Beam shaping offers many opportunities to both streamline and accelerate laser fabrication processes, closing the gap between lab research and large-scale manufacturing. In the field of embedded devices, a Bessel beam configuration allows for large volume engraving of transparent materials in a single laser pass. In this work, we take advantage of femtosecond Bessel beams with a length of 340 mu m and a diameter of 1 mu m to generate diffractive elements within three distinct optical glasses. This strategy represents a chemical-free and cost-effective alternative to the conventional manufacturing of holographic elements based on photoresist micro-patterning. Despite the different nonlinear effects taking place in each material, we report the successful fabrication of diffraction gratings operating at either normal or Bragg incidence, with efficiencies in the first combined order of up to 70%. Our experimental results show the potential of Bessel beams as a tool to produce buried light devices in a wide variety of glass materials.

Colorizing metals using micrometer and nanometer scale surface modifications has been vastly investigated and presents many advantages for applications across scientific and technological fields. By tuning the surface chemical composition or controlling its morphology, it is possible to produce a wide range of chromatic effects. Ultrafast laser processing presents here an interesting asset, as it allows to simultaneously provide chemical and morphological modifications at the micro-scale in a single step. In this article, the composite colorization of copper surfaces with mW-class average power deep ultraviolet (DUV) femtosecond laser pulses is demonstrated. The advantages of this setup are twofold: first, thanks to the increased absorption of copper in the DUV, the technique allows scaling down the requirement for laser power. Second, under ultrafast short-wavelength illumination molecular oxygen bond-breaks occur, enhancing the oxidation rate of the copper. The technique allows for highly controllable and efficient copper oxidation with the irradiation parameters. Taking these two effects into account, the generation of a wide spectrum of colors-from dark blue to shiny red-is demonstrated, and the role of the surface oxidation rate, the laser fluence, and laser scanning strategies in the colorization of copper surfaces employing DUV lasers is discussed. Copper surface colorization with mW-class deep ultraviolet femtosecond laser pulses offers two key benefits: increased copper absorption in deep ultraviolet (DUV), reducing power needs, and spatially precise enhanced copper oxidation, resulting in a broad palette of colors with micron pixel resolution. Composite colorization of copper surfaces using DUV ultrafast pulsesimage

The generation of surface plasmon resonances (SPR) in laser-induced periodic surface structures (LIPSS) allows their application in the field of optical sensing, such as the detection of refractive index variations in gases and liquids. We have fabricated gold-coated LIPSS nanostructures on stainless steel substrates by using femtosecond laser nano-ablation. This technique is a low-cost and high-throughput fabrication method applicable to fast and large-scale manufacturing. The depth profile of the fabricated LIPSS shows a central dip at the top of each ripple that split the geometry. The actual topography is modeled and included in a computational electromagnetism package to obtain the expected optical response under the experimental conditions. The measured and simulated spectral reflectances are compared, and the differences are explained by the departure of the fabricated LIPSS from the ideal topography. The experiments and simulations showed excellent agreement for the main spectral characteristics, like the Fano-like lineshapes of the spectral reflectance. This fitting provides the values used to determine the refractometric performance of the fabricated device, that shows a sensitivity of 518 nm/RIU and a figure of merit of 32 RIU-1 for an aqueous analyte. Our experimental results show that the fabricated devices are competitive in terms of cost and simplicity when compared to existing devices with similar performance.

The use of ultrashort-pulsed (USP) lasers in Additive Manufacturing (AM) enables the processing of different materials and has the potential to reduce the sizes and shapes manufactured with this technology. This work confirms that USP lasers are a viable alternative for Laser Powder Bed Fusion (LPBF) when higher precision is required to manufacture certain critical parts. Promising results were obtained using tailored and own-produced stainless steel powder particles, manufacturing consistent square layers with a series of optimized processing parameters. The critical role of processing parameters is confirmed when using this type of lasers, as a slight deviation of any of them results in an absence of melting. For the first time, melting has been achieved at low pulse repetition (500 kHz) and using low average laser power values (0.5-1 W), by generating heat accumulation at reduced scanning speeds. This opens up the possibility of further reducing the minimum size of parts when using USP lasers for AM.

We describe a theoretical approach based on Muller and tensor calculus for predicting the polarization state and gain of cascaded Stokes orders produced under coherent Raman scattering regime conditions. The formulation follows a Markovian-style implementation for F-2g-type modes in Raman cubic crystals. The theoretical model is supported by experimental results that corroborate that the polarization and power of the cascaded Stokes orders can be effectively predicted using sequential calculus. We extend these results to a variety of crystal propagation directions, with the aim of facilitating the design of advanced solid-state Raman lasers.

Laser-Induced Periodic Surface Structures (LIPSS) manufacturing is a convenient laser direct-writing technique for the fabrication of nanostructures with adaptable characteristics on the surface of virtually any material. In this paper, we study the influence of 1D laser wavefront curvature on nanoripples spatial regularity, by irradiating stainless steel with a line-focused ultrafast laser beam emitting 120 fs pulses at a wavelength of 800 nm and with 1 kHz repetition rate. We find high correlation between the spatial regularity of the fabricated nanostructures and the wavefront characteristics of the laser beam, with higher regularity being found with quasiplane-wave illumination. Our results provide insight regarding the control of LIPSS regularity, which is essential for industrial applications involving the LIPSS generation technique.

