JULIA MARIA GIEHL
20 resultados
Resultados de Busca
Agora exibindo 1 - 10 de 20
Artigo IPEN-doc 30193 Random lasers2023 - WETTER, NIKLAUS U.; VIEIRA, RENATO J.R.; SILVA, DANILO M. da; JORGE, KELLY C.; JIMENEZ-VILLAR, ERNESTO; GIEHL, JULIA M.; MIRANDA, ADRIANA R. de; DIPOLD, JESSICARandom lasers offer advantages such as low-cost fabrication and robustness in harsh environments and have applications in sensing, imaging, communications, and security. Our current research focuses on advanced materials, active control techniques, integration with other photonic structures, and exploration of Anderson localization and polydisperse effects. Coherent feedback in cavity-enhanced random lasers is discussed as means to achieve specific emission characteristics, and emission at 1300 nm is shown for the first time.Resumo IPEN-doc 25521 Polydispersed powders (Nd3+:YVO4) for ultra efficient random lasers2018 - WETTER, NIKLAUS U.; GIEHL, JULIA M.; JIMENEZ-VILLAR, ERNESTO; ANACLETO, DANILORandom lasers hold the potential for cheap, coherent light sources that can be miniaturized and molded into any shape with several other added benefits such as speckle-free imaging and cancer detectin, however, they require improvements specifically in terms of efficiency. This talk details for the first time a strategy for increasing the efficiency of a random laser that consists in using smaller particles, trapped between large particles to serve as absorption and gain centers whereas the large particles control mainly the light diffusion into the sample. In order to to determine the samples’ transport mean free path, fill fractions, laser efficiency and the average photon path lengths inside the scattering medium for backscattered pump photons, measurements of backscattering cone, sample absorption, reflection and laser emission are done. A record slope efficiency of 50% is reached by optimizing pump photon diffusion and absorption in a powder pellet composed by a polydispersed particle size distribution (smaller particles between bigger ones) from a grinded and sieved 1.33 mol% Nd:YVO4 crystal with mean particle size of 54 micrometers.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.Artigo IPEN-doc 24396 Polydispersed powders (Nd3+:YVO4) for ultra efficient random lasers2018 - WETTER, NIKLAUS U.; GIEHL, JULIA M.; BUTZBACH, FELIX; ANACLETO, DANILO; JIMENEZ-VILLAR, ERNESTORandom lasers hold the potential for cheap, coherent light sources that can be miniaturized and molded into any shape with several other added benefits such as speckle-free imaging; however, they require improvements specifically in terms of efficiency. This paper details for the first time a strategy for increasing the efficiency of a random laser that consists in using smaller particles, trapped between large particles to serve as absorption and gain centers whereas the large particles control mainly the light diffusion into the sample. Measurements of backscattering cone, sample absorption, reflection, and laser emission are used to determine the samples’ transport mean free path, fill fractions, laser efficiency, and the average photon path lengths inside the scattering medium for backscattered pump photons. A record slope efficiency of 50% is reached by optimizing pump photon diffusion and absorption in a powder pellet composed by a polydispersed particle size distribution (smaller particles between bigger ones) from a grinded and sieved 1.33 mol% yttrium vanadate doped with neodymium crystal with mean particle size of 54 μm.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 22708 Randon lasers for lab-on-chip applications2015 - GIEHL, J.M.; BUTZBACK, F.; JORGE, K.C.; ALVARADO, M.A.; CARRENO, M.N.P.; ALAYO, M.I.; WETTER, N.U.Random lasers are laser sources in which the feedback is provided by scattering instead of reflection and which, for this reason, do not require surfaces with optical finish such as mirrors. The investigation of such lasing action in a large variety of disordered materials is a subject of high interest with very important applications such as threedimensional and speckle-free imaging, detection of cancer tissue and photonic coding and encryption. However, potential applications require optimization of random laser performance especially with respect to optical efficiency and directionality or brightness. This work demonstrates such an optimization procedure with the goal of achieving a random laser with sufficient efficiency and brightness in order to be used in practical applications. Two random lasers are demonstrated, one solid and on liquid, that fulfil directionality and efficiency requirements. The first one consists of a neodymium doped powder laser with a record slope efficiency of 1.6%. The second one is a liquid random laser injected into a HC-ARROW waveguide which uses a microchannel connected to a much larger reservoir in order to achieve the necessary directionality. Both devices can be produced by low cost fabricating technologies and easily integrated into next-generation, lab-on-chip devices used for in-situ determination of infectious tropical diseases, which is the main goal of this project.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.Resumo IPEN-doc 20361 Study of the random laser emission of Ndsub(3+):YVOsub(4) powders as function of particle size and applied pressure2014 - GIEHL, J.M.; MIRANDA, A.R.; REIJN, S.M.; WETTER, N.U.Resumo IPEN-doc 20368 Rhodamine-doped aerogel random laser2014 - MIRANDA, ADRIANA R. de; PECORARO, EDISON; RIBEIRO, SIDNEY J.L.; GIEHL, JULIA M.; WETTER, NIKLAUS U.