Coulomb-Volkov approach of atom ionization by intense and ultrashort laser pulses

We present a nonperturbative theoretical approach, based on Coulomb-Volkov-type states, which is able to predict both angular and energy distributions of ejected electrons when atoms interact with a very short and intense laser pulse. In a previous paper [Eur. Phys. J. D 11, 191 (2000)], it was shown that, for atomic hydrogen targets, this theory makes accurate predictions as long as the interaction time does not allow more than two optical cycles. Recently, multigigawatt laser pulses with a full width at half maximum of less than two optical cycles have been generated by Nisoli et al. [Opt. Lett. 22, 522 (1997)] at lambda = 800 nm. In the present paper, it is shown that predictions of the Coulomb-Volkov approach for the ionization of a hydrogen atom by lasts pulses similar to the ones generated by Nisoli et al, are in very good agreement with the predictions of an ''exact'' numerical treatment. Further, the domain where the Coulomb-Volkov theory applies is marked out by means of a consistent accuracy parameter and by comparison with an ''exact" numerical treatment. It is shown that, subject to the above-mentioned condition, good predictions may always be issued as long as the interaction time does not exceed half the initial orbital period of the electron. For a given laser pulse duration, predictions are all the better that the laser field amplitude is high and the initial quantum number is large.