This diploma thesis deals with evaluation of toxicity and bioaccumulation of photon-upconversion nanoparticles (UCNPs) in model plant maize (Zea mays). Lanthanide-doped UCNPs with different composition and size were tested in three different concentrations in this work. The exposure took place for 168 hours. Toxicity was assessed based on four macroscopic toxicological endpoints (mortality, the length of belowground part of the plants, the length of aboveground part of the plants and whole plants length). Spatial distribution of elements yttrium, ytterbium, erbium and gadolinium in model plants was determined using laser induced breakdown spectroscopy with spatial resolution of 100 m and 26 m. Distribution of UCNPs in plants was further studied with photon-upconversion microscanning with spatial resolution of 40 m. Stability of UCNPs during and after the plant exposure was also discussed in this thesis.

We are living in an age where the demand for energy is growing rapidly. This means that supplies to easily accessible oil and natural gas is unlikely to keep up with the demand as times goes on. The world will have to use energy more efficiently and increase its use of other sources of energy. This study is aiming at developing materials that will improve the power conversion efficiency of photovoltaic cells by using up and down-converting phosphor materials. ZnTiO3-Zn2TiO4 composite and ZnTiO3 phosphors doped with Er3+,Yb3+, Eu3+ and Al3+, which display up and down-converted luminescence were synthesized by a simple high temperature conventional solid state reaction method. The structure, particle morphology, absorption, photoluminescent properties and elemental distribution were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis-NIR absorption spectrometer, photoluminescence (PL) spectroscopy and time of flight secondary ion mass spectroscopy (TOF-SIMS), respectively. ZnTiO3-Zn2TiO4 composite doped with different concentration of Er3+ ions was synthesized via solid state chemical reaction method at 1100 ℃. The X-ray diffraction (XRD) confirmed the crystallization of both the hexagonal ZnTiO3 and cubic spinel Zn2TiO4 phases of the composite. The SEM images of ZnTiO3-Zn2TiO4:Er3+ composite showed that the particle morphology was made up of faceted hexagons. Furthermore, the ZnTiO3-Zn2TiO4:Er3+ phosphors were excited in the near-infrared (NIR) region using a laser diode with a wavelength of 980 nm and displayed both green and red up-conversion emission bands in the visible range at 543, 553, 650 – 670 nm. These emission bands correspond to 2H11/2, 4S1/2→ 4 I15/2 and 4F9/2→ 4 I15/2 transitions of Er3+ ions. However, the interaction mechanisms involved in the upconversion process of ZnTiO3-Zn2TiO4:Er3+ phosphor is discussed with the help of an energylevel schematic diagram and the number of the photons involved in the up-conversion luminescence process were of a double photon mechanism. The decay lifetimes were studied by fitting the luminescence decay curve with a single-component exponential decay. Er3+ and Yb3+ incorporated zinc titanate (ZnTiO3) phosphor powders were synthesized using conventional solid-state reaction method at 800 ℃. A ZnTiO3:Er3+,Yb3+ phosphor that resembled an ecandrewsite single phase with space group R-3 (148) was obtained, as proven by X-ray diffraction (XRD). The SEM image showed a surface morphology composed of agglomerated irregular shaped particles. The energy band gap of ZnTiO3 was engineered by incorporating different concentration of the dopant ions. After irradiating ZnTiO3:Er3+with a 980 nm laser beam, the phosphor up-converted the photon energy to display green and red emissions in the visible range that were positioned at 527, 545 and 665 nm. Enhancement of the luminescence intensity of ZnTiO3:Er3+ phosphor was achieved by variation of Er3+ concentration. Co-doping with Yb3+ ions proved to be effective in enhancing the luminescence intensity of the optimized Er3+ ion emission and new emission bands at 410 and 480 nm, through an energy transfer mechanism were observed. The enhancement of the lifetime of the up-conversion luminescence was also achieved by co-doping ZnTiO3:Er3+ phosphor with Yb3+ ion. The energy transfer mechanisms involved in Er3+ - Yb3+ co-doped ZnTiO3 phosphor was illustrated and discussed in detail. The ZnTiO3:Er3+, Yb3+ thin films were successfully deposited by pulsed laser deposition (PLD) by varying the silicon (100) substrate temperature. The distribution of the ions in the films was investigated and the TOF-SIMS showed that