Plasma diagnostic techniques based on terahertz radiation

Plasma is a highly elusive state of matter, and measuring its properties presents a formidable challenge due to the extreme conditions of temperature and density, as well as the significant impact of any external perturbation on its energy content and stability. This is particularly true for nuclear fusion experiments, where conditions are even more extreme. The necessity of accurately measuring plasma properties has led to the development of a wide range of techniques and instrumentation, collectively known as plasma diagnostics. A crucial subset of these diagnostics falls within the far infrared radiation and sub-millimeter waves range (100–2000 GHz). The evolution of terahertz time domain spectroscopy (THz-TDS) represents a novel addition to the diagnostics landscape, and its relevance is rapidly increasing. This paper will review and discuss the recent developments, potential, and characteristics of THz-TDS diagnostics applications.