Coherent current control in semiconductors: a susceptibility perspective

We show that the all-optical generation and control of dc current in semiconductors, also known as coherent current control, can be described within the standard framework of nonlinear optics using perturbative susceptibilities. In particular, we find that such effects arise from zero frequency divergences in the susceptibilities; this identification provides a novel and convenient method to classify the various contributions in the response. However, these physical divergences are distinct from other unphysical divergences that are commonly encountered and which have led to incorrect results elsewhere in the literature. The susceptibility viewpoint offered here allows one to understand the optical response for both resonant and nonresonant excitation, exposes the relationship between second- and third-order (and higher) processes, and will provide a natural framework in which to include dissipative effects.