This article reports on a single pass amplifier based on stimulated Raman scattering in a methane-filled negative curvature hollow core fiber (HCF) to transition 1.06 μm power to 1.54 μm. The researchers measured the highest average Raman power at a single frequency in a methane filled HCF to date of 4.92 W (246 μJ/pulse), with a high average quantum efficiency of 95.9%. A numerical model for the system was developed and shows good agreement with measured thresholds and efficiencies. Model results from a trade space study indicate configuration regimes necessary to maximize 1.54 μm power while avoiding power loss from the secondary shift.