Hydrogen atom excitation in intense attosecond laser field: Dipole approximation

Validity of the dipole approximations for the excitation of the hydrogen atom by attosecond strong laser pulse is verified in the first order perturbation approximations. Our calculation show that the simple dipole approximations give the same results for the final value of the dipole transition probabilities as the more complicated nondipole calculations even when the pulse size is less than characteristic atomic size (n_f >; 3) where the dipole approximation is invalid.