High-resolution terahertz spectroscopy with quantum-cascade lasers

Terahertz (THz) quantum-cascade lasers (QCLs) are narrow band, high-power, and frequency-agile sources. These properties make them attractive for applications in high-resolution molecular and atomic spectroscopy. In the past few years, various techniques and methods regarding high-resolution spectroscopy with THz QCLs have been developed, namely, direct absorption spectroscopy, detection schemes such as wavelength and frequency modulation, differential spectroscopy, photoacoustic spectroscopy, and heterodyne spectroscopy. We briefly review the most relevant technological and methodological advances in this field, and we discuss perspectives and future directions.