# Diffraction-dominated observational astronomy

## TL;DR

This paper discusses the importance of diffraction in high-angular resolution astronomical imaging techniques like interferometry and adaptive optics, emphasizing the need to understand coherence properties for accurate data interpretation and future improvements.

## Contribution

It introduces the role of diffraction and coherence in high-contrast imaging, and explores how adaptive optics, apodization, and coronagraphy interact to improve observations.

## Key findings

- Understanding coherence is crucial for interpreting high-contrast imaging data.
- Adaptive optics systems are highly sensitive to instrumental biases.
- Focal-plane wavefront control can enhance direct exoplanet detection.

## Abstract

This paper is based on the opening lecture given at the 2017 edition of the Evry Schatzman school on high-angular resolution imaging of stars and their direct environment. Two relevant observing techniques: long baseline interferometry and adaptive optics fed high-contrast imaging produce data whose overall aspect is dominated by the phenomenon of diffraction. The proper interpretation of such data requires an understanding of the coherence properties of astrophysical sources, that is, the ability of light to produce interferences. This theory is used to describe high-contrast imaging in more details. The paper introduces the rationale for ideas such as apodization and coronagraphy and describes how they interact with adaptive optics. The incredible precision brought by the latest generation adaptive optics systems makes observations particularly sensitive to subtle instrumental biases that must be accounted for, up until now using post-processing techniques. The ability to directly measure the coherence of the light in the focal plane of high-contrast imaging instruments using focal-plane based wavefront control techniques will be the next step to further enhance our ability to directly detect extrasolar planets.