VLTI Unit Telescope coud\'e train vibration control upgrade for GRAVITY+

TL;DR

This paper discusses the implementation of accelerometers on the VLTI coudé train mirrors to mitigate high-frequency vibrations, enhancing the performance of the GRAVITY+ interferometry system.

Contribution

It introduces a vibration control upgrade using accelerometers for the VLTI coudé train, improving fringe tracking precision in the GRAVITY+ project.

Findings

Accelerometers effectively reduce vibration peaks between 40 and 200Hz.

Real-time optical path compensation improves fringe tracker performance.

Prospects for further upgrades of deformable mirrors and delay lines are outlined.

Abstract

Scaling up interferometry to 8m collectors should smooth-out the optical piston perturbations and allow a slow fringe tracker to obtain high precision correction on faint targets. In practice, the GRAVITY fringe tracker still observes high frequency OPD components that limit the exposure time, its precision and limiting magnitude. Perturbations seem to come from mechanical vibrations in the train of mirrors. As part of the GRAVITY+ efforts, accelerometers were added to all the mirrors of the coud\'e train to compensate in real-time the optical path using the main delay lines. We show their effectiveness on vibrations peaks between 40 and 200Hz and outline prospects for the upgrade of the deformable mirrors and the beam-compressor differential delay lines.