Terahertz vs millimeter waves
From MesoscopicWiki
One terahertz is 1012 Hz. Conventionally the microwave band extends to 30 GHz or so. While the far-IR is nominally reckoned to start at around 1 THz. So the terahertz band lies between micowaves and the far-IR. On the other hand, in this frequency range the wavelengths of electromagnetic waves (in vacuum) are millimeter or sub-millimeter. So, logically, terahertz waves are the same thing as millimeter or submillimeter waves. However, in practice people who use the term terahertz are generally speaking of signals generated by ultrafast optical techniques or far-IR lasers. Focusing a sub-picosecond pulse on a photoconductive antenna of suitable dimensions will produce EM waves in the THz band. On the other hand, people who use the term millimeter or submillimeter waves are invariably speaking of sources and detectors based on harmonic multiplication of microwave signals.
