  Nonlinear metasurfaces have become prominent tools for controlling and
engineering light at the nanoscale. Usually, the polarization of the total
generated third harmonic is studied. However, diffraction orders may present
different polarizations. Here, we design an high quality factor silicon
metasurface for third harmonic generation and perform back focal plane imaging
of the diffraction orders, which present a rich variety of polarization states.
Our results demonstrate the possibility of tailoring the polarization of the
generated nonlinear diffraction orders paving the way to a higher degree of
wavefront control.
