By working in a regime where the phase evolution of an optically excited system can be directly exploited, we can exact 'coherent control'. This requires moving beyond Einstein's model of absorption and emission to consider the phases of the induced dipoles. The goals of coherent control include the development of novel control parameters, the production of unusual end products, and the characterisation of material properties that cannot be measured by normal spectroscopy.
Applying these ideas to semiconductor systems has yielded many interesting results. We have controlled the attenuation of a visible beam in a bulk semicondcuctor using the phase of a second, infrared beam. Other work includes the generation of bias-free currents and the manipulation of electron populations in nanostructures. Special note will be made of certain key physical concepts related to this work, including nonlinear optics, quantum interference, and ultrafast phenomena in semiconductors.