Observation of extreme-ultraviolet light emission from an expanding plasma jet with multiply-charged argon or xenon ions

We report the first direct demonstration of possibility to generate the extreme ultraviolet (EUV) radiation with a freely expanding jet of dense plasma with multiply-charged ions supported by high-power microwaves. The detected emission power is about 20 W at 18--50 nm for argon and xenon and 0.3 W at 13--17 nm for xenon. The discharge with a peak electron density up to $3\times 10^{16}\,$cm$^{-3}$ and a characteristic size of $150\,\mu$m is supported by a focused radiation of a recently developed gyrotron with unique characteristics, 250~kW output power at 250~GHz, operating in a relatively long (50$\,\mu$s) pulse mode. Up-scaling of these experimental results gives grounds for development of a point-like kilowatt-level EUV source for a high-resolution lithography able to fulfill requirements of the microelectronics industry.