The characteristics of an electron beam excited ArF laser amplifier were investigated from the small‐signal region to the strongly saturated region (≥10 MW/cm2) as a function of Ar concentration. A single‐pass (L=50 cm) amplifier experiment was performed with atmospheric Ar/F2 and Ne/Ar/F2 gas mixtures pumped by an intense electron beam (1.3 MV, 90 kA, 65 ns full width half‐maximum). The extracted intensity (output intensity minus input intensity) from this single‐pass amplifier was maximized at input intensities ranging from 6.7 to 9.5 MW/cm2. The power efficiencies obtained were 13, 14.4, and 15.7%, and the extraction efficiencies were 65, 59.7, and 59.4% for Ar concentrations of 40, 70, and 99.6%, respectively. The amplifier parameters (small‐signal gain g0, nonsaturable absorption coefficient α, and saturated intensity Is) were estimated for each mixture using a Rigrod analysis [J. Appl. Phys. 36, 2487 (1965)].