Optimization of Sodium Guide Star Return using Polarization and/or Modulation Control


TECHNOLOGY AREA(S): SENSORS OBJECTIVE: Deliver analysis, design, optical components, and controls for system to optimally couple light from Sodium Guide Star laser (FASOR, Toptica) by manipulation of the beam's polarization state, modulation of laser, or combination of two. DESCRIPTION:Coupling of Sodium Guide Star light into the sodium layer is dependent upon characteristics of the light illuminating the layer and the alignment of the sodium atom in the layer. The sodium atoms tend to align their dipole with the magnetic field of the earth. This results in varying returns dependent upon the geographic location of the guide star laser and geometry of the illumination relative to the magnetic field. Strong returns from the sodium layer independent of geographic location and illumination geometry is needed to enable responsive space situational awareness capabilities for imaging dim LEO satellites and detecting proximity objects in GEO. Controlling polarization of the Guide Star laser relative to the sodium layer has potential to improve returns. Techniques to modulate the polarization to match Larmor precession of the sodium atoms could allow significant improvement in Guide Star efficiency. Other techniques for modulating the Guide Star beam and controlling polarization with the end goal of optimizing returns are of interest. PHASE I: 1) Develop concepts to optimize Sodium Guide Star laser return through modulation and/or polarization control. 2) Work with sponsoring facility to determine initial proof of concept and testing methods. PHASE II: 1) Refine design of optical components based on testing in Phase I. 2) Fabricate improved optical components and control system based on sponsoring facility requirements. 3) Deploy optical components and conduct on-sky testing to determine operational performance of the system. PHASE III: 1) Demonstrate assembled prototype unit ready to deliver to field along with an estimate of the life cycle cost.2) Deliver, install, and test at least one prototype at Air Force operated electro-optic tracking facility. REFERENCES: 1. “Improving sodium laser guide star brightness by polarization switching,” Tingwei Fan, Tianhua Zhou, & Yan Feng, Scientific Reports, 22 January 2016 (https://www.nature.com/articles/srep19859.pdf);2. “Sodium Laser Guide Star Brightness, Spotsize, and Sodium Layer Abundance,” Jian Ge, et. al., GE ’98 (http://www.oir.caltech.edu/twiki_oir/pub/Palomar/PalmLGS/LgsLinks/ge98.pdf);3. “Sodium Guidestar Radiometry Results from the SOR's 50W Fasor,” Jack Drummond, Steve Novotny, Craig Denman, Paul Hillman, John Telle, Gerald Moore, AMOS Technical Conference, 2006 (https://amostech.com/TechnicalPapers/2006/Lasers/Drummond.pdf) KEYWORDS:Guide Star Laser, Sodium Layer, Polarization, SSA CONTACT(S):RyanSwindle RDSM 8088917746 thomas.swindle@us.af.mil

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