the ions were homogeneously distributed throughout the ZnTiO3 host lattice which indicated a successful incorporation of the Er3+ and Yb3+ ions. The optical response of the phosphors revealed that the reflectance percentages of the ZnTiO3:Er3+, Yb3+ vary with the silicon substrate temperature due to the differences in the thickness and morphological roughness of the thin films. The ZnTiO3:Er3+, Yb3+ thin films also exhibited up-conversion emission from Er3+ electronic transitions, with violet, blue, green and red emission lines at 410, 480, 525, 545 and 660 nm from 2H9/2 → 4 I15/2, 4F7/2 → 4 I15/2, 2H11/2 → 4 I15/2, 4S3/2 → 4 I15/2 and 4F9/2 → 4 I15/2 transitions, respectively. These up-conversion emissions were enhanced by increasing the silicon substrate temperature during the deposition. ZnTiO3 host co-doped with Eu3+ and Al3+ was synthesized by solid state reaction to convert the UV photons to visible photons. Charge compensation effects of Al3+ incorporated ZnTiO3:Eu3+ as a co-dopant ion was reported in detail. The structural and morphological characterization show that the addition of Eu3+ and Al3+ does not affect the phase formation and the surface morphology of the host. The visible emission intensity of Eu3+ ions for an optimal concentration of 2 mol% under 395 nm excitation, was enhanced by incorporating Al3+. The energy level diagram showing the charge compensation mechanism was proposed for the co-doped system. / College of Engineering, Science and Technology

Les micro-résonateurs optiques comptent parmi les dispositifs les plus importants en photonique. Les résonateurs WGM sont assez particuliers. Il s'agit de composant présentant une symétrie circulaire comme c'est le cas des sphères, des anneaux, des disques et des tores. Les résonateurs WGM présentent un facteur de qualité exceptionnel et un volume modal très faible. Ces appareils peuvent être utilisés dans plusieurs domaines, notamment la télédétection, le filtrage optique et l'optique non linéaire. D'autres applications sont possibles en biologie, médecine, spectroscopie moléculaire, surveillance environnementale, astronomie et astrophysique grâce à l'exploitation du rayonnement moyen infrarouge. Les micro-résonateurs optiques comportent un grand nombre de transitions vibrationnelles qui agissent comme des «empreintes» pour de nombreuses molécules organiques permettant le développement d'applications spectroscopiques innovantes et de nouveaux capteurs. Il convient de noter que l'atmosphère de la terre est transparente au niveau des deux fenêtres de transmission atmosphérique. La première est comprise entre 3 et 5 μm et la seconde entre 8 et 13 μm, ce qui rend possible des applications telles que la détection d'explosifs à distance ainsi que le brouillage de communication confidentielles. La large fenêtre de transparence en verres de chalcogénures dans le domaine spectral infrarouge rend envisageable le développement de nombreuses applications. Les verres de chalcogénure sont caractérisés par une bonne résistance mécanique et une durabilité chimique suffisante dans l'eau et l'atmosphère. Par ailleurs, l'indice de réfraction élevé, le rendement quantique élevé, l'énergie de phonon faible et la solubilité importante des terres rares permettent des émissions dans le domaine spectral du moyen IR. Dans cette thèse, la conception de dispositifs innovants en chalcogénure pour des applications utilisant le moyen infrarouge est étudiée en utilisant un code d'ordinateur personnel formé de façon aléatoire. Les appareils reposent sur des trois types de micro-résonateurs : les microsphères, les micro-disques et les microbulles. Les résonateurs WGM sont efficacement excités à l'aide de fibres nervurées et de guides d'ondes optiques de forme conique. Le nouveau procédé de conception est développé en utilisant la méthode d'optimisation par essaims particulaires (PSO). Elle permet de maximiser le gain d'un amplificateur reposant sur une microsphère d'émission laser dopée à l'erbium à 4,5 μm. Une technique innovante permettant de caractériser les propriétés spectroscopiques de la terre rare intégrant la recherche électromagnétique en mode WGM grâce à l'algorithme PSO a été développée. Les valeurs récupérées sont entachées d’une erreur inférieure à celle prévue par les instruments de mesure ayant un coût élevé. Des applications intéressantes peuvent être obtenues en excitant le micro-résonateur avec une fibre conique présentant deux LPG identiques sur les côtés. En effet, les FLP peuvent sélectionner le couplage de modes de fibre