Optical and Opto-Mechanical Design of a Novel "Macro" Image Slicer for the MIRADAS Instrument

TL;DR

This paper introduces a novel macro-slicer design for MIRADAS, a high-resolution infrared spectrograph, enhancing target selection and spectral resolution stability with a robust, easy-to-align optical and opto-mechanical system.

Contribution

It presents the first macro-slicer design for MIRADAS, combining advanced image slicer IFUs with a 'bolt-and-go' approach for improved robustness and alignment simplicity.

Findings

Design achieves fixed spectral resolution R>20,000 across varying seeing conditions.

Macro-slicer effectively rearranges inputs into a tightly packed pseudo-slit.

The system is robust and easy to align, suitable for cryogenic infrared instruments.

Abstract

We present the innovative macro-slicer optical and opto-mechanical designs for the third-generation Mid-resolution InfraReD Astronomical Spectrograph (MIRADAS) instrument for the 10.4m Gran Telescopio Canarias (GTC) in the 1-2.5 $\mu$m bandpass. MIRADAS uses up to 12 cryogenic, fully steerable probes to select simultaneous targets in a 5 arcminute field of view. The spectrograph module is a cross-dispersed echelle spectrograph. The macro-slicer is effectively a stack of six advanced image slicer Integral Field Units (IFUs) such as FRIDA or FISICA, and like other IFUs designed and built at the University of Florida by our group, uses a `bolt-and-go' approach to minimize the difficulty in alignment and maximize robustness. Like other advanced image slicer IFUs, there are three sets of mirrors that work together to geometrically rearrange the loosely packed inputs from the probe arms into a tightly packed pseudo-slit. The macro-slicer also passively keeps the spectral resolution of MIRADAS fixed at $R>20,000$ in seeing from 1.2 arcseconds down to 0.4 arcseconds, (typical observing conditions at GTC).