On-sky results for the novel integrated micro-lens ring tip-tilt sensor

TL;DR

This paper reports the first on-sky testing of a novel micro-lens ring tip-tilt sensor that improves light coupling in telescopes by correcting misalignments, demonstrating promising accuracy and potential for adaptive optics applications.

Contribution

It introduces and validates the first on-sky implementation of the micro-lens ring tip-tilt sensor for adaptive optics correction in astronomy.

Findings

Achieved a root mean square reconstruction accuracy of 0.19 λ/D.

Reconstruction accuracy depends strongly on the Strehl ratio.

Residual adaptive optics aberrations limit the sensor's performance.

Abstract

We present the first on-sky results of the micro-lens ring tip-tilt (MLR-TT) sensor. This sensor utilizes a 3D printed micro-lens ring feeding six multi-mode fibers to sense misaligned light, allowing centroid reconstruction. A tip-tilt mirror allows the beam to be corrected, increasing the amount of light coupled into a centrally positioned single-mode (science) fiber. The sensor was tested with the iLocater acquisition camera at the Large Binocular Telescope in November 2019. The limit on the maximum achieved root mean square reconstruction accuracy was found to be 0.19 $\lambda$/D in both tip and tilt, of which approximately 50% of the power originates at frequencies below 10 Hz. We show the reconstruction accuracy is highly dependent on the estimated Strehl ratio and simulations support the assumption that residual adaptive optics aberrations are the main limit to the reconstruction accuracy. We conclude that this sensor is ideally suited to remove post-adaptive optics non-common path tip tilt residuals. We discuss the next steps for the concept development, including optimizations of the lens and fiber, tuning of the correction algorithm and selection of optimal science cases.