We develop polarimetric detector arrays for submillimeter Space astronomy. The technology is based on the all-silicon bolometer scheme established for the Herschel/PACS photometer. Each pixel detects two orthogonal polarization directions with an efficiency greater than 95%. Every other pixel in the array is rotated by 45° to retrieve the linear Stokes parameter of the incident light inside the Airy disc of the telescope optics. We reduced the temperature to 50 mK to improve sensitivity and introduced new readout schemes based on single or double Wheatstone bridge configurations for fully differential DC outputs. The detectors are grown directly on a CMOS circuit wafer to ensure the largest bandwidth with the highest response.
One of the main goals of the canceled Space Infrared Telescope for Cosmology and Astrophysics (SPICA), was to reveal the evidence of the influence of magnetic field in the structuration of different astrophysical objects, as for example the filamentary structure of star-forming regions. For this purpose, “instrument-in-pixel” detector arrays were developed under ESA, CNES and FOCUS contracts, to propose sensitive, compact and easy to integrate detection solutions for a Space Observatory. Magnetic field influences the light emission or absorption of small grains and molecules imprinting its characteristics in the received electromagnetic message in terms of polarization, degree, angle and intensity. Each pixel of the developed detectors absorb the radiation through two orthogonal dipole networks. The detector array is organized like a chessboard with every other pixel having absorbers rotated by 45° in order to unveil simultaneously the linear Stokes parameters without any optical loss. A very large absorption efficiency is obtained, as usual since PACS detectors, by a backshort-under-grid scheme. To obtain the goal sensitivity of 1 attoW/√Hz, detectors are cooled to 50 mK and linked to an Above IC CMOS readout circuit. For each pixel, four interleaved spiral silicon sensors gather the absorber power. They are organized in a Wheatstone bridge configuration that allows fully differential outputs: total power and polarization unbalanced intensity.
KEYWORDS: Bolometers, Sensors, Polarization, Polarimetry, Silicon, Space observatories, Mirrors, Magnetism, Semiconductors, Picture Archiving and Communication System
We present the B-BOP instrument, a polarimetric camera on board the future ESA-JAXA SPICA far-infrared space observatory. B-BOP will allow the study of the magnetic field in various astrophysical environments thanks to its unprecedented ability to measure the linear polarization of the submillimeter light. The maps produced by B-BOP will contain not only information on total power, but also on the degree and the angle of polarization, simultaneously in three spectral bands (70, 200 and 350 microns). The B-BOP detectors are ultra-sensitive silicon bolometers that are intrinsically sensitive to polarization. Their NEP is close to 10E-18 W/sqrt(Hz). We will present the optical and thermal architectures of the instrument, we will detail the bolometer design and we will show the expected performances of the instrument based on preliminary lab work.
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