Effects of F- ions and F2 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^- is 0.93 ×10 ¹⁵ cm^-3 at a total gas pressure of 2.5 atm, a gas mixture ratio of F₂-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^- density and the ArF laser output power on the F ₂ gas fraction in F₂-Ar-He mixture are investigated. The effects of F^- ions and F₂ molecules on the ArF laser oscillation process are discussed by considering the F₂ mixture-ratio dependences of particle densities, laser output power, mean electron energy, and laser power extraction efficiency. With increasing F₂ mixing ratio, the ArF* excimer formation first increases as F^- increases, but in F₂-rich conditions the laser power decreases because of the laser photon absorption due to F^- ions and quenching of ArF* with F₂ molecules