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Photoluminescence (PL) as a consequence of a two-photon absorption excitation was measured in a GaAs/AlGaAs (001) multiple quantum well (MQW) at room temperature and an optical anisotropy of the two-photon absorption was investigated by PL intensity depending on the polarization direction of the normal-incidence excitation light. The anisotropic behavior with a four-fold rotation symmetry was observed in the polarization dependence. Strength of the two-photon absorption reaches its maximum when the excitation light is polarized to the [110] and [10] directions. It was found that the anisotropic behavior becomes more significant as the excitation energy approaches near the two-photon absorption edge. The anisotropy parameter |σ| determined by the theoretical fitting curve reaches ∼ 2 at the two-photon absorption edge, which was about 4 times larger than that of the bulk GaAs (|σ| ∼ 0.5). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)