Quantum Cascade Lasers – Bridging the THz Gap with Semiconductor Lasers

Abstract

The frequency range 1-100 THz has long been devoid of compact semiconductor sources of coherent radiation, similar to diode lasers in near-infrared and visible. A breakthrough in this area occurred with the demonstration of a quantum cascade laser (QCL) in 1994. QCLs are unipolar devices based on intersubband transitions in a repeated stack of semiconductor superlattices. As a result, their emission frequency can be widely tailored within the same materials system. Currently, these devices can operate at room temperature in mid-infrared spectral range and at cryogenic temperatures in terahertz spectral range. There is a growing interest to utilize QCLs for a variety of applications, including chem/bio and environmental sensing, terahertz security screening, and spectroscopy.

I will give an introduction to the principles of QCLs, provide examples of QCL-based systems for chem/bio sensing, developed in our group, and then describe our progress towards developing a room-temperature terahertz QCL source. In particular, I will talk about our “traditional” THz QCLs, which currently operate at a record temperature of 178K, and a novel type of THz QCL source, operable at room temperature, based on intra-cavity terahertz difference-frequency generation in dual-wavelength mid-infrared QCLs engineered to possess giant second-order nonlinear susceptibility associated with intersubband transitions in the active region.

Speaker Biography

Mikhail Belkin received his B.S. degree in Physics and Mathematics from Moscow Institute of Physics and Technology in 1998 and his Ph.D. in Physics from the University of California at Berkeley in 2004. He is presently a research associate in the Harvard School of Engineering and Applied Sciences. His research interests include the development of terahertz quantum cascade laser sources for room temperature operation, studying nonlinear optical effects in coupled-quantum-wells systems, and the development of quantum-cascade-laser-based systems for chem/bio sensing in mid-infrared.