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Non-Mechanically Steered 3D Imaging LADAR


OBJECTIVE: Develop and demonstrate revolutionary technologies for high speed non-mechanical steering of 3D imaging Laser Detection and Ranging (LADAR) sensors for target acquisition, identification, and tracking. DESCRIPTION: A novel approach is needed to bridge the gap between the 3D LADAR focal plane array (FPA) size and the area coverage rates and resolution required by tactical targeting systems. Instantaneous 3D LADAR imagery is currently limited by FPA size and the laser power required to illuminate the region of interest. (ROI) One possible new approach is to use mosaic imaging, where narrow field of view (FOV) 3D images can be tiled to provide high resolution composite images and increased FOV. The conventional approach to perform mosaic imaging would use fast steering mirrors (FSM), however, this increases SWaP, increases the complexity of the optical train, reduces reliability, and is ultimately limited in speed by the mechanical assemblies. Non-mechanical (or micro-mechanical) steering systems are ideal candidates for providing the tiling capabilities at high speeds with low SWaP and could be installed in the gimbal system of a pod or a Unmanned Aerial Vehicle (UAV) to allow the existing designators and imagers to operate while providing off-boresight situational awareness and tracking capability for multiple target engagements. Non-mechanical beam steering (NMBS)devices can provide true random access, enabling selective scanning of a FOV for structured targets, potentially reducing the data transmitted for ISR type missions. The goal of the system is to integrate a 3D LADAR with a NMBS device in order to improve the 3D imaging area rate and FOV. The LADAR should provide a cross range and depth resolution of 15 cm voxels (VOlume piXELS) and an effective range in excess of 10 km. The steering system must provide both steering for the illuminator laser and the detector, though not necessarily through the same aperture. 3D LADAR are broadly classified into two categories. First, a scanned approach where small arrays of detectors are flood filled with laser energy and then scanned to provide a build up to a larger image. This requires relatively low peak pulse power, but high pulse repetition frequencies approaching 50 kHz. Second, are flash systems where the image is acquired using a single high energy, designator class pulse, in the MW/cm^2 range for ns pulses. Flash imagers may also be scanned to build up larger images, but at lower rates. Mosaic imaging is common to both designs and must minimally construct an overall FOV of 1 to 5 degrees, which is similar to that of a targeting pod Forward Looking Infra-Red (FLIR) camera. The 3D LADAR imaging system must also attain update rate of 30 Hz over the entire FOV. This corresponds to a steering rate of N*30Hz, where N is the number of tiles in the mosaic. The sensor system should operate at the short wave infrared (SWIR) wavelengths (nominally 1.5 microns). A UAV or pod has limited space and shared apertures are advantageous. The primary aperture is typically a mid wave infrared (MWIR) FLIR and transparency at 3-5 microns would allow placement of NMBS device at the front of the FLIR aperture. NMBS elements could also be placed behind the FLIR optics. PHASE I: In this initial phase; concepts will be developed, evaluated, and computer modeled. Design challenges and trade-offs will be tabulated and areas in need of additional research and development will be identified. A concept design will be developed and provide an integration pathway to aircraft. PHASE II: A bread board prototype sensor package will be built which demonstrates non-mechanical 3D LADAR mosaic imaging over at 5x5 degree FOV with the steering rates and resolutions in accordance with the Phase I design. PHASE III: The bread board prototype will be redesigned to fit in the SWaP constraints of a tactical pod. The system will be flown and evaluated. REFERENCES: 1."Optical Phased Array Technology", Paul F. McManamon et. al., Proceedings of the IEEE, Vol. 84, No. 2, February 1996. 2."Numerical analysis of polarization gratings using finite-difference time-domain method", Ch Chulwoo, Michael J. Escuti, Physical Review A, Vol 76, No. 4, 043815, 2007. 3."Resolution Enhanced Sparse Aperture Imaging,"Miller et. al, IEEE Aerospace Conference Proceedings, v 2006, 2006 IEEE Aerospace Conference, 2006, p 1655904. 4."Wide-Angle, Nonmechanical Beam Steering Using Thin Liquid Crystal Polarization Gratings"Jihwan Kim et. al., Advanced Wavefront Control: Methods, Devices, and Applications VI, Proc. of SPIE Vol. 7093, 709302, (2008). 5. C. G. Bachman, Laser Radar Systems and Techniques, Artech House, Boston, 1979. 6. A. Jelalian, Laser Radar Systems, Artech House, Boston, 1992.
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