Effect of an electric field on air filament decay at the trail of an intense femtosecond laser pulse

Abstract

Air plasma density decay in a filament produced by an intense femtosecond laser pulse in an external electric field was investigated experimentally and theoretically. It was demonstrated by means of the terahertz scattering technique that the rate of plasma decay decreases with increasing electric field. At the electric field of 7 kV/cm the lifetime of plasma with the density above 10(16) cm(-3) was prolonged from 0.5 ns to 1 ns. Numerical simulation of electron density decay and electron temperature evolution was performed, taking into consideration dissociative and three-body electron-ion recombination as well as formation of complex positive ions. The simulation showed that under the electric field the electron temperature evolves nonmonotonically and passes through a minimum due to varying contribution of electron-ion collisions to electron heating in the field. The rate of three-body electron recombination with O(2)(+) ions of 2×10(-19)(300/T(e))(9/2) cm(6)/s was found from the experimental measurements at electron temperatures in the 0.25-0.4 eV range and electron densities in the 10(15)-10(17) cm(-3) range.