Non Common Path Aberrations Correction

TL;DR

This paper presents a method to correct Non-Common-Path Aberrations in the SPHERE instrument, significantly improving contrast for exoplanet imaging through Electric Field Conjugation tested both in simulation and on the actual system.

Contribution

The thesis introduces and validates an Electric Field Conjugation method for NCPA correction in SPHERE, achieving a tenfold contrast improvement in real observations.

Findings

Contrast improved from 10^-6 to 10^-7

Method successfully tested on real system at VLT

Potential for automation and further enhancement

Abstract

The primary goal of this thesis was the correction of Non-Common-Path-Aberrations in the SPHERE instrument for helping it meeting its contrast requirements. SPHERE's purpose is the search and characterization of giant exo-planets around nearby stars. The author implemented a method called Electric Field Conjugation that he tested in simulation as well as on the real system. A full week was booked in SPHERE schedule a few days before the second commissioning in June 2014. It gave the opportunity to the author to travel to the VLT in Chile and experiment directly on the system. The contrast gain objective of another order of magnitude in a medium-sized area has successfully been reached bringing SPHERE raw speckle contrast from about $10^{-6}$ to $10^{-7}$. The algorithm has therefore proven its value and will be further investigated and hopefully automated by the SPHERE team based on the codes developed by the author. However it is important to keep in mind that Electric Field Conjugation is more effective for follow-up studies in order to improve the quality of the observations. Indeed the area for a good correction is very limited. It can't be used for exo-planets discovery unless the corrected area is made big enough but the performance will be less.