Selection of an electron path of high-order harmonic generation in a two-colour femtosecond laser field

We theoretically investigate the process of high-order harmonic generation ( HHG) in an intense two-colour femtosecond laser field, of which both fundamental field and its second harmonic are linearly polarized. With the second harmonic field added, new degrees of freedom become available for controlling the process-relative phase between the two components and angle between the two polarization axes. It is shown that these parameters can be adjusted so as to select an electron path contributing to the process, leading to HHG from either a short path or a long path. As a result of this selectivity, regular and strong attosecond pulses can be generated.