The ultrafast dynamics of short-pulse-laser-excited fused silica is investigated by measuring polarizationresolved reflectances of a wavelength-tunable probe pulse following a near-infrared pump pulse. These data, which should, in principle, allow the determination of both real and imaginary parts of the time-dependent electric permittivity, turn out to become incompatible with an isotropic optical response after ∼200 fs. This is reconciled with a uniaxial permittivity tensor, which predicts greatly enhanced absorption of p-polarized light, suggesting that an absorption channel is missing in the standard optical models for strongly excited dielectrics. The timescale for the excitation-induced variations in the optical properties exhibits a wavelength dependence that can be explained qualitatively by Pauli blocking in the electronic band structure.