We have measured the time-dependent electrical resistance of a plasma chann
el created in air by a self-guiding TW femtosecond laser pulse. The plasma
conductivity over a 200 ns time interval has been determined from a nonline
ar low-inductance circuit model of the experiment. The circuit model incorp
orates the decay kinetics of the plasma channel and the initial electron de
nsity. (C) 2001 Published by Elsevier Science B.V.