Terahertz Emitters and Detectors

Dear Colleagues,

Terahertz (THz) electromagnetic waves in the frequency f range between 0.1 and 10 THz have recently attracted much attention because of their enormous potential applications in various fields such as non-destructive imaging, spectroscopy, astronomy, medical sciences, food industries, high-speed communications, etc. The detection of several types of cancers is facilitated with circularly polarized THz waves. For such versatile applications, compact, high-performance, all-solid-state, and continuous wave (CW) monochromatic THz sources are in great demand. To be useful as a hand-held device, the emitters should have an output power of at least 1 mW. Resonant tunneling diodes (RTDs) operating at room temperature and quantum cascade lasers (QCLs) may be good candidates. The emission power of RTDs above the central frequency of the THz gap around 1.5 THz at present, however, has severely been limited to about 1 μW and is much lower at higher f values. The emission power of QCLs can be well above 1 mW, but not below 1.5 THz. Difference frequency generation QCLs can operate at about 1 THz. For frequencies near to 1~THz, but only at powers in the μW range. By using the intrinsic Josephson junctions (IJJs) in the layered high temperature superconductor, Bi₂Sr₂CaCu₂O_8+d (Bi2212), the range from 1 to 11 THz has been achieved for both single device emitters and detectors. Although the emission power is less than 1 μW, the power can in principle be increased substantially by forming emission arrays and making efficient use of internal and external electromagnetic cavities. One array was reported to emit at 0.6 mW below 1 THz. Although such devices require cryo-cooling, overall, devices including the cooler can now be made of hand-held size.  

Sensors authorizes both original and review articles on any of these topics in this special issue. Review articles on the state-of-the-art of RTDs, QCLs, Difference generation QCLs, and superconducting IJJs are especially welcome. Original articles that demonstrate or predict improvement upon the existing performance features of any of these or possibly other techniques are also most welcome. Also welcome are original and review articles on uses of such devices in applications.

Prof. Richard Klemm
Guest Editor

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