Final design and on-sky testing of the iLocater SX acquisition camera: broad-band single-mode fibre coupling
Jonathan Crass, Andrew Bechter, Brian Sands, Douglas J. King, Ryan Ketterer, Matthew Engstrom, Randall Hamper, Derek Kopon, James Smous, Justin R. Crepp, M. Montoya, Olivier Durney, David Cavalieri, R. Reynolds, Michael VanSickle, Eleanya Onuma, Joseph Thomes, Scott A. Mullin, Chris Shelton, J. Kent Wallace, Eric Bechter, A. Vaz, J. Power, Gustavo Rahmer, Steve Ertel
Abstract
ABSTRACT Enabling efficient injection of light into single-mode fibres (SMFs) is a key requirement in realizing diffraction-limited astronomical spectroscopy on ground-based telescopes. SMF-fed spectrographs, facilitated by the use of adaptive optics (AO), offer distinct advantages over comparable seeing-limited designs, including higher spectral resolution within a compact and stable instrument volume, and a telescope independent spectrograph design. iLocater is an extremely precise radial velocity (EPRV) spectrograph being built for the Large Binocular Telescope (LBT). We have designed and built the front-end fibre injection system, or acquisition camera, for the SX (left) primary mirror of the LBT. The instrument was installed in 2019 and underwent on-sky commissioning and performance assessment. In this paper, we present the instrument requirements, acquisition camera design, as well as results from first-light measurements. Broad-band SMF coupling in excess of 35 per cent (absolute) in the near-infrared (0.97–1.31 ${\mu {\rm m}}$) was achieved across a range of target magnitudes, spectral types, and observing conditions. Successful demonstration of on-sky performance represents both a major milestone in the development of iLocater and in making efficient ground-based SMF-fed astronomical instruments a reality.