ZnO conductometric gas sensors have been widely studied due to their good sensitivity, cost-efficiency, long stability and simple fabrication. This work is focused on NO2 sensing, which is a toxic and irritating gas. The developed sensor consists of interdigitated electrodes covered by a ZnO sensing layer. ZnO has been grown by means of the aerosol assisted chemical vapor deposition technique and then nanostructured by laser interference lithography with a UV laser. The SEM and XRD results show vertically oriented growth of ZnO grains and a 2D periodic nanopatterning of the material with a period of 800 nm. Nanostructuring lowers the base resistance of the developed sensors and modifies the sensor response to NO2. Maximum sensitivity is obtained at 175 degrees C achieving a change of 600% in sensor resistance for 4 ppm NO(2)versus a 400% change for the non-nanostructured material. However, the most relevant results have been obtained at temperatures below 125 degrees C. While the non-nanostructured material does not respond to NO2 at such low temperatures, nanostructured ZnO allows NO2 sensing even at room temperature. The room temperature sensing capability possibly derives from the increase of both the surface defects and the surface-to-volume ratio. The long stability and the gas sensing under humid conditions have also been tested, showing improvements of sensitivity for the nanostructured sensors.

Aerosol-assisted Chemical Vapor Deposition (AACVD) is a thermally activated CVD technique that uses micro-droplets as deposition precursors. An AACVD system with a custom-designed reaction chamber has been implemented to grow ZnO thin films using zinc chloride as a precursor. The present work aims to study the impact of the deposition parameters on the thin film, as well as the microstructure evolution and growth kinetics. Aerosol flow has an effect on the density of nucleation sites and on the grain size. The temperature affects the morphology of the grown ZnO, showing a preferential orientation along the c-axis for 350 degrees C, 375 degrees C and 400 degrees C substrate temperatures. The microstructural evolution and the growth kinetics are also presented. A different evolution behavior has been observed for 350 degrees C, where nucleation site density is the highest at the early stages and it decreases over time in contrast with the cases of 375 degrees C and 400 degrees C, where there is an initial increase and a subsequent decrease. The activation energy of the chemical reaction is 1.06 eV. The optical characterization of the material has been performed through reflection measurements showing a relationship between the spectrum and the ZnO film thickness. The electrical characterization has been done by means of an interdigital capacitor, with which it is possible to measure the grain and grain boundary resistance of the material. Both resistances are of the order of 10(5)-10(6) omega.

The control of the interaction between materials and biological tissues is a key factor to optimize the overall performance of implants and prostheses integrated into the body. With this objective in mind, biomimetic hierarchical one- and two-dimensional surface patterns textured at the micro and nano scales were fabricated on titanium alloys using femtosecond laser processing. The experimental results show that laser irradiation promotes surface oxidation together with a polarization-dependent nano-ripple formation. Human mesenchymal stem cells were subsequently cultured on different surface patterns aiming at determining their response to the underlying micro and nano structures. The ripple topography was demonstrated to induce a nonfouling behavior, which could be exploited in the fabrication of biomimetic hierarchical surface patterns to develop cell-trapping modules.

We demonstrate a continuously tunable, multi-Stokes Raman laser operating in the visible range (420 - 600 nm). Full spectral coverage was achieved by efficiently cascading the Raman shifted output of a tunable, frequency-doubled Ti:Sapphire laser. Using an optimized hemi-spherical external Raman cavity composed only of a diamond crystal and a single reflecting mirror, producing high power output at high conversion efficiency (>60% from pump to Stokes) for a broad range of wavelengths across the visible. Enhancement of the cascading was achieved by controlling the polarization state of the pump and Stokes orders. The Stokes outputs exhibited a linewidth of 11 +/- 1 GHz for each order, resembling the pump laser linewidth, enabling its use for the intended spectroscopic applications. Furthermore, the Raman laser performance was demonstrated by applying it for the resonance excitation of atomic transitions in calcium. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

There is an increasing interest in nanoscience and nanotechnology due to the new physics and chemistry that are accessible on the nanoscale and because of the large potential for new products and devices that they provide. Therefore, the ability to fabricate structures on the nanoscale with high precision and in a wide variety of materials is a crucial issue for the development of the nanoscience and nanotechnology. Lithography and the other processes associated with it are the core of the nanotechnology revolution. One of the most promising techniques for the fabrication of structures on the nanoscale is Laser Interference Lithography (LIL). LIL, also known as holographic or interferometric lithography, is a well-established concept largely explored in lithography. However, a pulsed multi- beam LIL tool for nanoscale structuring of materials that can scale beyond laboratory prototypes into cost effective industrial processes is not yet defined. In this document, a versatile and automatic high-power multiple beam interference lithography system design capable of overcoming the limitations of manual setups is presented.

Periodic structures in the sub-micro and nano scales have attracted the attention of researchers lately due to the novel properties they exhibit. One of the main issues which slow down the integration of this type of structures in real devices is the lack of fabrication techniques which can scale to mass production. The present work studies the fabrication of silver sub-micrometric structures by two different techniques: self-assembly of colloidal spheres and laser interference lithography. The self-assembly technique consists of different steps which are studied and optimized, starting with the optimization of the deposition conditions of indium tin oxide thin films. The next steps are the assembly of colloidal spheres, the infiltration of the resultant opals with silver and the inversion of the infiltrate opals, giving rise to ordered silver structures. The laser interference lithography technique is also used to obtain this type of structures. The resulting silver structures are structurally and optically characterized. It is demonstrated in this work that these structures present optical properties which make them feasible for future photonic applications.

Nanotechnology is the study of the controlling of matter on an atomic and molecular scale and is very diverse, ranging from extensions of conventional device physics to completely new approaches based upon molecular self-assembly, from developing new materials with dimensions on the nanoscale to investigating whether we can directly control matter on the atomic scale. This new book gathers and presents data on nanotechnology including the growth of zinc oxide (ZnO) nanostructured films by means of excimer laser ablation; modeling defective carbon nanotubes by molecular mechanics; advances in surface functionalization of carbon nanotubes; the catalytic, optical, and thermodynamic properties of amorphous TiO2 nanoparticles.