Title :
Time-Resolved Investigations of Electronic Transport Dynamics in Quantum Cascade Lasers Based on Diagonal Lasing Transition
Author :
Choi, Hyunyong ; Diehl, Laurent ; Wu, Zong-Kwei ; Giovannini, Marcella ; Faist, Jérôme ; Capasso, Federico ; Norris, Theodore B.
Author_Institution :
Dept. of Electr. Eng. & Comput. Sci., Univ. of Michigan, Ann Arbor, MI
fDate :
4/1/2009 12:00:00 AM
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 :
Monte Carlo methods; anisotropic media; dielectric relaxation; high-speed optical techniques; laser beams; laser cavity resonators; laser transitions; optical pumping; optical waveguides; quantum cascade lasers; stimulated emission; superlattices; transport processes; Esaki-Tsu model; Monte Carlo simulation; active waveguide; carrier heating; diagonal lasing transition; dielectric relaxation; electronic transport dynamics; gain compression; gain recovery; gain recovery dynamics; oscillating intracavity laser intensity; phonon-limited relaxation; photon-driven transport; picosecond transport; polarization anisotropy; pump-probe optical technique; quantum cascade laser; resistor model development; stimulated emission; subpicosecond dynamics; superlattice relaxation; tight-binding tunneling model; time-resolved investigation; Atom lasers; Electron optics; Laser excitation; Laser modes; Laser transitions; Optical pumping; Optical superlattices; Quantum cascade lasers; Semiconductor lasers; Stimulated emission; Carrier dynamics; electronic transport; mid infrared (mid-IR); quantum cascade laser (QCL); time-resolved;
Journal_Title :
Quantum Electronics, IEEE Journal of
DOI :
10.1109/JQE.2009.2013091