Coherent control of spin-orbit precession with shaped laser pulses

Spin precession in rubidium atoms is investigated through a pump - probe technique. The excited wave packet corresponds to a precession of spin and orbital angular momentum around the total angular momentum. We show that using shaped laser pulses allows us to control this dynamics. With a Fourier transform limited pulse, the wave packet is initially prepared in the bright state ( coupled to the initial state) whereas a pulse presenting a p step in the spectral phase prepares the wave packet in the dark state ( uncoupled to the initial state).