Optical AR coatings of the Mid-IR band for ZnGeP2 single crystals based on ZnS and oxide aluminum

In this work, the parameters of antireflection interference coatings based on alternating layers of ZnS/Al2O3 on the laser-induced damage threshold (LIDT) of ZGP crystals under the action of Ho:YAG laser radiation at a wavelength of 2.097 μm were determined. The coating deposition was carried out using the ion-beam sputtering method. The LIDT of the sample with a coating based on alternating layers ZnS and Al2O3 was equal to WEo = 3.45 J/cm2, and the LIDT of the uncoated sample was equal to WEo = 2.23 J/cm2. An increase in the optical breakdown threshold by ~55% was observed after the deposition of an AR coating based on ZnS and Al2O3 materials. An assumption was made about the absence of local fluctuations in the composition and mechanical stresses in the case of the coated sample, namely that this leads to good adhesion of the multilayer coating to the polished surface of the crystal, and as a result to an increase in the optical breakdown threshold as compared to the uncoated sample due to closure of the dangling chemical bonds and bulk defects emerging on the polished surface

Investigation of the distribution of laser damage precursors at 1064 nm, 12 ns on Niobia-Silica and Zirconia-Silica mixtures

International audienceSimple Nb 2 O 5 , ZrO 2 , SiO 2 oxide coatings and their mixtures with SiO 2 have been prepared by the Ion Beam Sputtering (IBS) technique. The Laser-Induced Damage of these samples has been studied at 1064 nm, 12 ns. The laser induced damage threshold (LIDT) decreases in both sets of the mixtures with the volumetric fraction of high index material. We find that the nanosecond LIDT of the mixtures is related to the band gap of the material as it has been widely observed in the subpicosecond regime. The laser damage probability curves have been fitted firstly by a statistical approach, i.e. direct calculation of damage precursor density from damage probability and secondly by a thermal model based on absorption of initiator. The distributions of damage precursors versus fluence extracted from these fittings show a good agreement. The thermal model makes it possible to connect damage probability to precursor physical properties. A metallic defect with a maximum radius of 18 nm was proposed to the interpretation. The critical temperature in the laser damage process exhibited a dependence on the band-gap of the material

Advances in Middle Infrared Laser Crystals and Its Applications

In the last twenty years, there has been a growing interest in middle infrared (mid-IR) laser crystals and their application to achieve mid-IR laser radiations, which has benefited from the development of novel mid-infrared crystals and the improving quality of traditional mid-IR crystals. Moreover, these works have promoted the development of related technical applications. This Special Issue of the journal Crystals focuses on the most recent advances in mid-IR laser crystals, from materials to laser sources and applications. It aims to bring together the latest developments in novel mid-IR crystals, improvements in the quality of mid-IR crystals, mid-IR non-linear crystals and mid-IR lasers, as well as the application of mid-IR technology in spectroscopy, trace gas detection and remote sensing, optical microscopy and biomedicine. Aspiring authors are encouraged to submit their latest original research, as well as forward-looking review papers, to this Special Issue

Reaktive ionengestützte Prozesse für optische Hochleistungsschichten

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Caracterización estructural y funcional de películas delgadas nanoporosas mediante microscopías electrónicas de transmisiónbarrido y espectroscopías ópticas

Nano-structuration of materials at the mesoscale to give rise to porosity-controlled coatings represents an important breakthrough in the area of Materials Science and Engineering, offering new and enhanced functionalities of interest in fields such as optics, optronics and optoelectronics. In order to optimize their performances, in-depth analyses are required: local information about the morphology, composition and atomic structure, the compactness distribution, but also layer homogeneity, interface and interpenetration between stacked layers or oxidation are extremely important factors that can ruin their way of operation. In this particular context, the objective of the present PhD Thesis is to make significant contributions to the study and development of multifunctional porous nanostructured systems, from their design and elaboration, to the maximum knowledge of their structure and properties, through advanced (S)TEM methods, including 3D reconstructions, elemental analyses at the nanoscale and atomic-scale imaging, combined with optical spectroscopy techniques. In the first instance, given the great potential of the slanted nanostructures generated by means of oblique angle depositions, in which the refractive index gradient can be tuned by the columns tilt and density imposed via the growth angles and parameters, OAD broadband antireflective coatings based on Si, Ge or SiO2 OAD films have been designed, manufactured, and extensively characterized with the aim of maximizing the performance of the optical elements in the vis-IR wavelength range. This same approach has also been implemented to enhance the antireflective capabilities of transparent conductive ITO thin films in the near-IR window without compromising too much their electrical response. On the other hand, the advanced structural and functional characterization of porosity-controlled GaN NW arrays grown by plasma-assisted MBE through (S)TEM methods and vis-IR SE elliposmetry, has helped not only to improve growth processes but also to optimize their resulting optical and electrical properties. Finally, the knowledge and methodologies acquired during the study and optimization of the previous porous systems have been transferred to the development of a two-step procedure, based on the deposition and the subsequent fast oxidation of vanadium-based OAD films in open air atmosphere, for the synthesis of thermochromic VO2 coatings of tunable metal-to-insulator response and controlled grain sizes and crystallinities

Optical Properties of Porous Alumina Assisted Niobia Nanostructured Films–Designing 2-D Photonic Crystals Based on Hexagonally Arranged Nanocolumns

Three types of niobia nanostructured films (so-called native, planarized, and column-like) were formed on glass substrates by porous alumina assisted anodizing in a 0.2 M aqueous solution of oxalic acid in a potentiostatic mode at a 53 V and then reanodizing in an electrolyte containing 0.5 M boric acid and 0.05 M sodium tetraborate in a potentiodynamic mode by raising the voltage to 230 V, and chemical post-processing. Anodic behaviors, morphology, and optical properties of the films have been investigated. The interference pattern of native film served as the basis for calculating the effective refractive index which varies within 1.75–1.54 in the wavelength range 190–1100 nm. Refractive index spectral characteristics made it possible to distinguish a number of absorbance bands of the native film. Based on the analysis of literature data, the identified oxide absorbance bands were assigned. The effective refractive index of native film was also calculated using the effective-medium models, and was in the range of 1.63–1.68. The reflectance spectra of all films show peaks in short- and long-wave regions. The presence of these peaks is due to the periodically varying refractive index in the layers of films in two dimensions. FDTD simulation was carried out and the morphology of a potential 2-D photonic crystal with 92% (wavelength 462 nm) reflectance, based on the third type of films, was proposed