Photoelectron momentum distribution for double ionization in strong laser fields

Non-sequential double ionization of atoms in a strong Linearly polarized laser field is studied on the basis of the generalized Keldysh model. The transition amplitude is calculated using a saddle-point method and the distribution in the total and relative momenta of two emitted electrons is found in an analytical form. The obtained result is compared with that from the simple-man approach. By integrating over the relative momentum we calculate the distribution in the total momentum. Its shape with two maxima and their positions are in good agreement with recent experimental measurements and elaborate numerical calculations of the recoil momentum distribution for doubly charged ions. We show that positions of the maxima depend strongly on the differential cross section of (e --> 2e) inelastic collisions.