The BIFROST instrument will be the first VLTI instrument optimised for high spectral resolution up to R=25,000 and operate between 1.05 and 1.7 μm. A key component of the instrument will be the spectrograph, where we require a high throughput over a broad bandwidth. In this contribution, we discuss the four planned spectral modes (R=50, R=1000, R=5000, and R=25,000), the key spectral windows that we need to cover, and the technology choices that we have considered. We present our plan to use Volume Phase Holographic Gratings (VPHGs) to achieve a high efficiency > 85%. We present our preliminary optical design and our strategies for wavelength calibration.
@article{arxiv.2208.05397,
title = {Spectrograph design for the Asgard/BIFROST spectro-interferometric instrument for the VLTI},
author = {Sorabh Chhabra and Michele Frangiamore and Stefan Kraus and Andrea Bianco and Francisco Garzon and John Monnier and Daniel Mortimer},
journal= {arXiv preprint arXiv:2208.05397},
year = {2022}
}