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| Author(s): |
Sergio Leonardo Gómez
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física (IF/SBI) |
| Defense date: | 2000-05-30 |
| Examining board members: |
Antonio Martins Figueiredo Neto;
Antonio Carlos Bento;
Carla Goldman;
Daniel José Pusiol;
Sérgio Carlos Zilio
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| Advisor: | Antonio Martins Figueiredo Neto |
| Abstract | |
Nonlinear optical properties of ferrofluid-doped lyotropic liquid crystals in the millisecond range were studied using the Z-Scan technique. These properties were characterized in different mesophases as function of the incident power of the laser, ferrofluid concentration, direction of the director (calamitic nematic mesophase), signal\'s temporal evolution and relative concentrations of the samples. We suggest that the lyotropic\'s nonlinear optical properties, in millisecond range, come from a thermal effect. The experimental data were analyzed using the Sheik- Bahae\'s model and the Thermal Lens model. The Sheik-Bahae\'s model allows to get the nonlinear refractive index n2 and the Thermal Lens model gives the thermal conductivity k and the thermo optic coefficient dn/dT. It is possible to set a relationship between Sheik-Bahae\'s model and Thermal Lens model that is experimentally verified. Analyzing the influence of ferrofluid on the lyotropics\'s nonlinear optical response, we conclude that it introduces a small anisotropy in the optical absorption in the presence of an external magnetic field. A possible mechanism that could be present in the ferro-lyotropic sample illuminated by the laser beam is the hyperthermia. The study of the nonlinear optical response of lyotropic samples with different concentrations, in a nematic domain, at constant temperature, shows that it is possible to relate the behaviors observed on k, dn/dT and n2 to a change of microscopic structure of micelles. (AU) | |