1 October 2013 Understanding beam alignment in a coherent lidar system
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Abstract
Optical beam alignment in a coherent lidar (or ladar) receiver system plays a critical role in optimizing its performance. Optical alignment in a coherent lidar system dictates the wavefront curvature (phase front) and Poynting vector) matching of the local oscillator beam with the incoming receiver beam on a detector. However, this alignment is often not easy to achieve and is rarely perfect. Furthermore, optical fibers are being increasingly used in coherent lidar system receivers for transporting radiation to achieve architectural elegance. Single mode fibers also require stringent mode matching for efficient light coupling. The detector response characteristics vary with the misalignment of the two pointing vectors. Misalignment can lead to increase in DC current. Also, a lens in front of the detector may exasperate phase front and Poynting vector mismatch. Non-Interaction of Waves, or the NIW property indicates the light beams do not interfere by themselves in the absence of detecting dipoles. In this paper, we will analyze the extent of misalignment on the detector specifications using pointing vectors of mixing beams in light of the NIW property.
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Narasimha S. Prasad, Narasimha S. Prasad, Chandrasekhar Roychoudhuri,, Chandrasekhar Roychoudhuri,, } "Understanding beam alignment in a coherent lidar system", Proc. SPIE 8832, The Nature of Light: What are Photons? V, 88320A (1 October 2013); doi: 10.1117/12.2025460; https://doi.org/10.1117/12.2025460
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