Volume ultraviolet preionization from bare sparks

Volumetric photoionization in CO
2
-laser gas mixtures by UV emission from bare sparks was studied in two ways: by spectroscopic emission and absorption measurements, and by direct collection of photoionized electrons. The physical processes were understood sufficiently to permit prediction of initial electron distributions in arbitrary geometries of CO
2
, N
2
, He gas mixtures containing known concentrations of ionizable impurity.