@article { ISI:000264410900001,
	title = {Time-Resolved Investigations of Electronic Transport Dynamics in Quantum Cascade Lasers Based on Diagonal Lasing Transition},
	journal = {IEEE JOURNAL OF QUANTUM ELECTRONICS},
	volume = {45},
	number = {4},
	year = {2009},
	month = {APR},
	pages = {307-321},
	publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC},
	type = {Article},
	address = {445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA},
	abstract = {In this study, the nature of electronic transport in quantum cascade lasers (QCLs) has been extensively investigated using an ultrafast time-resolved, degenerate, pump-probe optical technique. Our investigations enable a comprehensive understanding of the gain recovery dynamics in terms of a coupling of the electronic transport to the oscillating intracavity laser intensity. In QCLs that have a lasing transition diagonal in real space, studies of the near-threshold reveal that the transport of electrons changes bias region from phonon-limited relaxation (tens of picoseconds) below threshold to photon-driven transport via stimulated emission (a few picoseconds) above threshold. The gain recovery dynamics in the photon-driven regime is compared with conventional four-level lasers such as atomic, molecular, and semiconductor interband lasers. The depopulation dynamics out of the lower lasing state is explained using a tight-binding tunneling model and phonon-limited relaxation. For the superlattice relaxation, it is possible to explain the characteristic picosecond transport via dielectric relaxation; Monte Carlo simulations with a simple resistor model are developed, and the Esaki-Tsu model is applied. Subpicosecond dynamics due to carrier heating in the upper subband are isolated and appear to be at most about 10\% of the gain compression compared with the contribution of stimulated emission. Finally, the polarization anisotropy in the active waveguide is experimentally shown to be negligible on our pump-probe data, supporting our interpretation of data in terms of gain recovery and transport.},
	keywords = {Carrier dynamics, electronic transport, midinfrared (mid-IR), quantum cascade laser (QCL), time-resolved},
	issn = {0018-9197},
	doi = {10.1109/JQE.2009.2013091},
	author = {Choi, Hyunyong and Diehl, Laurent and Wu, Zong-Kwei and Giovannini, Marcella and Faist, Jerome and Federico Capasso and Norris, Theodore B.}
}
