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Title: Trans-spectral transfer of orbital angular momentum and creation of an ultra high density cold atom trap
Author: Walker, Graeme
ISNI:       0000 0004 2741 4043
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2013
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In recent years there has been great interest in the applications of the interaction of the phase and intensity of laser light in atomic vapours. The generation of light beams with arbitrary phase and intensity patterns can now be easily achieved by using Spatial Light Modulators (SLMs). The transformation of quantized units of phase information to atomic vapours has implications in the fields of quantum optics for the realisation of sources of entangled photons, optical switching, and quantum information storage. Spatially shaped beams with non-trivial intensity geometries have found use in single atom quantum well traps and for the enhancement of density of standard Magneto Optical Traps. The work in this thesis is focussed around two main pro jects, involving the interaction of holographically shaped light beams with cold trapped atoms and with a hot atomic vapour respectively. An enhancement to the previously investigated technique of a SPontaneous force Optical Trap SPOT of 87 Rb is presented here which aims to solve various issues which naturally arise from compressing cold atoms in a Magneto Optical Trap (MOT) such as unavoidable heating during the compression. High density/high atom number traps are highly sought after in many experiments for more efficient transfer of atoms to Bose Einstein Condensates and for improved quantum storage capabilities in cold atom traps. The highest density achieved in our SPOT was 2.5 × 10^12 atoms cm−3 for 2 × 10^8 atoms at a temperature of approximately 100µK. This represents almost 2 orders of magnitude increase in density from the standard MOT setup with no adverse heating of the trap while maintaining 75% of the atoms. In the second part of this work hot atomic vapours are utilized for the efficient transfer of orbital angular momentum information from near infra-red pump fields, driving from 5S_1/2 to 5D_5/2 on a two-photon transition, to a cascade from 5D_5/2 to 6P_3/2 to 5S_1/2 generating 5230nm light and a coherent blue, 420nm, beam respecitively. This generation is performed using four wave mixing in 85 Rb. We observe the complete conversion of all input quantum information, the Orbital Angular Momentum (OAM) from the pump fields to the blue. In addition we show the additional phase coherence effects of this experiment through the use of simple superpositions of Laguerre-Gaussian (LG) modes showing that the process is indeed quantum in nature. A theoretical basis for the transfer of all OAM information to only the 420nm beam is also discussed here.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics