NKT Photonics A/S has introduced a new version of its double-clad rod-type fiber for use in fiber amplifiers. The DC-285/100-PM-Yb-ROD is based on proprietary and patented Crystal Fibre air-clad technology and features a single-mode 100-µm polarization-maintaining core with high absorption and low photodarkening. The ytterbium-doped rod is used in output stages of amplifier chains for high-power pulsed laser amplification, where it can sustain megawatt peak power levels. The ytterbium core has an effective mode field area of >4500 µm2. The 285-µm pump core diameter accepts pump light at numerical apertures up to 0.55 for pumping at 915 or 976 nm. Pump absorption is 30 dB/m for 976 nm and is polarization-independent. Output of the fiber is single-transverse-mode beam quality, and it has been tested with >100-W average power over a range of pulse durations and repetition rates.