High-contrast spectroscopy testbed (HCST): low-order wavefront control loop in reflection of the vector vortex coronagraph (VVC)

The Astro2020 Decadal Survey has identified exoplanet imaging technologies as a top priority, especially for the design of the Habitable Worlds Observatory (HWO), which must image and characterize Earth-like planets. Achieving this goal requires reaching and maintaining an extreme contrast of 1×10-10. The High Contrast Spectroscopy Testbed (HCST) in the Caltech Exoplanet Technology Laboratory (ETLab) is an in-air coronagraphic imaging demonstration testbed. Using a high-order deformable mirror and a vector vortex coronagraph (VVC), HCST has reached 1×10⁻⁸ contrast in broadband light. A low-order wavefront sensor (LOWFS) placed at the VVC reflection now tracks tip/tilt drift. We present results from implementing a tip/tilt control loop at the VVC reflection for the first time. Our results achieve an over 100x suppression of drift frequencies < 1 Hz.