Plasma-assisted temporal shifts of bichromatic femtosecond laser pulses in air

Terahertz and third-harmonic generation by tightly focused bichromatic femtosecond pump pulses with comparable input intensities in air is studied both experimentally and theoretically. Plasma-assisted temporal shifts in the field of intense laser pulses are shown to lead to the time delay between the pump pulses in the vicinity of the focus. This delay can be compensated by the initial time delay that is evidenced by the measured as well as calculated correlation functions of the fundamental and second harmonics. The possibility to characterize the plasma channel length from the correlation function is discussed.