High contrast demonstrations of novel scalar vortex coronagraph designs at the high contrast spectroscopy testbed

For direct imaging of exoplanets, Scalar Vortex Coronagraphs (SVCs) are an attractive alternative to the popularly used Vector Vortex Coronagraphs (VVCs). This is primarily because they are able to induce the same phase ramp regardless of the incoming light's polarization state without compromising throughput while maintaining small inner working angle. We tested a set of stepped SVC staircase masks in the Exoplanet Technology Laboratory (ET Lab) at Caltech on the High-Contrast Spectroscopy Testbed (HCST). Here we present some preliminary findings of their starlight suppression ability, achieving raw contrasts on the order of 10⁻⁵ for 7 to 9 λ/D. We also characterized their chromatic performance and performed wavefront control to achieve preliminary contrasts on the order of 10⁻⁷ with EFC for 6 to 10 λ/D. These initial experimental results with SVCs have shown scalar vortex technology has a great potential for future exoplanet direct imaging missions.