  The vector vortex coronagraph is an instrument designed for direct detection
and spectroscopy of exoplanets over a broad spectral range. Our team is working
towards demonstrating contrast performance commensurate with imaging temperate,
terrestrial planets orbiting solar-type stars using the High Contrast Imaging
Testbed facility at NASA's Jet Propulsion Laboratory. To date, the best
broadband performance achieved is $\sim$10$^{-8}$ raw contrast over a bandwidth
of $\Delta\lambda/\lambda$=10\% in the visible regime (central wavelengths of
550-750 nm), while monochromatic tests yield much deeper contrast
($\sim$10$^{-9}$ or better). In this study, we analyze the main performance
limitations on the testbeds so far, focusing on the quality of the focal plane
mask manufacturing. We measure the polarization properties of the masks and the
residual electric field in the dark hole as a function of wavelength. Our
results suggest that the current performance is limited by localized defects in
the in the focal plane masks. A new generation of masks is under test that have
fewer defects and promise performance improvements.
