Tests of Fundamental Physics Using Quasar Spectroscopy

Quasar absorption lines are used extensively in astrophysics to place constraints on cosmological models. In this thesis, we focus on the measurement of two important parameters in cosmology, the electromagnetic coupling constant, or fine-structure constant, $\alpha\equiv{e^2}/(4\pi\epsilon\hbar{c})$, and the primordial deuterium-to-hydrogen ratio, D/H. Any cosmological variation of $\alpha$ will cause its value to be different in the early stage of the Universe, therefore impacting the production of the primordial light elements during Big Bang Nucleosynthesis.\\ We provide updated \da\ measurements from 280 absorption systems previously published in the literature using the non-linear least-square Voigt Profile fitting program \vpfitused. We also investigate the impact of long-range wavelength-scale distortions on those measurements. We found that long-range distortions are unlikely to explain the 4.1\,$\sigma$ evidence for an $\alpha$ dipole as reported in the literature even though they do impact on the $\alpha$-dipole significance.\\ The above work led us to examine the kinematics of each absorption system in our sample. We report a correlation between the complexity of the velocity structure of Damped Lyman-$\alpha$ systems and the apparent position of the Lyman limit break in quasar spectra. We develop a new technique, based on this correlation, to identify suitable Damped Lyman-$\alpha$ systems for D/H measurements.\