Electron temperature of Gd plasma produced by laser resonance ionization

In atomic vapor laser isotope separation (AVLIS), it is necessary to extract ions efficiently from plasma produced by laser resonance ionization. It is important to know electron temperature of the plasma, since the aimed isotope ions are accelerated by electric potential of the order of electron temperature in the plasma. The electron temperature of Gd plasma produced by laser resonance ionization was measured by a Langmuir probe. This measured electron temperature is much lower than the released electron energy and is close to the atomic excitation temperature of Gd. This result seems to show that electrons collide with Gd atoms with excitated or de-excitated ground or metastable Gd atoms, and the electron temperature becomes close to the atomic excitation temperature.