A TES focal plane for SPICA-SAFARI

We describe the design of a focal plane array assembly incorporating transition edge superconducting bolometers (TES) for the SAFARI instrument aboard the SPICA satellite. SPICA consists of a 3.5 metre telescope actively cooled to a temperature of < 7 K, designed to be diffraction limited at a wavelength of 3 μm. The active cooling of the telescope reduces its emission to a level below the astrophysical background power level over the entire wavelength range of operation (~4 – 210 μm). This represents a reduction in loading at far-infrared (FIR) wavelengths of more than a factor of 10,000 over the 50 K HERSCHEL telescope. SAFARI is a proposed FIR instrument for SPICA consisting of an imaging Fourier Transform Spectrometer (FTS) covering The wavelengths from 34 – 210 μm with science goals of furthering our understanding of planetary system formation, the life cycle of dust and gas in the galaxy and the formation of galaxies. The SAFARI wavelength coverage is divided into 3 bands in the focal plane covering the wavelength ranges from 35 – 60 mm, 60 – 110 μm, and 110 – 210 μm. Each band requires a 2D focal plane array of 0.5 fλ spaced pixels covering a 2' x 2' field of view. The total number of pixels in all three bands is approximately 6000. In order to take advantage of the reduction in background power provided by the cooled telescope, SAFARI requires detectors with a combination of low optical NEP (~ 2 x 10-19 W√ x Hz) and high optical efficiency. There are several detector technologies that have been under development to meet these requirements including Kinetic Inductance Detectors (KIDs), Transition Edge Superconducting bolometers (TES), Silicon bolometers, Ge:Ga photoconductors and Quantum Well detectors. We describe the conceptual design of a TES focal plane array including the detector array, coupling optics, cold electronics and interconnections and mechanical and thermal design. We also describe the results of measurements of performance of single pixel prototypes as well as small prototype arrays and compare these results with the required performance