Terahertz quantum cascade lasers — The past, present, and potential future

Since their first demonstration in 2002, the development of terahertz frequency quantum cascade lasers has been extremely rapid. We overview some of the advances that have taken place and which have made the terahertz quantum cascade laser such a ubiquitous source. We also consider potential future directions for terahertz quantum cascade laser technology, including its use in satellite-borne instrumentation for future Earth observation and planetary science missions.