This thesis relates a technique for increasing the optical strength of NaCl and KCl single-crystal samples. The 1.06-μm pulsed laser damage thresholds were increased by factors as large as 4.6 for a bulk NaCl single-crystal sample. The bulk laser damage breakdown threshold (LDBT) of the crystal was measured prior to and after heat treatment at 800*C using a Nd:YAG laser operating at 1.06 μm. Bulk and surface LDBTs were also studied on samples annealed at 400° C. These samples showed differences in damage morphology on both cleaved and polished surfaces, and the cleaved surfaces had improved damage thresholds. However, neither the polished surfaces nor the bulk showed improved threshold at the lower annealing temperature.

Thesis (Elec.E)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 172-176. / by Chon Meng Wong. / Elec.E

This thesis presents studies on a novel ‘meta-material’ as a potential candidate to replace the traditional Electro-Optic crystals (GaP, ZnTe) used in ultrashort bunch monitors for electron/positron accelerators. This study is aimed at showing the linear and non-linear optical properties of such materials, and creating a toolbox for both optical characterisation and manipulation of their properties using an ultra-short pulsed laser. The material studied throughout this thesis is a composite of silver nanoparticles (a “nanocomposite”) embedded within soda-lime glass. The Surface Plasmon Resonance (SPR) is a feature of these particles that is responsible for its unique optical properties. It is shown in this work how SPR is utilised for shape modification of silver nanoparticles with the use of a ps- pulsed laser with various laser beam polarisations. The impact of linear polarisation irradiation is investigated. It is found that multipulse irradiation has the effect of elongating nanoparticles to form prolate spheroids, which results in a dichroic effect on the composite as a whole, caused by the anisotropic SPR band shift. It is also shown that changing the laser polarisation from linear to radial and/or azimuthal changes the character of the reshaped nanoparticles. It was observed that a localised change of ellipsoid orientation is achieved, resulting in a non-directionally-dependent SPR band shift. Second Harmonic Generation (SHG) has been observed from reshaped nanoparticles embedded in soda-lime glass. A comparison of the effect was made between ps-pulsed reshaped, fs-pulsed reshaped and mechanically stretched samples containing silver nanoparticles. Multiphoton Absorption Induced Luminescence (MAIL) was observed along with the SHG and characterised for the various laser polarisation components. The dependence of the aforementioned effects on the elongated nanoparticle aspect ratio was shown to have a great impact. A novel method for reshaped nanoparticles characterisation is presented. It is based on the laser-induced SHG and MAIL signal and is proved to give a precise measurement of the nanoparticle shape and orientation. Frequency Resolved Optical Gating (FROG) measurement of a fs-pulse is measured with great accuracy, in the case where the BBO nonlinear crystal is replaced by the reshaped nanoparticle composite. This was demonstrated to be caused by the anisotropic SHG of the ellipsoidal nanoparticles. Preliminary THz based measurements were performed as a part of a feasibility study of the application of these composites in the EO-based detection of ultrashort electron bunches. Future work is suggested in order to achieve more efficient EO detection.

Graduation date: 1993

Two-dimensional thermal, mechanical and optical simulations are carried out to investigate the effect of Nd3+ concentration on thermal, mechanical and optical behavior of Nd:YAG ceramic laser materials under continuous wave laser operation. In the analyses, rods are pumped longitudinally with laser diodes, in three, six, nine and twelve fold structures. Rods having diameters of 3 and 6 mm are pumped with 808 nm and 885 nm sources separately having Nd+3 concentrations of 0.6, 1, 2, 3, 4 and 6 at. %. Total absorbed pump power are kept constant for all rods. Absorbed pump power distribution are obtained for each rod using ray tracing method and Beer&amp / #8217 / s Law. In the analysis, temperature dependent material properties are incorporated. Nonlinear numerical solutions of thermal and stress equations have been performed. Temperature and stress results are obtained to investigate the effect of Nd concentration on the optical properties of ceramic YAG laser material. Analysis results reveal that, increase in Nd3+ concentration of YAG ceramic laser material, decreases the temperature and stress developed during optical pumping. Rods pumped with 808 nm source have large temperature and stress values compared to 885 nm pumped ones. Optical path difference (OPD) of each ray passed trough the material is calculated using thermal and elastic strain results together with photo-elastic constants of Nd:YAG material. Focal length and depolarization of each rod is calculated numerically from OPD results. Focal length of each rod is found to increase, in contrary depolarization is found to decrease with increase in the dopant concentration.

