Effects of F/sup -/ ions and F/sub 2/ molecules on the oscillation process of a discharge-pumped ArF excimer laser

Time-resolved number densities of the fluorine negative ion in a discharge-pumped ArF excimer laser are measured by a dye laser absorption method. The peak density of F/sup -/ is 0.93 /spl times/10/sup 15/ cm/sup -3/ at a total gas pressure of 2.5 atm, a gas mixture ratio of F/sub 2/-Ar-He=0.2-10.0-89.8, and a charging voltage of 28 kV for a 68-nF storage capacitor bank. The dependences of the peak F/sup -/ density and the ArF laser output power on the F/sub 2/ gas fraction in F/sub 2/-Ar-He mixture are investigated. The effects of F/sup -/ ions and F/sub 2/ molecules on the ArF laser oscillation process are discussed by considering the F/sub 2/ mixture-ratio dependences of particle densities, laser output power, mean electron energy, and laser power extraction efficiency. With increasing F/sub 2/ mixing ratio, the ArF* excimer formation first increases as F/sup -/ increases, but in F/sub 2/-rich conditions the laser power decreases because of the laser photon absorption due to F/sup -/ ions and quenching of ArF* with F/sub 2/ molecules.