The SAFARI grating spectrometer for the SPICA space observatory (Conference Presentation)

The European/Japanese SPace Infrared telescope for Cosmology and Astrophysics, SPICA, will provide astronomers with a long awaited new window on the universe. Having a large cold telescope cooled to less than 8K above absolute zero, SPICA will provide a unique environment where instruments are limited only by the cosmic background itself. A consortium of European, north American and Asian institutes has been established to design and implement the SpicA FAR infrared Instrument SAFARI, an extremely sensitive spectrometer designed to fully exploit this extremely low far infrared background environment provided by the SPICA observatory. SAFARI’s extremely sensitive Transition Edge Sensing detectors will allow astronomers to very efficiently obtain moderate to high resolution spectra of many thousands of obscured celestial objects in the far infrared, allowing a full spectroscopic characterisation of this objects. Efficiently obtaining such a large number of complete spectra will be essential to address several fundamental questions in current astrophysics: how do galaxies form and evolve over cosmic time?, what is the true nature of our own Milky Way?, and why and where do planets like those in our own solar system come into being? The basic SAFARI instrument is a highly sensitive Grating Spectrometer with a spectral resolution R of about 300 and a line sensitivity of a few x 10^-20 W/√Hz (5σ-1h). By routing the signal through a Martin-Puplett interferometer a high resolution mode is implemented providing R~11000 at 34 μm to R~1500 at 230 μm. The instrument operates in four wavelength bands, simultaneously covering the full 34-230μm range. Each band has three arrays of about 300 TES sensors providing three spatial and 300 spectral outputs. To limit the number of signal wires between the cold focal plan and the warm electronics units a 160 pixel/channel Frequency Domain Multiplexing scheme is employed.