Controlling high-order harmonic cut-off extension using two delayed pulses of the same colour

We present an extension of the cut-off frequency in High-Order Harmonic Generation using two delayed few-cycles laser pulses, identical in all parameters except the carrier envelope phase (CEP), which is shifted by π in the second pulse. We find parameters which can generate high-order harmonics up to 5.5U p +I p as presented in Fig.1.