Zusammenfassung
The major noise source limiting high-contrast imaging is due to the presence
of quasi-static speckles. Speckle noise originates from wavefront errors caused
by various independent sources, and it evolves on different timescales pending
to their nature. An understanding of quasi-static speckles originating from
instrumental errors is paramount for the search of faint stellar companions.
Instrumental speckles average to a fixed pattern, which can be calibrated to a
certain extent, but their temporal evolution ultimately limit this possibility.
This study focuses on the laboratory evidence and characterization of the
quasi-static pinned speckle phenomenon. Specifically, we examine the coherent
amplification of the static speckle contribution to the noise variance in the
scientific image, through its interaction with quasi-static speckles. The
analysis of a time series of adaptively corrected, coronagraphic images
recorded in the laboratory enables the characterization of the temporal
stability of the residual speckle pattern in both direct and differential
coronagraphic images. We estimate that spoiled and fast-evolving quasi-static
speckles present in the system at the angstrom/nanometer level are affecting
the stability of the static speckle noise in the final image after the
coronagraph. The temporal evolution of the quasi-static wavefront error
exhibits linear power law, which can be used in first order to model
quasi-static speckle evolution in high-contrast imaging instruments.
Nutzer