Abstract

We perform a joint measurement of coherent terahertz radiation and high order harmonic generation from gas ionizing by intense two-color laser fields. The relative phase of the superposed two-color field is determined according to the emission time of even high order harmonics. Terahertz radiation maximizes its intensity when this phase delay is locked in 0.8^π The deviation from the prediction of four-wave-mixing and directional photoelectron current models originates from the soft re-scattering of the ionized electronic wave packet with the Coulomb potential of the parent ion, which is confirmed by theoretical model and simulations. Thus terahertz radiation supplies an alternative tool to study the electronic dynamics in addition to high-order harmonic generation and above threshold ionization.

© 2012 Optical Society of America