Sculpting shadows : on the spatial structuring of fields & atoms : a tale of light and darkness

• Main Author: Clark, Thomas William
• Published: University of Glasgow 2016
• Subjects: 621.36; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.712613

Whether in art or physics, two dimensions are better than one. And in this context, we consider the spatial shaping of optical fields and atomic polarisations. This work begins with a comprehensive review of how to accurately and arbitrarily modulate transverse beam profiles using six different methods. The methods are presented in the context of a general complex input beam and the shaping and measuring of the input beam with a single SLM is discussed and demonstrated. A simple setup is then considered that allows for the rapid switching between arbitrary profiles, using only a single holo- graphic component and an acousto-optical modulator (AOM). In this setup, a switching speed of approximately 10 kHz is demon- strated explicitly, limited by the current detection system, but where speeds of up to 20 MHz are estimated to be possible. The following discussion then concentrates on the spatial structure of atoms, reviewing the conceptual tools needed to measure and interpret an atomic cloud in the presence of a mag- netic field from fundamental concerns, both in theory and in practice: assuming a classical light field and a quantum atomic system. The specific implementation of both a magneto-optical trap and a holographically-shaped dynamic dark SpOT follows. The crux of the work then concerns how polarisation-structured light can be used to create spatial patterns of transparency (spa- tial EIT) within an atomic cloud. Beginning with a review of EIT in general, with particular focus on an F = 1 → F = 0 transition, the spatial modulation of absorption, dispersion, polarisation rotation and change in ellipticity is predicted for systems in the presence of a transverse magnetic field. The depth of this mag- netic field dependency is then explored in some detail, where the relationship between observed patterns and applied magnetic field suggests the possibility of a visual magnetometer. The final section then considers how linearly polarised light and a q-plate was used to demonstrate spatially dependent transparency in a real atomic cloud.