Far-IR laser diagnostics of low-temperature plasma

Diagnostics methods based on the interaction of far-IR laser radiation with plasma are reviewed. The characteristics of the mostfrequently employed sources of radiation, detecting devices, quasioptic elements, and other components of diagnostic systems are presented. Some physical aspects and the technique of interferometry in the presence of attenuation in low-temperature plasma are examined. The problems of performing measurements on large setups as well as diagnostics of small-scale nonuniformities of plasma objects are analyzed. Examples of the use of interferometry and scattering for the study of electron density and the effect of electron collision frequency, the ion temperature and ion density, and the spectrum of diverse fluctuations of the plasma density are presented. The questions of increasing the temporal resolution, the sensitivity, and the information content of the methods in connection with progress achieved in the far-IR technique – in the field of optically pumped tunable lasers, matrix detectors, and other achievements – are discussed.