| Summary: | In this thesis, the theory of quantum electrodynamics (QED) is utilised to study the interaction between radiation and matter. In particular, the non-relativistic limit of the theory is employed, describing the optical processes and coupling between molecules and light. The predictive power of this theory is highlighted from the outset, whereby it is shown that a new form of quantum uncertainty, with its origins in delocalised photon emission and absorption, exists in non-linear optics: a non-localised mechanism for the processes of both spontaneous parametric down-conversion and second harmonic generation is established by accounting for virtual photon propagation. The subsequent chapter brings forth the often ignored diamagnetic couplings to optical processes. Their interesting and unique physical properties are shown to manifest themselves in scattering and two-photon absorption processes, and an argument for their inclusion in any multiphoton optical process is outlined. Next, the question of whether the sign of the topological charge (handedness) of a beam possessing optical orbital angular momentum (structured light) engages in chiroptical processes with chiral molecules is resolved. It is shown that through the engagement of the electric quadrupole molecular moment, discriminatory effects with regards to the direction of the vortex twist are anticipated with anisotropic matter. Finally, the laser-induced intermolecular forces that exist between molecules present within an intense laser beam are focused on. Specifically, it is shown that there exists a discriminatory force between chiral molecules when subjected to circularly polarised light.
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