ELT-HIRES the high resolution instrument for the ELT: optical design and instrument architecture

Abstract

The first generation of ELT instruments will include an optical-infrared High Resolution Spectrograph, conventionally indicated as ELT-HIRES. This paper describes the optical design and overall architecture of the instrument whose main capabilities can be summarized as follows. - Fibers fed specrographs with resolving power R=100,000 (HR-modes), R=150,000 (UHR-modes) and R=20,000 (MR-modes). - Simultaneous wavelength coverage from 400 nm to 1800 nm; extendable to 300-2400 nm. - Spectrometers with fixed configurations and without moving optical parts. - Maximum size of entrance apertures ideal for seeing limited observations. - Many observing modes, including seeing-limited single-object spectroscopy, multi-objects medium resolution spectroscopy and IFU observations with different spatial scales, down to the diffraction limit of the ELT telescope. - Observing modes defined and selected in interfaces outside of the spectrographs. - Modular design compatible with a minimal baseline that can be subsequently expanded and upgraded.