LAUSR

In this Letter, we have demonstrated a triple-cladded fiber (TCF)-based master oscillator power amplifier (MOPA), with an output power scaling up to 4.67 kW, an optical-to-optical efficiency of 78%, and a beam quality factor ${{\rm M}^2}$M2 of 1.57. The MOPA output power was limited by stimulated Raman scattering (SRS) of which our design yielded a 31.2 dB suppression ratio at the 4.67 kW output power. Such a unique design of a TCF-based structure allows a wide range of flexibility over fiber parameters, mitigation of nonlinear effects, low-loss splice integration, reliable high-power pump guiding in turn, and an ease in overall thermal management at multi-kW output power levels. Together with direct diode-pumping configuration, TCF-based designs promise thermally and mechanically robust, compact, and highly efficient MOPA systems of a superior beam quality.