avec le résonateur WGM. En utilisant différentes paires de FLP identiques, opérant dans différentes bandes de longueurs d'onde, il est possible de coupler de façon sélective différents résonateurs à l'aide de la même fibre optique. Un code informatique aléatoire a été développé et validé. Il a démontré la faisabilité d'un capteur de microbulles de glucose. Un microdisque en terre rare dopé est étudié pour obtenir une source de lumière compacte et économique dans l'infrarouge moyen. Un code informatique est développé afin de simuler un micro-disque de terre rare dopé et associé à deux guides d'ondes nervurés, un pour le signal et l'autre pour la pompe. Le modèle est validé à l'aide d'un micro-disque dopée à l'erbium émettant à 4,5 μm. Ce dispositif très prometteur pour des applications dans le moyen infrarouge est obtenu en utilisant un micro-disque de praséodyme dopé émettant à 4,7 μm. / Optical micro-resonators represent one of the most important devices in photonics. A special kind is constituted by the WGM resonators, i.e. devices with circular symmetry such as spheres, rings, disks and toroids. They are characterized by very small dimensions, exceptionally quality factor and very low modal volume becoming a valuable alternative to the traditional optical micro-resonators, such as Fabry-Pérot cavities. These devices allow applications in several fields, such as sensing, optical filtering and nonlinear optics. In particular, different applications in biology and medicine, molecular spectroscopy, environmental monitoring, astronomy and astrophysics are feasible in Mid-Infrared wavelength range. For example, it includes a lot of strong vibrational transitions that act as “fingerprints” of many bio-molecules and organic species allowing the develop of innovative spectroscopic applications and novel sensors. In addition, the earth's atmosphere is transparent in two atmospheric transmission windows at 3–5 μm and 8–13 μm and then applications such as remote explosive detection, e.g. in airports and for border control, and covert communication systems are feasible. The wide transparency window of chalcogenide glasses in Mid-Infrared makes possible the development of several devices. Chalcogenide glasses are characterized by good mechanical strength and chemically durability in water and atmosphere. Furthermore, the high refractive index, high quantum efficiency, the low phonon energy and high rare-earth solubility enables the emissions at long wavelengths.In this thesis, the design of innovative chalcogenide devices for applications in Mid-Infrared is investigated using an ad-hoc home-made computer code. The devices are based on three kinds of micro-resonators: microspheres, micro-disks and microbubbles. The WGM resonators are efficiently excited by using tapered fiber and ridge waveguides. A novel design procedure is developed using the particle swarm optimization approach (PSO). It allows to maximize the gain of an amplifier based on an erbium-doped microsphere lasing at 2.7 μm.An innovative technique in order to characterize the spectroscopic properties of rare-earth is developed integrating the WGM electromagnetic investigation with PSO algorithm. The method is based on two subsequent steps: in the first one, the geometrical parameters are recovered, in the second one, the spectroscopic parameters. The recovered values are affected by an error less than that provided by high-cost measurement instruments. Furthermore, the procedure is very versatile and could be applied to develop innovative sensing systems.Interesting applications could be obtained exciting the micro-resonator by a tapered fiber with two identical LPGs on the sides. Indeed the LPGs can select the fiber modes coupling with the WGM resonator. Using different pairs of identical LPGs operating in different wavelength bands, it is possible to selective couple different micro-resonators by using the same optical fiber. An ad-hoc computer code is developed and validated and it demonstrated the feasibility of a microbubble glucose sensor.In order to obtain a compact and cost-saving light source in Mid-Infrared, rare-earth doped micro-disk are investigated. A computer code is developed in order to simulate a rare-earth doped micro-disk coupled to two ridge waveguide, one at signal wavelength and the other one at pump wavelength. The model is validated using an erbium-doped micro-disk emitting at 4.5 μm. A very promising device for application in Mid-Infrared is obtained using a praseodymium-doped micro-disk emitting at 4.7 μm.

