David Freeman

HARMONI: a single-field wide-band integral-field spectrograph for the European ELT

We describe the results of a Phase A study for a single field, wide band, near-infrared integral field spectrograph for the European Extremely Large Telescope (E-ELT). HARMONI, the High Angular Resolution Monolithic Optical & Nearinfrared Integral field spectrograph, provides the E-ELTs core spectroscopic requirement. It is a work-horse instrument, with four different spatial scales, ranging from seeing to diffraction-limited, and spectral resolving powers of 4000, 10000 & 20000 covering the 0.47 to 2.45 μm wavelength range. It is optimally suited to carry out a wide range of observing programs, focusing on detailed, spatially resolved studies of extended objects to unravel their morphology, kinematics and chemical composition, whilst also enabling ultra-sensitive observations of point sources. We present a synopsis of the key science cases motivating the instrument, the top level specifications, a description of the opto-mechanical concept, operation and calibration plan, and image quality and throughput budgets. Issues of expected performance, complementarity and synergies, as well as simulated observations are presented elsewhere in these proceedings[1].

SWIFT image slicer: large format, compact, low scatter image slicing

We present the SWIFT image slicer and its novel de-magnifying design. It is based on the MPE-3D and SPIFFI image slicers, uses plane mirrors to slice the input field, but achieves a considerable de-magnification through the use of a mosaic of spherical lenses. As only plane and spherical surfaces are used in the design, classical polishing techniques can be applied to achieve very high surface accuracy and quality. This reduces aberrations and scattered light, mandatory for an image slicer working at optical wavelengths and behind an adaptive optics system. Except for the lens mosaic, the SWIFT slicer is built entirely from Zerodur and is assembled using optical contacting. We present a detailed description of the design as well as results of the early stages of its fabrication.

HARMONI: the first light integral field spectrograph for the E-ELT

HARMONI is a visible and near-infrared (0.47 to 2.45 μm) integral field spectrometer, providing the E-ELTs core spectroscopic capability, over a range of resolving powers from R (≡λ/Δλ)~500 to R~20000. The instrument provides simultaneous spectra of ~32000 spaxels at visible and near-IR wavelengths, arranged in a √2:1 aspect ratio contiguous field. HARMONI is conceived as a workhorse instrument, addressing many of the E-ELT’s key science cases, and will exploit the E-ELTs scientific potential in its early years, starting at first light. HARMONI provides a range of spatial pixel (spaxel) scales and spectral resolving powers, which permit the user to optimally configure the instrument for a wide range of science programs; from ultra-sensitive to diffraction limited, spatially resolved, physical (via morphology), chemical (via abundances and line ratios) and kinematic (via line-of-sight velocities) studies of astrophysical sources. Recently, the HARMONI design has undergone substantial changes due to significant modifications to the interface with the telescope and the architecture of the E-ELT Nasmyth platform. We present an overview of the capabilities of HARMONI, and of its design from a functional and performance viewpoint.

SWIFT de-magnifying image slicer: diffraction limited image slicing at optical wavelengths

We present the manufacturing and first results from testing and characterising the SWIFT image slicer. The SWIFT image slicer design is based on the MPE-3D and SPIFFI image slicers. It uses plane mirrors to slice the input field but through a novel, de-magnifying design, using a mosaic of spherical lenses, it achieves a considerable de-magnification. Classical polishing techniques can be applied to manufacture both plane and spherical surfaces with very high surface accuracy and quality reducing aberrations and scattered light. The SWIFT image slicer was manufactured over a 18 months period and was delivered to Oxford in September 2007. The commissioning of the SWIFT instrument will take place in August/September 2008.

