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Master's Dissertation
DOI
10.11606/D.43.2000.tde-05032002-142325
Document
Author
Full name
Jacinto da Silva Esteves
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2000
Supervisor
Committee
Figueiredo Neto, Antonio Martins (President)
Catunda, Tomaz
Vieira Junior, Nilson Dias
Title in Portuguese
Estudo de propriedades ópticas não-lineares de cristal líquido dopado com corante em função da temperatura.
Keywords in Portuguese
corante
cristal líquido
fluídos complexos
óptica não-linear
Abstract in Portuguese
Com o objetivo de estudar os efeitos provocados pela adição de um corante em um cristal líquido termotrópico (CL), pesquisamos neste trabalho a influência da temperatura na reorientação das moléculas deste composto, bem como o índice de refração e a absorção não-linear, devido à presença de um campo eletromagnético. O CL estudado apresenta a reorientação de suas moléculas na presença de luz polarizada. Esta reorientação se deve à polarização provocada pelo campo eletromagnético da luz incidente nas moléculas do CL. O torque, que ocasiona tal reorientação, é denominado torque óptico Gammaopt. Quando estes CLs são dopados com determinados corantes, o campo incidente também interage com o corante, induzindo assim dipolos elétricos. Estes dipolos, por sua vez, interagem com as moléculas do CL provocando nelas um torque adicional Gammadye. Este torque adicional é proporcional ao torque óptico Gammadye = eta Gammaopt, onde eta é uma característica do corante denominado de fator de amplificação do torque óptico e depende da temperatura em que a amostra se encontra. A principal ferramenta do nosso estudo é a técnica de varredura z e, é através dela, que observamos a influência da temperatura nos efeitos não-lineares, refrativo e absortivo, exibidos pelas amostras. Através de tal técnica, calculamos, em função da temperatura, o fator de amplificação do torque óptico (eta); os índices de refração não-lineares (n2) devido à reorientação molecular da amostra, com e sem corante; e os coeficientes de absorção não-lineares (Beta) da amostra dopada devido a efeitos térmicos, de reorientação (torque) e de todos os efeitos somados.
Title in English
Studies of non-linear optical properties of dye doped liquid crystal in function of the temperature.
Keywords in English
complex fluids
dye
liquid crystal
non-linear optics
Abstract in English
With the objective of studying the effects due to the addition of a dye in a thermotropic liquid crystal (LC), we investigated in this work the influence of the temperature in the reorientation of the molecules of this compound, as well as the refraction index and the non linear absorption, in the presence of a electromagnetic field. The studied LC presents the reorientation of its molecules in the presence of polarized light. This reorientation is due to the polarization induced by the electromagnetic field of the incident light in the molecules of LC. The torque, that causes such reorientation, is named Gammaopt. When these LCs are doped with certain dyes, the incident field also interact with the dye, inducing electric dipoles. These dipoles, interact with the molecules of the LC producing an additional torque Gammadye. This additional torque is proportional to the optical torque Gammadye = eta Gammaopt, where eta is a characteristic of the dye, a factor of amplification of the optical torque, that is temperature dependent. The main tool of our study is the z-scan technique and, it is through it, that we observed the influence of the temperature in the non linear, refractive and absorptive effects, exhibited by the samples. Through this technique, we calculated, as a function of the temperature, the amplification factor of the optical torque (eta); the non linear refractive index (n2) due to the molecular reorientation of the sample, with and without dye; and the non linear absorption coefficient (Beta) of the doped sample due to thermal effects, of reorientation (torque) and of all the effects together.
 
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Publishing Date
2002-06-18
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
  • ESTEVES, J. S., and Neto, A.M.F. Temperature dependence of the director reorientation of dye-doped nematic liquid crystals subjected to an optical field and its relation with the non-linear absorption coefficient [doi:10.1080/02678290210127760]. Liquid Crystals [online], 2002, vol. 29, p. 733-742.
  • ESTEVES, J., and Neto, A.M.F. Temperature dependence of the director reorientation of dye-doped nematic liquid crystals and its relation with the non-linear absorption coefficient. In 19th International Liquid Crystal Conference, Edinburgh, 2002. 19th International Liquid Crystal Conference., 2002. Abstract.
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