Narrow-linewidth, multi-Watt Yb-doped fiber amplifier at 1014.8 nm

We report on an efficient, narrow linewidth, two-stage fiber amplifier at 1014.8 nm based on Yb-doped double-clad fibers. The fibers are cooled to liquid-nitrogen temperatures in order to suppress absorption at the operating wavelength. We achieved output powers of up to 5.0 W at a linewidth of less than 3 MHz by seeding the amplifier with the radiation from an external cavity diode laser.