Self-oscillating clouds in magneto-optical traps

Abstract

In this Thesis, we study the fundamental aspects of self-oscillating atomic clouds in a large, balanced Magneto-Optical Trap (MOT). These instabilities bear analogies with astrophysical systems such as Cepheid variable stars, whose self-oscillations depend on radiation pressure and gravity, as well as technological systems such as confined plasmas, where self-oscillations may arise due to interactions between the plasma particles and the confining magnetic field. We begin with an experimental study of self-oscillating balanced MOT instabilities, investigating first the instability threshold behavior versus various MOT parameters, including magnetic field gradient, atom number and laser intensity. We proceed then investigating the spatio-temporal properties of the unstable regime and identify distinct instability regimes. Different analysis techniques are employed that allow us to learn about the oscillation modes of clouds of these regimes as well as the size distribution of the structures developing in clouds of these regimes. In a theoretical approach, we develop a kinetic 3D model for the MOT with many-atom effects included and successfully use it in numerical simulations of our instabilities. We find qualitative agreements with the instability thresholds from the experiments as well as predict experimentally obtained instability regimes. We investigate the impact of our model’s physical ingredients on the instabilities, to aid the understanding of the complex physics at work. Finally, we show a preliminary simulated result for a self-oscillating instability in the misaligned MOT, known to experimentally exist, in that way demonstrating that our developed numerical tool can be employed beyond the balanced MOT.