Multiplexing 32,000 spectra onto 8 detectors: the HARMONI field splitting, image slicing, and wavelength selecting optics

HARMONI, the High Angular Resolution Monolithic Optical & Near-infrared Integral field spectrograph is one of two first-light instruments for the European Extremely Large Telescope. Over a 256x128 pixel field-of-view HARMONI will simultaneously measure approximately 32,000 spectra. Each spectrum is about 4000 spectral pixels long, and covers a selectable part of the 0.47-2.45 μm wavelength range at resolving powers of either R≈4000, 10000, or 20000. All 32,000 spectra are imaged onto eight HAWAII4RG detectors using a multiplexing scheme that divides the input field into four sub-fields, each imaged onto one image slicer that in turn re-arranges a single sub-field into two long exit slits feeding one spectrograph each. In total we require eight spectrographs, each with one HAWAII4RG detector. A system of articulated and exchangeable fold-mirrors and VPH gratings allows one to select different spectral resolving powers and wavelength ranges of interest while keeping a fixed geometry between the spectrograph collimator and camera avoiding the need for an articulated grating and camera. In this paper we describe both the field splitting and image slicing optics as well as the optics that will be used to select both spectral resolving power and wavelength range.

15x optical zoom and extreme optical image stabilisation: diffraction limited integral field spectroscopy with the Oxford SWIFT spectrograph

When commissioned in November 2008 at the Palomar 200 inch Hale Telescope, the Oxford SWIFT I and z band integral field spectrograph, fed by the adaptive optics system PALAO, provided a wide (3×) range of spatial resolutions: three plate scales of 235 mas, 160 mas, and 80 mas per spaxel over a contiguous field-of-view of 89×44 pixels. Depending on observing conditions and guide star brightness we can choose a seeing limited scale of 235 mas per spaxel, or 160 mas and 80 mas per spaxel for very bright guide star AO with substantial increase of enclosed energy. Over the last two years PALAO was upgraded to PALM-3000: an extreme, high-order adaptive optics system with two deformable mirrors with more than 3000 actuators, promising diffraction limited performance in SWIFTs wavelength range. In order to take advantage of this increased spatial resolution we upgraded SWIFT with new pre-optics allowing us to spatially Nyquist sample the diffraction limited PALM-3000 point spread function with 16 mas resolution, reducing the spaxel scale by another factor of 5×. We designed, manufactured, integrated and tested the new pre-optics in the first half of 2011 and commissioned it in December 2011. Here we present the opto-mechanical design and assembly of the new scale changing optics, as well as laboratory and on-sky commissioning results. In optimal observing conditions we achieve substantial Strehl ratios, delivering the near diffraction limited spatial resolution in the I and z bands.

The opto-mechanical design of HARMONI: a first light integral field spectrograph for the E-ELT

HARMONI is a visible and near-IR integral field spectrograph, providing the E-ELTs spectroscopic capability at first light. It obtains simultaneous spectra of 32000 spaxels, at a range of resolving powers from R~4000 to R~20000, covering the wavelength range from 0.47 to 2.45 μm. The 256 × 128 spaxel field of view has four different plate scales, with the coarsest scale (40 mas) providing a 5″ × 10″ FoV, while the finest scale is a factor of 10 finer (4mas). We describe the opto-mechanical design of HARMONI, prior to the start of preliminary design, including the main subsystems - namely the image de-rotator, the scale-changing optics, the splitting and slicing optics, and the spectrographs. We also present the secondary guiding system, the pupil imaging optics, the field and pupil stops, the natural guide star wavefront sensor, and the calibration unit.

Preliminary design study of the integral field unit for the E-ELT Harmoni instrument

HARMONI is a visible and near-infrared (0.47 to 2.45 μm) integral field spectrograph over a range of resolving powers from R~3000 to R~20000. We will present in this paper, the different concepts of the HARMONI Integral Field Unit that makes the link between HARMONI Preoptics and the 4 Spectrographs. It is composed of a field splitter/relay system and an image slicer that creates from a rectangular Field of View a very long (532mm) pseudo-slit for each spectrograph. HARMONI is also considering a separate visible spectrograph and we present a possible image slicer for this option.

MICADO: optical configuration, performance and folding

MICADO will be the IR imaging camera for the E-ELT. It has been designed to work in conjunction with both SCAO (in the early phase) and LGS-MCAO system MAORY (for which it has been optimized) and delivers diffraction limited quality over about 1 arcmin field of view covering the wavelength range from 0.8 to 2.5 micron. In this paper, we describe the optical configurations and the observing modes, for both the primary and the auxiliary arms, of the current baseline and we show the expected performances and how the optical path can be folded to fit the available limited space in the cryo-chamber.