The MPIR 100mK bolometer array for 2mm continuum observations (original) (raw)

We are developing bolometer arrays for continuum detection in millimeter and submillimeter astronomy . For the 2 mm atmospheric window, where the transmission is comparatively high, a bolometer temperature of about 100 mK is necessary in order to avoid being limited by the system noise. Our new 2 mm array is cooled by a He/He-dilution refrigerator with a base temperature of 30 mK. The substrate for the 19 channel bolometer array consists of a singlecrystal silicon wafer with silicon-nitride membranes. Radiation is collected by a single-mode horn array in front of the wafer and coupled into e$cient absorbers in the center of the membranes. Resulting temperature changes of the absorbers are measured with NTD-germanium thermistors. In the "rst stage of the read out electronics, we use JFETs working at 150 K. Cold RF-"lters prevent RF interference from entering the bolometer array cavity. The combination of several mesh "lters and a short piece of cylindrical waveguide at the end of each horn de"nes the bandpass for the incoming radiation, which is matched to the 2 mm atmospheric window.