Generation of unipolar electromagnetic pulses in semiconductor nanocrystals

We show that excitation of a semiconductor nanocrystal with a short pulse of electromagnetic field can result in the generation of a unipolar electric pulse, which is the distribution of field with a nonzero electric pulse area. The effect is caused by the exciton nonlinearity in a nanocrystal. The microscopic theory of the effect is presented. We also discuss related proposals of unipolar pulse generation, including the optical rectification effect and electric field-induced interband ionization of a nanocrystal.