The CEA Cryo-Mechanism (CM) was created to actuate infrared instruments wheels equipped with filters, coronographs or diffractive optics. Based on an optimized integration of basic industrial components, the CM operates with a high positioning repeatability (down to ±13 arcsec) in infrared astrophysical environment (very low temperatures and under vacuum). In 2004, for the first light of the mid-infrared imager/spectrometer VISIR, 12 CM units were produced. Among them, 10 units are operating once every hour since 13 years with a very high reliability.
From 2010, the CM was improved with the goal of space missions. Today, the CM reaches the status of a flight model mechanism already delivered for the EUCLID space mission (launch expected by 2021). It is also derived into a cost optimized actuator so called ICAR that will be manufactured in approximately 20 units for the ELT-METIS ground based instrument.
This paper gives an overview of the CM design and its different configurations. The paper will describe more in details the different tests that were carried out on the Euclid-CM, covering performances, vibrations, electromagnetism, thermal cycles, exported torques and life-time tests.
Two DRS Technologies (formerly Boeing Sensors and Electronic Systems) 256 x 256 Si:As Blocked Impurity Band (BIB) focal plane arrays have been rigorously tested in 2001 and 2002 in the IR laboratory of CEA/Saclay/Service d'Astrophysique. These mid-IR arrays equip VISIR, the mid-infrared imager and spectrometer made under contract by CEA (France) and ASTRON (Netherlands) for the ESO Very Large Telescope. Measurement results crucial to the project appliction are presented. These include array dark current versus temperature and the Background Limited noise Performance (BLIP) capability. Operational optimization for astronomical use is also discussed in this paper.
In this paper, we present the status of VISIR, the mid-infrared instrument to be installed in 2003 at the Cassegrain focus of MELIPAL, one of the four 8-meter telescopes of the European Very Large Telescope. This cryogenic instrument, optimized for diffraction-limited performance in both mid-infrared atmospheric windows (N and Q band), combines imaging capabilities over a field up to about 1x1 arcmin2, and long-slit (0.5 arcmin) grating spectroscopy with various spectral resolutions up to R=25000 at 10 μm and 12500 at 20 μm. The contract to design and build VISIR was signed in November 1996 between the European Southern Observatory (ESO) and a French-Dutch consortium of institutes led by Service d'Astrophysique of Commissariat l'Energie Atomique (CEA). A key step in the project has been passed in December 2001, with the first infrared images in the laboratory and in April 2002 with the first infrared spectra in the laboratory. We present the results of the laboratory tests of the instrument, which is scheduled to be shipped to Paranal at the end of 2002.
Since the beginning of the VISIR project, the calibration aspects have been taken into account as an integral part of the design. In order to provide the user and the archive with high quality and well-controlled data, it is mandatory to have, during the routine observation phase, all calibration observations as part of the instrument set-up activities and as part of the actual Astronomical Observing Template. We propose here to review the calibration of VISIR observations. After a description of the various hardware
tools which have been introduced for calibration purposes (warm calibration unit, distortion grid, pupil imaging optics, wavelength calibration modules), we will present the calibrations in four astronomical categories (spatial resolution, photometry, astrometry and wavelength calibration). Cross-calibrations between the Imager and Spectrometer subsystems will also be addressed.
MIRI is the mid infrared instrument planned for the NGST. Working in the 5-28 μm band, it includes 3 units: a spectrograph, an imager and a calibration facility. We describe here the optical design of the MIRI imager channel as it is at teh end of the phase A study. The MIRI imager provides 3 observing modes: an imaging mode with a field of view of 1.3 arcmin x 1.7 arcmin and a Pixel Field of View of 0.1 arcsec/pixel, a coronagraphic mode and a low resolution spectroscopic mode for point sources, between 5 μm and 10 μm, with a spectral resolution R = λ/Δλ around 100.
CAMIRAS, the Saclay ground-based mid-IR camera, was built in 1990. At the time it was equipped with a 64 X 64 pixels Si:Ga array, developed by LETI/LIR, as a by-product of the detectors for ISOCAM. CAMIRAS has been intensively used at CFHT and at the Nordic Optical Telescope since 1991. In 1995, LETI/LIR delivered 192 X 192 Si:Ga arrays. Such a detector has been integrated in CAMIRAS in March 1995, and its acquisition system has been upgraded. The instrument is very versatile; several configurations allow to optimize it either at 10 microns or at 17 microns. CAMIRAS was mounted with the new 192 X 128 detector array at CFHT in July 1996. THis paper gives a full instrumental description of CAMIRAS. A particular attention is given to the spectro- imaging capability of the instrument achieved with a circular variable filter. Results from the last 3 observing campaigns carried out at the TIRGO observatory and at the Nordic Optical Telescope illustrate this paper. Spectra of comet Hale-Bopp showing the silicates features in the 8-13 microns wavelength range are presented.
New gallium-doped silicon 128 by 192 element arrays have been achieved at CEA-LETI-LIR (Infrared Laboratory) for imaging in the 8 - 14 micrometer spectral range. This program is in keeping with the previous detector development for the ISOCAM camera (32 by 32 element arrays) and for ground-based observation (64 by 64 element arrays). The main features of the new detectors are: a pitch of 75 micrometer which leads to 10 by 15 mm2 chip dimensions, two selectable storage capacitors (respectively 0.1 and 0.5 pF), a DVR readout circuit achieved in an NMOS silicon line with 1.5 micrometer design rules. The main electro- optical performances are the following: a peak responsivity of 4.0 A/W, a noise of 58 fA rms over the 0.1 - 128 Hz spectral range which is very close to the BLIP noise, and a corresponding noise equivalent power of 1.4 10-14 W.
New gallium-doped silicon 128 X 192 element arrays have been achieved at CEA-LETI- LIR (Infrared Laboratory) for imaging in the 8 - 14 micrometers spectral range. This program is in keeping with the previous detector developments for the ISOCAM camera (32 X 32 element arrays) and for ground-based observations (64 X 64 element arrays). The main features of the new detectors are: a pitch of 75 micrometers which leads to 10 X 15 mm2 chip dimensions, two selectable storage capacities (respectively 0.1 and 0.5 pF), a DVR readout circuit achieved in an NMOS silicon line with 1.5 micrometers design rules. The main electro-optical performances are the following: a peak responsivity of 4.0 A/W, a noise of 58 fArms over the 0.1 - 128 Hz spectral band which is very close to the BLIP noise, and a corresponding noise equivalent power of 1.4 10-14 W.
In 1992, the European Southern Observatory (ESO) committed a phase A study of a mid- infrared instrument for the 2nd unit VLT telescope, to a consortium of laboratories (SAp at Saclay, France; SRON at Groningen, Germany; and the Kapteyn Observatory at Roden, Netherlands). The results of the study are presented. One key scientific objective for this instrument is foreseen to be the study of dust. The required observing modes are (1) diffraction limited imaging both at 10 and 20 microns, and (2) spectroscopy at low resolution (R approximately equals 500) both at 10 and 20 microns. Another key domain is the study of atomic, molecular, and ionic lines observable in the atmospheric window at 10 and 20 microns. Given the various environments where the lines originate, medium (approximately equals 5000) to high (approximately equals 30,000) spectral resolution is needed. The optical design, as well as a mechanical layout, incorporating the various modes is described. The imaging and spectroscopic channels are separated. The spectrometer is based on a long slit all reflective design. Two optical configurations have been studied in detail. Because of the need for variable magnifications, the imager is based on refractive optics.