Facilement excitable au moyen de diode InGaAs, l’ion Ytterbium trivalent présenteune émission infrarouge intéressante pour des applications laser. Les matériaux étudiés sontnombreux. Parmi eux, les borates sont des composés stables, transparents dans l’UV et présentant un seuil élevé au dommage. Ils sont par conséquent des bons candidats pour desapplications optiques. D’un point de vue structural, ils présentent une diversité de sitesd’accueil pour la terre rare ce qui permet de moduler les émissions obtenues en fonction de lacomposition.Nous avons mené une étude d’élaboration et de caractérisation sur un borate (à fusioncongruente) et deux oxyborates (à fusion non congruente) de composition : Li6Ln(BO3)3 ;LiGd6O5(BO3)3 ; Na3La9O3(BO3)8.Les différentes croissances cristallines, par la méthode Czochralski ou par la méthodedu flux, nous ont permis d’obtenir des cristaux de taille centimétrique comportant de largeszones transparentes, utiles pour les tests en cavité laser. L’étude spectroscopique de l’ionytterbium nous a permis d’évaluer l’éclatement des niveaux d’énergie et de localiser les ionsterres rares dans ces matrices. Différentes caractérisations thermiques, mécaniques et optiquesont aussi été réalisées sur les cristaux afin de pouvoir estimer les paramètres laser.Finalement, de premiers tests lasers ont été réalisés et ont montré la potentialité de cesmatériaux en tant que matériaux amplificateurs. / By the mean of InGaAs diode, trivalent ytterbium ions can give rise to an interestinginfrared emission for laser applications. Numerous compounds are in study. Among them,borates are stable, UV-transparent compounds and they have a high damage threshold. Thusthey are good candidates for optical applications. From a structural point of view, they exhibita diversity of host sites for the rare earth which allows to modulate emission withcomposition.We carry out an elaboration and characterization study on a borate and two oxyboratecompounds of formula Li6Ln(BO3)3 ; LiGd6O5(BO3)3 ; Na3La9O3(BO3)8.Crystal growth, by Czochralski or flux method depending on the meltingcharacteristic, enable us to obtain centimetric sized crystals with large transparent areas.Ytterbium ion spectroscopy study enables us to estimate energy levels splitting and to locaterare earth ions in these matrices. Several thermal, mechanical and optical characterizations were also performed on the crystals to estimate laser parameters. Finally, first laser tests werecarried out and have shown the potentiality of these materials as amplifier media.

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Made available in DSpace on 2014-10-09T12:41:19Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:03Z (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:08/10721-9

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-02-03T11:49:25Z No. of bitstreams: 0 / Made available in DSpace on 2016-02-03T11:49:25Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:41:19Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:03Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Estudou-se neste trabalho a preparação de LiLa(WO4)2:TR3+ (LLW:TR) nas formas de fibras monocristalinas (micro-pulling-down) e de microcristais pó cerâmico (método dos precursores poliméricos). No que se refere às fibras: a taxa de puxamento no crescimento de LiLa(1-x)Eux(WO4)2 para 0≤x≤1 é influenciada pela diferença de raio iônico do Li e das TR; a estrutura tetragonal da scheelita descreve as composições 0≤x≤1; a incorporação do Eu gera distorções na estrutura sem reduzir a simetria local do íon; uma queda de luminescência para x>0,20 é observada; e as estruturas para 0≤x≤1 foram modeladas através de simulação atomística com bastante precisão. No que se refere aos microcristais: o efeito do controle de pH na preparação de LLW:Nd 1,0 mol% foi avaliado; obteve-se aglomerados de morfologia irregular e com tamanhos médios entre 22-48 μm, cujo aumento é maior em função da temperatura do que do tempo de calcinação. No que se refere à construção experimental do diagrama de fases do sistema xLi2W2O7-(1-x)La2W2O9: confirmou-se que o LLW (formado numa região de homogeneidade de 0,48≤x≤0,55) se decompõe peritéticamente a 1000°C; a dopagem por TR influencia sua fusão; dados do crescimento, de DTA e de DRX de fibras de LLW, crescidas com composições baseadas neste diagrama, corroboram o mesmo. O processo de obtenção de fibras foi otimizado, com um excesso mínimo de 1,5 mol% de Li2W2O7. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP:08/10721-9