vortices and other complex modes-we enable a more flexible and efficient representation of complex wavefronts. Furthermore, a trainable rigid transform is implemented to account for misalignment. Utilizing principles from compressed sensing and sparse coding, we enforce sparsity in the coefficient space to avoid overfitting and enhance robustness to noise. Mon, 24 Mar 2025 00:00:00 GMT http://hdl.handle.net/10366/170575 2025-03-24T00:00:00Z http://hdl.handle.net/10366/169902 [EN]In this Letter we report the realization of a femtosecond-laser-written diode-pumped Pr:LiLuF4 visible waveguide laser. The waveguide studied in this work consisted of a depressed-index cladding, whose design and fabrication were optimized to minimize the propagation loss. Laser emission has been achieved at 604 nm and 721 nm, with output power of 86 mW and 60 mW, respectively, and slope efficiencies of 16% and 14%. In addition, we obtained, for the first time in a praseodymium-based waveguide laser, stable continuous-wave laser operation at 698 nm (3 mW of output power and 0.46% of slope efficiency), corresponding to the wavelength necessary for the clock transition of the strontium-based atomic clock. The waveguide laser emission at this wavelength is mainly in the fundamental mode (i.e., the larger propagation constant mode) showing a nearly Gaussian intensity profile. Wed, 01 Mar 2023 00:00:00 GMT http://hdl.handle.net/10366/169902 2023-03-01T00:00:00Z http://hdl.handle.net/10366/169901 [EN]We report on the complete temporal characterization of ultrashort pulses, generated by resonant dispersive wave emission in gas-filled hollow-capillary fibers, with energy in the microjoule range and continuously tunable from the deep-ultraviolet to the ultraviolet. Temporal characterization of such ultrabroad pulses, particularly challenging in this spectral region, was performed using an all-in-vacuum setup for self-diffraction frequency resolved optical gating (SD-FROG). Sub-3-fs pulses were measured, tunable from 250 nm to 350 nm, with a minimum pulse duration of 2.4 ± 0.1 fs. Sat, 01 Jul 2023 00:00:00 GMT http://hdl.handle.net/10366/169901 2023-07-01T00:00:00Z http://hdl.handle.net/10366/169898 [EN]The advent of ultrafast laser science offers the unique opportunity to combine Floquet engineering with extreme time resolution, further pushing the optical control of matter into the petahertz domain. However, what is the shortest driving pulse for which Floquet states can be realised remains an unsolved matter, thus limiting the application of Floquet theory to pulses composed by many optical cycles. Here we ionized Ne atoms with few-femtosecond pulses of selected time duration and show that a Floquet state can be observed already with a driving field that lasts for only 10 cycles. For shorter pulses, down to 2 cycles, the finite lifetime of the driven state can still be explained using an analytical model based on Floquet theory. By demonstrating that the amplitude and number of Floquet-like sidebands in the photoelectron spectrum can be controlled not only with the driving laser pulse intensity and frequency, but also by its duration, our results add a new lever to the toolbox of Floquet engineering. Tue, 01 Nov 2022 00:00:00 GMT http://hdl.handle.net/10366/169898 2022-11-01T00:00:00Z http://hdl.handle.net/10366/169897 [EN]We present an ultraviolet (UV) - extreme-ultraviolet (XUV) pump-probe beamline with applications in ultrafast time-resolved photoelectron spectroscopy. The UV pump pulses, tuneable between 255 and 285 nm and with µJ-level energy, are generated by frequency up-conversion between ultrashort visible/infrared pulses and visible narrow-band pulses. Few-femtosecond XUV probe pulses are produced by a high-order harmonic generation source equipped with a state-of-the-art time-delay compensated monochromator. Two-colour UV-XUV sidebands are used for a complete in situ temporal characterization of the pulses, demonstrating a temporal resolution of better than 20 fs. We validate the performances of the beamline through a UV-XUV pump-probe measurement on 1,3-cyclohexadiene, resolving the ultrashort dynamics of the first conical intersection. This instrument opens exciting possibilities for investigating ultrafast UV-induced dynamics of organic molecules in ultrashort time scales. Tue, 01 Oct 2024 00:00:00 GMT http://hdl.handle.net/10366/169897 2024-10-01T00:00:00Z http://hdl.handle.net/10366/169879 [EN]While chiral spin structures stabilized by Dzyaloshinskii-Moriya interaction (DMI) are candidates as novel information carriers, their dynamics on the fs-ps timescale is little known. Since with the bulk Heisenberg exchange and the interfacial DMI two distinct exchange mechanisms are at play, the ultrafast dynamics of the chiral order needs to be ascertained and compared to the dynamics of the conventional collinear order. Using an XUV free-electron laser we determine the fs-ps temporal evolution of the chiral order in domain walls in a magnetic thin film sample by an IR pump - X-ray magnetic scattering probe experiment. Upon demagnetization we observe that the dichroic (CL-CR) signal connected with