Generation of pure ion beams by field ionization of laser-excited Rydberg atoms

Abstract

Sodium atoms (108–1011 cm−3) effused from an oven were stepwise excited from their ground state to a Rydberg state ns or nd (20≤n≤26) by two pulsed dye lasers (∼5–10 ns, ∼100 μJ, ∼1.6-mm-diam spot). The laser energy density necessary to saturate the excitation processes from the ground state to the Rydberg state is ∼ several mJ/cm2. About 50 ns after the laser irradiation, a pulsed electric field (0.5–5.5 kV/cm) was applied to the Rydberg atoms to ionize them and accelerate the resulting ions. Thus, a pulsed sodium ion beam of purity >99.99% was obtained with a maximum total electric charge of ∼5 pC and a pulse width of ∼120 ns full width at half maximum. The total electric charge of the ion beam is estimated including the effect of space-charge field of the beam ions, and is in good agreement with the experimental values.