Initiation and channelling of a microwave discharge by a plasma filament created in atmospheric air by an intense femtosecond laser pulse

We study the initiation of a pulsed microwave discharge in atmospheric air by a plasma channel induced by intense femtosecond laser pulses. It is shown that the electric field threshold for the initiated discharge is lowered compared with the self-discharge by about a factor of two, from 25 to 12 kV cm−1. Channelling of the atmospheric-pressure microwave discharge in the direction of the plasma filament has been detected. The time of existence of the initiated discharge plasma was determined by the duration of the microwave pulse and amounted to 1–2 µs for the maximum electron density estimated as about 4 × 1015 cm−3. The developed theory of propagation of the microwave radiation along the plasma channel created by a femtosecond laser pulse predicts that the relatively low conductivity of the plasma and its rapid decay limit the characteristic scale of decay of the microwave fields confined by the plasma channel to a few centimetres.