kHz-Level Linewidth 509 nm Single Frequency Laser by Frequency Doubling an All-Fiber Yb Fiber Laser

Narrow linewidth 509 nm single frequency lasers have important applications in interdisciplinary science and advanced practical applications. Here we demonstrate a kHz-level-linewidth 509 nm single frequency laser with single-pass second harmonic generation (SHG) configuration experimentally. The 1018 nm single frequency fiber laser consists of a ring cavity seed source by applying dynamic grating and two stage Yb³⁺-doped fiber amplifier, contributing a 2.55 kHz narrow linewidth laser with 10.71 W output power. Furthermore, a 1.01 W 509 nm single frequency laser is obtained by using single-pass SHG method, of which the linewidth is essentially concluded to be ∼5.1 kHz. To the best of our knowledge, this is the narrowest linewidth among reported single frequency 509 nm laser by frequency doubling a fiber laser, which could be used for advanced underwater optical communication and preparation of cesium Rydberg state.