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High Power Coherent Beam Combined Laser for Army Platforms

Description:

TECHNOLOGY AREA(S): Weapons, 

OBJECTIVE: To develop a high-power laser system with high beam quality utilizing coherent beam combination methods. 

DESCRIPTION: Current HEL Weapon System demonstrators are primarily using spectrally beam combined fiber laser technology. Laser system output powers are pushing towards the 100 kilowatt threshold and all of that laser power must be combined via a physical beam-combining element. Beam combining elements, as well as the optical beam control systems, are rapidly approaching the physical limit of how much power they can handle before damage occurs. Similarly, as the Army explores options of integrating laser systems onto smaller, more compact platforms, the overall footprint of the laser source must decrease. A potential approach to overcoming these two limitations is to switch to a coherently combined laser system. Tiled aperture designs and monolithic filled-aperture designs each present intriguing advantages; one completely eliminates the need for individual optical elements to handle tens of kilowatts of power, while the other avoids the fill-factor losses associated with tiled arrays. Current platforms integrating lasers are finding that the predominant SWaP driver is the thermal management system of the laser. Obtaining electrical to optical efficiencies over 65% would enable integration onto previously unfeasible platforms but current fiber-based systems fundamentally will struggle to reach this objective. Resent results suggest that a laser system consisting of multitude of diodes with coherent combination between individual channels could be scaled up to the kilowatt-class level while maintaining efficiencies and SWaP superior to fiber-based lasers. These systems still have hurdles to overcome in beam quality and consistent mass manufacturing. This solicitation looks for a solution to achieve all parameters in one prototype: • Continuous Wave Power Output: Threshold: 15 kW; Objective: 60 kW • Electrical to Optical Efficiency: Threshold: 45%; Objective: 65% • Beam Quality (M2): Threshold: 1.5; Objective: 1.1 • Wavelength: Wavelengths that transmit through the atmosphere 

PHASE I: The phase I effort shall include analysis and design of the proposed laser architecture concept. The analysis shall provide confidence that the proposed concept design will be successful in meeting the specifications. Power, efficiency, and beam quality expectations out of the laser shall be addressed in the Phase I effort. 

PHASE II: During phase II, the phase I designs will be utilized to fabricate, test and evaluate a laser system prototype. The power scaling potential, efficiency, and beam quality specifications shall be demonstrated during the phase II effort. 

PHASE III: During phase III, the contractor will develop a 10s of kilowatt class coherently beam combined laser system and work with the government to integrate the technology into a laser weapon system. This coherently combined laser will be tested in one of the Army’s high energy laser demonstrators or testbeds. 

REFERENCES: 

1: P. Albrodt et. al., "Coherent Combining of High Brightness Tapered Amplifiers for Efficient Non-Linear Conversion," 11 January 2019, Vol. 27, No. 2, OPTICS EXPRESS 928

KEYWORDS: Coherently Combined Lasers, High Energy Lasers, High Power Fiber Lasers, High Power Diode Lasers 

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