700 W single-frequency all-fiber amplifier at 1064 nm with kHz-level spectral linewidth

In this work, a single-frequency fiber amplifier with output power of 703 W was demonstrated at 1,064.4 nm in an all-fiber configuration. Cascaded Yb 3+ -doped structure different dopant concentration and hybrid 915/976 pump scheme were employed scaling stage to improve the gain saturation for higher transverse mode instability threshold. An overall optical efficiency 67.5% achieved maximum M 2 measured be ?1.4. A spectral linewidth kHz obtained from 703-W laser. To best our knowledge, is first time that kHz-level such high power.