COHERENCE CONTROL OF PHOTOCURRENTS IN SEMICONDUCTORS

It has not been widely appreciated that the phase of an optical beam c an be used as a parameter to control the properties of matter. However , if two or more phase-related beams connect the same initial and fina l quantum states of a system, interference between the different quant um mechanical pathways can influence the final configuration. When har monically-related optical beams generate carriers in semiconductors th e relative phase of the two beams can be used to generate and control the directionality of an electrical current in the absence of any exte rnal bias. We briefly review recent activity in coherently controlled photocurrents for quantum well and bulk semiconductors and indicate ho w the effects can also be understood in terms of nonlinear optics.