A NOVEL BOLOMETER FOR INFRARED AND MILLIMETER-WAVE ASTROPHYSICS

We are developing a novel bolometer which uses a fine mesh to absorb r adiation. The filling factor of the mesh is small, providing a small h eat capacity and a low geometric cross-section to cosmic rays. The mes h is patterned from a free-standing silicon nitride membrane and is th ermally isolated by long radial legs of silicon nitride. A thin metall ic film evaporated on the mesh absorbs radiation by matching the surfa ce impedance to that of free space. A neutron transmutation doped germ anium thermistor attached to the center of the mesh detects the temper ature increase from absorbed radiation. The low thermal conductivity a nd heat capacity of silicon nitride provide improved performance in lo w background applications. We discuss the theoretical limits of the pe rformance of these devices. We have tested a device at 300 mK with an electrical NEP = 4 x 10(-17) W Hz(-1/2) and a time constant tau = 40 m s.