Spectroscopic refractometry by broadband interference within the ultraviolet, visible and near infrared ranges

Resumo

Optical characterization is a fundamental part of the design and development of photonic devices, being the refractive index one of the most important magnitudes to be analyzed. The most spread refractometric techniques study the refractive index only at one wavelength. In order to characterize a wide spectrum, a huge quantity of measures at different wavelengths is required, considerably increasing the acquisition time. This thesis is about the Spectroscopic Refractometry based on Broad Band Interferometry (Spanish acronym, REIBA), a technique capable of obtaining the refractive index fast and continuously over a wide spectrum. Although this technique was proposed three decades ago, it has not been properly implemented yet due to the lack resolution on spectrometers and the inaccurate determination of the phase's ambiguity. This work presents a device based on REIBA capable of recovering the refractive index with high precision over a spectrum between 255 to 1550 nm, covering the visible, near infrared and ultraviolet regimes. The work is composed by six publications. Five of them describe the device, its components and the modifications incorporated in order to improve its capacities. Special attention was paid to design and optimize the components as function of the spectral range analyzed. There is also included a discussion about experimental procedure for obtaining the maximum range from the minimum number of measures. Besides, an error analysis is done as well as the influence of the phase’s ambiguity. The fifth of these articles presents a novel methodology which allows the characterization of partially absorbent samples in the visible range by using different thickness samples. The last publication is focused on the application of the technique REIBA to the characterization and modeling of the refractive index variation with temperature for a group of novel materials, the ionic liquids. These materials arouse interest due to its possible applications on diverse technologies thanks to its tunability on physical properties by small changes of the molecular structure. A model that describes the refractive index of a group of eleven of such liquids based on the methyl-alkyl-imidazolium cation was obtained from the experimental data. Aside from showing the suitability of the technique to the optical characterization over a wide spectral range, this publication shows an efficient strategy for the optical analysis of ionic liquids.