The University of Rochester's Laboratory for Laser Energetics has designed, built, and characterized a modern, 20-cm clear aperture, Nd:glass Brewster-disk amplifier. This device will be used as the final amplifier in the upgrade of the existing OMEGA laser system. This article describes results of the energy characterization of that amplifier. Specifically, spatially resolved measurements of small-signal gain and whole-beam measurements of large-signal gain are described. The amplifier met its small-signal design goal of 3.0 at only 70% of the design capacitor-bank energy with adequate spatial uniformity. A storage efficiency of 1.7% was achieved. Large-signal-gain measurements, both with and without 5-angstroms-FM bandwidth on the extracting beam, display no measurable change in gain because of the impressed bandwidth.