Low pressure gas discharge in the quasioptical beams of the powerful terahertz radiation

Results of the experimental investigation of the gas discharge in the beams of the powerful terahertz radiation are presented. Study of the self-sustained and initiated discharges by using the radiation of one of the two pulsed gyrotrons (developed in IAP RAS) with frequency values of 0.55 THz@1kW (8 μs pulse length) and 0.67 THz@100kW (20 μs) was made in the wide range of pressures (0.01-1500 Torr) in different gases (helium, argon). Self-sustained discharge could be maintained in the pressure range from 20 Torr to two atmospheres. By using the several methods of discharge initiation it was possible to expand the range of discharge existence to the pressure value of about 0.01 Torr. It was shown that the low pressure (dozens of Torr and less) discharge has a number of features compared with the discharge of high pressure: the presence of the powerful afterglow with length of about 20-50 microseconds after gyrotron pulse, the lack of a strongly inhomogeneous spatial structure of the discharge glow (at pressures less than 10 Torr), the lack of screening of the discharge appearance location from the gyrotron radiation. The size of the discharge plasma at pressure value of 0.01 Torr was about of 1 mm. Such a discharge can be used as the pointed source of UV radiation, including the projection lithography.