Efficient Laser Production of aNa+Ground-State Plasma Column: Absorption Spectroscopy and Photoionization Measurement ofNa+

We report the first observation of ionization of dense Na vapor by laser radiation. A 1-MW pulsed laser at 589.6 nm produced almost complete ionization of a 10-Torr-cm column of Na. Measurements of the ${\mathrm{Na}}^{+}$ photoionization cross section, the neonlike series $2s^{2}2p^6\to 2s^{2}2p^5\mathrm{ns}$ and $\mathrm{nd}$, and several autoionizing resonances of the type $2s^{2}2p_6^6\to 2s2p^6\mathrm{np}$ were obtained using a spark source to provide the continuum background for absorption spectroscopy of the ion.