We report the on-sky performance of two new integral field units (IFUs) for the Gemini Near-Infrared Spectrograph (GNIRS). The IFUs were designed and built at the Centre for Advanced Instrumentation in Durham University, as part of Gemini's Instrument Upgrade Program. The Low Resolution IFU (LR-IFU) has a field-of-view of 3.15 '' x 4.80 '' sampled with a pixel scale of 0.15 ''. It currently covers the X, J, H, and K near-infrared bands with a spectral resolution of R similar to 1700-7200 depending on the grating. Observations with the LRIFU can be combined with the "super-seeing" mode offered by Gemini-North (LGS+PWFS1), which can improve the sharpness of the PSF to below the Nyquist sampling. The High Resolution IFU (HR-IFU) has a 1.80 '' x 1.25 '' field-of-view at a 0.05 '' sampling, and is optimized for fully adaptively corrected images delivered by the Gemini North ALTAIR AO system. In addition, the GNIRS HR-IFU extends Gemini's integral field capabilities in wavelength out to the thermal infrared, i.e., in the L and M bands, with 0.2 '' spatial resolution and up to a spectral resolution of R similar to 18,000. Thanks to their exceptional throughput (70-85% of the long slit width matching the size of the slicer), the commissioning of these modes opens up new scientific opportunities for spatially resolved spectroscopy on Gemini, including study of the kinematics of stellar outflows around high-mass young stellar objects, probing the AGN-Starburst connection in active galactic nuclei, estimating black hole masses from infrared line diagnostics, resolving spectroscopy of gravitationally lensed galaxies and resolving jet dynamics in Herbig-Haro objects.

Lightweight, aluminum, freeform prototype mirrors have been designed and fabricated by a Thai led team, with UK support, for intended applications within the Thai Space Consortium (TSC) satellite series. The project motivation was to explore the different design strategies and fabrication steps enabled by both conventional (mill, drill, and lathe) and additive (3D printing) manufacture of the prototype substrates. Single Point Diamond Turning was used to convert the substrates into mirrors and optical metrology was used to evaluate the different mirror surfaces. The prototype criteria originated from the TSC-1 satellite tertiary mirror, which is designed to minimize the effect of Seidel aberrations before the beam enters the hyperspectral imager. To converge upon the prototype designs, Finite Element Analysis (FEA) was used to evaluate the different physical conditions experienced by the prototypes during manufacture and how these influence the optical performance. The selected designs satisfied the mass and surface displacement criteria of the prototype and were adapted to either the conventional or additive manufacturing process. This paper will present the prototype design process, substrate manufacture, optical fabrication, and an interferometric evaluation of the optical surfaces comparing the conventional and additive manufacturing processes.

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 similar to 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.

The KBand Multi-Object Spectrograph (KMOS) is an astronomical spectrograph designed for integration with the VLT (Very Large Telescope) and capable of surveying 24 independent fields. The IFU (Integral Field Unit) subsystem is a complex instrument with no less than 1080 optical surfaces. We focus here on the design of the manufacturing and test process for this subsystem. Design of this system is based on experience gained on similar complex optical systems, such as the NIRSPEC (Near Infra Red Spectrometer) IFU that will be integrated into the James Webb Space Telescope. Surfaces are produced in aluminium using a freeform diamond machine. Many surfaces are multi-faceted and of complex form. The requirement for 15 nm RMS form accuracy poses a significant challenge for the machining process. In particular, the large number of highly complex surfaces represents the most serious design challenge. Design of the part fixturing is critical to the consistent achievement of the required surface accuracy. Furthermore, efficient test procedures must be developed to characterise all surfaces. In recognition of this, particular emphasis is placed on the metrology of these components. Moreover, the volume of complex metrology involved offers a unique opportunity to fully characterise and optimise the manufacturing process.

We describe our work towards the manufacture of micro-optical arrays using freeform diamond machining techniques. Simulations have been done to show the feasibility of manufacturing micro-lens arrays using the slow-tool servo method. Using this technique, master shapes can be produced for replication of micro-lens arrays of either epoxy-on-glass or monolthic glass types. A machine tool path programme has been developed on the machine software platform DIFFSYS, allowing the production of spherical, aspherical and toric arrays. In addition, in theory spatially varying lenslets, sparse arrays and dithered lenslet arrays (for high contrast applications) are possible to produce. In practice, due to the diamond tool limitations not all formats are feasible. Investigations into solving this problem have been carried out and a solution is presented here. ∗

We describe our work towards the manufacture of micro-optical arrays using freeform diamond machining techniques. Simulations have been done to show the feasibility of manufacturing micro-lens arrays using the slow-tool servo method. Using this technique, master shapes can be produced for replication of micro-lens arrays of either epoxy-on-glass or monolthic glass types. A machine tool path programme has been developed on the machine software platform DIFFSYS, allowing the production of spherical, aspherical and toric arrays. In addition, in theory spatially varying lenslets, sparse arrays and dithered lenslet arrays (for high contrast applications) are possible to produce. In practice, due to the diamond tool limitations not all formats are feasible. Investigations into solving this problem have been carried out and a solution is presented here. ∗

Durham University's Centre for Advanced Instrumentation (CfAI) are currently prototyping key components for the KMOS and JWST NIRSpec Integral Field Units (IFUs). These next-generation IFUs will make extensive use of complex monolithic multi-faceted metal mirror arrays, which are fabricated by means of 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 obtain the necessary optical surface quality for each individual facet, thus facilitating the integration and subsequent testing of these complex systems. The CfAI have pioneered the use of such arrays in the IFU for the Gemini Near-InfraRed Spectrograph (GNIRS IFU), which was installed at Gemini South in April, 2004. The requirements for the next generation of IFUs, however, demand a considerable improvement in the optical performance of these components, e.g. alignment accuracy of the facets, surface form accuracy and roughness. In our paper we briefly discuss the optical designs of KMOS and JWST NIRSpec IFU, and summarise the requirements on the optical components. We then present details of the diamond machining techniques employed to fabricate these highquality components and discuss the latest results from our prototyping activities, which demonstrate our capability of producing optical components that meet the demanding specifications.

We describe our work towards the manufacture of micro-optical arrays using freeform diamond machining techniques. Simulations have been done to show the feasibility of manufacturing micro-lens arrays using the slow-tool servo method. Using this technique, master shapes can be produced for replication of micro-lens arrays of either epoxy-on-glass or monolthic glass types. A machine tool path programme has been developed on the machine software platform DIFFSYS, allowing the production of spherical, aspherical and toric arrays. In addition, in theory spatially varying lenslets, sparse arrays and dithered lenslet arrays (for high contrast applications) are possible to produce. In practice, due to the diamond tool limitations not all formats are feasible. Investigations into solving this problem have been carried out and a solution is presented here.