| We present a theoretical description of the THz charge oscillations that appears in a biased super-lattices after a short interband light pulse excitation. We solve the time dependent Schrödinger equation and compute the average of the current operator using the time dependent wavefunction. We obtain that the charge current oscillates with the Bloch frequency and, at the same time, we identify the effects of the different experimental parameters on the amplitude of such oscillations. By the inclusion of dumping effects we can associate the time derivative of the current to the electric field emission in actual samples. In particular, we obtain that the field emission is proportional to the excitation intensity, even though it is not proportional to the density of photocreated electron/hole pairs. Indeed, we find that the amplitude is very weak at large negative detuning (excitation well below the central Wannier-Stark transition), grows quickly with increasing the mean laser energy, reaches a maximum near the resonant interband excitation and then decreases for large positive detunings (excitation well above the interband absorption edge). |
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