MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument developed for ESO (European Southern
Observatory) to be installed on the VLT (Very Large Telescope) in year 2012. The MUSE project is supported by a
European consortium of 7 institutes. After a successful Final Design Review the project is now facing a turning point
which consist in shifting from design to manufacturing, from calculation to test, ... from dream to reality.
At the start, many technical and management challenges were there as well as unknowns. They could all be derived of
the same simple question: How to deal with complexity? The complexity of the instrument, of the work to de done, of
the organization, of the interfaces, of financial and procurement rules, etc.
This particular moment in the project life cycle is the opportunity to look back and evaluate the management methods
implemented during the design phase regarding this original question. What are the lessons learn? What has been
successful? What could have been done differently? Finally, we will look forward and review the main challenges of the
MAIT (Manufacturing Assembly Integration and Test) phase which has just started as well as the associated new
processes and evolutions needed.
We propose a new concept of diffractive optics: Fresnel arrays, for a 4 m aperture space telescope in the UV
Fresnel arrays focus light by diffraction through a very thin binary mask. They form images optically and
deliver very high quality wavefronts, specially in the UV. Up to 8% of the incident light is focussed, providing
high angular resolution and high contrast images of compact objects.
Due to their focal lengths of a few kilometers in the UV, large Fresnel arrays will require two spacecraft
in formation flying, but with relatively tolerant positioning. Diffraction focusing is also very chromatic; this
chromatism is corrected, allowing relatively broad (30 to 100 nm) spectral channels in the 120-350 nm range.
A 4 m aperture Fresnel imager providing 7 to 10 milli arc seconds resolution is very competitive for imaging
compact and high contrast objects such as protoplanetary disks and young planetary systems, AGNs, and deep
We have developed prototypes to validate the optical concept and related technologies : first a laboratory
setup, then a 20 cm aperture ground-based prototype, which provides high contrast and diffraction limited images
of sky objects in the visible and close IR. A new laboratory prototype is also being prepared for validation in
the 250 - 350 nm wavelength range.
MUSE is the Multi Unit Spectroscopic Explorer, an AO-assisted integral field spectrograph for visible and
near-IR wavelengths which is planned to be commissioned at the UT4 of the Very Large Telescope in 2012.1 We
present the status on the modeling of the spatial PSF at the UT focus and its Field-of-View (FoV) and spectral
variations. Modeling these variations and studying their implications is a cornerstone for some MUSE data
analysis and processing problems such as fusion, source extraction and deconvolution of MUSE datacubes.
In Wide Field Mode (WFM, 1 square arc-minute FoV, 0.2 arcsec spatial sampling), MUSE can operate
without Adaptive Optics (AO) correction or with a Ground Layer Adaptive Optics facility aimed at providing
an almost uniform correction over a large field of view. In Narrow Field Mode (7.5 square arcseconds FoV, 0.025
arcsec spatial sampling) MUSE will make use of a Laser Tomography Adaptive Optics reconstruction, implying
stronger spatial variations. By using the adaptive optics simulation tool PAOLA, we simulate in WFM the
spatial PSF as a function of atmospheric turbulence parameters, observed wavelengths, AO mode and position
in the field of view. We then develop a mathematical model fitting the generated data which allows, with a small
number of parameters, to approximate the PSF at any spatial and spectral position of MUSE datacube. Finally,
we evaluate the possibility to estimate the model parameters directly from the (future) MUSE data themselves.
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 arcmin<sup>2</sup> sampled at
0.2x0.2 arcsec<sup>2</sup> 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 concept of a gamma-ray telescope based on a Laue lens offers the possibility to increase the sensitivity by more
than an order of magnitude with respect to existing instruments. Laue lenses have been developed by our
collaboration for several years : the main achievement of this R&D program was the CLAIRE lens prototype, which
has successfully demonstrated the feasibility of the concept in astrophysical conditions. Since then, the endeavour
has been oriented towards the development of efficient diffracting elements (crystal slabs) in order to increase both
the effective area and the width of the energy bandpass focused, the aim being to step from a technological Laue lens
to a scientifically exploitable lens. The latest mission concept featuring a gamma-ray lens is the European Gamma-
Ray Imager (GRI) which intends to make use of the Laue lens to cover energies from 200 keV to 1300 keV.
Investigations of two promising materials, low mosaicity copper and gradient concentration silicongermanium
are presented in this paper. The measurements have been performed during three runs: 6 + 4 days at the
European Synchrotron Radiation Facility (Grenoble, France), on beamline ID15A, using a 500 keV monochromatic
beam, and 14 days on the GAMS 4 instrument of the Institute Laue Langevin (Grenoble, France) featuring a highly
monochromatic beam of 517 keV. Despite it was not perfectly homogeneous, the presented copper crystal has
exhibited peak reflectivity of 25 % in accordance with theoretical predictions, and a mosaicity around 26 arcsec, the
ideal range for the realization of a Laue lens such as GRI. Silicon-germanium featuring a constant gradient have
been measured for the very first time at 500 keV. Two samples showed a quite homogeneous reflectivity reaching
26%, which is far from the 48 % already observed in experimental crystals but a very encouraging beginning. The
measured results have been used to estimate the performance of the GRI Laue lens design.
This paper presents the results of a Fresnel Interferometric Array testbed. This new concept of imager involves
diffraction focussing by a thin foil, in which many thousands of punched subapertures form a pattern related
to a Fresnel zone plate. This kind of array is intended for use in space, as a way to realizing lightweight large
apertures for high angular resolution and high dynamic range observations. The chromaticity due to diffraction
focussing is corrected by a small diffractive achromatizer placed close to the focal plane of the array.
The laboratory test results presented here are obtained with an 8 centimeter side orthogonal array, yielding
a 23 meter focal length at 600 nm wavelength. The primary array and the focal optics have been designed and
assembled in our lab. This system forms an achromatic image. Test targets of various shapes, sizes, dynamic
ranges and intensities have been imaged. We present the first images, the achieved dynamic range, and the
This paper presents progress made regarding the field to resolution ratio for aperture synthesis interferometers. In order to overcome a limit established for the field to resolution ratio of interferometric arrays, we propose an interferometer configuration which allows a better coverage of the spatial frequency plane. This setup requires large sub-apertures, which can be built more easily with a diffractive Fresnel plates than with large mirrors. We compare a dense array of 9 Fresnel sub-apertures, which gives a snapshot field-resolution ratio of 400, versus a sparse array of 150 small apertures, which yields a field-resolution ratio of 150.