Abstract

Laser-assisted Penning ionization (LAPI) is detected in a Ne/Eu hollow cathode (HC) discharge lamp using the pulsed optogalvanic (OG) method. In the Ne/Eu discharge, doubly ionized europium excited energy levels $\mathrm{Eu}[{4\mathrm{f}}^7({}^6{\mathrm{P}}_{7/\mathrm{2,5}/2})]$ lie within the thermal limit ($\sim kT$) from the laser-excited neon’s energy level $[2{\mathrm{p}}^5({}^2{\mathrm{P}}_{3/2}^0)3\mathrm{p}$ or $2{\mathrm{p}}_8$ (in Paschen notation)] lying at $149,848{\mathrm{cm}}^{-1}$. Therefore, Penning ionization (PI) of europium atoms likely to occur into its highly excited ionic states is investigated. To probe the PI of europium, the temporal profiles of its counterpart neon OG signal are studied as a function of discharge current for the transitions ($1{\mathrm{s}}_4\to 2{\mathrm{p}}_8$) and ($1{\mathrm{s}}_2\to 2{\mathrm{p}}_2$), corresponding to 650.65 and 659.89 nm wavelengths, respectively. It is observed that PI of europium alters the overall discharge characteristics significantly and, hence, modifies the temporal profile of the OG signals accordingly. The quasi-resonant ionizing energy transfer collisions between laser-excited Ne $2{\mathrm{p}}_8$ atoms and electronically excited europium ${}^{10}{\mathrm{P}}_{9/2}$ atoms are used to explain the LAPI mechanism. Such LAPI studies carried out in HC discharge could be useful for the discharge of a metal-vapor laser with appropriate Penning mixtures.

© 2015 Optical Society of America

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