This manuscript is focusing on some research activities between laser instrumentation and physics of atomic clocks. The main goal is to develop new atomic clocks using laser spectroscopy on weakly allowed and completely forbidden optical transitions. Starting from a theoretical study of the atomic structure of ceasium atom, I focus then on the theoretical and experimental studies of nuclear spin states in a magnetic field by laser spectroscopy of a weakly allowed atomic transition in two electron atoms. I will also present the possibility to create a "magic" static field which can eliminate the linear and the quadratic Zeeman shift by dressing the nuclear spin with a radiofrequency field. The manuscript will then focus on the possibility to probe the completely forbidden transition of the bosonic isotope by making atoms trapped into a state superposition transparent to the laser light. In order to satisfy a rapid atomic preparation of the state superposition while eliminating any light shift affecting the clock transition, we propose to use a two-photon pulsed spectroscopy which is extended to the more recent Hyper-EIT/Raman spectroscopy.
