Intraband polarization and terahertz emission in biased semiconductor superlattices with full excitonic basis

We report theoretical and experimental results for the intraband dynamics of biased semiconductor superlattices excited by ultrashort optical pulses. The theoretical model used employs an excitonic basis that includes $1s$ and all higher-energy in-plane excitonic states. These excitonic states are used to calculate the intraband polarization and terahertz emission of the superlattice system in response to excitation via an ultrashort optical pulse. Our results show that the higher in-plane excitonic states often modify considerably the terahertz emission relative to the results obtained using a $1s$ exciton basis, but that under some excitation conditions a $1s$ exciton basis gives accurate results. Good agreement between experimental and theoretical results is obtained.