Spin Quantum Beats in GaAs

The short laser pulses (FWHM 2ps) of a Ti:Sapphire laser are used to excite a GaAs sample with circularly polarized light perpendicular to an applied magnetic field (0–16Tesla). This excitation geometry (Voigt geometry) leads to a coherent excitation of the two energetically separated Zeeman states (\(s_z = +\frac{1}{2},s_z = -\frac{1}{2}\)) in the GaAs conduction band. Due to the coherent superposition of the excited states a beating in the time-resolved luminescence signal with a frequency equal to the Larmor frequency can be observed if circularly polarized light is detected.