BICEP2 Focal Plane under the Microscope
The BICEP2 telescope’s focal plane uses novel technology, developed at NASA’s Jet Propulsion Laboratory, to build an array of devices that use superconductivity to gather, filter, detect, and amplify polarized radiation from the cosmic microwave background. Each pixel is made from a printed antenna sensitive to polarized millimeter-wave radiation, with a filter that determines the spectral response at 150 GHz, and a sensitive detector fabricated on a thin micro-machined membrane. The antennas and filters are made from superconducting and dielectric materials with extremely low propagation loss. The detector uses a superconducting transition-edge film as a sensitive thermometer to detect the heat from millimeter-wave radiation that was collected by the antenna and dissipated at the detector. Finally a tiny electrical current from the sensor is measured with amplifiers on the focal plane called SQUIDs (Superconducting QUantum Interference Devices). The focal planes are manufactured using optical lithography techniques, similar to those used in the industrial production of integrated circuits for computers.