AFRL Invents Coherent Beam Combination Technique Published Dec. 12, 2006 By Plans and Programs Directorate AFRL/XP WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- AFRL scientists invented a coherent beam combination technique--Locking of Optical Coherence by Single-Detector Electronic-Frequency Tagging (LOCSET)--that is scalable to a large number of array elements. Existing fiber amplifiers, which are suitable for high-quality beam combination, exhibit 400 W in a single amplifier. The Department of Defense is interested in developing fiber amplifiers that provide high-efficiency, high-brightness, high-power lasers for tactical missions. The fiber waveguide structure determines the beam quality in single-mode fiber amplifiers and is not affected by thermal gradients. Fiber amplifiers do not require the complex, heavy, power-consuming cooling systems that conventional solid-state amplifiers need for maintaining high beam quality. However, the fiber amplifier obtains its diffraction-limited beam quality by limiting power handling capability. To reach the high power, efficiency, and brightness that tactical applications demand, systems must combine the output of many fiber amplifiers into a single, high-quality beam. The LOCSET technique easily combines the output of 100 optical fiber amplifiers, providing a clear technical path to an electrically excited coherent fiber laser array with an output of 40 kW and requiring no additional advances in fiber amplifiers. Users can steer the LOCSET coherent array output beam over a small angle and readily apply it to programs using optical phased-array technologies. Efficient, high-brightness, high-power laser systems provide the warfighter with increased capability. The LOCSET technique combines a world-record nine optical fiber beams through coherent beam combination that uses active phase control. Currently, coherent beam combination using active phase control provides the highest power and best beam quality of any beam combination method under investigation.