A Novel Method for Measuring the Absolute Phase of a Few-Cycle High Intensity Laser

The effect of the absolute phase of the few-cycle driving laser field on the generation and measurement of high-order harmonic attosecond pulses is investigated theoretically. We find that the generated attosecond soft-x-ray pulse is locked to the oscillations of the driving laser field, but not to the envelope of the laser pulse, and the intensity ratio of two adjacent attosecond pulses is exponential as a function of the absolute phase. Based on these results, 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 the driving laser field.