Spatially Resolved Rydberg Doppler broadening Thermometry of an ultracold atomic gas

This thesis presents experiments and results on the implementation of a spatially resolved temperature measurement method. The technique is based on Doppler broadening, used to extract temperature from the transition spectrum by probing a small spatial region of the sample. A two-photon transition with orthogonally arranged laser beams confines the excitation region spatially. To ensure a good signal-to-noise ratio, Rydberg states were chosen as the excited states. The method was tested on a rubidium atom cloud in a MOT, which has been theoretically predicted to exhibit a spatial temperature gradient. Two approaches were used to demonstrate spatial resolution. The first examines linewidth broadening due to the MOT’s magnetic field gradient. The second uses a ballistic expansion, comparing local and global excitations. In local measurements, faster atoms leave the region quickly, narrowing the Doppler width. In global measurements, instead shows a plateau since energetic atoms stay longer in the probed volume. Experimental data support these findings. Additionally, Doppler heating near resonance was characterized to enhance the observed temperature drop. With spatial resolution and reliable temperature extraction confirmed, the method was applied to map the temperature variation within the atomic cloud. Results, despite limitations, consistently show a temperature difference between the cloud center and edges, validating the method's effectiveness.