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| Author(s): |
Maria Luiza Miguez
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) |
| Defense date: | 2017-12-08 |
| Examining board members: |
Lino Misoguti;
Tomaz Catunda;
Paulo Clóvis Dainese Júnior;
Paulo Henrique Dias Ferreira;
Niklaus Ursus Wetter
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| Advisor: | Lino Misoguti |
| Abstract | |
In this work we have developed a method to increase accuracy and sensitivity of the nonlinear rotation of elliptical polarization measurements by NER using a rotating polarizer as an analyzer and a dual-phase lock-in amplifier. NER measurements are useful in determining the magnitude and signal of the nonlinear refractive index, n2, of different materials. Because this is a new methodology, we compared our results with those obtained by Z-scan, a well-established and widely used method in determining n2. For this purpose we performed NER and Z-scan measurements on samples with pure non-resonant electronic nonlinearity, at weakly focused beam condition. The results obtained have shown the equivalence between both techniques in terms of sensitivity, precision and simplicity. We also proposed a configuration in which multiple samples are measured simultaneously in a single scan, at strongly focused beam condition. This self-referenced method allows better comparison between the materials since the signal of a reference and the sample under study are obtained simultaneously, under the same experimental conditions, besides allowing measuring the local nonlinearities. Once we verified the potential of NER measurements in the tightly focused condition we proceeded to study the contribution of non-instantaneous nonlinearities by measuring n2 as a function of the pulse duration. By varying the pulse duration we studied nonlinearities in liquid samples that have, besides the contribution of electronic instantaneous effect, contribution of non-instantaneous nuclear effects of slow orientational origin. An empirical model of the dependence of nonlinearity as a function of pulse duration was proposed to explain the results obtained, in which instantaneous nonlinearities and non-instantaneous nonlinearities could be discriminate and a response time to the latter could be assigned. (AU) | |
| FAPESP's process: | 13/11514-5 - Study of nonlinear elliptical polarization rotation: refractive nonlinearity origin influence |
| Grantee: | Maria Luiza Miguez |
| Support Opportunities: | Scholarships in Brazil - Doctorate |