Methods and systems for characterizing a plasma with radiation, particularly, terahertz (THz) radiation, are disclosed. The disclosed method of characterizing a plasma includes directing THz radiation into the plasma; and detecting an emission due to interaction of the THz radiation with the plasma to characterize the plasma. A disclosed plasma characterizing device includes a means for directing THz radiation into a plasma; and a detector adapted to detect an emission emitted by the plasma due to interaction of the THz radiation with the plasma to characterize the plasma. A plasma characterizing system is also disclosed. The emission detected may be a fluorescence, a variation in fluorescence and/or an acoustic emission.