Coherent Excitation of N = 3 Stark States of Hydrogen-atoms

We describe a method for producing a fast atomic hydrogen beam with a large amount of population selected in 3l(j,mj) levels. This is realized by a one-step tunable laser excitation of the metastable component of the atomic beam inside a non-homogeneous static electric field. The linear laser polarization is taken either parallel or perpendicular with respect to the external field. It allows the selective excitation of all the states of the n = 3 Stark manifold (with the exception of the mj = 5/2 state). The electric field strength vanishes immediately after the laser excitation. At this point the population of the excited states are better referred to the atomic basis. The shapes of the resonant lines show that two transient effects are leading the excitation process. The first is of an optical kind (i.e. Rabi oscillation and rapid adiabatic passage) and the second is the intra Stark manifold state mixing due to the non-adiabatic time evolution of the external field strength. The internal state of the atoms crossing these fields is completely described by the density matrix evolution calculated independently on two bases (the atomic basis and the Stark instantaneous basis).