consists of electromagnetic waves within the ITU(International Telecommunication Union)-designated band of frequencies from 0.3 to 3 terahertz (THz, 1 THz = 1012 Hz).
Wavelengths of radiation in the Terahertz band correspondingly range from 1 mm to 0.1 mm (or 100 μm)
When an intense laser pulse is focused in air or gases, it produces a plasma and propagates through it.
In this case, the electrons in the plasma oscillate at the frequency of the plasma frequency, which then yields THz radiation. The plasma frequency is given as:
From this, plasma density(or electron density in the plasma) can be deduced from the THz radiation by the laser-plasma interaction.
In our laboratory, we expect the new plasma diagnosis technique that could be applied to the diagnostics of the plasma state in TOKAMAK by harnessing the laser-plasma interaction THz radiation.