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Physical Review A

Space-charge ion detection of multiphoton absorption phenomena in lithium vapor

Mark E. Koch, C. B. Collins

Published Mar 1, 1979• 32 citations
Publisher

Abstract

The method of space-charge ion detection has been extended to the case of lithium. This was accomplished by the insertion of a space-charge-limited diode into a heat-pipe oven. Lithium vapor was probed with a ${\mathrm{N}}_{2}$ laser-pumped tunable dye laser from 7150 to 4400 \AA{} and with a Xe arc lamp from 7500 to 2300 \AA{}. One-through four-photon events leading to ionization were observed. The atomic transitions observed were the principal series to $n=10$ and the $2s$ to $3d$, $4s$, and $4d$ two-photon transitions. The two-photon absorption signals depended upon the third and fourth powers of the light intensity, indicating a new ionization process not heretofore considered important in diode signals. This new process appears to be excitation transfer from excited-state atoms to other excited-state atoms or molecules. For the high excited-state densities achieved in this experiment, this process appears to predominate over photoionization of excited-state atoms and other collisional processes involving excited-state and ground-state species. The $B\ensuremath{\leftarrow}X$, $C\ensuremath{\leftarrow}X$, and $D\ensuremath{\leftarrow}X$ molecular transitions, investigated by previous workers, were observed here.

DOI
10.1103/physreva.19.1098

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