Coulomb Corrections in Photoelectron Spectra in the Adiabatic Limit

A momentum-dependent Coulomb correction to the probability of nonlinear ionization in a strong low-frequency laser field is derived analytically in the adiabatic limit, when the quasi-static tunneling model applies. Obtained formulas show that the Coulomb modification of photoelectron spectra can be significant both in linearly and circularly polarized fields. For linear polarization, it leads to a relative enhancement of the ionization probability for photoelectron energies of the order of the ponderomotive energy. This Coulomb effect is expected to be most significant for atomic species with relatively low ionization potentials, such as alkali atoms