Abstract
The relaxation dynamics of optical excitations in solids is a field of intense research. Recently, much of the experimental and theoretical effort has focused on two topics: the relation of the initial, coherent regime of the excitations and the generation of terahertz radiation by ultrafast dynamics of photoexcited carriers. In the coherent regime, a number of studies have addressed the relaxation dynamics of the polarization itself, e.g., collective effects in the decay of the polarization, by using time-integrated1 and time-resolved2 transient four-wave mixing. Recently, it also became possible to study the dynamics of optically excited superpositions of transitions (wave packets) in semiconductors. The freedom in the design of semiconductor heterostructures makes them an ideal time-dependent quantum-mechanics laboratory, in which wave functions and transition energies can be adjusted over a wide range, both by sample design and, in situ, by varying a bias field. Of particular interest for both basic research and applications arc experiments in which the wave packets show distinct spatial dynamics, which can also lead to efficient emission of coherent terahertz radiation.
© 1993 Optical Society of America
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