Incoherent Combining of High-Power Fibers Lasers for Long-Range Directed Energy Applications

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR I MONITOR'S ACRONYM(S)Office of Naval Research ONR One Liberty Center 11. SPONSOR / MONITOR'S REPORT 875 North Randolph St. We present a configuration for incoherently combining fiber lasers, which can be used for long-range directed energy applications. Unlike coherent beam combining approaches, incoherent combining does not require phase locking, the polarization of the lasers can be random, and the linewidths can be large. These relaxed requirements allow for the use of recently developed high-power (>2 kW/fiber), single mode, high quality (M 2 < 1.2) fiber lasers having relatively large linewidths (>1%). These high-power lasers cannot be used for coherent beam combining. The proposed incoherent combining configuration consists of a fiber laser array in which the beams diffract to a spot size of-4 cm onto individual collimating lenses. The collimated beams can be directed to a target many kilometers away by individual steering mirrors, which form the beam director. We present parameters for an incoherently combined laser system that can deliver 100 kW of CW power on a target area of 100 cm 2 at a range of 5 kin. The system has 49 fiber lasers and a beam director with transverse dimension 60 cm x 60 cm. This configuration is readily scalable to higher powers. NUMBER(S)Arlington

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