We obtain a spectral width less than 0.1 nm and a tunability about 1 nm by adding a grating, a beam expander, shutters and a combining lens in the oscillator of a discharge pumped ArF laser oscillator amplifier system. The output power is injected into the amplifier that produces an average energy of 30 mJ/pulse, and the tunable, narrow spectral, and very low beam divergence laser output. The efficiency is increased about 50 percent after injection. A peak output of more than 50 mJ/pulse is achieved. The O2 absorption of the ArF laser is also measured.