The terahertz gap is an engineering term for a band of frequencies in the terahertz region of the electromagnetic spectrum between radio waves and infrared light for which practical technologies for generating and detecting the radiation do not exist. It is defined as 0.1 to 10 THz (wavelengths of 3 mm to 30 µm). Currently, at frequencies within this range, useful power generation and receiver technologies are inefficient and impractical. Mass production of devices in this range and operation at room temperature are mostly unfeasible. Hence, a gap exists between mature microwave technologies in the lower frequencies of the electromagnetic spectrum and the well developed optical technologies in  infrared wavelengths and higher frequencies of the electromagnetic spectrum. Research that attempts to resolve this issue has been conducted over recent decades .