Sub-cycle dynamics in two-color high-harmonic generation from laser-produced plasmas

We present high-order harmonic generation (HHG) in laser-produced aluminium and tin plasmas driven by a two-color field with orthogonal polarization, leading to the generation of both odd and even harmonics. We shape the effective drive field with sub-cycle resolution by controlling the phase between the fundamental wave and its second harmonic. The shape of the drive field influences the electron trajectories of the various harmonics generated in these plasmas. Here we focus on intermediate harmonic orders, with energies around the ionization potential of the target atoms. Clear oscillatory signals are observed in the HHG signals, with strongly harmonic-order-dependent modulation depth and oscillation phase. These results provide evidence for a significant influence of the Coulomb potential on the laser-driven electron trajectories in this spectral range.