Semiclassical approach to time-dependent tunnelling

We present an exact time-dependent semiclassical formulation of the dynamics of a δ-atom subjected to an oscillating electric field. Through a simple approximation the results of Ergenzinger's more intuitive analysis are obtained. We also comment on the important role played by the imaginary tunnelling time t0, which is quite distinct from the usual adiabatic tunnelling time. (orig.)