13 kW monolithic linearly polarized single-mode master oscillator power amplifier and strategies for mitigating mode instabilities

Abstract

We report on the high power amplification of 1064nm linearly-polarized laser\nin all-fiber polarization-maintained MOPA, which can operate at output power\nlevel of 1.3kW. The main amplifier was pumped with six 915nm laser diodes, and\nthe slope efficiency is 65.3%. The beam quality (M2) was measured to be <1.2 at\nfull power operation. The polarization extinction rate of the fiber amplifier\nwas measured to be above 94% before mode instabilities (MI) sets in, which\nreduced to about 90% after the onset of MI. Power scaling capability of\nstrategies for suppressing MI is analyzed based on a novel semi-analytical\nmodel, the theoretical results of which agree with the experimental results. It\nshows that mitigating MI by coiling the gain fiber is an effective and\npractical way in standard double-cladding large mode area fiber, and, by tight\ncoiling of the gain fiber to the radius of 5.5cm, the MI threshold can be\nincreased to 3 times higher than that without coiling or loose coiling.\nExperimental study has been carried out to verify the idea, which has proved\nthat MI was suppressed successfully in the amplifier by tight coiling.\n