TERAHERTZ EMISSION FROM QUANTUM BEATS IN COUPLED QUANTUM-WELLS

We have investigated the terahertz (THz) emission from quantum beats i n coupled quantum wells by time-resolved THz spectroscopy. It is found that the intensity of the THz emission exhibits a clear resonance in the excitation wavelength, suggesting that quantum beats in coupled qu antum wells are caused by excitons. It is also found that the dephasin g time of quantum beats is almost constant (similar to 6 ps) up to 50 K and decreases rapidly with increasing temperature, indicating that t he coherence of quantum beats is broken by impurity and/or roughness s cattering at low temperatures and by optical phonon scattering at high temperatures.