Ultralong pulse (≳40 μs) fluorescence of ArF excimer molecules at 193 nm has been generated by dynamically mixing a pulse discharge excited He jet with neutral Ar/F2 gas located downstream in a vacuum chamber. Rapid cooling of the high temperature He plasma through neutral gas collisions and efficient energy transfer to Ar gas create Ar metastable atoms, which form ArF excimer molecules through harpoon reactions with F2, in relatively field-free space. The fluorescence intensity increased with increasing F 2 concentration up to ∼10% F2 in Ar with 2-atm backing pressure. In a preliminary experiment with an ArF probe laser, this mixture showed an amplification gain.
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