Refractive index spectroscopy and material dispersion in fused silica glass.

In this study, we aimed to measure material dispersion in fused silica using a low coherence interferometric method. The measurement was carried out quickly and efficiently in a wide spectral range using this method. The refractive index and group index of fused silica were determined by capturing a few interferograms. The material dispersion was modeled using a Sellmeier equation with three resonances. Three different fits were investigated; the most appropriate fit was the one that used both the measured refractive and group indexes to model the dispersion. Second-order dispersion was also quantified, and zero-dispersion wavelength was determined.

An experimental and computational study on the material dispersion of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids.

The material dispersion of the [Ckmim][BF4] (k = 2, 3, 4, 6, 7, 8, 10) family of ionic liquids is measured at several temperatures over a broad spectral range from 300 nm to 1550 nm. The experimental curves are fitted to a modified three-resonance Sellmeier model to understand the effects of temperature and alkyl chain length on the dispersion behaviour. From the parameters of the fitting, we analyze the influence that the different constituents of these ionic liquids have on the dispersion behaviour. In addition, a semi-empirical approach combining simulated electronic polarizabilities and experimental densities for predicting the material dispersion is successfully tested by using a direct comparison with the experimental results. The limitations of this method are analyzed in terms of the molecular structure of the ionic liquids. The results of this work aim to increase our knowledge about how the molecular structure of an ionic liquid influences its material dispersion. Understanding this influence is fundamental to producing ionic liquids with tailored optical properties.

Refractive index measurements in absorbing media with white light spectral interferometry.

White light spectral interferometry is applied to measure the refractive index in absorbing liquids in the spectral range of 400-1000 nm. We analyze the influence of absorption on the visibility of interferometric fringes and, accordingly, on the measurement of the refractive index. Further, we show that the refractive index in the absorption band can be retrieved by a two-step process. The procedure requires the use of two samples of different thickness, the thicker one to retrieve the refractive index in the transparent region and the thinnest to obtain the data in the absorption region. First, the refractive index values are retrieved with good accuracy in the transparent region of the material for 1-mm-thick samples. Second, these refractive index values serve also to precisely calculate the thickness of a thinner sample (~150 µm) since the accuracy of the methods depends strongly on the thickness of the sample. Finally, the refractive index is recovered for the entire spectral range.

Spectrally resolved white light interferometry to measure material dispersion over a wide spectral band in a single acquisition.

In this paper we apply spectrally resolved white light interferometry to measure refractive and group index over a wide spectral band from 400 to 1000 nm. The output of a Michelson interferometer is spectrally decomposed by a homemade prism spectrometer with a high resolution camera. The group index is determined directly from the phase extracted from the spectral interferogram while the refractive index is estimated once its value at a given wavelength is known.