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Novel Phased Array Beam Director Development


OBJECTIVE: Develop a novel, fully functional high energy laser phased array beam director architecture with supporting analysis to quantify size, weight, power, thermal and mechanical responses to include global and sub-aperture jitter components. DESCRIPTION: The US Air Force has a need to place a laser weapon on small high-speed air platforms. Previous research has determined this objective mandates a low size, weight and power (SWaP) fuselage conformal laser array weapon in order to eliminate the aero-dynamic drag generated by a conventional turret and dramatically reduce the severity of the aero-optics distortion. This development focuses on a novel fuselage conformal beam director utilizing a hexagonal close-packed array of lasing telescopes. The designed director will accommodate all acquisition, pointing, and tracking (APT) functions currently defined in one or more of the existing phasing algorithms with a field-of-regard set at 0.5 steradians operating under the conditions set by the expected engagement scenarios provided by the Air Force Research Laboratory provided in the references. The total diameter of the director"s exit pupil is set at 75 centimeters where all sensing, command, and high power laser transmissions will take place. The diameter of the high energy lasing pupil is set at 37.5 centimeters. The volume goal of the director goal is 0.5 cubic meter. Ideally the beam director will be completely conformal to the fuselage and beam steering will be accomplished, electronically. However, with strong technical justification a low profile gimbal may be considered as part of the solution. The director should be designed to accommodate 49 or more fibers emitting 1 kilowatt of energy. Use of beam combination technology is acceptable as is spatially distributing a number of fibers in each sub-aperture. A high energy laser linear pupil fill factor must be greater than 75%. The beam director must be robust under a variety of mechanically and thermally stressing conditions endemic to the airborne environment, while also maintaining a low SWaP footprint. Several target based phase sensing, synthetic aperture imaging techniques, and local phase stabilization schemes have been developed under previous efforts. It is expected that those will be used in the design of this beam director. Refinements to these methods for implementation in the beam director are relevant to this effort, however the development of new phasing and beam control techniques is beyond the scope of this topic. Important items under consideration in this effort are: nominal responses to mechanical vibrations including jitter, thermal response, optical train packaging and performance, and thermal, mechanical, and optical isolation and control. Nominal vibrational data can be provided upon request for jitter analysis and simulation. Special consideration will be given to new and novel optical techniques to improve performance or reduce the SWaP footprint while maintaining excellent beam and phasing control. PHASE I: Identify the technology to develop and deliver a fully functional beam director concept that shows traceability to an airborne platform. PHASE II: Develop, analyze, and deliver a detailed optical/mechanical design where the analysis is focused on the optical, mechanical, and thermal response of the beam director. Develop a laboratory prototype funding and schedule permitting. PHASE III: Integration of the beam director into a complete functional laser array system using a high energy laser. Field demonstration of the system against real world targets. Possible dual use applications in free space laser communication and astronomy. REFERENCES: 1 Merritt, P. (2011). Beam Control for Laser Systems. Albuquerque: Directed Energy Professional Society. 2 Sasiela, R. J. (2007). Electromagnetic Wave Propagation in Turbulence (Second ed.). Bellingham, WA: SPIE Press. 3 Motes, R. A., & Berdine, R. W. (2009). Introduction to High Power Fiber Lasers. Albuquerque: Directed Energy Professional Society 4 Probst, K et al,"HELPAS Reference Missions", DARPA/AFRL/HELJTO Report. 2011 5 Green, W. Target Based Phase Sensing and Local Phase Stabilization. HELPAS Workshop, DEPS Beam Control Conference. 2012
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