Above-threshold ionization by a strong circularly polarized laser pulse assisted by a terahertz pulse

We investigate how the above-threshold ionization by an intense circularly polarized infrared laser pulse is modified in the presence of a strong circularly polarized terahertz pulse. It is shown that both the differential ionization probability and the maximum photoelectron kinetic energy can be increased or decreased by an order of magnitude by changing the time delay between the laser and terahertz pulses. The results obtained by numerical integration agree well with those obtained using the modified saddle-point method. The used laser and terahertz pulse parameters are readily available at the modern experimental facilities.