Experimental investigation of photoionization cross section for the 3d 2D excited states of lithium and sodium

We report experimentally measured photoionization cross sections for the 3d2D excited states of lithium and sodium at first ionization threshold. The experiments were performed using two dye lasers simultaneously pumped by the second harmonic of a Nd:YAG laser. The vapor contentment and the detection system was a thermionic diode ion detector operating in a space charge limited mode. Photoionization cross sections of the excited states were deduced from the dependence of ion signal intensity on the ionizing laser energies as 19 ± 3 Mb and 21.5 ± 3.5 Mb for lithium and sodium respectively, which are in good agreement with the previously computed theoretical results.