Polarization conversion on nanostructured metallic surfaces fabricated by LIPSS

Conference on Laser-Based Micro-and Nanoprocessing (LBMP) at Photonics West Conference (13ª. 2019. San Francisco, California). ISBN: 978-1-5106-2455-9 © 2019 SPIE. This work is part of the following projects: ECOGRAB, funded by the Government of Spain under the RETOS COLABORACIÓN I+D+i programme. LASER4SURF has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 768636.Waveplates modify polarization by generating a phase change. Laser Induced Periodic Surface Structures (LIPSS) have recently started to be studied as waveplates due to the birefringence in-duced by the nanoripples, easily fabricated in a one-step process by laser, where LIPSS morphology is defined by the characteristics of the laser process parameters and the substrate material. The optical properties of these waveplates are defined by LIPSS parameters such as period, depth or width of the ripples. In this work we have deposited thin film coatings on stainless steel samples containing LIPSS for different coating thickness and composition. Results show that thin film coatings are a good candidate for the tunability of LIPSS birefringence since the coating modifies the induced polarization change and reflectivity of the sample depending on coating thickness and composition, as expected from numerical simulations.Depto. de ÓpticaFac. de Ciencias FísicasTRUEUnión Europea. H2020Ministerio de Ciencia e Innovación (MICINN)pu

Optimum single-gap solar cells for missions to Mercury

The power supply for space probes is usually based on photovoltaic (PV) systems. The first solar cells used in these systems were single-gap solar cells fabricated with Si and GaAs. Later on, multijunction solar cells (MJSC) based on III–V semiconductors were developed because of their higher efficiency and tolerance to a radiation environment [1]. All these solar cells have been based on semiconductors that fulfill the needs of most near-Earth missions. However, those same semiconductors fail to meet the needs of some other missions involving harsh environments such as high-intensity high-temperature (HIHT) environments [2]. In this work, we investigate which semiconductor material is optimum to implement single-gap solar cells for missions to Mercury, where HIHT conditions are expected. Because solar cell efficiency decreases as temperature increases [3], achieving high-efficiency photovoltaic conversion at HIHT conditions is a big challenge. Previous works have pointed out the need of using wide-bandgap semiconductors to reach this goal [4,5]. In this context, we will study the potential of solar cells based on AlxGa1−xAs, a well-known semiconductor whose physical properties have been extensively investigated. The limiting efficiency of these solar cells performing in near-Mercury missions will be calculated to determine the optimum composition for AlxGa1−xAs

Femtosecond laser fabrication of LIPSS-based waveplates on metallic surfaces

A fast and reliable method for the fabrication of polarization modifying devices using femtosecond laser is reported. A setup based on line focusing is used for the generation of LIPSS on stainless steel, processing at different speeds between 0.8 and 2.4 mm/s with constant energy per pulse of 1.4 mJ. SEM and AFM characterizations of the LIPSS show a progressive increase in period as the processing speed increases, while height remains approximately constant in the studied range. Optical characterization of the devices shows an induced change in the polarization of the reflected beam that varies with the processing speed, which allows a controlled fabrication of these devices

Femtosecond laser fabrication of LIPSS-based waveplates on metallic surfaces

A fast and reliable method for the fabrication of polarization modifying devices using femtosecond laser is reported. A setup based on line focusing is used for the generation of LIPSS on stainless steel, processing at different speeds between 0.8 and 2.4 mm/s with constant energy per pulse of 1.4 mJ. SEM and AFM characterizations of the LIPSS show a progressive increase in period as the processing speed increases, while height remains approximately constant in the studied range. Optical characterization of the devices shows an induced change in the polarization of the reflected beam that varies with the processing speed, which allows a controlled fabrication of these devices

Light-trapping in photon enhanced thermionic emitters

A series of photonic crystal structures are optimized for a photon enhanced thermionic emitter. With realistic parameter values to describe a p-type GaAs device we find an efficiency above 10%. The light-trapping structures increases the performance by 2% over an optimal bilayer anti-reflective coating. We find a device efficiency very close to the case of a Lambertian absorber, but below its maximum performance. To prevent an efficiency below 10% the vacuum gap must be dimensioned according to the concentration factor of the solar irradiance

Migrations and habitat use of the smooth hammerhead shark (Sphyrna zygaena) in the Atlantic Ocean

The smooth hammerhead shark, Sphyrna zygaena, is a cosmopolitan semipelagic shark captured as bycatch in pelagic oceanic fisheries, especially pelagic longlines targeting swordfish and/or tunas. From 2012 to 2016, eight smooth hammerheads were tagged with Pop-up Satellite Archival Tags in the inter-tropical region of the Northeast Atlantic Ocean, with successful transmissions received from seven tags (total of 319 tracking days). Results confirmed the smooth hammerhead is a highly mobile species, as the longest migration ever documented for this species (> 6600 km) was recorded. An absence of a diel vertical movement behavior was noted, with the sharks spending most of their time at surface waters (0-50 m) above 23 degrees C. The operating depth of the pelagic long-line gear was measured with Minilog Temperature and Depth Recorders, and the overlap with the species vertical distribution was calculated. The overlap is taking place mainly during the night and is higher for juveniles (similar to 40% of overlap time). The novel information presented can now be used to contribute to the provision of sustainable management tools and serve as input for Ecological Risk Assessments for smooth hammerheads caught in Atlantic pelagic longline fisheries.Oceanario de Lisboa through Project "SHARK-TAG: Migrations and habitat use of the smooth hammerhead shark in the Atlantic Ocean"; Investigador-FCT from the Portuguese Foundation for Science and Technology (FCT, Fundacao para a Ciencia e Tecnologia) [Ref: IF/00253/2014]; EU European Social Fund; Programa Operacional Potencial Human

Reduction of elasmobranch by-catch in the hake semipelagic near-bottom longline fishery in the Algarve (Southern Portugal)

Elasmobranch fish, particularly deep-sea sharks, are the most important component of the by-catch of the hake semipelagic near-bottom 'pedra-e-bola' longline fishery in the Algarve (South Portugal) and most of these fish are discarded. The effects of the removal of the lower hooks were evaluated, in terms of target and by-catch reductions, by quantifying the catches of each hook relative to the distance from the bottom. The analysis showed that most European hake (Merluccius merluccius), the target species of this fishery, were caught in the middle range of the hooks, with very few individuals caught near the bottom, whereas for sharks the situation was the opposite, with most hooked near the bottom. The removal of the lower three pairs of hooks would result in a small reduction in the catch of the target species, but a much more significant reduction in elasmobranch by-catch. In the specific case of the blackmouth catshark (Galeus melastomus), discard mortality would be further minimized due to the fact that the lower hooks capture significantly smaller animals that are always discarded compared with hooks that are more distant from the bottom