Influence of an electric field on Rydberg nD states of cold lithium atoms

Influence of a weak electric field on the coherent Rydberg resonances was studied on two-photon transitions 2S-nD by recording the resonance fluorescence of lithium atoms in a magneto-optical trap. It was observed that an isolated spectral line 2P-nD transferred to the spectral band width growing with a principal number n (or an electric field E). It was shown that the frequency tuning of a resonant radiation on the left ( right) edge of the band allows to create a gas of Rydberg atoms with fixed and large dipole moments d alpha ea(0)n(2) (e is the elementary charge, a(0) is the Bohr radius), oriented against (along) the electric field. The radiation frequency was tuned on the center of the band would produced atomic states with zero dipole moments, but with a big contribution of states with maximum angular momentum quantum number l similar to n.