Amplitude variations on a MEMS-based extreme adaptive optics coronagraph testbed.

Area of Science:

• Astronomy and Astrophysics
• Optical Engineering

Background:

• High-contrast imaging, using coronagraphy, is crucial for detecting extrasolar planets.
• Existing adaptive optics (AO) systems correct for dynamic atmospheric wavefront errors but not systematic amplitude variations.

Purpose of the Study:

• Investigate discrepancies between simulated and observed coronagraphic images.
• Identify and quantify sources of systematic amplitude variations in extreme AO systems.

Main Methods:

• Utilized the Laboratory for Adaptive Optics (LAO) extreme AO testbed.
• Measured intensity variations across the microelectrical mechanical (MEM) plane.
• Compared experimental data with a Fresnel model and analyzed deformable mirror surface structure.

Main Results:

• Observed up to 7% root-mean-square (rms) intensity variations, unexplained by phase errors alone.
• Deformable mirror surface structure contributed minimally (≤2% rms) to intensity variations.
• Nonuniform fiber illumination and Talbot effect-induced amplitude mixing were identified as primary sources.

Conclusions:

• Systematic amplitude errors, alongside phase errors, generate problematic speckle artifacts in high-contrast imaging.
• Addressing non-pupil-plane amplitude variations is essential for improving exoplanet detection capabilities.