All-fiber single-mode PM Yb-doped pre-amplifier at 0.976 μm

Yb-doped fiber lasers operating near 0.98 μm attract considerable interest in recent years. In particular, the pulsed lasers at 0.98 μm are promising for frequency doubling and quadrupling. At the same time, the Yb-doped fibers optimized for 0.98 μm generation have been designed to achieve high laser efficiency at a high average output power and hardly can be used in preamplifier stages or in scheme of master oscillator lasers. Such fibers have a large core diameter (in excess of 25 μm) and high splicing losses with standard single-mode step-index fibers (maximum diameter of those does not exceed 10 μm). The pulsed lasers based on such fibers require utilization of bulk elements [1, 2] that eliminate advantageous of all-fibers schemes (compactness, reliability, low-cost). Moreover, due to a very high lasing threshold (tens of Watts) such fibers are unsuitable for signal amplification to a middle-level output power (0.1-1 W), required for pre-amplifiers and for many of master-oscillator schemes. In opposite, core-pumped schemes are power-limited by available single-mode pump diodes at 915 nm and typically do not allow output power higher than ~100 mW.