Configuration for scanning drift tube apparatus: ultraviolet laser light pulse (1.7 µJ, 5 ns); stainless steel electrode with 105 mm diameter serving as cathode; detector consisting of a grounded nickel mesh and stainless steel electrode 1 mm behind it; drift length between 7.8 to 58.3 mm; reduced electric field range (E/N) between 2 and 1603 Td; vacuum level of about 1 x 10^-7 mbar; sub-ns time resolution recording; averaging over 20000 to 150000 pulses