Durham University's Centre for Advanced Instrumentation (CfAI) have developed a technique for fabricating monolithic multi-faceted mirror arrays using freeform diamond machining. Using this technique, the inherent accuracy of the diamond machining equipment is exploited to achieve the required relative alignment accuracy of the facets, as well as an excellent optical surface quality for each individual facet. Monolithic arrays manufactured using this technique, have been successfully applied in the Integral Field Unit for the GEMINI Near-InfraRed Spectrograph (GNIRS IFU), which was recently commissioned at GEMINI South. In this paper, we present details of the fabrication process and optical performance of these components. We will also briefly discuss how their implementation has facilitated the GNIRS IFU's opto-mechanical system design and subsequent integration and test, and highlight the resulting improvement in
system performance.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.