  Ground-based high contrast imaging (HCI) and extreme adaptive optics (AO)
technologies have advanced to the point of enabling direct detections of
gas-giant exoplanets orbiting beyond the snow lines around nearby young star
systems. However, leftover wavefront errors using current HCI and AO
technologies, realized as "speckles" in the coronagraphic science image, still
limit HCI instrument sensitivities to detecting and characterizing lower-mass,
closer-in, and/or older/colder exoplanetary systems. Improving the performance
of AO wavefront sensors (WFSs) and control techniques is critical to improving
such HCI instrument sensitivity. Here we present three different ongoing
wavefront sensing and control project developments on the Santa cruz Extreme AO
Laboratory (SEAL) testbed: (1) "multi-WFS single congugate AO (SCAO)" using the
Fast Atmospheric Self-coherent camera (SCC) Technique (FAST) and a Shack
Hartmann WFS, (2) pupil chopping for focal plane wavefront sensing, first with
an external amplitude modulator and then with the DM as a phase-only modulator,
and (3) a laboratory demonstration of enhanced linearity with the non-modulated
bright Pyramid WFS (PWFS) compared to the regular PWFS. All three topics share
a common theme of multi-WFS SCAO and/or second stage AO, presenting
opportunities and applications to further investigate these techniques in the
future.
