Optics and Photonics Society of Iran

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Transverse Mode Instability (TMI) as a substantial restriction for further power scaling of high-power fiber lasers has been investigated and its occurrence power threshold in a 3.02 kW level fiber oscillator has been compared in co-, counter- and bidirectional pumping schemes. Experimental results show that TMI power threshold in a bidirectional-pumping scheme is higher than that of co- and counter-pumping configurations. It is also observed that counter pumping method has higher TMI threshold than co-pumping scheme. The TMI threshold of bidirectional-pumping is higher than co/counter-pumping because the index gratings generated in the bidirectional-pumping scheme is smoother than that of co/counter-pumping configuration.