Characterization of optical fibers by two- and multiple-beam interferometry

Fringes of equal chromatic order in transmission across a thin liquid or a thin solid sample inside a wedge interferometer, followed with a grating spectrograph, are produced. A single-shot interferogram of the air and sample regions is recorded. Locations of fringes maxima in the air region are fitted in a numerical procedure based on Cauchy's dispersion function. Then it is used for measuring the interferometric gap thickness. The order of interference in the sample region is represented by a third-order polynomial in the wavenumber for deducing the sample group refractive index. An error analysis of the measured group refractive index is given. The method is applied for measuring the group refractive index of water and mica samples across the visible spectrum. The method measures both the sample thickness and its group refractive index. It is static with no moving parts and suitable for thin liquid or solid samples without immersion liquids.

Group refractive index measurement by fringes of equal chromatic order

Multiple-beam interference fringes of equal chromatic order are produced in air and liquid sample interferometric gaps. The two gaps are of the same thickness and simultaneously enclosed in a wedge interferometer. A single shot interferogram containing fringes in the two gaps is sufficient to deduce the needed experimental data. Locations of the fringe maxima, in the two gaps, are introduced in a non-numerical procedure for determining the gap thickness and the liquid-phase refractive indices across the visible spectrum. The method has been used for measuring the phase refractive indices of human blood-serum, saliva, sweat, urine and water liquids. A third-order polynomial dispersion relation is applied for fitting the measured phase indices. Group refractive indices have been derived and fitted to the same dispersion formula.

Interferometric determination of refraction and dispersion of human blood-serum, saliva, sweat and urine

EPR study of radical annihilation kinetics of γ-ray-irradiated acrylic (PMMA) at elevated temperatures

Context. Accounting for partial or complete frequency redistribution when interpreting solar polarization spectra requires data on various collisional processes. Data for depolarization and polarization transfer are needed, but are often lacking, while data for collisional broadening are usually more readily available. Recently it was concluded that despite underlying similarities in the physics of collisional broadening and depolarization processes, the relations between them cannot be derived purely analytically. Aims. We aim to derive accurate numerical relations between the collisional broadening rates and the collisional depolarization and polarization transfer rates that are due to hydrogen atom collisions. These relations would enable accurate and efficient estimates of collisional data for solar applications.Methods. Using earlier results for broadening and depolarization processes based on general (i.e., not specific to a given atom), semi-classical calculations that employ interaction potentials from perturbation theory, we used genetic programming (GP) to fit the available data and generate analytical functions describing the relations between them. The predicted relations from the GP-based model were compared with the original data to estimate the accuracy of the method.Results. We obtain strongly nonlinear relations between the collisional broadening rates and the depolarization and polarization transfer rates. They are shown to reproduce the original data with an accuracy of about 5%. Our results allow determining the depolarization and polarization transfer rates for hyperfine or fine-structure levels of simple and complex atoms. Conclusions. We show that by using a sophisticated numerical approach and a general collision theory, useful relations with sufficient accuracy for applications are possible.

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Unified numerical model of collisional depolarization and broadening rates that are due to hydrogen atom collisions

Multiple-beam white-light interference fringes across an irradiated GRIN fibre, of length 2 cm and immersed in a liquid wedge interferometer that is followed by a grating spectrograph, are produced. These fringes are used to investigate the effect of gamma radiation, with different doses from 0.01 to 1 MGy, on the optical parameters of both the cladding (pure silica) and the core (germanium-doped silica) of the GRIN fibre. Optical parameters such as refractive index, refractive index difference, numerical aperture, V-number, index profile, chromatic dispersion and zero-dispersion wavelength are determined and studied. A two-term Sellmeier dispersion relation is adopted and fitted to the experimental data of the refractive index. Then, a dose-dependent Sellmeier formula is deduced to represent the effect of gamma radiation on different optical parameters.

https://iopscience.iop.org/article/10.1088/1464-4258/4/4/320/pdf

Saleh M Abdou

Papers

Interferometric determination of gamma radiation effects on optical parameters of a GRIN optical fibre