Ultrafast Photoinduced Coherent Spin Dynamics in Ferromagnetic Ga$_{1-x}$Mn$_x$As/GaAs Structure

Ultrafast pump-probe magneto-optical spectroscopy is used to study coherent spin dynamics in the ferromagnetic semiconductor Ga$_{1-x}$Mn$_x$As systems. Above GaAs bandgap $E_g$, the temporal Kerr signal is found to be strongly dependent on pump photon polarization. This polarization dependence is attributed to spins of electrons photoexcited to the conduction band, and disappears for $E_{ph}