The optical design of the G-CLEF Spectrograph: the first light instrument for the GMT

The GMT-Consortium Large Earth Finder (G-CLEF), one of the first light instruments for the Giant Magellan Telescope (GMT), is a fiber-fed, high-resolution echelle spectrograph. G-CLEF is expected to proceed towards fabrication in the coming months. In this paper, we present the current, pre-construction G-CLEF optical design, with an emphasis on the innovative features derived for the spectrograph fiber-feed, the implementation of a volume-phase holographic (VPH)-based cross disperser with enhanced blue throughput and our novel solutions for a multi-colored exposure meter and a flat-fielding system.