A quantum cascade laser (QCL) is a semiconductor laser that emits in the mid- to far-infrared region of the electromagnetic spectrum. Contrary to the typical semiconductor lasers which emit radiation by recombination of electron-hole pairs across the band-gap, emission from QCLs results from inter-subband transitions in a repeated stack of quantum well semiconductor heterostructures.
QCLs illustrates the power of structure engineering offered by molecular beam epitaxy. THz QCLs can be based on different kinds of super-lattice structures such as GaAs/AlGaAs, InAs/AlSb and InGaAs/GaAsSb. The main challenge is to have the QCL lasing without the need of cryogenic cooling – a key factor for a variety of novel applications such as pollutant sensors, dynamic radar cruise control, medical diagnostics and infrared spectroscopy. While working at the National Research Council (NRC) and in collaboration with scientists from other institutions, Prof. Wasilewski developed a structure which lases in the 3 THz frequency at 200K. To date, this is the record maximum lasing temperature; but we are in the quest to beat it!