  We study the suppression of reflections in the numerical simulation of the
time-dependent Schr\"odinger equation for strong-field problems on a grid using
exterior complex scaling (ECS) as absorbing boundary condition. It is shown
that the ECS method can be applied in both the length and the velocity gauge as
long as appropriate restrictions are applied in the ECS transformation of the
electron-field coupling. It is found that the ECS method improves the
suppression of reflection as compared to the conventional masking technique in
typical simulations of atoms exposed to an intense laser pulse. Finally, we
demonstrate the advantage of the ECS technique to avoid unphysical artifacts in
the evaluation of high harmonic spectra.
