Ge- and Al-related point defects generated by gamma irradiation in nanostructured erbium-doped optical fiber preforms

International audienceErbium-doped amplifiers (EDFAs) are of special interest for space applications.In this environment, the ionizing radiations decrease the gain of these opticalamplifiers, due to the ionization of defects precursors, mainly linked to dopantsas Germanium (Ge), Aluminum (Al), or Phosphorus (P). The aim of this work isto study the influence of the Ge and Al relative concentration on the radiationresistance of different nanostructured fiber preforms, manufactured by ModifiedChemical Vapor Deposition (MCVD), in which various types of nanoparticles(Er@SiO2-NP, Al2O3-NP, and Er@Al2O3-NP) have been introduced in thesilica matrix. The radiation resistance of these fibers has been compared withthat of standard MCVD Er-doped preforms. All of them have been characterizedby optical absorption and Electronic Paramagnetic Resonance (EPR) spectroscopiesbefore and after irradiation with a total gamma dose of 5.9 kGy. EPRresults show that Al-related defects are not observed in fiber preforms with Geconcentrations higher than 4.4 wt%. We also demonstrated that NP technologycan limit the formation of Aluminum-Oxygen Hole Centers (AlOHCs), reducingthe Radiation-Induced Attenuation at the energy of interest for EDFAs

Ultrasound lung "comets" increase after breath-hold diving.

The purpose of the study was to analyze the ultrasound lung comets (ULCs) variation, which are a sign of extra-vascular lung water. Forty-two healthy individuals performed breath-hold diving in different conditions: dynamic surface apnea; deep variable-weight apnea and shallow, face immersed without effort (static maximal and non-maximal). The number of ULCs was evaluated by means of an ultrasound scan of the chest, before and after breath-hold diving sessions. The ULC score increased significantly from baseline after dynamic surface apnea (p = 0.0068), after deep breath-hold sessions (p = 0.0018), and after static maximal apnea (p = 0.031). There was no statistically significant difference between the average increase of ULC scores after dynamic surface apnea and deep breath-hold diving. We, therefore, postulate that extravascular lung water accumulation may be due to other factors than (deep) immersion alone, because it occurs during dynamic surface apnea as well. Three mechanisms may be responsible for this. First, the immersion-induced hydrostatic pressure gradient applied on the body causes a shift of peripheral venous blood towards the thorax. Second, the blood pooling effect found during the diving response Redistributes blood to the pulmonary vascular bed. Third, it is possible that the intense involuntary diaphragmatic contractions occurring during the "struggle phase" of the breath-hold can also produce a blood shift from the pulmonary capillaries to the pulmonary alveoli. A combination of these factors may explain the observed increase in ULC scores in deep, shallow maximal and shallow dynamic apneas, whereas shallow non-maximal apneas seem to be not "ULC provoking".Clinical TrialJournal Articleinfo:eu-repo/semantics/publishe