The role of absolute phase of few-cycle laser field in the generation and measurement of attosecond high-order harmonic pulses

Abstract

The effect of the absolute phase of the few‐cycle driving laser pulse on the generation and measurement of high‐order harmonic attosecond pulses is investigated theoretically. We find that the position of the generated attosecond soft‐x‐ray pulse in cutoff region is locked to the oscillations of the driving laser field, but not to the envelope of the laser pulse. This property ensures the success [M. Hentschel et al. Nature vol. 414, 509 (2001)] of the width measurement of attosecond soft‐x‐ray pulse based on the cross‐correlation between the attosecond pulse and its driving laser pulse. However, there is a timing jitter of the order of tens of attoseconds between the attosecond pulse and the driving laser field. This sets a limit for the measurement with the shorter attosecond pulses if we cannot control the absolute phase of the few‐cycle laser field. Also, we propose a novel method to detect the absolute phase of the driving laser field by measuring the spatial distribution of the photoelectrons induced by the attosecond soft‐x‐ray pulse and its driving laser pulse.