This article reviews the current knowledge on the main properties and applications of hydrogen in LiNbO₃. The review is divided into three parts. The first is devoted to general properties such as methods of defect production and control, techniques used for their detection and characterization, as well as interactions with other lattice defects. The second part considers the central role played by OH^- defects in the fabrication of optical waveguides by the protonexchange method. Conditions for the exchange process, the structure of exchanged layers, optical properties of exchanged waveguides and connection with relevant practical devices are examined. Finally, the third part discusses the production of permanent volume photorefractive gratings by the fixing process, where OH^- ions are also considered to be the main responsible defects. In particular, the physics of the fixing process, current mathematical models and two major applications are discussed.

In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The techniques used are the most relevant ones in the AM of metals, i.e., direct laser deposition (DLD) with a high-power diode laser and selective laser melting (SLM) using a fiber laser and a novel CO₂ laser, a novel technique that has not yet been reported with this material. The microstructure of all samples showed austenitic and ferritic phases, which were coarser with the DLD technique than for the two SLM ones. The hardness of the fiber laser SLM samples was the greatest, but its bending strength was lower. In SLM with CO₂ laser pieces, the porosity and lack of melting reduced the fracture strain, but the strength was greater than in the fiber laser SLM samples under certain build-up strategies. Specimens manufactured using DLD showed a higher fracture strain than the rest, while maintaining high strength values. In all the cases, crack surfaces were observed and the fracture mechanisms were determined. The processing conditions were compared using a normalized parameters methodology, which has also been used to explain the observed microstructures.