  Irradiating a semiconductor with circularly polarized light creates
spin-polarized charge carriers. If the material contains atoms with non-zero
nuclear spin, they interact with the electron spins via the hyperfine coupling.
Here, we consider GaAs/AlGaAs quantum wells, where the conduction-band electron
spins interact with three different types of nuclear spins. The hyperfine
interaction drives a transfer of spin polarization to the nuclear spins, which
therefore acquire a polarization that is comparable to that of the electron
spins. In this paper, we analyze the dynamics of the optical pumping process in
the presence of an external magnetic field while irradiating a single quantum
well with a circularly polarized laser. We measure the time dependence of the
photoluminescence polarization to monitor the buildup of the nuclear spin
polarization and thus the average hyperfine interaction acting on the electron
spins. We present a simple model that adequately describes the dynamics of this
process and is in good agreement with the experimental data.
