ProtoPol is a medium-resolution echelle spectro-polarimeter initially conceived as a prototype instrument of the currently under development M-FOSC-EP (Mt. Abu Faint Object Spectrograph and Camera-Echelle Polarimeter) instrument - a two-channel multimode instrument which is currently being designed for PRL 1.2m and 2.5m telescopes at Mt. Abu. Though ProtoPol was initially conceived to evaluate the development methodology of M-FOSC-EP with commercially available off-the-shelf components, it was later elevated to the level of a full-fledged back-end instrument for PRL telescopes. ProtoPol was designed on the concept of echelle and cross-disperser gratings to record the cross-dispersed spectra in the wavelength range from 390 to 940 nm with a resolution (λ/δλ) in the range of 7000-8000. ProtoPol has been successfully developed and commissioned on PRL 1.2m and 2.5m telescopes since December 2023, and a variety of observations are being carried out for instrument characterization and scientific purposes. The design and development methodology of ProtoPol with complete off-the-shelf components offers a cost-effective way to develop spectro-polarimeters with such resolutions for small aperture (2-3m) telescopes around the world with a shorter development period.
Mt. Abu Faint Object Spectrograph and Camera-Echelle Polarimeter (M-FOSC-EP) is a two-channel multimode instrument currently under design for the upcoming PRL 2.5m telescope at Mt. Abu, India. M-FOSC-EP would provide capabilities of seeing limited imaging, low-resolution spectroscopy (R∼500-800), and high-resolution spectro-polarimetry (R∼15000) over the visible waveband. This design uses a common collimator optics, followed by a movable fold mirror to direct the incoming telescope beam into either of the low-resolution and spectropolarimetry modules, which are equipped with their separate detector system. As a precursor of M-FOSC-EP, a prototype spectro-polarimeter named ProtoPol is also being developed with commercially off-the-shelf optical components. ProtoPol could be used on existing 1.2m as well as on upcoming 2.5m PRL telescopes. Here we present the optical designs and performances of M-FOSC-EP and ProtoPol. In addition, the opto-mechanical design of ProtoPol has been presented.
Mt. Abu Faint Object Spectrograph and Camera-Pathfinder (MFOSC-P) is an instrument currently under development for PRL 1.2m Optical-Near Infrared Telescope at Mt. Abu. It is a pathfinder instrument for a bigger and more complex next generation instrument on upcoming PRL 2.5m telescope. MFOSC-P has been conceptualized as a general purpose user’s instrument with sufficient ease in its operation. It offers options for both the imaging as well spectroscopy within the same optical chain in visible waveband (4500-8500 angstroms). The optics has been designed to provide ‘seeing limited imaging’ in astronomy standard Bessell’s B, V, R and I filters. Three modes of spectroscopy with resolutions (λ/Δλ) 2000, 1000 and 500 around 6500, 5500 and 6000 angstroms are achieved with plane reflection gratings. The mechanical system of the instrument has been designed and successfully evaluated for its structural integrity using finite element analysis. Here we present the optical and opto-mechanical designs of the instrument, which have been successfully developed in house under several existing technical constraints. The results of finite element analysis of the instrument are also presented.
The 24 IFU from MUSE are equipped with 4K x 4K CCD detectors which are operated at cryogenic temperature around
160 K. The large size of the chip combined with a rather fast camera (F/2) impose strong positioning constrains. The
sensitive surface should remain in an angular envelope of less than 30 arc sec in both directions. The ambitious goal of
having the same spectrum format on every detector imposes also a very accurate positioning in the image plane. The
central pixel has to be located in a square smaller 50 microns relative to the external references.
The first part of the paper describes the mechanical design of the detector head. We concentrate on the various aspects of
the design with its very complex interfaces. The opto-mechanical concept is presented with an emphasis on the
robustness and reliability. We present also the necessary steps for the extreme optimization of the cryogenic performance
of this compact design driven with a permanent view of the production in series.
The techniques and procedures developed in order to meet and verify the very tight positioning requirements are
described in a second part. Then the 24 fully assembled systems undergo a system verification using one of the MUSE
spectrographs. These tests include a focus series, the determination of the PSF across the chip and a subsequent
calculation of the tip/tilt and shift rotation of the detector versus the optical axis.
The Multi-Unit Spectroscopic Explorer (MUSE), an integral-field spectrograph for the ESO Very Large Telescope, has
been built and integrated by a consortium of 7 European institutes. MUSE can simultaneously record spectra across a
field of view of 1 square arcminute in the wavelength range from 465nm to 930nm. The calibration unit (CU) for MUSE
was developed to provide accurate flat fielding, spectral, geometrical, image quality and efficiency calibration for both
the wide-field and AO-assisted narrow-field modes. This paper describes the performance of the CU and electronics,
from the subsystem validation to the integration, alignment and use in the MUSE instrument.
Martin Roth, Karl Zenichowski, Nicolae Tarcea, Jürgen Popp, Silvia Adelhelm, Marvin Stolz, Andreas Kelz, Christer Sandin, Svend-Marian Bauer, Thomas Fechner, Thomas Jahn, Emil Popow, Bernhard Roth, Paul Singh, Mudit Srivastava, Dieter Wolter
Astronomical instrumentation is most of the time faced with challenging requirements in terms of sensitivity, stability,
complexity, etc., and therefore leads to high performance developments that at first sight appear to be suitable only for
the specific design application at the telescope. However, their usefulness in other disciplines and for other applications
is not excluded. The ERA2 facility is a lab demonstrator, based on a high-performance astronomical spectrograph, which
is intended to explore the innovation potential of fiber-coupled multi-channel spectroscopy for spatially resolved
spectroscopy in life science, material sciences, and other areas of research.
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