Laser ionisation of H-in the presence of a DC field

A non-perturbative, complex eigenvalue, laser ionisation many-electron theory which incorporates the effects of the simultaneous presence of a DC field is presented. Application is made to the H - ionisation cross section with AC fields up to 10 11 W cm -2 , with and without a DC field. The effect of the ground state correlation is of the order of 30%. Most important is the degree of accuracy of the representation of the Gamow function describing the free electron. The Gamow function is expanded in terms of a large number of spherical harmonics (up to l=16), each associated with a large number of complex-coordinate-scaled Slater orbitals. Convergence is tested thoroughly via the overall stability of the resulting complex eigenvalues.