435 W single-frequency all-fiber amplifier at 1064 nm based on cascaded hybrid active fibers

Abstract In this paper, we report a high-power single-frequency all-fiber amplifier at 1064 nm based on cascaded hybrid active fibers. The cascaded gain fiber design, where a piece of active fiber with lower dopant concentration is spliced before the highly doped gain fiber, is proposed to effectively alleviate the thermal loads of high-power amplifier. By virtue of hybrid pump at 976 nm and 915 nm to increase the threshold of mode instability (MI) effect, an output power of 435 W is achieved from the Yb 3 + -doped fiber with large core diameter of 30 μ m. The beam quality is well maintained with a M2 of 1.40 even at the maximum laser power.