Technical requirements and optical design of the Hi-5 spectrometer
C. Dandumont (ULiège, Université de Liège)
A. Mazzoli (Université de Liège, ULiège)
Victor Laborde (Université de Liège, ULiège)
R. Laugier (Katholieke Universiteit Leuven)
A. Bigioli (Katholieke Universiteit Leuven)
G. Garreau (Katholieke Universiteit Leuven)
S Gross (Macquarie University)
M. Ireland (Australian National University)
Jérôme Loicq (ULiège, TU Delft - Spaceborne Instrumentation)
G.B. Cavadini (External organisation)
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Abstract
Hi-5 is a proposed L' band high-contrast nulling interferometric instrument for the visitor focus of the Very Large Telescope Interferometer (VLTI). As a part of the ERC consolidator project called SCIFY (Self-Calibrated Interferometry For exoplanet spectroscopY), the instrument aims to achieve sufficient dynamic range and angular resolution to directly image and characterize the snow line of young extra-solar planetary systems. The spectrometer is based on a dispersive grism and is located downstream of an integrated optics beam-combiner. To reach the contrast and sensitivity specifications, the outputs of the I/O chip must be sufficiently separated and properly sampled on the Hawaii-2RG detector. This has many implications for the photonic chip and spectrometer design. We present these technical requirements, trade-off studies, and phase-A of the optical design of the Hi-5 spectrometer in this paper. For both science and contract-driven reasons, the instrument design currently features three different spectroscopic modes (R=20, 400, and 2000). Designs and efficiency estimates for the grisms are also presented as well as the strategy to separate the two polarization states.