Amplitude Decay and Instantaneous Frequency Dynamics of Excitonic Polarization in Semiconductor Quantum Wells

Coherent light scattering is an ideal tool to investigate the microscopic interactions that take place in various diluted or condensed phase systems1. It is of particular interest in semiconductors where the Coulomb interaction between electrons and holes brings new features in the dynamics of the polarization established by ultrashort optical pulses2. Due to this Coulomb coupling the coherent emission observed in different wave-mixing geometries behaves in a non-trivial fashion. The usual description of the material relaxation with a simple transverse time T 2, as is done for atomic-like systems3, is no longer sufficient. Although the underlying physics is more complex, one may picture these different regimes by analogy with oscillators: the exponential T 2 behavior corresponds to a damped harmonic oscillator, while the Coulomb interacting system leads to a non-exponential damping, as with nonlinear coupled oscillators.