  We perform an all-optical spin-dynamic measurement of the Rashba spin-orbit
interaction in (110)-oriented GaAs/AlGaAs quantum wells. The crystallographic
direction of quantum confinement allows us to disentangle the contributions to
spin-orbit coupling from the structural inversion asymmetry (Rashba term) and
the bulk inversion asymmetry. We observe an unexpected temperature dependence
of the Rashba spin-orbit interaction strength that signifies the importance of
the usually neglected higher-order terms of the Rashba coupling.
