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.
The Multi-Unit Spectroscopic Explorer (MUSE) is an integral-field spectrograph for the ESO Very Large Telescope.
After completion of the Final Design Review in 2009, MUSE is now in its manufacture and assembly phase. To achieve
a relative large field-of-view with fine spatial sampling, MUSE features 24 identical spectrograph-detector units. The
acceptance tests of the detector sub-systems, the design and manufacture of the calibration unit and the development of
the Data Reduction Software for MUSE are under the responsibility of the AIP. The optical design of the spectrograph
implies strict tolerances on the alignment of the detector systems to minimize aberrations. As part of the acceptance
testing, all 24 detector systems, developed by ESO, are mounted to a MUSE reference spectrograph, which is illuminated
by a set of precision pinholes. Thus the best focus is determined and the image quality of the spectrograph-detector
subsystem across wavelength and field angle is measured.
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.
We attempt to perform real time detection and direct high resolution imaging of millimeter blackbody sources using
sparse aperture interferometry. We reject heterodyne technology for a multitude of factors including bulky equipment,
cryogenic cooling, long integration times, and indirect imaging. An alternative method is to convert the incoming
millimeter waves into optical and perform optical image-plane interferometry in real time. This method is suitable for
snapshot-imaging of short-lived phenomena, often encountered in defense and security applications. The approach
presented in this work utilizes a millimeter wave antenna array coupled to an optical interferometer which images
directly on a detector array for image read-out, processing, and storage.
To minimize the maximum sidelobes of the point spread function, we choose an antenna array composed of two
concentric hexagonal rings, such that the outer ring is ~3 times the inner ring. This design ensures more or less uniform
and isotropic spatial frequency coverage, eliminating difficulties associated with resolving out structures whose spatial
frequencies are in between that of the single aperture diameter and those of the baselines. The Fourier coverage of this
array is the sum of the Fourier coverage of the outer ring plus that of the inner ring added to that of the baselines
between the inner and outer rings. The need for delay lines is done away with by mounting all the apertures on the same
The incoming millimeter signals are fed through electro-optical modulators for upconversion onto an optical carrier,
which can be readily captured, routed, and processed using optical techniques. The optical waves are fed via a fiber optic
array onto a microlens array which is a scaled down version of the antenna array configuration. Then homodyne
interferometry is performed. We reject pupil-plane (Michelson) interferometry based on a multitude of factors. The main
drawback is that pupil-plane interferometers don't produce images but rather gives the information about the
autocorrelation of the object. We instead use a classical image-plane interferometer (Fizeau) setup and direct detection is
performed on a detector array. Image-plane interferometry has its advantages. Unlike its pupil-plane cousin, a Fizeau
interferometer is a true imaging device, where each beam is used to make an image of the object and are superimposed.
Because Fizeau beam combiners work in the image plane, they don't suffer from ambiguities associated with the
interpretation of visibility measurements. Also since the beams traverse the same paths and superpose, unmeasured
phase changes do not creep in. In the design of the Fizeau interferometer, we preserve homothetic mapping, i.e., the
entrance and exit pupils are replicas of one another, scaled only by a constant factor. This ensures direct imaging over a
wide bandwidth with high angular resolution, high sensitivity, and a wide field of view. Since the Fizeau setup allows
access to large fields, mosaicing wide fields is possible.
For many applications, the usefulness of millimeter-wave imagers is limited by the large aperture sizes required to obtain images of sufficient resolution. Sparse aperture techniques could open up wider range of applications by mitigating the volume requirements of high resolution imagers. In previous proceedings, we have presented an approach towards the realization of millimeter-wave, sparse-aperture imagers using optical techniques. By using electro-optic modulators to upconvert received millimeter-wave fields onto an optical carrier, such fields can be readily captured, routed, and processed using optical techniques. Such techniques could provide significant advantages over traditional heterodyne techniques. Herein, we present progress towards the physical realization of such an imager. Specifically, we discuss the implementation challenges that must be addressed to create such an imager and present in further detail the numerous advantages such an approach will yield. We also present results obtained from a working prototype system and show that these results are in good agreement with theoretical performance models.