Made available in DSpace on 2017-07-21T19:26:00Z (GMT). No. of bitstreams: 1 Cristiano Santos Lopes.pdf: 13551286 bytes, checksum: 1ba67329a96370d271e71e39f117ec62 (MD5) Previous issue date: 2010-11-19 / In this work we report on conductivity fluctuation measurements in polycrystalline samples of the Er1xPrxBa2Cu3O7 and Gd1xPrxBa2Cu3O7superconductor. Pr contents are 0.00, 0.05 and 0.10. Samples were prepared by the standard solid-state reaction technique and characterized by SEM, X-ray diffraction and electrical transport experiments. The samples were granular and homogeneous. The results were analyzed in terms of the temperature derivative of the resistivity and of the logarithmic temperature derivative of the conductivity, what allowed identifying power-law divergences of the conductivity. For Er1−xPrxBa2Cu3O7 samples, the results show that the transition proceeds in two stages: pairing and coherence transition. Also, our results, from the critical exponent analysis, show a two-peak splitting at pairing transition, indicating possibly a phase separation. On approaching the zero resistance state, our results show a power-law behavior that corresponds to a phase transition from paracoherent to a coherent state of the granular array. For Gd1−xPrxBa2Cu3O7 samples, it was observed that the critical temperature decreases and that the transition width increases with increasing Pr doping. Systematic measurements of fluctuation conductivity are reported and special attention is taken above the critical temperature, where Gaussian and critical regimes are observed. Below the critical temperature, on approaching the zero resistance state, our results show a power-law behavior consistent with a phase transition from a paracoherent to a coherent state of the granular array. / Neste trabalho foram estudados os efeitos das flutuações térmicas na condutividade elétrica de amostras policristalinas com base nos supercondutores Er1xPrxBa2Cu3O7 e Gd1xPrx Ba2Cu3O7. A quantidade de Pr considerada foi x = 0, 00, 0, 05 e 0, 10. As amostras foram preparadas pela técnica padrão de reação de estado sólido e caracterizadas por microscopia eletrônica de varredura, difração de raios-X e medidas de transporte eletrônico. As amostras são homogêneas e granulares. Para a obtenção dos expoentes críticos, os dados foram analisados em termos da derivada da resistividade em função da temperatura e da derivada logarítmica da resistividade em função da temperatura. Essa análise permitiu identificar regimes em lei de potência na paracondutividade durante a transição normal-supercondutora. Para a amostra de Er1−xPrxBa2Cu3O7, os resultados mostraram que a transição ocorre em dois estágios: transição de pareamento e transição de coerência. Contudo, os resultados obtidos através da análise dos expoentes críticos mostraram o desdobramento em dois picos da transição de pareamento, indicando uma possível separação de fase. Na aproximação do estado de resistência nula, os resultados mostraram um comportamento em lei de potência que corresponde à transição de fase paracoerente-coerente, típica de sistemas granulares. Para a amostra de Gd1−xPrxBa2Cu3O7, foi observado que a temperatura crítica diminuiu e que a largura da transição aumentou com o acréscimo da dopagem de Pr. Medidas sistemáticas na condutividade são apresentadas e é dada atenção especial em temperaturas ligeiramente acima da temperatura crítica, região na qual regimes Gaussianos e críticos são observados. Abaixo da temperatura crítica, na aproximação ao estado de resistência nula, os resultados mostram claramente regimes em lei de potência consistentes com a transição de fase paracoerente-coerente.

Ce travail s'insère, non seulement, dans la compréhension de la relation entre la résonance des terres rares et l'indice non linéaire, mais aussi, dans la recherche de nouveaux matériaux dopés terres rares pour la commutation optique. L'introduction d'oxyde d'erbium dans des verres tellurites et borophosphates de niobium, présentant intrinsèquement une non linéarité optique de 3ème ordre élevée, a été étudiée. Il a été montré qu'il est possible de contrôler le gain et la non linéarité de matériaux dopés grâce à la corrélation établie entre l'analyse structurale et l'étude des propriétés spectroscopiques, de gain et de non linéarité qui dépendent des probabilités de transition 4f –4f. L'ensemble des résultats permet de mieux comprendre et prédire la variation de l'indice non linéaire d'un matériau amplificateur.

