The Basic Regimes of Dynamics

Lasers emitting (ultra-)short optical pulses with pulse durations from the nano- to the attosecond range, i.e., with pulses down to only a partial cycle of the electromagnetic field allow the dynamics of the optical excitations in semiconductors to be measured directly in the time domain. Since the characteristic time constants can be as short as a few fs, this field of research is also known as ultrafast spectroscopy. The general idea of this chapter is to sort the vast variety of dynamic phenomena into a few regimes. These regimes can overlap with respect to their basic time constants, but they are characterized by typical experimental methods and theoretical procedures to explored them. We concentrate on the properties of electronic excitations in semiconductors and present the basic mechanisms. The main regimes of dynamics discussed here are the coherent regime, the regime of relaxation and thermalization, and the regime of recombination.