Alban Remillieux

The MUSE second-generation VLT instrument

Summary: The Multi Unit Spectroscopic Explorer (MUSE) is a second-generation VLT panoramic integral-field spectrograph currently in manufacturing, assembly and integration phase. MUSE has a field of 1x1 arcmin2 sampled at 0.2x0.2 arcsec2 and is assisted by the VLT ground layer adaptive optics ESO facility using four laser guide stars. The instrument is a large assembly of 24 identical high performance integral field units, each one composed of an advanced image slicer, a spectrograph and a 4kx4k detector. In this paper we review the progress of the manufacturing and report the performance achieved with the first integral field unit.

The E-ELT first light spectrograph HARMONI: capabilities and modes

HARMONI is the E-ELT’s first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R ~3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 – 2.4 μm wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument’s technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline.

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].

MUSE Integral Field Unit: Test results on the first out of 24

MUSE (Multi Unit Spectroscopic Explorer) is a second generation VLT panoramic integral field spectrograph developed for the European Southern Observatory (ESO), operating in the visible wavelength range (0.465-0.93 μm). It is composed of 24 identical Integral Field Units (IFU); each one incorporates an advanced image slicer associated with a classical spectrograph and a detector vessel. The Image Slicer subsystem -ISS- is composed of two mirror arrays of 48 spherical elements each. It is made of Zerodur and uses an innovative polishing approach where all individual components are polished together by classical method. The MUSE Spectrograph -SPS-, with fast output focal ratio of f/1.95, implements a Volume Phase Holographic Grating - VPHG. The last subsystem, the Detector Vessel -DV- includes a chip of 4k by 4k 15μm pixels supported by a Vacuum and Cryogenic System - VCS - provided by ESO. The first out of 24 IFUs for MUSE instrument has been manufactured, aligned and tested last months. First, this paper describes the optical design, the manufacturing and test results (image quality, pupil and field of view positioning) of each subsystem independently. Second, we will focus on overall system performance (image quality and positioning) of the spectrograph associated with the detector vessel. At the end, the test results (image quality, positioning, throughput, mechanical interfaces) of the first IFU for MUSE instrument will be reported. Most of them are compliant with requirements that it demonstrates that the manufacturing, integration, alignment and tests processes are mature and gives good confidence for serial production by 24 times applied to MUSE instrument.

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.

MUSE image slicer: test results on largest slicer ever manufactured

An image slicer breadboard has been designed, manufactured and tested for MUSE (Multi Unit Spectroscopic Explorer) instrument, a second generation integral field spectrograph developed for the European Southern Observatory (ESO) for the VLT. MUSE is operating in the visible and near IR wavelength range (0.465-0.93 μm) and is composed of 24 identical Integral Field Units; each one incorporates an advanced image slicer associated with a classical spectrograph. This paper describes the original optical design, the manufacturing, component test results (shape, roughness, reflectivity, microscopic visualization) and overall system performance (image quality, alignment) of the image slicer breadboard. This one is a combination of two mirror arrays of 48 elements each. It is made of Zerodur and uses a new polishing approach where all individual optical components are polished together by classical method. This image slicer constitutes the first one which has the largest number of active slices (48) associated with strict tolerances in term of positioning. The main results of the tests on this image slicer breadboard will then be presented. Most of them are compliant with requirements. This demonstrates that the manufacturing process is mature and gives good confidence for serial production applied to MUSE instrument.

MUSE instrument global performance test

MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument developed for ESO (European Southern Observatory) and will be assembled to the VLT (Very Large Telescope) in 2013. The MUSE instrument can simultaneously record 90.000 spectra in the visible wavelength range (465-930nm), across a 1*1arcmin² field of view, thanks to 24 identical Integral Field Units (IFU). A collaboration of 7 institutes has partly validated and sent their subsystems to CRAL (Centre de Recherche Astrophysique de Lyon) in 2011, where they have been assembled together. The global test and validation process is currently going on to reach the Preliminary Acceptance in Europe in 2012. The sharing of performances has been based on 5 main functional sub-systems. The Fore Optics sub-system derotates and anamorphoses the VLT Nasmyth focal plane image, the Splitting and Relay Optics associated with the Main Structure are feeding each IFU with 1/24th of the field of view. Each IFU is composed of a 3D function insured by an image slicer system and a spectrograph, and a detection function by a 4k*4k CCD cooled down to 163°K. The 5th function is the calibration and data reduction of the instrument. This article depicts the sequence of tests that has been completely reshafled mainly due to planning constraints. It highlights the priority given to the most critical performances tests of the sub-systems and their results. It enhances then the importance given to global tests. Finally, it makes a status on the verification matrix and the validation of the instrument and gives a critical view on the risks taken.

