Analyzing the potential of ion chambers to measure laser-induced ionization rates.

Abstract

We demonstrate and analyze the use of an ion chamber for measuring laser-induced ionization in cesium gas for the first time, which is of recent interest due to research in diode pumped alkali lasers (DPALs). In this report, the viability of an ion chamber diagnostic with high plasma density and ionization localized to a laser beam is investigated. A simulation of the laser-induced plasma in the ion chamber, based on the Thomson model with diffusion, is developed and will be shown to display similar qualitative behavior to measurements, and bound test results within model uncertainty. The analysis will show that complex processes occur: (1) space-charge limited ion drift, (2) Debye shielding preventing the electric field from penetrating a bulk plasma region, and (3) ambipolar diffusion across the bulk with possibly elevated electron temperature. However, these processes are well understood and do not limit the accuracy of an ion chamber diagnostic for laser-induced ionization rate measurement.