Ion beam generation by field ionization of laser-excited Rydberg atoms

Sodium atoms (108--1011 cm-3) effused from an oven where excited by two pulsed dye lasers (--8--15 ns, --100 μJ) from the ground state 3s, via an intermediate state 3p, to a Rydberg state ns or nd (20≤n≤25). 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 ion beam was obtained with a maximum total electric charge of --5 pC, corresponding to a peak current of --25 μA with an output pulse of --200 ns full width at half-maximum