La maitrise de l'information représente un avantage concurrentiel de nos jours. Malgré une intensification des moyens développés pour protéger les flux de données, il n'est actuellement pas possible d'échanger à distance et de façon complètement sure, une information entre deux interlocuteurs. Néanmoins, des travaux menés par Bennett et Brassard ont montré qu'il est possible d'atteindre un niveau de sécurité maximum en utilisant un protocole quantique de transmission de l'information. Ce protocole se base sur l'utilisation de réseaux télécom utilisant des répéteurs quantiques à la place des répéteurs classiques. La voie étudiée dans cette thèse, réalisée en partie dans le cadre du projet européen QuRep, a pour but l'amélioration des connaissances sur les monocristaux dopés aux ions de terre rare qui sont des candidats de choix pour la mise au point de répéteurs quantiques. Deux grands axes ont émergés : dans un premier temps nous avons essayé de comprendre quels sont les facteurs de succès et limitatifs dans l'utilisation du cristal de Nd : YSO en tant qu'hôte pour les mémoires quantiques avec pour objectif le transfert de la cohérence électronique vers des niveaux hyperfins. Dans un second temps, nous avons étudié un cristal présentant une structure hyperfine directement accessible en optique, Er : YLF afin de vérifier sa potentielle utilisation pour les mémoires quantiques. Ces travaux ont permis, entre autre, de réaliser un transfert de cohérence d'un niveau Zeeman électronique vers un niveau hyperfin avec un temps de stockage de plus de 300 μs, ce qui permet d'envisager une mémoire quantique dans Nd : YSO permettant de réémettre un photon à la demande

The research that is presented in this thesis can be divided into two major parts. The first part concerns longitudinally pumped, bulk Er-Yb lasers. In these lasers, the main limitation is the thermal shortcomings of the phosphate glass host material. From the laser experiments and the spectroscopic measurements on crystalline host materials, as well as an investigation to bring further light to the physical background of the involved dynamics, the thesis presents some novel results that contribute to the search for a crystalline replacement. The second part concerns novel laser concepts applied to Yb-doped double tungstate lasers. Different crystal orientations are investigated, such as an athermal orientation for reduced thermal lensing and a conical refraction orientation for complete polarization tuning. Furthermore, the introduction of volume Bragg gratings in the cavity enables wide spectral tuning ranges and extremely low quantum defects. Regarding the first part, the main results are the achievement of 15 % slope efficiency in a monolithic, continuous-wave Yb:GdCOB laser and the achievement of Q-switching of the same laser. The Q-switched pulse durations were around 5-6 ns and the Q-switched slope efficiency was 11.6 %. For both lasers, a maximum output power of 90 mW was obtained, which is close to ordinary glass lasers under similar conditions. A spectroscopic investigation into the Er,Yb-codoped double tungstates was also performed and the results have enabled mathematical modeling of the fluorescence dynamics in these materials. Finally, the temperature dependence of the dynamics in Er,Yb:YAG was studied and the results have given some insight into the physical background of the mechanisms involved. Regarding the second part, different end-pumped Yb:KReW laser cavities were constructed to demonstrate the different concepts. With a laser crystal cut for propagation along the athermal direction at 17º angle clockwise from the dielectric direction Nm, the thermal lens could be reduced by 50 %. In these experiments the maximum output power was 4 W at 60 % slope efficiency. In another cavity incorporating a volume Bragg grating in a retroreflector set-up, the wavelength could be continuously tuned between 997 - 1050 nm. The spectral bandwidth was 10 GHz and the peak output power was 3 W. The same output power could also be obtained at 1063 nm with the grating positioned as an output coupler instead. If, on the other hand, the grating was positioned as an input coupler, 3.6 W output power at 998 nm was obtained at a quantum defect of only 1.6 %. Furthermore, using a crystal oriented for propagation along an optic axis, internal conical refraction could be used to establish arbitrary control of the polarization direction as well as the extinction ratio. Even unpolarized light could be enforced despite the highly anisotropic medium. With this configuration, the maximum output power was 8.6 W at 60 % slope efficiency which equals the performance of a reference crystal with standard orientation. The completely novel concepts of laser tuning with Bragg grating retroreflectors, of low quantum defect through Bragg grating input couplers and of polarization tuning by internal conical refraction can all easily be applied to several other laser materials as well. / QC 20100713

The realisation of signal processing algorithms in fixed-point offers substantial performance advantages over floating-point realisations. However, it is widely acknowledged that the task of realising algorithms in fixed-point is a challenging one with limited tool support. This thesis examines various aspects related to the translation of algorithms, given in infinite precision or floating-point, into fixed-point. In particular, this thesis reports on the implementation of a given algorithm, an EDFA (Erbium-Doped Fibre Amplifier) control algorithm, on a FPGA (Field Programmable Gate Array) using fixed-point arithmetic. An analytical approach is proposed that allows the automated realisation of algorithms in fixedpoint. The technique provides fixed-point parameters for a given floating-point model that satisfies a precision constraint imposed on the primary output of the algorithm to be realised. The development of a simulation framework based on this analysis allows fixed-point designs to be generated in a shorter time frame. Albeit being limited to digital algorithms that can be represented as a data flow graph (DFG), the approach developed in the thesis allows for a speed up in the design and development cycle, reduces the possibility of error and eases the overall effort involved in the process. It is shown in this thesis that a fixed-point realisation of an EDFA control algorithm using this technique produces results that satisfy the given constraints.

