SBS Suppression and Coherent Combination of Fiber MOPAs via Chirped Diode Lasers Final Report

Report No. ARL-TR-6945
Authors: Jeffrey O. White
Date/Pages: May 2014; 28 pages
Abstract: This is the final report for a High Energy Laser Joint Technology Office (HEL-JTO) contract to investigate the use of a chirped seed laser to suppress stimulated Brillouin scattering (SBS) in high power fiber amplifiers. Both experimental and theoretical results are described. The conventional way of suppressing SBS shortens the coherence length of the laser output to the point where coherently combining multiple amplifiers requires carefully matching the amplifier path lengths. The method we report on here has the advantage of allowing coherent combination without strict path length matching. Another disadvantage of the conventional method of suppressing SBS is that the threshold decreases as 1/L, where L is the length of the delivery fiber. The advantage of a chirped seed laser is that the SBS threshold decreases slower than 1/L and is almost independent of L in the limit of long fibers and high chirps.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2014