Experimental investigations on the splitting of coherent population trapping resonances by the nuclear magnetic moment

Full text: Coherent population trapping (CPT) is a resonance phenomenon due to a quantum mechanical interference effect within an atomic system. The resonantly driven atomic level population is being trapped into a superpositional dark state, yielding the atomic medium transparent for the exciting electromagnetic fields. The observation of this effect requires a special electronic structure (Λ-System) and suitable lifetimes which can be found e.g. in alkali atoms. In the experiments transitions are excited by a bi-chromatic laser radiation within the manifold of the D1-line of 87Rb . If a magnetic field is applied, a dark resonance spectrum of several Zeeman components appears as a result of the sublevel structure of the D1-line. An additional splitting of CPT resonances is observable by virtue of a lifted degeneracy with respect to the nuclear magnetic moment even before the Paschen-Pack regime is reached. We present experimental investigations on the behavior of the CPT resonances split by the nuclear magnetic moment under different external magnetic fields, laser polarizations and laser intensities. We focus our considerations on a special type of the Λ-System formation. In this case the center of gravity of the pair of split CPT resonances (called pseudoresonance) is sensitive to external magnetic fields only to second order in the magnetic field strength. The short term frequency stability of this pseudoresonance approaches the level of 10-14/ √τ making this standard as a good candidate for applications in compact atomic clocks used e.g. in GPS receivers and satellites. (author)