Quantum cascade lasers for the mid-IR to far-IR and applications

Summary form only given. Quantum cascade lasers (QCL) are fundamentally new in that: (1) their wavelength can be tailored over a wide range (so far from 3.4 μm to 21.5 μm and in the future from 1 to 100 μm) using the same combination of materials (e.g. AlInAs/GaInAs lattice matched to InP) by a suitable choice of the active layer thicknesses (a few nm), (2) their optical power is greatly enhanced by the cascade effect (one injected electron creates 25-100 photons in traversing the active region depending on the number of stages). These devices now outperform all other mid-IR semiconductor lasers in peak and CW optical power (with pulse peak power approaching 1 W at 300 K and CW powers >0.5 W at 80 K and CW operating temperatures now already in the range of thermoelectric coolers), and broad (up 150 nm) single mode tunability with >30 dB side mode suppression ratio. This tutorial will discuss in a simple way the underlying device physics, design principles and performance of our state-of-the-art top-of-line QCLs used in scientific, commercial and military application. These designs are based on a vertical optical transition between excited quantum states in a 3 or 4 well active regions, in which the lower level is empty due to a single or double phonon resonance between the lower energy levels. Alternative advanced designs are based on superlattice (SL) heterostructures for the active a swell as for the injector regions. These include chirped SL designs, multi-wavelength and bidirectional QCLs as well as injector-less lasers