High Peak Power Pulse Amplification in Large-Core Yb-Doped Fiber Amplifiers

High peak power fiber lasers are important for a variety of applications ranging from material processing and remote sensing to laser-plasma produced extreme ultraviolet lithography (EUV) generation. These applications require high peak powers in the megawatt range, < 1-10-ns pulse durations and high average powers in preferably diffraction-limited beams. In this paper, we review our work on high peak power pulse generation using large- mode-area (LMA) Yb-doped fibers with very large cores. We report achieving up to > 5-MW peak power with subnanosecond pulses, the highest peak power achieved so far from a fiber laser. Use of a variety of core sizes between 65 and 200 mum has been explored and it has been shown that for core sizes as large as 80 mum, a good output beam quality of M² ~ 1.3 can be maintained. This corresponds to the largest ever demonstrated mode area (2750 mum²) of a conventional LMA fiber with nearly diffraction-limited output. We also demonstrate average-power scaling of megawatt peak power pulses of up to ~90 W.