The KMOS Integral Field System: fabrication, alignment, and test of 1000+ optical surfaces

Cornelis M. Dubbeldam; Paul Clark; Robert Content; Andrew K. Kirby; Ken Parkin; David J. Robertson; Stephen Rolt; David A. Ryder; Ray M. Sharples

doi:10.1117/12.925134

13 September 2012 The KMOS Integral Field System: fabrication, alignment, and test of 1000+ optical surfaces

Cornelis M. Dubbeldam, Paul Clark, Robert Content, Andrew K. Kirby, Ken Parkin, David J. Robertson, Stephen Rolt, David A. Ryder, Ray M. Sharples

Author Affiliations +

Proceedings Volume 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II; 84501M (2012) https://doi.org/10.1117/12.925134
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

The Centre for Advanced Instrumentation (CfAI) of Durham University (UK) has recently successfully completed the development of 24 Integral Field Units (IFUs) for the K-band Multi-Object Spectrometer (KMOS). KMOS is a second generation instrument for ESO’s Very Large Telescope (VLT) which is due for delivery during the summer of 2012. The KMOS IFU is based on the Advanced Image Slicer Concept developed by the CfAI and previously successfully implemented on the Gemini Near-InfraRed Spectrograph and JWST NIRSpec. Each IFU contains 14 channels which have to be accurately aligned. In addition, all 24 IFUs have to be co-aligned requiring the accurate alignment of an unprecedented grand total of 1152 optical surfaces. In this paper we describe how this has been achieved through the use of complex monolithic multi-faceted metal mirror arrays, which were fabricated in-house by means of freeform diamond machining. We will summarise the results from the metrology performed on each of the optical components and describe how these were integrated and aligned into the system. We will also summarise the results from the system level acceptance tests, which demonstrate the excellent performance of the IFUs. Each of the 24 IFUs is essentially diffraction limited across the entire field (Strehl ratios ~ 0.8) with throughput predictions (based on measurements of the surface roughness) rising from 86% at a wavelength of 1 micron to 93% at 2.5 micron. We believe that this level of performance has not previously been achieved in any image slicing IFU and showcases the potential of the current state-of-the-art technology.

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Cornelis M. Dubbeldam, Paul Clark, Robert Content, Andrew K. Kirby, Ken Parkin, David J. Robertson, Stephen Rolt, David A. Ryder, and Ray M. Sharples "The KMOS Integral Field System: fabrication, alignment, and test of 1000+ optical surfaces", Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 84501M (13 September 2012); https://doi.org/10.1117/12.925134

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