Phase-dependent ionization in the barrier suppression regime

Here the dependence of atomic ionization on the absolute phase of sub-10-fs pulses in the barrier suppression regime is investigated. The results obta ined show that it is possible to find a parameter range for the laser pulse where the phase dependence of the ionization after the pulse is a nonoscil lating curve with a well defined minimum (or maximum). This effect is expla ined by a simple model based on the assumption that in this regime the ioni zation is dominated by the electrons ejected when the field exceeds the cri tical value for suppression of the Coulomb barrier. These findings can be u sed to design phase-dependent absorbers with a potential application to sta bilize the absolute phase into the cavity of a femtosecond laser, which is of major importance for extreme nonlinear optics.