@article { ISI:000246367600028,
	title = {Terahertz quantum-cascade-laser source based on intracavity difference-frequency generation},
	journal = {NATURE PHOTONICS},
	volume = {1},
	number = {5},
	year = {2007},
	month = {MAY},
	pages = {288-292},
	publisher = {NATURE PUBLISHING GROUP},
	type = {Article},
	address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND},
	abstract = {The terahertz spectral range (lambda = 30-300 mu m) has long been devoid of compact, electrically pumped, room-temperature semiconductor sources(1-4). Despite recent progress with terahertz quantum cascade lasers(2-4), existing devices still require cryogenic cooling. An alternative way to produce terahertz radiation is frequency down-conversion in a nonlinear optical crystal using infrared or visible pump lasers(5-7). This approach offers broad spectral tunability and does work at room temperature; however, it requires powerful laser pumps and a more complicated optical set-up, resulting in bulky and unwieldy sources. Here we demonstrate a monolithically integrated device designed to combine the advantages of electrically pumped semiconductor lasers and nonlinear optical sources. Our device is a dual-wavelength quantum cascade laser(8) with the active region engineered to possess giant second-order nonlinear susceptibility associated with intersubband transitions in coupled quantum wells. The laser operates at lambda(1) = 7.6 mu m and lambda(2) = 8.7 mu m, and produces terahertz output at lambda = 60 mu m through intracavity difference-frequency generation.},
	issn = {1749-4885},
	doi = {10.1038/nphoton.2007.70},
	url = {https://doi.org/10.1038/nphoton.2007.70},
	author = {Belkin, Mikhail A. and Federico Capasso and Belyanin, Alexey and Sivco, Deborah L. and Cho, Alfred Y. and Oakley, Douglas C. and Vineis, Christopher J. and Turner, George W.}
}