Made available in DSpace on 2014-10-09T12:51:51Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:32Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:00/11446-0

Made available in DSpace on 2014-10-09T12:51:51Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:32Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Foram estudados os processos de transferência de energia (TE) dos níveis 4I13/2 ; 4I11/2 do Er3+ e 5I7 ; 5I6 do Ho3+ no LiYF4 (YLF) e no ZBLAN, para os íons desativadores Nd3+, Tb3+ ou Eu3+. Os microparâmetros de interação dessas TE foram obtidos utilizandose o método da integral de sobreposição e os resultados indicaram que o íon de Eu3+ é o melhor desativador do primeiro estado excitado do Ho3+ no YLF e o Nd3+ é o mais eficiente desativador do Er3+ no YLF e ZBLAN. A dependência temporal das fluorescências do Er3+ em 1,5 ; 2,7 m e do Ho3+ em 2,1 ; 2,9 m foram medidas utilizandose excitações laser pulsadas provenientes do Nd-YAG+2 +OPO sintonizável. Foi proposto um critério geral para a discriminação dos processos de TE assistidos pela migração da excitação entre doadores (difusão ou saltos). Verificou-se que o modelo de migração por difusão ajusta melhor os processos de TE do segundo estado excitado do doador (Er3+ or Ho3+) independentemente da razão CD-D / CD-A, enquanto que o modelo de migração por saltos aplica-se ao primeiro estado excitado do doador. Foi proposta uma modificação no modelo de saltos que descreve os resultados experimentais para sistemas com CD-D / CD-A> 10. Utilizando-se os parâmetros de TE verificamos que os melhores sistemas para a ação laser em 3µm são: Ho:Eu:YLF, Ho:Nd:YLF e Er:Nd:YLF. Por outro lado, verifica-se que os sistemas com baixas concentrações (1,5mol%) de Er:Nd; Er:Tb e Er:Eu no ZBLAN não apresentaram potencial de inversão de população para a ação laser em 2,8 m. Os processos de conversão ascendente no sistema Er:YLF foram estudados em função da concentração de Er3+, sendo que os processos de absorção de estado excitado (ESA) e de conversão ascendente por transferência de energia (ETU) foram discriminados utilizando as curvas de decaimento resolvidas no tempo. Observou-se que o comprimento de onda de excitação em 980nm é o mais adequado para o bombeamento do sistema Er:YLF para a emissão laser quase contínua (cw) em 2,8 m. A técnica de pump-probe foi utilizada a fim de serem investigados os efeitos nos tempos de vida do sistema Er:YLF, sendo verificada uma diminuição da contribuição da migração da excitação nos tempos de vida do primeiro e segundo estados excitados do Er3+ no YLF com o aumento da potência de bombeamento cw ( pump ). As taxas experimentais de TE, determinadas para os melhores sistemas por meio do parâmetro RN, foram utilizadas no sistema de equações de taxa e, resolvendo-as pelo método numérico de Runge-Kutta de 4a ordem, pudemos avaliar a densidade de população invertida para as emissões em 2,8 m do Er3+ e 2,9 m do Ho3+ em função das taxas de bombeamento e das concentrações dos íons ativador e desativador. A melhor concentração do sistema Er:YLF foi de 20mol% e no sistema Er:Nd:YLF foi de 4mol% de Er3+ e 1,5mol% de Nd3+. Verificou-se que o sistema Er(4mol%):Nd(1.5mol%):YLF favorece o aumento da freqüência máxima de operação de 14Hz no Er:YLF para 391Hz baseando-se na medida do tempo de vida do nível laser inferior (4I13/2) do Er3+. O sistema Ho3+ no YLF é otimizado utilizando-se 0,6mol% de Ho3+ e 1,5mol% de Nd3+ ou pelo sistema Ho(3mol%):Eu(1,2mol%):YLF, sendo que a densidade de população invertida observada no sistema Ho(3mol%):Eu(1,2mol%) é 2,4 vezes maior que no sistema Ho(0,6mol%):Nd(1,5mol%). / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:00/11446-0