Potential optical design of a multi-conjugate adaptive optics instrument based on a modified Offner concentric relay for Gemini North

The Gemini North Adaptive Optics (GNAO) project will deliver the first ground-based Adaptive Optics (AO) facility for wide-field studies on Mauna Kea in Hawaii. This document presents the potential optical design of a Multi-Conjugate Adaptive Optics (MCAO) instrument. In the aim of designing an instrument with enhanced performance, a design based on a Modified Offner Concentric relay is proposed as an alternative option to the pair of unmatched off-axis parabolic mirrors. A diffraction-limited image quality is achieved in the NIR domain over a wide field-of-view of 60-arcsec radius. Petzval field curvature is cancelled and static optical distortion is reduced by a factor of 4 at the image plane. This work shows the Modified Offner Concentric relay is a feasible design for the wide-field AO instrumentation of the 8.1-meter Gemini North telescope.