Energy Pooling Collisions: A Step Towards Ionization

Abstract

Different collisional processes may contribute to the of a gas under resonant laser excitation¹⁾. The aim of this paper is to put in evidence the role of the collisional process called “energy pooling” (EPC) with respect to a possible complete ionization of the vapor under relatively low laser power densities. EPC is described by the reactions:

$$ {{A}^{*}} + {{B}^{*}} \to \left\{ {\begin{array}{*{20}{c}} {{{A}^{{**}}} + B + \Delta E.} \\ {A + {{B}^{{**}}} + \Delta E} \\ \end{array} } \right. $$

((1))

where A^*,B^* are the resonantly laser excited atoms, A^**.B^** are the atoms in a highly excited level and AE is the energy defect. Being thermal collisions, the reaction is effective when AE is of the order of KT. Alkali atoms satisfy this condition and are, up to now, the more studied atoms for this process²⁾.