MUSE Optical Alignment Procedure

MUSE (Multi Unit Spectroscopic Explorer) is a second generation VLT integral field spectrograph (1x1arcmin² Field of View) developed for the European Southern Observatory (ESO), operating in the visible wavelength range (0.465-0.93 μm). A consortium of seven institutes is currently assembling and testing MUSE in the Integration Hall of the Observatoire de Lyon for the Preliminary Acceptance in Europe, scheduled for 2013. MUSE is composed of several subsystems which are under the responsibility of each institute. The Fore Optics derotates and anamorphoses the image at the focal plane. A Splitting and Relay Optics feed the 24 identical Integral Field Units (IFU), that are mounted within a large monolithic instrument mechanical structure. Each IFU incorporates an image slicer, a fully refractive spectrograph with VPH-grating and a detector system connected to a global vacuum and cryogenic system. During 2011, all MUSE subsystems were integrated, aligned and tested independently in each institute. After validations, the systems were shipped to the P.I. institute at Lyon and were assembled in the Integration Hall This paper describes the end-to-end optical alignment procedure of the MUSE instrument. The design strategy, mixing an optical alignment by manufacturing (plug and play approach) and few adjustments on key components, is presented. We depict the alignment method for identifying the optical axis using several references located in pupil and image planes. All tools required to perform the global alignment between each subsystem are described. The success of this alignment approach is demonstrated by the good results for the MUSE image quality. MUSE commissioning at the VLT (Very Large Telescope) is planned for 2013.

The MUSE project face to face with reality

MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument built for ESO (European Southern Observatory) to be installed in Chile on the VLT (Very Large Telescope). The MUSE project is supported by a European consortium of 7 institutes. After the critical turning point of shifting from the design to the manufacturing phase, the MUSE project has now completed the realization of its different sub-systems and should finalize its global integration and test in Europe. To arrive to this point many challenges had to be overcome, many technical difficulties, non compliances or procurements delays which seemed at the time overwhelming. Now is the time to face the results of our organization, of our strategy, of our choices. Now is the time to face the reality of the MUSE instrument. During the design phase a plan was provided by the project management in order to achieve the realization of the MUSE instrument in specification, time and cost. This critical moment in the project life when the instrument takes shape and reality is the opportunity to look not only at the outcome but also to see how well we followed the original plan, what had to be changed or adapted and what should have been.

Efficiency measurements performed on the MUSE VPHG

Volume Phase Holographic Gratings (VPHG) are key elements for the second generation instrument MUSE (Multi Unit Spectroscopic Explorer) developed for the VLT (Very Large Telescope) for ESO (European Southern Observatory). MUSE operates in the visible wavelength range (465-930nm) and is composed of 24 spectrographs including one VPHG each. This article briefly describes the design of the grating manufactured by Kaiser Optical Systems, to reach the MUSE spectral resolution and efficiency. On the other hand the set up developed in CRAL (Centre de Recherche Astrophysique de Lyon) to test the VPHG final performance is deeply discussed. This set up uses a broadband source coupled to a monochromator, and a compensation arm to remove the source intensity fluctuations. The source is amplitude modulated by a chopper, and a lock-in amplifier extracts the modulated signal from the photodiodes. The measurement arm scans the 0, 1st and 2nd diffraction orders of the grating and allows tests of different areas over its whole surface of 120mm*60mm. The accuracy reached is below one percent in efficiency, allows us to validate the performance and its uniformity over the surface of the gratings.