Observation of Electron Swarms produced by Laser Light

Abstract

OBSERVATION of the displacement current caused by the motion of charge carriers in a discharge gap can yield quantitative information on many basic processes¹, such as ionization, electron attachment and charge carrier mobilities. A relatively large number of charge carriers is, however, required to produce a signal which exceeds the high inherent noise level of any wideband detection system by a sufficient margin. Hitherto, it was necessary, except in one or two special cases, to rely on gas amplification to raise the electron current to an observable level; this is only possible, however, when ionization dominates attachment of electrons to neutral molecules. The number of initial electrons required is particularly high when measurements in electronegative gases (high voltage insulants such as SF₆ and air) are to be made over the technically important range of low ratios of field strength to pressure for which the electron loss by attachment is at least as probable as the production of additional electrons by ionization.