On the Observability of Bloch Oscillations in Time-Resolved Four-Wave-Mixing In the presence of a homogeneous electric field, 𝐹→, each Bloch state in a crystal changes quasimomentum according to the so-called acceleration theorem Thus, in the absence of interband tunneling and scattering processes, each Bloch state moves at a constant velocity in k-space and executes a periodic motion in the reduced zone scheme by undergoing a Bragg reflection between each two traversals of the Brillouin zone.