Determinação de propriedades térmo-ópticas de vidros e cristais utilizados como meio ativo para lasers de estado-sólido utilizando técnicas de interferometria óptica

• Autor(a) principal: Steimacher, Alysson
• Data de Publicação: 2004
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Estadual de Maringá (RI-UEM)
• Texto Completo: http://repositorio.uem.br:8080/jspui/handle/1/2676
• topic: Lente térmica; Propriedades termoópticas; Vidros especiais; Laser (Estado sólido); Interferometria óptica; Índice de refração.; Ciências Exatas e da Terra; Física

In this work, the optical interferometric technique was used to determine the temperature coefficient of the optical path length (dS/dT) as a function of the temperature for several glasses and single crystals. The temperature range was between room temperature and 180°C. The studied samples included oxide glasses, such as low silica calcium aluminosilicate (LSCA), phosphates and borates, at different preparation conditions and doped with Nd or Cr, and also chalcogenides glasses (GLS and GLSO). Where also studied single crystals LiSrAlF6 (LISAF) and LiSrGaF6 (LISGAF). At room temperature, among the oxide glasses, the borate showed the smallest dS/dT value: 1.05x10-5 K-1, while for phosphate and LSCA the dS/dT values were 1.22 x10-5 K-1 and 1.95 x10-5 K-1, respectively. These values are independent of the ion-doping concentration and the samples preparation conditions. For the chalcogenides glasses, the dS/dT values are around five times greater than value found for oxide glasses. The results showed that dS/dT increases about 20% for all samples with the temperature reaching. This behavior can be attributed to both an increase of the thermal expansion coefficient or the thermal polarizability coefficient. Two different interferometric techniques were used for the determination of the thermal expansion coefficient and refractive index coefficient (dn/dT) in LSCA sample as a function of temperature, between room temperature and 150°C. In this temperature range, the thermal expansion coefficient is essentially constant, while dn/dT increases about 15%. This result indicate that the coefficient of the electronic polarizability (j) is dominant in the thermal behavior of the dS/dT. For the single crystal LISAF and LISGAF, it was observed a modulation in the interferogram if a unpolarized laser is used. This fact is due to the anisotropy of the thermal - optical proprieties of these materials. Considering this effect, dS/dT was estimated for different crystallographic axis and the difference in dn/dT for these axis, using a single measurement. These results were confirmed by measurements of dS/dT as a function of temperature for different axis orientations, by means of experiments with polarized laser. The results are in agreement with dS/dT values calculated using the data from literature and indicate that this low cost and considerably simple method, is a useful tool to measure the thermal - optical proprieties as a function of the temperature for semitransparent glasses and single crystals used in solid state lasers