Improvement of Beam Stability in Yb-Doped Tapered Fiber Amplifiers

Yb-doped tapered fiber amplifier become one of the most promising tools for amplification of pulsed radiation near 1 μm to a high peak power (sub-MW directly after amplifier), while keeping superior beam quality (M<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>~ 1.1). Such fibers consist of a thin part with a single-mode core, tapered section with a gradually increased core and cladding diameter and a thin part with large fundamental mode field diameter, where main signal amplification take place. If signal propagates from a thin to the thick end and tapered transition is long enough almost no high order modes are excited during signal propagation and beam quality remain to be diffraction-limited. According to S<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> measurements content of high order modes in output radiation is less than 0.3% [1].