Natural optical activity of metals

We derive the current response of noncentrosymmetric metal in normal and in superconducting states to the electromagnetic field with finite frequency and wave vector. The conductivity tensor is found contains the linear in wave vector off diagonal part generating natural optical activity. The Kerr rotation of polarization of light reflected from the metal surface is calculated. Its value is expressed through the fine-structure constant and the ratio of light frequency to the band splitting due to the spin-orbit interaction.