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Nature Photonics 1, 517–525 (1 September 2007) | doi:10.1038/nphoton.2007.166

Terahertz quantum-cascade lasers

Benjamin S. Williams

Six years after their birth, terahertz quantum-cascade lasers can now deliver milliwatts or more of continuous-wave coherent radiation throughout the terahertz range — the spectral regime between millimetre and infrared wavelengths, which has long resisted development. This paper reviews the state-of-the-art and future prospects for these lasers, including efforts to increase their operating temperatures, deliver higher output powers and emit longer wavelengths.