Time resolved measurement of spatially averaged microwave conductivity of air plasmas formed by 100 picosecond laser pulses

Summary form only given, as follows. Applications of gaseous plasma switching and relativistic ionization front studies can require measurements of microwave complex conductivity spatially integrated over many microwave wavelengths. Time-dependent conductivities and permittivities of 1-atm air plasmas formed by focusing energetic 100-picosecond laser pulses of 1064-nm wavelength into a long section of rectangular waveguide (WR90) have been determined. Laser propagation is along the waveguide length perpendicular to the electric field of the 10 GHz, TE/sub 10/, CW (continuous wave) probe. Laser and microwave waveforms counterpropagate. Visible arcs of length typically exceeding 40 cm were formed using a 9-meter focal length lens. X-band interferometric results are therefore spatially averaged longitudinally and transversely. Time resolved results have been obtained using laser pulse energies from 300 mJoules to a few Joules.