JULIA MARIA GIEHL
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Artigo IPEN-doc 24975 Influence of the fraction of absorbed pump power on the performance of Nd3+:YVO4 powder random lasers2018 - WETTER, NIKLAUS U.; SILVA, DANILO A.A. da; JIMENEZ-VILLAR, ERNESTO; GIEHL, JULIA M.Understanding light absorption in random lasers and its distribution within the scattering gain media is a key issue to increase the lasers’ efficiency. Here we compare monodispersed and polydispersed powders of Nd3+:YVO4 and investigate the influence of the powder size distribution on scattering mean free path, absorption volume and, eventually, the lasers efficiency. The highest efficiency is achieved for polydispersed powders and we conjecture that these polydispersed powders, composed of pockets containing small grains trapped between large particles, present locally higher pump power densities than the monodispersed powders. We establish a figure of merit, based on measurable powder parameters, that agrees well with the obtained output power results of the monodispersed and polydispersed samples.Resumo IPEN-doc 23251 Optimized grain size distributions for maximum efficiency in neodymium doped powder random lasers2017 - WETTER, N.U.; GIEHL, J.M.; BUTZBACH, F.; ANACLETO, D.; SIMONE, G. de; JIMENEZ-VILLAR, E.We show that polydispersed powders can have much higher random laser output power and efficiency than monodispersed powders. A more than 50% slope efficiency is achieved by using highly doped Nd:YVO4 powders composed of average grains size of 50 μm and 10% volume fraction of grains below 1 μm. We demonstrate that the smaller particles, trapped between large particles, serve as gain centers whereas the large particles control the light diffusion into the sample. A detailed light diffusion analysis of the samples explains the observed differences.Artigo IPEN-doc 23094 Optimizing grain size distribution in Nd:YVO4 powder pellets for random laser action with high efficiency2017 - WETTER, NIKLAUS U.; JIMENEZ-VILLAR, E.; GHIEL, JULIA M.; BUTZBACH, FELIX; TAYRA, VICTORWe demonstrate a volumetric random laser with an optical efficiency of 15%. We use a 1.33 mol% Nd:YVO4 crystal, grind it and mix the particles into ten different size distributions with mean particle sizes ranging from approximately 10 micrometers to 100 micrometers. After pressing into pellets, each of the ten groups has its transport mean free path calculated from the distribution spectra and experimentally measured by means of its backscattering cone. We then calculate the fill fractions of each sample. The pellets are diode-pumped at 806.5 nm. Linewidth narrowing and output power are measured as a function of absorbed pump power. We demonstrate that the smaller particles, trapped between large particles, serve as gain centers whereas the large particles control the light diffusion into the sample. By optimizing diffusion and gain we achieve high slope efficiency.Artigo IPEN-doc 21390 Grain size distribution for optimized random laser emission in Ndsup(3+):YVOsub(4) powder pellets2015 - GIEHL, J.M.; WETTER, N.U.Artigo IPEN-doc 19605 Dependence of particle size and applied pressure on the random laser emission of Ndsup(3+):YVOsub(4) powders2013 - GIEHL, J.M.; MIRANDA, A.R.; RIBAMAR VIEIRA, R.J.; REIJN, S.M.; WETTER, N.U.