  Large-area metasurfaces composed of discrete wavelength-scale scatterers
present an extremely large number of degrees of freedom to engineer an optical
element. These degrees of freedom provide tremendous design flexibility, and a
central challenge in metasurface design is how to optimally leverage these
degrees of freedom towards a desired optical function. Inverse design can be
used to explore non-intuitive design space for metasurfaces. We report an
inverse design method exploiting T-Matrix scattering of ellipsoidal scatterer
based metasurfaces. Multifunctional, polarization multiplexed metasurfaces were
designed using this approach. Finally, we apply this method to optimize the
efficiency of an existing high numerical aperture (0.83)metalens design, and
report an increase in efficiency from 26% to 32%
