Terahertz quantum-cascade-laser source based on intracavity difference-frequency generation
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The terahertz spectral range ( = 30-300 m) has long been devoid of compact, electrically pumped, room-temperature semiconductor sources. Despite recent progress with terahertz quantum cascade lasers, 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. 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 with the active region engineered to possess giant second-order nonlinear susceptibility associated with intersubband transitions in coupled quantum wells. The laser operates at 1 = 7.6 m and 2 = 8.7 m, and produces terahertz output at = 60 m through intracavity difference-frequency generation. 2007 Nature Publishing Group.
