High-power single-frequency single-mode all-solid photonic bandgap fiber laser with kHz linewidth.

There have been several demonstrations of single-frequency single-mode ytterbium-doped fiber lasers operating at a few hundred watts of power. A narrow spectral linewidth of these lasers is critical for many applications but has never been properly measured before at high powers. In this work, we report the first spectral linewidth measurement at kHz resolution of high-power single-frequency fiber lasers using a heterodyne technique and can confirm that these lasers can indeed operate at a few kHz spectral linewidth. Furthermore, we have improved the power from single-frequency single-mode all-solid photonic bandgap fiber lasers to 500 W using an improved photonic bandgap fiber.