Single-photon double ionization of helium in the presence of dc electric field

We study the influence of the external dc electric field on the process of single-photon double ionization of helium at photon energies of 85 and 90 eV. Calculation is based on a numerical solution of the time-dependent Schrödinger equation and subsequent projection of the solution on a final state furnished by the convergent close coupling expansion. We find that for the range of the field strengths studied (F_dc⩽3×10⁻² a.u.) the presence of the external dc field leads to a monotonous decrease of the total probability of single-photon double electron ionization. This decrease is achieved primarily due to decreasing probability to detect electrons with unequal energy sharing.