Photonic Systems Brown Bag Seminar

Thursday, December 2, 2004, 12 noon      Haus Room, 36-428, RLE

Terahertz Quantum Cascade Lasers: Bridging the Terahertz Gap

Ben Williams

The terahertz spectral regime roughly consists of the frequencies between 0.3-10 THz (wavelengths between 30-1000 um), between the millimeterwave and the infrared ranges.  Historically, scientific and technological development in this  "terahertz gap" has been impeded by the lack of efficient, compact, and convenient radiation sources.  This talk focuses on the recent development of a novel light source, the terahertz quantum cascade laser, which is a unipolar semiconductor heterostructure laser, where light is emitted as electrons make transitions in quantum wells  entirely within the conduction band.  Because the emission wavelength can be tailored by engineering the multiple-quantum-well structure, semiconductor lasers can be made with extremely long emission wavelengths that are no longer limited by the material bandgap.  At present, using a novel resonant-phonon depopulation design in combination with a low-loss metal-metal waveguide, we have obtained lasing from 2.1-4.0 THz (75-141 um) with milliwatt power levels, and up to record operating temperatures of 137 K in pulsed mode, and 97 K in continuous wave mode.