  Current and future high contrast imaging instruments aim to detect exoplanets
at closer orbital separations, lower masses, and/or older ages than their
predecessors, with the eventual goal of directly detecting terrestrial-mass
habitable-zone exoplanets. However, continually evolving speckles in the
coronagraphic science image still limit state-of-the-art ground-based exoplanet
imaging instruments to contrasts at least two orders of magnitude worse than
what is needed to achieve this goal. For ground-based adaptive optics (AO)
instruments it remains challenging for most speckle suppression techniques to
attenuate both the dynamic atmospheric and quasi-static instrumental speckles.
We have proposed a focal plane wavefront sensing and control algorithm to
address this challenge, called the Fast Atmospheric Self-coherent camera (SCC)
Technique (FAST), which enables the SCC to operate down to millisecond
timescales even when only a few photons are detected per speckle. Here we
present preliminary experimental results of FAST on the Santa Cruz Extreme AO
Laboratory (SEAL) testbed. In particular, we illustrate the benefit "second
stage" AO-based focal plane wavefront control, demonstrating FAST closed-loop
compensation of evolving residual atmospheric turbulence on
millisecond-timescales.
