Terahertz quantum-cascade-laser source based on intracavity difference-frequency generation

• DOI: 10.1038/nphoton.2007.70
• Publication Date: 2007-05-01T09:11:48Z
• Authors: Mikhail A. Belkin; Federico Capasso; Alexey Belyanin; Deborah L. Sivco; Alfred Y. Cho; Douglas C. Oakley; Christopher J. Vi...; George W. Turner
• Keywords: 0103 physical sciences; 530; 7. Clean energy; 01 natural sciences

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.