The Centre for Advanced Instrumentation (CfAI) of Durham University (UK) has developed a conceptual design for the
Integral Field Unit (IFU) for EAGLE based on diamond-machined monolithic multi-faceted metal-mirror arrays as an
alternative to the glass IFU which is currently baselined. The CfAI has built up substantial expertise with the design,
manufacture, integration, alignment and acceptance testing of such systems, through the successful development of IFUs
for the Gemini Near-InfraRed Spectrograph (GNIRS) and JWST NIRSpec and 24 IFUs for ESO’s K-band Multi-Object
Spectrometer (KMOS). The unprecedented performance of the KMOS IFUs (Strehl < 0.8 across the field, throughput
rising from 86% at a wavelength of 1 micron to 93% at 2.5 micron) demonstrates that the current state-of-the-art
technology is sufficiently mature to meet the demanding requirements for EAGLE. In addition, the use of monolithic
multi-faceted metal mirror arrays will greatly simplify the manufacture, integration and alignment of such systems thus
potentially reducing technical and programmatic risks and cost. Through the timely completion of the KMOS IFUs,
which required the fabrication of an unprecedented 1152 optical surfaces, the CfAI have demonstrated that they have the
capacity to produce the required volume within reasonable schedule constraints. All the facilities (design, fabrication e.g.
diamond machining, metrology, integration and test) required for the successful realisation of such systems are available
in-house, thus minimising programmatic risks. This paper presents the opto-mechanical design and predicted
performance (based on the actual measured performance of the KMOS IFUs) of the proposed metal IFU.