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Dr. Brandon Zimmerman

NASA (GSFC), Greenbelt, Maryland

November 30th, 2016, 3:30PM,  
Thirkield Hall (Physics), room 103

Unconventionally Polarized Sources for Remote Aerosol Sensing

ABSTRACT:  In 1950, Kerker and La Mer developed a method of extracting particle size from the polarization
ratio, or the phase angle of scattered light as a function of scattering angle. In 1957, Van De Hulst presented computational formulae for particle scattering, which predict the angular dependence of the linear and circular polarization components of a scattered light field. In this he was able to show that the polarimetric light scattering from clouds and aerosols can be used to characterize the size distribution, complex refractive indices, shape, roughness, and orientation of the particles that make up that given aerosol. Since then, the use of polarized light to characterize the physical properties of particle ensembles has become important in the characteristics of planetary atmospheres and aerosol monitoring in understanding pollution, climate, and energy balance.

We introduce a class of unconventional, spatially inhomogeneous polarized beams for their application in aerosol remote sensing and polarimetry. One such beam may be formed by the unique superposition of right and left circularly polarized beams by a customized Nomarski prism. Such superposition results in a beam that repeatedly traverses the equator of the Poincaré sphere in one of the beams spatial dimensions, such that, an image of light scattered from the beam yields the phase functions of the scatterers without temporal modulation of the input polarization. We call this a One Dimensional Poincaré Beam. We show that by illuminating an ensemble of Mie scatterers with our beam, that we can extract the phase functions, and size of the scatterers (amongst other physical parameters), in a manner that is both faster and more efficient than conventional methods. Furthermore, we present the design and fabrication of a single frame imaging polarimeter, based off of our own concepts of Star Test Polarimetry. Our Star Test Imaging Polarimeter possesses the capability to characterize the variation of Stokes parameters across a given object in real time with a single irradiance measurement. We conclude our results by integrating the two aforementioned systems into a single experiment; such that an ensemble of Mie scatterers illuminated by our Poincaré Beam, and imaged through our polarimeter, will yield the full phase matrix, and size parameter of the scatterers in a single image. We conclude by laying out the next steps of integrating this system on aircraft modules for in-situ aerosol remote sensing measurements.