Fresnel diffraction in an interferometer: application to MATISSE

TL;DR

This paper investigates Fresnel diffraction effects in an interferometer module used for the MATISSE instrument, focusing on how pupil diffraction and spatial coherence influence instrumental contrast, with broader applicability to similar optical systems.

Contribution

It presents an analysis of Fresnel diffraction in a non-collimated pupil mask module, highlighting its impact on contrast and coherence in interferometric instruments.

Findings

Fresnel diffraction significantly affects the contrast in interferometric measurements.

Pupil diffraction must be considered in the design and calibration of interferometers.

The study's approach is applicable to various instruments beyond MATISSE.

Abstract

While doing optical study in an instrument similar to the interferometers dedicated to the Very Large Telescope (VLT), we have to take care of the pupil and focus conjugations. Modules with artificial sources are designed to simulate the stellar beams, in terms of collimation and pupil location. They constitute alignment and calibration tools. In this paper, we present such a module in which the pupil mask is not located in a collimated beam thus introducing Fresnel diffraction. We study the instrumental contrast taking into account the spatial coherence of the source, and the pupil diffraction. The considered example is MATISSE, but this study can apply to any other instrument concerned with Fresnel diffraction.