Coulomb-Volkov approach of atom ionization by intense and ultrashort laserpulses - art. no. 053411

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 las er pulse. In a previous paper [Eur. Phys. J. D 11, 191 (2000)], it was show n that, for atomic hydrogen targets, this theory makes accurate predictions as long as the interaction time does not allow more than two optical cycle s. Recently, multigigawatt laser pulses with a full width at half maximum o f less than two optical cycles have been generated by Nisoli et al. [Opt. L ett. 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 hyd rogen atom by lasts pulses similar to the ones generated by Nisoli et al, a re in very good agreement with the predictions of an ''exact'' numerical tr eatment. Further, the domain where the Coulomb-Volkov theory applies is mar ked out by means of a consistent accuracy parameter and by comparison with an ''exact" numerical treatment. It is shown that, subject to the above-men tioned condition, good predictions may always be issued as long as the inte raction time does not exceed half the initial orbital period of the electro n. For a given laser pulse duration, predictions are all the better that th e laser field amplitude is high and the initial quantum number is large.