Nonlinear Magneto-Optical Rotation in Rubidium Vapour

Abstract

The field of magnetometry has played a pivotal role in developing our understanding of the world around us, by providing a wealth of unique information via non-invasive magnetic measurements. In many applications the characteristics of magnetic fields — their strength and temporal dependence, for example — constitute a unique fingerprint of their source, and provide a window into both their origin and any underlying physical processes that produced them. The invention of the laser, and recent advancements in anti-relaxation coatings for vapour cells, has revolutionised the field of magnetometry and given rise to a myriad of optical magnetometers which demonstrate exquisite sensitivity. This has seen a movement away from traditional cryogenic magnetometry techniques — which utilise superconducting quantum interference devices — and has ushered in a slew of optical techniques which offer a whole host of benefits such as room-temperature operability, intrinsic accuracy, and portability. Applications which were previously inaccessible due to demanding requirements such as high sensitivity at ambient temperatures, are now permissible using these newly developed optical techniques. This thesis details the development of an ultrastable optical magnetometer based on nonlinear magneto-optical rotation in rubidium vapour, that has been optimised for high sensitivity over long timescales. Additionally, a novel measurement technique — which relies on tracking the instantaneous phase of atomic spin precession — has been developed and demonstrated, resulting in significant improvements to both the amplitude and frequency response of the device when compared to conventional measurement techniques described in the literature. Significant attention is paid to technical and fundamental noise sources, which must be minimised in order to achieve high performance — especially over long timescales. The latter chapters discuss the development of the magnetometer into a sensitive and reliable system, capable of measuring extremely small magnetic-field fluctuations, and transient fields with arbitrarily complex temporal dependence. The capability of the device to measure minute field fluctuations, as well as rapid transient disturbances, may find use in real-world applications such as geophysical exploration, medical diagnostics and imaging, and magnetic anomaly detection. Furthermore, any fundamental physics applications which demand accurate and precise measurements of magnetic fields may find application of this device — and the novel measurement techniques developed within this thesis—extremely beneficial.