Bolometers operated at 0.1 K and 0.2 K cooled by adiabatic demagnetization

The construction of bolometers operating at temperatures of 0.1 K and 0.2 K and cooled by adiabatic demagnetization is reported. The electrical noise-equivalent power (NEP) of the bolometers was found to be 1.8 and 6.6 x 10 to the -16th W/sq rt Hz, respectively. These values are within a factor of two of the expected performance based upon bolometer theory. The thermistor material used was gallium-doped single-crystal germanium, for which a resistivity temperature dependence is found.