title: Characterization of the transmitted near-infrared wavefront error for the GRAVITY/VLTI Coudé Infrared Adaptive Optics System.
abstract: The adaptive optics system for the second-generation VLT-interferometer (VLTI) instrument GRAVITY consists of a novel cryogenic near-infrared wavefront sensor to be installed at each of the four unit telescopes of the Very Large Telescope (VLT). Feeding the GRAVITY wavefront sensor with light in the 1.4 to 2.4 micrometer band, while suppressing laser light originating from the GRAVITY metrology system, custom-built optical components are required. In this paper, we present the development of a quantitative near-infrared point diffraction interferometric characterization technique, which allows measuring the transmitted wavefront error of the silicon entrance windows of the wavefront sensor cryostat. The technique can be readily applied to quantitative phase measurements in the near-infrared regime. Moreover, by employing a slightly off-axis optical setup, the proposed method can optimize the required spatial resolution and enable real time measurement capabilities. The feasibility of the proposed setup is demonstrated, followed by theoretical analysis and experimental results. Our experimental results show that the phase error repeatability in the nanometer regime can be achieved.
authors.affiliation: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Pengqian
authors.initials: P
authors.lastname: Yang
authors.forename: Stefan
authors.initials: S
authors.lastname: Hippler
authors.forename: Casey P
authors.initials: CP
authors.lastname: Deen
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Brandner
authors.forename: Yann
authors.initials: Y
authors.lastname: Clénet
authors.forename: Thomas
authors.initials: T
authors.lastname: Henning
authors.forename: Armin
authors.initials: A
authors.lastname: Huber
authors.forename: Sarah
authors.initials: S
authors.lastname: Kendrew
authors.forename: Rainer
authors.initials: R
authors.lastname: Lenzen
authors.forename: Oliver
authors.initials: O
authors.lastname: Pfuhl
authors.forename: Jianqiang
authors.initials: J
authors.lastname: Zhu
mesh_terms: D016477:Artifacts; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007259:Infrared Rays; D007909:Lenses; D061351:Telescopes