Testbed strategies to improve broadband contrast of the dimpled scalar vortex coronagraph

Scalar vortex coronagraphs are promising for future high-contrast imaging missions because they provide a true dual-polarization coronagraph solution. Recent demonstrations of the dimpled scalar vortex coronagraph on the In-Air Coronagraph Testbed (IACT) have achieved contrasts at the current testbed floor (~1e-8). To push beyond this limit, we are exploring upgrades to IACT as well as testing the same mask in vacuum with two deformable mirrors (DMs) for full amplitude and phase control. IACT improvements include replacing the DM electronics with a 16-bit system to reduce noise and increase actuator precision, upgrading the broadband light source, and refining electric-field-conjugation parameters to better model the optical setup. We also verify the dimpled vortex performance in fully unpolarized broadband light, ensuring astrophysical relevance. Together, these upgrades define a clear path toward establishing a new broadband contrast record for the scalar vortex coronagraph.