Slow light using excitonic population oscillation

We develop a theoretical model for slow light using excitonic population oscillation in a semiconductor quantum well. In a two-level system, if the resonant pump and the signal have a difference frequency within the range of inverse of the carrier lifetime, coherent population beating at this frequency will be generated. We analyze the excitonic population oscillation using an atomiclike model extended from semiconductor Bloch equations for both spin subsystems of the excitonic population and the electrical polarization density. The two spin subsystems are coupled by the excitation-induced dephasing rate, which depends on the net population difference in conduction and heavy hole quantized bands and the population exchange due to flip of the spins of electrons or holes. We present our theoretical results for the absorbance, the refractive index spectra, and the slowdown factor due to population oscillation at various pump intensities, and show very good agreement with experimental data. It is shown that a slowdown factor of $3.12\times {10}^4$ has been achieved for a semiconductor quantum-well structure. We also obtain analytical solutions from our theory and account for different response behaviors of the signal when its polarization is either parallel or orthogonal to that of the pump, which has also been confirmed by experiments.