the chiral order correlator mzmx in the domain walls recovers significantly faster than the (CL + CR) sum signal representing the average collinear domain magnetization mz2 + mx2. We explore possible explanations based on spin structure dynamics and reduced transversal magnetization fluctuations inside the domain walls and find that the latter can explain the experimental data leading to different dynamics for collinear magnetic order and chiral magnetic order. Tue, 01 Dec 2020 00:00:00 GMT http://hdl.handle.net/10366/169879 2020-12-01T00:00:00Z http://hdl.handle.net/10366/169878 [EN]In this article we report the fabrication of a diode-pumped Dy,Tb:LiLuF4 waveguide laser operating in the yellow region of the visible spectrum. The circular depressed-cladding waveguides have been fabricated by direct femtosecond laser writing, and showed propagation losses as low as 0.07 dB/cm. By employing these structures, we obtain a maximum output power of 86 mW at 574 nm from a 60 µm diameter waveguide, and a highest slope efficiency of 19% from a 80 µm diameter depressed cladding waveguide. In addition, we demonstrate lasing at 574 nm from a half-ring surface waveguide, with a maximum output power of 12 mW. Moreover, we also obtained dual wavelength operation at 568–574 nm, with a maximum output power of 15 mW, and stable lasing at 578 nm, with an output power of 100 mW. The latter wavelength corresponds to the main transition of the atomic clock based on the neutral ytterbium atom. To the best of the authors’ knowledge, this is the first demonstration of a yellow waveguide laser based on Dy-doped materials. Sat, 01 Feb 2025 00:00:00 GMT http://hdl.handle.net/10366/169878 2025-02-01T00:00:00Z http://hdl.handle.net/10366/169876 [EN]Nanostructured thin films of Co-doped zinc sulfide were synthesized through femtosecond pulsed laser deposition. The scheme involved ablation of physically mixed Co and ZnS with pairs of ultrashort pulses separated in time in the 0–300 ps range. In situ monitorization of the deposition process was carried out through a simultaneous reflectivity measurement. The crystallinity of generated nanoparticles and the inclusion of Co in the ZnS lattice is demonstrated by transmission electron microscopy and energy dispersive X-ray microanalysis (TEM-EDX) characterization. Surface morphology, Raman response, and photoluminescence of the films have also been assessed. The role of interpulse temporal separation is most visible in the thickness of the films obtained at the same total fluence, with much thicker films deposited with short delays than with individual uncoupled pulses. The proportion of Co in the synthesized doped ZnS nanoparticles is found to be substantially lower than the original proportion, and practically independent on interpulse delay.Nanostructured thin films of Co-doped zinc sulfide were synthesized through femtosecond pulsed laser deposition. The scheme involved ablation of physically mixed Co and ZnS with pairs of ultrashort pulses separated in time in the 0–300 ps range. In situ monitorization of the deposition process was carried out through a simultaneous reflectivity measurement. The crystallinity of generated nanoparticles and the inclusion of Co in the ZnS lattice is demonstrated by transmission electron microscopy and energy dispersive X-ray microanalysis (TEM-EDX) characterization. Surface morphology, Raman response, and photoluminescence of the films have also been assessed. The role of interpulse temporal separation is most visible in the thickness of the films obtained at the same total fluence, with much thicker films deposited with short delays than with individual uncoupled pulses. The proportion of Co in the synthesized doped ZnS nanoparticles is found to be substantially lower than the original proportion, and practically independent on interpulse delay. Sun, 01 Nov 2020 00:00:00 GMT http://hdl.handle.net/10366/169876 2020-11-01T00:00:00Z http://hdl.handle.net/10366/168590 [EN]Ultrafast pulse optical vortices are spatiotemporal structures with a diverse range of applications. There are different ways to generate them, often restricted to a wavelength range. Likewise, characterization techniques frequently possess similar limitations. In this work, we first generate ultrashort optical vortices in the near-infrared from Ti:sapphire laser pulses by means of structured waveplates and beam manipulation. Then, we produce the visible vortices through up-conversion using a second-harmonic generation crystal. The resulting beams require spatiotemporal characterization, which is performed by bulk lateral shearing interferometry. The reference pulse is temporally characterized with the amplitude swing technique. In this manner, we present the generation of these pulses in the visible range, which is experimentally validated, and demonstrate that bulk lateral shearing interferometry can be used for pulsed beams across widely different spectral regions with the same setup. This finding is significant for future applications of the technique with various sources. Thu, 01 May 2025 00:00:00 GMT http://hdl.handle.net/10366/168590 2025-05-01T00:00:00Z