The ArT\'eMiS wide-field submillimeter camera: preliminary on-sky performances at 350 microns

ArTeMiS is a wide-field submillimeter camera operating at three wavelengths simultaneously (200, 350 and 450 microns). A preliminary version of the instrument equipped with the 350 microns focal plane, has been successfully installed and tested on APEX telescope in Chile during the 2013 and 2014 austral winters. This instrument is developed by CEA (Saclay and Grenoble, France), IAS (France) and University of Manchester (UK) in collaboration with ESO. We introduce the mechanical and optical design, as well as the cryogenics and electronics of the ArTeMiS camera. ArTeMiS detectors are similar to the ones developed for the Herschel PACS photometer but they are adapted to the high optical load encountered at APEX site. Ultimately, ArTeMiS will contain 4 sub-arrays at 200 microns and 2x8 sub-arrays at 350 and 450 microns. We show preliminary lab measurements like the responsivity of the instrument to hot and cold loads illumination and NEP calculation. Details on the on-sky commissioning runs made in 2013 and 2014 at APEX are shown. We used planets (Mars, Saturn, Uranus) to determine the flat-field and to get the flux calibration. A pointing model was established in the first days of the runs. The average relative pointing accuracy is 3 arcsec. The beam at 350 microns has been estimated to be 8.5 arcsec, which is in good agreement with the beam of the 12 m APEX dish. Several observing modes have been tested, like On-The-Fly for beam-maps or large maps, spirals or raster of spirals for compact sources. With this preliminary version of ArTeMiS, we concluded that the mapping speed is already more than 5 times better than the previous 350 microns instrument at APEX. The median NEFD at 350 microns is 600 mJy.s1/2, with best values at 300 mJy.s1/2. The complete instrument with 5760 pixels and optimized settings will be installed during the first half of 2015.Comment: 11 pages, 11 figures. Presented at SPIE Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII, June 24, 2014. To be published in Proceedings of SPIE Volume 915

Corrosion of T91 and pure iron in flowing and static Pb-Bi alloy between 450 °C and 540 °C: experiments, modelling and mechanism

International audienceT91 (Fe-9Cr steel) and pure iron were corroded in pure dissolution domain in liquid lead bismuth eutectic (LBE) from 450 to 540°C in static and in dynamic LBE flow. The modelling showed that corrosion rates were controlled: (i) for LBE natural convection, by the iron diffusion in the diffusion boundary layer; (ii) for flowing LBE, by a mixed process combining both the interfacial reaction rate of iron dissolution and the iron diffusion rate in the diffusion boundary layer. By fitting the modelling on the experimental points, the iron dissolution reaction rate constant was determined

Spectral definition of the ArTeMiS instrument

ArTeMiS is a sub-millimetre camera to be operated, on the Atacama Pathfinder Experiment Telescope (APEX). The ultimate goal is to observe simultaneously in three atmospheric spectral windows in the region of 200, 350 and 450 microns. We present the filtering scheme, which includes the cryostat window, thermal rejection elements, band separation and spectral isolation, which has been adopted for this instrument. This was achieved using a combination of scattering, Yoshinaga filters, organic dyes and Ulrich type embedded metallic mesh devices. Design of the quasi-optical mesh components has been developed by modelling with an in-house developed code. For the band separating dichroics, which are used with an incidence angle of 35 deg, further modelling has been performed with HFSS (Ansoft). Spectral characterization of the components for the 350 and 450 bands have been performed with a Martin-Puplett Polarizing Fourier Transform Spectrometer. While for the first commissioning and observation campaign, one spectral band only was operational (350 microns), we report on the design of the 200, 350 and 450 micron bands

Spectral definition of the ArTeMiS instrument

ArTeMiS is a sub-millimetre camera to be operated, on the Atacama Pathfinder Experiment Telescope (APEX). The ultimate goal is to observe simultaneously in three atmospheric spectral windows in the region of 200, 350 and 450 microns. We present the filtering scheme, which includes the cryostat window, thermal rejection elements, band separation and spectral isolation, which has been adopted for this instrument. This was achieved using a combination of scattering, Yoshinaga filters, organic dyes and Ulrich type embedded metallic mesh devices. Design of the quasi-optical mesh components has been developed by modelling with an in-house developed code. For the band separating dichroics, which are used with an incidence angle of 35 deg, further modelling has been performed with HFSS (Ansoft). Spectral characterization of the components for the 350 and 450 bands have been performed with a Martin-Puplett Polarizing Fourier Transform Spectrometer. While for the first commissioning and observation campaign, one spectral band only was operational (350 microns), we report on the design of the 200, 350 and 450 micron bands

