Abstract

We investigate theoretically the simultaneous exposure of a quantum well (QW) to a broadband (τ_p ≤ 100fs) optical pulse — to excite both free and Coulombically bound electron-hole (e-h) pairs (excitons) from the crystal ground state — and a ${ℰ}_0~1{\text{kVcm}}^{-1}$, ω₀ ~ 1THz driving field to enable the generation of sub-ps ~ 4-15THz electromagnetic (EM) transients. The double excitation scenario produces quantum beating, e-h relative motion wavepackets—whose anisotropic structure can be coherently controlled to manifest in unique spectral and time-dependent features in both the optical and THz regimes of the EM spectrum. Our theoretical approach is based on a unified, tour-de-force solution of the full 2D-anisotropic semiconductor Bloch equations in the presense of both an optical pulse and a THz driving field. We study QW excitation by realistic driving frequencies (as available from free electron lasers) with arbitrary polarisations. New and intriguing carrier dynamics emerge, and a series of relative motion wavepackets will be depicted and analysed.

© 1998 IEEE