Is there any deep reason of using the new (and trendy) words “terahertz” and “multi-terahertz” when the traditional and well-established terms of far-infrared and mid-infrared have been available for decades? The answer is that the terms (multi-)terahertz are closely connected to specific quasi-optical techniques of coherent generation and detection of radiation, which provide some added value compared to “classical” experimental methods. Among others they allow one to observe directly the oscillations of terahertz light in time during various interactions.