On-chip spectroscopic solutions for polarimetric bolometer arrays in submillimeter astronomy

International audienceTwo technologies of all-silicon on-chip spectrometers based on the Fabry-Perot interferometer principle are studied and under development for a target wavelength of 158µm ([CII]). We are developing these spectroscopic capabilities with the objective of including them in polarimetric detector arrays cooled at 50mK. The first solution is a tunable cavity Fabry-Perot with silicon mirrors driven by cryogenic piezoelectric motors with a sub-micron step size. Each mirror is a dielectric Bragg structure made of quarter-wave layers of silicon and air providing a high reflectivity without metal losses. The theoretical performance of a Fabry-Perot resonator with such Bragg mirrors has been confirmed by measurement in a low temperature FTS: the finesse of this interferometer is more than twice that of a traditional Fabry-Perot. The second solution is a fixed Fabry-Perot array with a silicon microstructured cavity, which allows having different optical indices in different areas. The cavity is made of deep-etched silicon microstructures whose section is adapted to obtain the adequate optical index. Therefore, multiple wavelengths around 158µm, distributed on the array, are transmitted by this Fabry-Perot. The mirrors of this spectrometer are metallic capacitive grids designed to be highly reflective at the targeted wavelength, easy to manufacture with reduced metal losses. The simulations show high performances in resolution, close to the Bragg mirrors Fabry-Perot. The first prototypes of this solution have been manufactured by the CEA/LETI and will be soon measured in the cryogenic facilities in Saclay

LWIR quantum efficiency measurements using a calibrated MCT photodiode read by a cryo-HEMT-based amplifier

International audienceWe present a new development for the measurement of the Quantum Efficiency (QE) of a Mercury Cadmium Telluride (HgCdTe or MCT) detector array in the long wave infrared (LWIR) spectral band. To measure the incident photon flux on the detector, CEA-LETI has designed and produced a calibrated MCT photodiode which, under the test setup conditions used for the QE measurement, delivers a total (dark plus photonic) current of 1nA at 60K. The readout of such a low level of current makes a standard room temperature amplifier inconvenient due to the length of the wires between the focal plane (FP) at cold and the outside of the cryostat (>2m in the current cryostat). A much better approach is to use High Electron Mobility Transistors (Cryo-HEMTs), optimized by CNRS/C2N laboratory for ultra-low noise at very low temperatures (<1K). We have developed a Cryo-HEMT-based transimpedance amplifier to readout the photonic current of the calibrated MCT chip. The paper describes the calibrated photodiode, the Cryo-HEMT amplifier and the test setup, and shows the results of the QE measurements of the LWIR detector

Second generation of portable gamma camera based on Caliste CdTe hybrid technology

International audienceIn the framework of a national funded program for nuclear safety, a first prototype of portable gamma camera was built and tested. It integrates a Caliste-HD CdTe-hybrid detector designed for space X-ray astronomy coupled with a new system-on-chip based acquisition system (FPGA and ARM microprocessor) and thermo-electrical coolers for a use at room temperature. The complete gamma part of the camera fits in a volume of for a mass lower than 1 kg and a power consumption lower than 10 W. Localization and spectro-identification of radionuclides in a contaminated scene were demonstrated during several test campaigns. A new generation of system is under development taking into account feedback experience from in-situ measurements and integrating a new generation of sensor cost-optimized by industrial applications called Caliste-O. Caliste-O holds a 16x16 pixel detector of 14x14 mm2 and 2 mm thick with 8 full-custom front-end IDeF-X HD ASICs. Two prototypes were fabricated and tested. The paper will present the results of in-situ measurements with the first gamma camera, the spectroscopic performance of Caliste-O and the design of the second generation of gamma camera which aims for real time imaging and spectro-identification

