Laser frequency stabilization for a source of cold Barium atoms

The goal of the Master Thesis project is to stabilize the frequency of a 553.7 nm laser in the visible range (green) used in a spectroscopy experimental setup for the energy levels associated with the following atomic transition (related to cooling) of neutral 138Ba atoms: 6s2 1S0 → 6s6p 1P1. Additionally, it is used a Hollow Cathode Lamp (HCL) as the source of neutral 138Ba atoms that interact with the laser beam. More specifically, the laser frequency will be stabilized with the use of polarization spectroscopy, which is a Doppler-free technique that consists in the use of a strong pump laser beam, which saturates the population of the excited state, therefore, a weak counter-propagating probe beam faces a reduction in its absorption spectrum, after interacting with the atomic medium, when the detuning is close to zero, characterizing a Lamb dip. Additionally, in polarization spectroscopy, the signal-to-noise ratio is enhanced due to the manipulation of the laser light by using different polarizations, which leads to the coupling between different Zeeman sublevels. As the optical transition of interest is from the S to P sublevels, we can take advantage of polarized light in order to have specific transitions. Finally, another objective of the project is to computationally simulate the overall dynamics of 138Ba atoms in a Magneto-Optical Trap (MOT), in which the atoms are impinged with specific laser lights. The laser-atom interactions, considering specific energy levels that form a cooling cycle, are related to the process of decreasing the motion of the atoms as much as possible, which is the cooling process. After performing the polarization spectroscopy experiment, we were able to observe the Doppler broadening containing the Lamb dip in the absorption spectrum of the probe beam, as well as a Doppler-free signal, which was used to lock the laser frequency in a stable long scan measurement. Finally, we obtained the evolution of the population of the considered energy levels of the 138Ba atom with different numbers of repumping lasers and, also, the optical force in function of the atomic velocity in the central region of a MOT, in order to extract the damping coefficients for each setup configuration for the cooling process.