Javier Solis

In this work we report a new and simple method that combines pulsed laser ablation in liquids (PLAL) and sol–gel techniques to obtain nanocomposite glasses and gelatins. Using this combination, we obtained two kinds of materials, bulk glasses on the one hand and gelatin films on the other hand. In the case of glasses, gold nanoparticles (Au-NPs) are generated by PLAL using an Au target submerged in a transparent liquid solution made previously with tetraethyl orthosilicate (TEOS) adding diluted hydrochloric acid as catalyzer. For gelatins, the same procedure is employed; however, in this case only commercial gelatin and tap water are used. We have found that a successful synthesis strongly depends on time and temperature since the viscosity of the gels increases with time. For the drying process the gels are sealed and stored at room temperature for several days. We identify the principal parameters that have to be considered in order to achieve a successful synthesis. The samples are characterized by UV–vis spectroscopy, HRTEM, ellipsometry and AFM microscopy. UV–vis spectra show a surface plasmon resonance band with its maximum at 540 nm indicating the presence of Au-NPs. HRTEM reveals crystalline Au-NPs with an average size of 20 nm. AFM measurements indicate that the glasses have a very smooth surface. In the case of gelatins, self-sustained, transparent, and pink flexible films are obtained. Despite having determined the principal parameters involved in the obtention of these materials, we emphasize that a lot of work remains to be done in order to optimize this novel method of synthesis.

We have analyzed the formation and coherent propagation of laser-induced periodic surface structures (LIPSS) upon fs-laser irradiation of fluorine-doped tin oxide (FTO) films. The aim is the generation of large electrical anisotropies in macroscopic areas for applications including laser-written transparent heaters, sensors, or substrates for electrically controllable wettability, among others. The films have been processed with high-repetition-rate (hundreds of kHz) fs-laser pulses at 1030 nm using different laser (fluence and pulse duration) and scanning parameters (speed and line overlap). Optimal LIPSS formation and coherent propagation are conditioned by the dynamic evolution of the F content in the laser-processed regions that can be controlled via processing parameters. However, the homogeneity in the spatial distribution of F in the microscale in the pristine samples can generate important issues that are carefully considered and discussed in the present work. Still, the formation of optically and electrically highly anisotropic surfaces for laser scanning speeds well above 1.0 m/s has been demonstrated, reaching electrical resistivity anisotropy factors of >10³. Consequently, the potential development of large-area applications using LIPSS-structured FTO films seems feasible, as we have demonstrated by fabricating an efficient laser-written electrothermal transparent device as a proof-of-concept.

The design and fabrication of a integrated symmetric directional coupler dependent o the pumping power and operating at a 1534 nm wavelength is reported. The twin-core waveguide was inscribed into Er³⁺/Yb³⁺ co-doped phosphate glass by a femtosecond laser direct writing technique. By optical pumping, the coupling ratio can be modulated due to the changes induced in the refractive index of the material. The experimental results demonstrated that the coupling ratio can be tuned continuously from 100/0 to 50/50 by increasing the pump’s power from 0 to 350 mW. The developed twin-core coupler has promising applications for on-chip all-optical signal processing and communication systems.

ZnO nano- and microstructures doped with K were grown by the Vapor–Solid method. Wires and needles are the main morphology observed, although some structures in the form of ribbons and triangular plates were also obtained. Besides these, ball-shaped structures which grow around a central wire were also detected. Raman and cathodoluminescence investigations suggest that variations in morphology, crystalline quality and luminescence emissions are related to the different lattice positions that K occupies depending on its concentration in the structures. When the amount is low, K ions mainly incorporate as interstitials (K_i), whereas K occupies substitutional positions of Zn (K_Zn) when the amount of K is increased. Electron Backscattered Diffraction shows that ribbons and triangular plates are oriented in the (0001) direction, which indicates that the growth of this type of morphologies is related to distortions introduced by the K_i since this position favors the growth in the (0001) plane. In the case of the ball-shaped structures, the compositional analysis and Raman spectra show that they consist of K₂SO₄. Finally, the capability of the elongated structures to act as waveguides and optical resonators was investigated. Due to the size of the K ion, practically double that of the Zn, and the different positions it can adopt within the ZnO lattice (K_i or K_Zn), high distortions are introduced that compromise the resonators performance. Despite this, quality factor (Q) and fineness (F) show acceptable values (80 and 10 at 544 nm, respectively), although smaller than those reported for doping with smaller size alkali, such as Li.