An Optical Magnetometry Mechanism Above the Surface of Seawater

This paper analyzes a mechanism for the remote optical measurements of magnetic field variations above the surface of seawater. This magnetometry mechanism is based on the polarization rotation of reflected polarized laser light, in the presence of the earth's magnetic field. Here the laser light is reflected off the surface of the water and off an underwater object. Two mechanisms responsible for the polarization rotation are the surface magneto-optical kerr effect (SMOKE) and the Faraday effect. In both the mechanisms, the degree of polarization rotation is proportional to the earth's local magnetic field. Variations in the earth's magnetic field due to an underwater object will result in variations in the polarization rotation of the laser light reflected off the water's surface (SMOKE) and off the underwater object (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 water's surface. We find that the polarization rotated field due to SMOKE is small compared with that due to the Faraday effect.