(color online) (a) Photoluminescence modulation by THz pulse in n-type bulk GaAs at room temperature. (b) Physical mechanism for the PL-modulation. The red arrow denotes the recombination of the electrons in the conduction band valley and the holes in the valence band, and thus forming PL. Green arrows refer to the intervalley scattering mechanism that causes the electrons to transfer from the valley to the L and X valleys.