title: Novel applications of structured light in the field of atom optics. Imagining optical magnetometry with images
Creators: name: Castellucci, Francesco
Publisher: name: University of Glasgow
Year: 2022

description: Complex vectorial light fields offer unprecedented information capacity and flexibility to design light potentials with correlated or multiplexed intensity, phase and polarisation structures. In recent years many different new techniques and technological devices have been developed with the goal of allowing for the efficient generation of these fields with maximum flexibility and reliability. During my studies I employed some representatives of these newer techniques, as the light fields involved in the experiments were generated with setups containing equipment such as Digital Micromirror Devices (DMDs), Spatial Light Modulators (SLMs) and Q-plates, all of which can be regarded as being on the forefront of the development in the world of structured optics. The main beneficiaries of this "expansion" in the generation of light fields are topics traditionally linked to optics such as microscopy, imaging and spectroscopy. However, another field that could benefit from these newer applications is atom optics. In fact, the interaction between atoms and light is vectorial in nature, as it is manifest in the electric dipole coupling which is the principal avenue of interaction between them. Main consequence of this kind of interaction are the appearance of non-linear behaviours, even for light parameters associated to a semiclassical description, e.g. coherent light from a laser source. The principal investigation during my Ph.D. can be regarded as one of the tentative efforts to introduce the innovation of structured light and atom optics, since I have focused my efforts around the experimental study of the mutual interaction of a cloud of cold rubidium atoms with a vectorial light field, carrying Orbital Angular Momentum (OAM) in the presence of a magnetic field. The main goal of the study was to describe and demonstrate how 3D magnetic field alignment can be inferred from single absorption images of an atomic cloud. The atomic cloud was prepared in a particular state of density, temperature and population distribution with the employ of a Magneto Optical Trap (MOT) first, and Spontaneous Force Optical Trap (SpOT) second, which are widely utilized techniques in the world of atom optics. Then a vector vortex beam was used to interrogate the magnetic spin states population of the atoms cloud. In fact due to the relative position between the local light polarisation, which varies in the beam, and the magnetic field direction, fixed for the whole atomic sample, the absorption of the light would be affected. By varying the magnetic field inclination or azimuthal angles, the absorption pattern would vary as well confirming the previous model developed by former PhD students. In the future it is planned to address some of the limitations that are intrinsic to the selected method, the Q-plate, of generating the vector vortex light by switching to one of the other above mentioned SLM or DMD setups to obtain a wider selection of polarisation patterns to stimulate the atoms. Another venue of development is the translation of the whole system at room temperature, with the prospect of achieving a faster rate of repetition for the experiment at the expense of some control over the atomic medium. In addition to the atomic magnetometry experiment in Glasgow, during my PhD I have been collaborating on other projects with various other physics group both within the same University of Glasgow and in the wider optics fields worldwide. The most relevant of these has been the European Training Network (ETN) called Collective Effects and Optomechanics in Ultra-cold Matter (ColOpt), which is the main funder of my PhD position.