Optimizing the pump wavelength to improve the transverse mode instability threshold of fiber laser by 3.45 times

Transverse mode instability (TMI) in fiber lasers refers to the phenomenon of dynamic coupling between the fundamental mode (FM) and high-order modes (HOMs) when the pumping power exceeds a certain threshold, which seriously affects the power scaling of fiber laser. In order to improve the TMI threshold in the fiber laser, we optimized the pump wavelength both consider the quantum defect and the pump absorption. In the experiment, the pump wavelength is optimized and a wavelength-stabilized laser diode (LD) with a central wavelength of 969 nm is proposed as the pump source to suppress the TMI. A forward-pumped Yb-doped fiber laser oscillator with a core/cladding diameter of 30/400 mu m was built experimentally. Experimental results show that the TMI threshold of the laser is 719 W when pumped by 969 nm LDs, which is 3.45 times that value when pumped by commonly used 976 nm LDs.