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

In this paper, 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 pi in the second pulse. We use two pulses of the same colour at fixed CEP difference and control the delay between the two pulses which enables us to shape the fundamental field with a high accuracy under one optical cycle. These quantities correspond to macroscopic parameters that can be manipulated experimentally.