Crosstalk in image plane beam combination for optical interferometers

TL;DR

This paper investigates the impact of atmospheric seeing and beam propagation on crosstalk in image plane beam combination for optical interferometers, quantifying how wavefront errors can cause systematic measurement errors.

Contribution

It provides a detailed analysis of crosstalk sources in optical interferometry, especially highlighting the role of aperture stops and realistic atmospheric conditions.

Findings

Wavefront errors can cause significant crosstalk-induced visibility errors.

Idealized conditions show negligible crosstalk from atmospheric effects.

Aperture stops amplify the impact of wavefront errors on measurements.

Abstract

Image plane beam combination in optical interferometers multiplexes the interference fringes from multiple baselines onto a single detector. The beams of starlight are arranged in a non-redundant pattern at the entrance of the combiner so that the signal from each baseline can be separated from one another in the frequency domain. If the signals from different baselines overlap in the frequency domain, this can give rise to a systematic error in the fringe measurements known as baseline crosstalk. In this paper we quantify crosstalk arising from the combination of atmospheric seeing and beam propagation over distances of order hundreds of metres. We find that in idealised conditions atmospheric wavefront errors and beam propagation do not contribute to crosstalk. However, when aperture stops are included in the optical beam train we observe that wavefront errors can result in squared visibility errors arising from crosstalk as high as $\Delta V^{2} = 6.6\times10^{-3}$ under realistic observing conditions.