magistrsko delo
Jure Brence (Author), Irena Drevenšek Olenik (Mentor)

Abstract

Nematski tekoči kristali imajo v homogeni ureditvi centrosimetrično strukturo, zato podvajanje optične frekvence v njih ni mogoče. Zunanje električno polje centrosimetrijo poruši preko pojava električno inducirane polarizacije ter preko fleksoelektričnega pojava, ki je posledica reorientacije direktorja v zunanjem polju. Suspenzija magnetnih nanoploščic v nematskem tekočem kristalu tvori tekoči kristal s feromagnetnimi lastnostmi, v katerem lahko reorientacijo poleg električnega polja dosežemo tudi z magnetnim poljem, kar omogoča meritev prispevka fleksoelektričnega pojava k podvajanju frekvence brez prispevka električno induciranega podvajanja frekvence. V magistrskem delu sta predstavljeni prva meritev in analiza podvajanja optične frekvence v feromagnetnem tekočem kristalu. Dodatek magnetnih ploščic razen povečanja absorpcije nima pomembnega vpliva na optične lastnosti materiala. Pri uporabi električnega polja je signal frekvenčnega podvajanja znaten v treh od šestih proučevanih polarizacijskih kombinacij, pri uporabi magnetnega polja pa le v eni polarizacijski kombinaciji. Izmerjeni izkoristek podvajanja pri uporabi magnetnega polja je približno petkrat manjši kot izkoristek pri uporabi električnega polja.

Keywords

nelinearna optična susceptibilnost;podvajanje optične frekvence;nematski tekoči kristali;feromagnetni tekoči kristali;električno polje;magnetno polje;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [J. Brence]
UDC: 535:538.9
COBISS: 3368292 Link will open in a new window
Views: 714
Downloads: 194
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Other data

Secondary language: English
Secondary title: Second harmonic generation in feromagnetic liquid crystals
Secondary abstract: Liquid crystals in the homogeneous nematic phase possess a centrosymmetric structure, in which second harmonic generation is not possible. The application an external electric field breaks the centrosymmetry through an effect called electric poling, as well as through the flexoelectric effect, caused by reorientation of the director feld. A liquid crystal with ferromagnetic properties can be created by suspending magnetic nanoplatelets in a conventional nematic liquid crystal. In such a material reorientation can be induced not only by applying an external electric field, but also by applying an external magnetic field, which allows the study of the flexoelectric contribution to second harmonic generation without the presence of the contribution from the electric field-induced second harmonic generation. This thesis reports the First experimental measurement and analysis of second harmonic generation in a ferromagnetic liquid crystal. The addition of magnetic nanoplatelets has no significant effect on optical properties of the material other than increased absorption. When using an applied electric field, the second harmonic signal is significant in three out of six investigated polarization combinations, while by the use of a magnetic field a significant signal is observed only in one polarization combination. The conversion efficiency in the case of reorientation with a magnetic field is about five times smaller than the conversion efficiency when using an electric field.
Secondary keywords: nonlinear optical susceptibility;second harmonic generation;nematic liquid crystals;ferromagnetic liquid crystals;electric field;magnetic field;
Type (COBISS): Master's thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages: 57 str.
ID: 11227637