Interaction of microwaves with gaseous plasmas formed by abrupt laser-induced ionization

The authors have investigated microwave characteristics of plasmas produced by laser-induced ionization with intense, short pulse. Localized critical electron densities can be reached within time intervals shorter than microwave periods. Focusing pulse energy into a section of {open_quote}S{close_quote} band wavequide containing air at atmospheric density facilitated their study of microwave interactions without limitations imposed by window requirements. They noted the rapid onset of significant microwave reflectivity from the plasma. However, in the absence of any probe the laser plasma itself is a significant microwave source. For a 120 picosecond FWHM, pulse energies above 800 mjoules produced observable microwave power corresponding to peak fields of a few V/cm for ultra-short durations representing only 2 or 3 cycles. Results using a 1064 nm wavelength will be presented for laser pulse energies up to 2 Joules, (focussed intensities up to 10{sup 14} W/cm{sup 2}). This work has general application to pulsed power generation and to related pulse compression using rapid cavity switching.