Above-threshold ionization with few-cycle laser pulses and the relevance of the absolute phase
In a recent 'stereo above-threshold ionization experiment, the influence of the absolute phase (the phase of the carrier wave with respect to the laser-pulse envelope) on the left-right asymmetry of the emitted photoelectrons ionized by a few-cycle pulse was analyzed. Two detectors were used, positioned opposite each other in a plane perpendicular to the propagation direction of the laser beam. Depending on the value of the absolute phase, one detector registers more electrons than the other. Applying the Keldysh theory of above-threshold ionization, adjusted to the case of few-cycle pulses, we explore this left-right asymmetry in more detail. We investigate the absolute-phase dependence of the differential ionization probabilities and explain it using the saddle-point method. A theoretical analysis of the experiment, based on a correlation technique, is presented. The time dependence of the laser-field intensity of a few-cycle laser pulse is analyzed both for circular and for linear polarization.