Gas mixture for deep-UV plasma emission in a hollow-core photonic crystal fiber

We report on the first deep-ultraviolet/ultraviolet (DUV/UV) emission using a highly compact microwave-driven plasma-core photonic crystal fiber. The latter consists of a few centimeter long micro-plasma column of a gas mixture in the core of Kagome hollow-core photonic crystal fiber. The plasma is generated by nonintrusively exciting a ternary gas mixture of argon, nitrogen, and oxygen ($\mathrm{Ar}/{\mathrm{N}}_2/{\mathrm{O}}_2$) with a microwave resonator. Several spectral lines in the wavelength range of 200–450 nm were produced, guided by an $\mathrm{Ar}\text{-}{\mathrm{N}}_2\text{-}{\mathrm{O}}_2$ plasma-filled fiber, and controlled by simply varying the gas ratio of this gas mixture. An optimum gas mixture ratio was experimentally and theoretically identified for the strongest emission in the DUV range of 200–275 nm. The developed DUV emitting plasma-core fiber represents an important milestone towards the development of tunable and miniaturized DUV/UV laser sources.