Recent progress in quantum cascade lasers and applications

TLDR

Quantum cascade lasers are semiconductor injection devices that use intersubband transitions in engineered multiple‑quantum‑well heterostructures grown by molecular‑beam epitaxy. The review surveys quantum cascade lasers. Key advantages include tunable emission wavelength set by quantum‑well thickness, a cascade process enabling multiple photons per electron for high power, and ultrafast carrier dynamics with negligible linewidth enhancement that enhance performance.

Abstract

Quantum cascade (`QC') lasers are reviewed. These are semiconductor injection lasers based on intersubband transitions in a multiple-quantum-well (QW) heterostructure, designed by means of band-structure engineering and grown by molecular beam epitaxy. The intersubband nature of the optical transition has several key advantages. First, the emission wavelength is primarily a function of the QW thickness. This characteristic allows choosing well-understood and reliable semiconductors for the generation of light in a wavelength range unrelated to the material's energy bandgap. Second, a cascade process in which multiple - often several tens of - photons are generated per electron becomes feasible, as the electron remains inside the conduction band throughout its traversal of the active region. This cascading process is behind the intrinsic high-power capabilities of the lasers. Finally, intersubband transitions are characterized through an ultrafast carrier dynamics and the absence of the linewidth enhancement factor, with both features being expected to have significant impact on laser performance.