Development of an atomic frequency standard in the optical domain based on ultracold Ytterbium atoms

The work described in this thesis was done at the Istituto Nazionale di Ricerca Metrologica (I.N.Ri.M.), in the optic division, within the Ph.D. of Metrology of the Politecnico di Torino. My work consisted in developing a new generation optical frequency standard based on Ytterbium atoms: the goal of this project is to realize a clock whose performance overcomes the ones of the standard which actually realizes the Second, the atomic Cesium fountain. This means realizes an apparatus which shows stability and accuracy better then the fountain ones: a possible way adopted in several new generation clock is using optical transitions, because they offer an higher quality factor of the clock transition itself, which means a better stability and the possibility to reach the 10^-17 level in the global accuracy of the clock. The fundamental idea of a clock is to realize as close as possible the basic idea under the actual definition of the Second, that is to fix the unit if time with a particular atomic transition, when the atom is completely unperturbed. Accomplishing this prescription means a lot of work in cooling down the atoms until the 10^-6 K regime using laser cooling techniques, developing a trap where atoms can be excited by the clock laser (the optical lattice) and of course a very careful frequency and amplitude stabilization of the clock laser itself is needed to reach our goal. The work described in this thesis regards the development of the two cooling stages of the Yb atoms and it is presented as follows. Chapter 1 explains with more details why an optical clock is needed to improve the accuracy of the actual realization of the Second, then describing the theoretical framework in which the clock will be developed. Chapter 2 contains a description of the experimental apparatus used, with more attention on the instrumentation related to the laser cooling of the atoms. Chapter 3 is about the characterization of the first cooling stage, both in a static and in a dynamic way, with some attention on the theoretical model developed to perform both the characterizations. Chapter 4 focuses on the development of the second cooling stage and it describes the actual state of the art of this stage.