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Optical Magnetometry for Detecting Underwater Objects

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Technical Report,01 Oct 2014,30 Aug 2015

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Naval Research Laboratory Washington United States

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A method for remote optical measurements of magnetic field variations above the surface of seawater is analyzed. This magnetometry mechanism is based on the fact that polarized laser light, in the presence of the Earths magnetic field, will exhibit a polarization rotation when reflected off the surface of the water and off an underwater object. The two mechanisms responsible for the polarization rotation are the Surface Magneto-Optical Kerr Effect SMOKE and the Faraday effect. In both mechanisms, the degree of polarization rotation is proportional to Earths local magnetic field. Variations in the Earths magnetic field due to an underwater object will result in variations in the polarization rotation of the laser light reflected off the waters surface SMOKE and off the underwater object itself Faraday effect. An analytical expression is obtained for the polarization-rotated field when the incident plane wave is at arbitrary angle and polarization with respect to the waters surface.

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