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Ionization of an atom by a few-cycle attosecond xuv pulse is analyzed using perturbation theory ͑PT͒, keeping terms in the transition amplitude up to second order in the pulse electric field. Within the PT approach, we present an ab initio parametrization of the ionized electron angular distribution ͑AD͒ using rotational invariance and symmetry arguments. This parametrization gives analytically the dependence of the AD on the carrier envelope phase ͑CEP͒, the polarization of the pulse, and on the ionized electron momentum direction, p . For the general case of an elliptically polarized pulse, we show that interference of the first-and secondorder transition amplitudes causes a CEP-dependent asymmetry ͑with respect to p → −p ͒ and both elliptic and circular dichroism effects. All of these effects are maximal in the polarization plane and depend not only on the CEP but also on the phase of dynamical atomic parameters that enter our parametrization of the AD. Within the single active electron model of an atom, for an initial s or p state we define all dynamical parameters in terms of radial matrix elements ͑analytic expressions for which are given for the Coulomb and zero-range potentials͒. For ionization of the H atom by linearly polarized pulses, our PT results are in excellent agreement with results of numerical solutions of the time-dependent Schrödinger equation of Peng et al. ͓New J. Phys. 10, 025030 ͑2008͔͒. Also, our numerical results show that the asymmetries and dichroism effects at low electron energies have a different physical origin from those at high electron energies. Moreover, our results for Gaussian and cosine-squared pulse shapes are in good qualitative agreement. Finally, we show that our analytic formulas may prove useful for determining few-cycle extreme ultraviolet ͑xuv͒ pulse characteristics, such as the CEP and the polarization.

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We apply our recently developed, model-independent quantum approach for intense laser detachment of a weakly bound electron to interpret a recent experiment on above-threshold detachment (ATD) of the F− ion. We find that the measured electron energies correspond to the ‘Keldysh part’ of the ATD spectrum, just below the onset of our predicted rescattering plateau. Overall, our predicted ATD spectrum (using a scaled peak intensity and focal averaging) is in excellent agreement with the experimental data, except for certain structures observed for electron energies above 12.6 eV that we attribute to known two-electron resonances of F−. A number of analytical approximations to our exact p-state ATD amplitude are obtained, and their accuracy is investigated.

The momentum distributions of electrons ionized from H atoms by chirped few-cycle attosecond pulses are investigated by numerically solving the time-dependent Schrödinger equation. The central carrier frequency of the pulse is chosen to be 25 eV, which is well above the ionization threshold. The asymmetry ͑or difference͒ in the yield of electrons ionized along and opposite to the direction of linear laser polarization is found to be very sensitive to the pulse chirp ͑for pulses with fixed carrier-envelope phase͒, both for a fixed electron energy and for the energy-integrated yield. In particular, the larger the pulse chirp, the larger the number of times the asymmetry changes sign as a function of ionized electron energy. For a fixed chirp, the ionized electron asymmetry is found to be sensitive also to the carrier-envelope phase of the few-cycle pulse.