Lyot-based Low Order Wavefront Sensor for Phase-mask Coronagraphs: Principle, Simulations and Laboratory Experiments

Abstract

High performance coronagraphic imaging of faint structures around bright stars at small angular separations requires fine control of tip, tilt and other low order aberrations. When such errors occur upstream of a coronagraph, they results in starlight leakage which reduces the dynamic range of the instrument. This issue has been previously addressed for occulting coronagraphs by sensing the starlight before or at the coronagraphic focal plane. One such solution, the coronagraphic low order wave-front sensor (CLOWFS) uses a partially reflective focal plane mask to measure pointing errors for Lyot-type coronagraphs. To deal with pointing errors in low inner working angle phase mask coronagraphs which do not have a reflective focal plane mask, we have adapted the CLOWFS technique. This new concept relies on starlight diffracted by the focal plane phase mask being reflected by the Lyot stop towards a sensor which reliably measures low order aberrations such as tip and tilt. This reflective Lyot-based wavefront sensor is a linear reconstructor which provides high sensitivity tip-tilt error measurements with phase mask coronagraphs. Simulations show that the measurement accuracy of pointing errors with realistic post adaptive optics residuals are approx. 10^-2 lambda/D per mode at lambda = 1.6 micron for a four quadrant phase mask. In addition, we demonstrate the open loop measurement pointing accuracy of 10^-2 lambda/D at 638 nm for a four quadrant phase mask in the laboratory.

9 Pages, 11 Figures, to be published in PASP June 2014 issue

References in corpus (11)

• A probable giant planet imaged in the Beta Pictoris disk
• Theoretical Limits on Extrasolar Terrestrial Planet Detection with Coronagraphs
• Limits of Adaptive Optics for high contrast imaging
• Phase-Induced Amplitude Apodization of Telescope Pupils for Extrasolar Terrestrial Planet Imaging
• The Vector Vortex Coronagraph: Laboratory Results and First Light at Palomar Observatory
• Coronagraphic Low Order Wavefront Sensor: Principle and Application to a Phase-Induced Amplitude Coronagraph
• An Eight-Octant Phase-Mask Coronagraph
• Tip-tilt Error in Lyot Coronagraphs
• Coronagraphic Low Order Wave Front Sensor : post-processing sensitivity enhancer for high performance coronagraphs
• Low Order Aberrations in Band-Limited Lyot Coronagraphs
• Diffraction-Based Sensitivity Analysis of Apodized Pupil Mapping Systems

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