Capabilities have greatly advanced for vacuum-electronic-device (VED) sources of terahertz and near-terahertz coherent radiationboth continuous wave (CW) and pulsed sources. Quantum-theory models of some terahertz VEDs have been developed and used with some success. Yet all terahertz VEDs can be explained with purely classical models, which is the approach taken by the following group of researchers: John H. Booske from the University of Wisconsin; Richard J. Dobbs from CPI Canada; Colin D. Joye from the US Naval Research Laboratory; Carol L. Kory from Teraphysics, Inc.; George R. Neil with the Thomas Jefferson National Accelerator Facility; Gun-Sik Park with Seoul National University; Jaehun Park from Korea's Pohang University of Science and Technology; and Richard J. Temkin from the Massachusetts Institute of Technology.

For high-power devices needing to generate high-power electron currents in particular, the vacuum is an ideal propagation medium. VEDs do have tradeoffs, though. These include the need for a three-dimensional (3D), vacuum-tight enclosure.

The researchers note that terahertz devices based on VED technology cover a total bandwidth exceeding 10.0 THz. Terahertz-device choices can be roughly broken down into three classes. Compact sources with high mobility include backwards-wave oscillators (BWOs). They range from 0.1 to 1.0 THz with 10T-3 through 103 W (CW and pulsed) output power. Another option is compact gyrotons with moderate mobility, which cover 0.1 to 1.0 THz with 10-3 through 106 W (CW and pulsed) output power. Stationary accelerator-based sources, including free electron lasers (FELs), range from 0.2 to 10.0 THz and beyond with 10 through 109 W (average and pulsed) output power. See "Vacuum Electronic High Power Terahertz Sources," IEEE Transactions On Terahertz Science And Technology, Sept. 2011, p. 54.