We propose to induce the spin precession of an electron trapped on an impurity by means of an unabsorbed laser pulse made of circularly polarized photons. These photons induce a splitting of the spin degenerate electron level which comes from electron-exciton interaction: the electron sees the virtual excitons coupled to unabsorbed photons through Coulomb interaction and also through Pauli exclusion if its spin and the one of the exciton electron are the same while it sees them by Coulomb interaction only if they are different. The exchange processes producing this splitting which induce a spin precession of the trapped electron - are nicely visualized through the Shiva diagrams we have recently proposed to represent our new many-body theory for composite excitons.