Simultaneous Water Vapor and Dry Air Optical Path Length Measurements and Compensation with the Large Binocular Telescope Interferometer

TL;DR

This paper introduces a new method at the Large Binocular Telescope Interferometer for simultaneously measuring and compensating for water vapor and dry air-induced optical path length variations, enhancing high-precision infrared interferometry.

Contribution

It presents a novel sensing approach to separately monitor water vapor and dry air effects on optical path length, improving atmospheric turbulence correction in interferometric observations.

Findings

Demonstrated simultaneous H-, K-, and N-band measurements

Showed feasibility of feedforward stabilization of path length fluctuations

Improved high-precision infrared interferometry accuracy

Abstract

The Large Binocular Telescope Interferometer uses a near-infrared camera to measure the optical path length variations between the two AO-corrected apertures and provide high-angular resolution observations for all its science channels (1.5-13 $\mu$m). There is however a wavelength dependent component to the atmospheric turbulence, which can introduce optical path length errors when observing at a wavelength different from that of the fringe sensing camera. Water vapor in particular is highly dispersive and its effect must be taken into account for high-precision infrared interferometric observations as described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this paper, we describe the new sensing approach that has been developed at the LBT to measure and monitor the optical path length fluctuations due to dry air and water vapor separately. After reviewing the current performance of the system for dry air seeing compensation, we present simultaneous H-, K-, and N-band observations that illustrate the feasibility of our feedforward approach to stabilize the path length fluctuations seen by the LBTI nuller.