Abstract
The terahertz spectral range (λ = 30–300 µm) has long been devoid of compact, electrically pumped, room-temperature semiconductor sources1,2,3,4. Despite recent progress with terahertz quantum cascade lasers2,3,4, 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 lasers5,6,7. 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 laser8 with the active region engineered to possess giant second-order nonlinear susceptibility associated with intersubband transitions in coupled quantum wells. The laser operates at λ1 = 7.6 µm and λ2 = 8.7 µm, and produces terahertz output at λ = 60 µm through intracavity difference-frequency generation.
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Acknowledgements
This work was supported by Air Force Office of Scientific Research under Contract No. FA9550-05-1-0435. A.B. acknowledges partial support from National Science Foundation through grants ECS-0547019, EEC-0540832 and OISE 0530220. Fabrication was carried out in the Center for Nanoscale Systems at Harvard University. Harvard-CNS is a member of the National Nanotechnology Infrastructure Network.
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Belkin, M., Capasso, F., Belyanin, A. et al. Terahertz quantum-cascade-laser source based on intracavity difference-frequency generation. Nature Photon 1, 288–292 (2007). https://doi.org/10.1038/nphoton.2007.70
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DOI: https://doi.org/10.1038/nphoton.2007.70
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