The influence of cooling temperature on the thermal mode instability in the Yb-doped fiber oscillator

We explore the influence of cooling temperature on mode instability (MI) effect based a 2kW oscillator that can work stably at low temperature. The corresponding MI threshold of the oscillator is carefully measured with different operating temperatures of the Ytterbium-doped fiber (YDF) and laser diodes (LDs). It is found that whether decreasing the cooling temperature of the LDs or YDF, the MI threshold would rise, but decreasing the cooling temperature of the LDs has better effects. In our experiments, the MI threshold increases by 21.6%，from 1752W to 2130W when the operating temperature of the LDs changes from 25°C to 5°C due to the central wavelength of the LDs shifts from 976nm to 970nm, corresponding to a lower thermal load. In the process that only the cooling temperature of the YDF drops, although the increase is small, we have observed a rising trend of the laser MI threshold. This work can clarify the influence of cooling temperature on the laser thermal effect, which is conducive to perfecting the theoretical model of the MI effect of the fiber lasers.

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