Terahertz-field-modified electron dynamics in above-threshold ionization

We experimentally demonstrate the possibility of control of electron dynamics during above-threshold ionization (ATI) of argon provided by a moderately strong single-cycle terahertz (THz) field with vector potential amplitude comparable to that of the ionizing near-infrared pulse. The maximum photoelectron energy in ATI spectra, the energy distance between the ATI peaks, as well as the total electron yield, are determined by the THz field vector potential, which varies with the time delay between the ionizing and the THz pulse. Dependence of electron energy spectra on the delay between the pulses is analyzed using the improved strong-field approximation and classical electron trajectories. This information can be used for precise THz pulse characterization.