Currently, the development teams for this sub-millimeter camera are switching the thrust of their effort along two directions:
The first direction involves taking the PACS bolometer arrays to longer wavelengths, in order to fit them to large ground-based telescopes. Such an operation requires that these arrays are first adjusted to cater to the various atmospheric “windows,” i.e. the various narrow spectral bands for which the atmosphere (at altitude) does not prove wholly opaque (200mm, 350mm, 450mm, 865mm). The benefit accruing from this development work has less to do with measurement sensitivity (there being no way of matching spaceborne performance) than with the use of very large telescopes (12–15 meters in diameter), affording far higher resolving power. Adjusting the arrays to the longer wavelengths will chiefly involve increasing the size of the hybridization bumps.
The other avenue is concerned with the development of far more sensitive detectors, intended for future space missions.
Currently, two projects are already benefiting from this development work. The ArTéMis (Architecture de bolomètres pour les télescopes submillimétriques au sol: Bolometer Architecture for Ground-based Submillimeter Telescopes) is a 5,000-pixel bolometer-array camera intended for the Atacama Pathfinder Experiment (APEX) Telescope, sited in Chile. The PILOT (Polarized Instrument for Long-wavelength Observation of the Tenuous Interstellar Medium) is an experiment featuring two focal planes, carried by balloon, to measure the polarized radiation emission from the Milky Way.
Finally, bolometer optimization should also prove useful to a variety of very-low-background-flux applications. Such is the case in SPICA (Space Infrared Telescope for Cosmology and Astrophysics), a space mission conducted by the Japan Aerospace Exploration Agency (JAXA), in collaboration with the European Space Agency (ESA). Launch is scheduled for 2018. This space telescope will use the same mirror as Herschel, cooled however to –268°C. In order to optimize to the utmost this new configuration, researchers will need to raise detector sensitivity by a factor 100, at least. To achieve such sensitivity (background noise power of 10–18 watt), the silicon bolometer cooling will be enhanced, down to 0.05 Kelvin.
In order to meet the challenges set by this new mission, CEA has embarked on a preliminary study phase. For example, research scientists at CEA’s Low Temperatures Service are already working on the design of an adiabatic demagnetization cryocooler for space applications. SPICA should pave the way for other exciting projects, e.g. the spaceborne FIRI (Far-Infrared Interferometry) experiment, involving use of bolometers, or the BPOL (Cosmic Microwave Background Polarization) experiment, at 3 K.
About the authors:
. Patrick Agnese
Electronics and Information Technology Laboratory (Leti)
Technological Research Division (DRT)
CEA Grenoble Center
. Louis Rodriguez
Astrophysics Service (SAp)
Institute of Research into the Fundamental Laws of the Universe (IRFU)
Physical Sciences Division (DSM)
Joint Astrophysics Research Unit on Multiscale Interactions (CEA–Paris-VII University–CNRS)
CEA Saclay Center (Orme des Merisiers)
A successor to bipolar transistor technology, CMOS technology involves fabricating electronic components featuring low power consumption, dedicated to processor design requirements.
A bolometer (from the Greek bolê, meaning “sunbeam,” “ray of light,” hence “radiation,” and metron, “measure”) is a thermal detector of radiation. This involves a device having the ability to measure an incident flux of energy, whether carried by photons, or massive particles, and to convert it into heat. For a given quantity of energy, the lower the mass (and hence the heat capacity) of the device, the higher the rise in temperature is found to be. At very low temperatures, this phenomenon is amplified, owing to a steep drop in the heat capacity of matter.