BRAHMS: polarimetric bolometer arrays for the SPICA observatory camera (Conference Presentation)

International audienceIn the last decades, a very large effort has been made to measure, with high sensitivity, the intensity and spectral contents of millimetric (mm) and submillimetric (submm) light from the Universe. Today this picture is in the way to be routinely completed by polarization measurements that give access to previously hidden processes, for example the traces of primordial gravitational waves in the case of CMB (mainly mm), or the effect of magnetic field for star formation mechanisms (submm and mm optical ranges). The classical way to measure the light polarization is to split the two components by a polarizer grid and record intensities with two conjugated detection setups. This approach implies the deployment of a complex instrument system, very sensitive to external constraints (vibrations, alinement, thermal expansion…), or internal ones: determine low degrees of polarization implies a large increase in sensitivity when compared with intensity measurements. The need of detector arrays, with in pixel polarization measurement capabilities, has been well understood for years: all the complexity being reported at the focal plane level. Subsequently, the instrument integration, verification and tests procedure is considerately alleviated, specially for space applications.All silicon bolometer arrays using the same micromachining techniques than the Herschel PACS modules are well suited for this type of development. New thermometers doped for 50 mK operations permit to achieve, with a new design, sensitivities close to the aW/√Hz. It is based on all-legs bolometers (ALB), where the absorbing, insulating and thermometric functions are made by the same suspended silicon structure. This ALB structure, with in this case a spiral design, permits to separate the absorption of the two electromagnetic components of the light polarization. Each pixel consists of four bolometer divided in two pairs, each sensitive to one direction of polarization. This permits to combine the bolometer bridges in a fully differential global structure with a Wheatstone bridge arrangement. Total intensity and polarization unbalance are available directly at the detector level, thanks to a cold readout circuit integrated in the detector structure. This combination of functions is achieved by above IC manufacture techniques (IC for Integrated Circuit).All these developments take place in the prospect of the joint JAXA-ESA SPICA project, to equip a 1344 pixels polarimetric and imaging camera covering three spectral bands (100, 200 and 350 µm)

Optical design for the 450, 350, and 200 µm ArTeMiS camera

ArTeMiS is a submillimeter camera planned to work simultaneously at 450 mum, 350 mum and 200 mum by use of 3 focal planes of, respectively, 8, 8 and 4 bolometric arrays, each one made of 16 x18 pixels. In July 2013, with a preliminary setting reduced to 4 modules and to the 350 mum band, ArTeMiS was installed successfully at the Cassegrain focus of APEX, a 12 m antenna located on the Chajnantor plateau, Chile. After the summary of the scientific requirements, we describe the main lines of the ArTeMiS nominal optical design with its rationale and performances. This optical design is highly constrained by the room allocation available in the Cassegrain cabin. It is an all-reflective design including a retractable pick off mirror, a warm Fore Optics to image the focal plane of the telescope inside the cryostat, and the cold optics. The large size of the field of view at the focal plane of the telescope, 72 mm x 134 mm for the 350 mum and 450 mum beams, leads to the use of biconical toroidal mirrors. In this way, the nominal image quality obtained on the bolometric arrays is only just diffraction limited at some corners of the field of view. To keep a final PSF as much uniform as possible across the field of view, we have used the technic of manufacturing by diamond turning to machine the mirrors. This approach, while providing high accuracy on the shape of the mirrors, made easier the control of the two sub units, the Fore Optics and the cold optics, in the visible domain and at room temperature. Moreover, the use of the similar material (Aluminium alloy 6061) for the optical bench and the mirrors with their mount ensures a homothetic shrinking during the cooling down. The alignment protocol, drew up at the early step of the study, is also presented. It required the implementation of two additional mechanisms inside the cryostat to check the optical axis of the cold optics, in the real conditions of operation of ArTeMiS. In this way, it was possible to pre-align the Fore Optics sub unit with respect to the cold optics. Finally, despite the high constraints of the operating conditions of APEX, this protocol allowed to align ArTeMiS with respect to the telescope in a single adjustment. The first images obtained on the sky, Saturn with its rings, are give