Quantum Cascade Lasers

Abstract

Quantum cascade (QC) lasers are semiconductor light sources based on intersubband (ISB) transitions, that is, electronic transitions between quantized conduction-band states in quantum-wells. As such, their emission wavelength is independent of the specific materials system employed and can be tuned by design over a broad spectral range. Following extensive research efforts, QC lasers have now become the leading semiconductor laser technology for the mid- and far-infrared spectral regions. This chapter begins with an introduction to the basic physics of ISB transitions, followed by a discussion of the key design principles of QC-laser gain media and optical cavities. The main operational parameters, including steady-state, dynamic, and spectral properties, are then described based on a simple rate-equation model. Finally, the performance of current state-of-the-art QC lasers and prospects for further developments are reviewed.