SIMBAD references

We present results on the performance of the integral field spectroscopy (IFS) capability of the Gemini Near-Infrared Spectrograph installed on the Gemini-North telescope. This makes use of the innovative Advanced Image Slicer optical concept described in Paper 1 and uses new developments in diamond-machining to produce its complex micro-optics. The system delivers near-optimal performance for IFS in a small package that can be adapted to work with a wide range of spectrographs.

In this paper, we present results of extensive tests carried out on the telescope to verify the measurements of throughput, image quality and scattered light obtained in the laboratory and characterize the instrument's geometry and spectroscopic performance. This shows that the performance model, when fed with results of the component surface metrology, provides a good match to the throughput of the integral field unit measured on the telescope between 1 and 2.5 µm (65 and 90 per cent, respectively). At longer wavelengths, the throughput exceeds 90 per cent and the way that the design handles diffraction means that its performance can actually exceed that of the spectrograph alone with a slit of equivalent width.

We also present examples of data obtained during commissioning and system verification and compare this with data obtained in other ways, to verify the system performance in recovering astrophysical data. Finally, we review the performance and its relevance to future terrestrial and space observatories, in particular for large-scale multiple-IFS applications. We make the case that our design is of great relevance to instrumentation for Extremely Large Telescopes. We show that the throughput can be improved further by techniques to improve the quality of the optical surfaces.