On the possibility of unipolar terahertz pulses generation in nonequilibrium plasma formed by the ultrashort UV laser pulse

We perform the new approach to produce highly unipolar terahertz pulses. The idea is based on the nonuniform amplification of seed ultrashort one-cycle CEP pulses in nonequilibrium fast relaxing plasma of air or nitrogen. If the gain coefficient drops significantly within the duration of one-cycle CEP pulse, it undergoes significant distortion where the leading edge of the pulse is amplified and the trailing tail of opposite polarity is absorbed. The obtained results involve self-consistent solution of second-order wave equation and kinetic Boltzmann equation for the electron velocity distribution function relaxation.