In this work, we describe the construction and characterization of an Ambient-Radiation Thermometer (ART) which can measure non-contact temperatures from -50 deg C to 150 deg C. To increase the long-term stability of the responsivity, optical components within the field-of-view of the detector and the detector itself are thermally stabilized in an optical assembly using three separate thermo-electric control setups. The ART is constructed with ZnSe lenses for collecting and focusing the thermal-infrared radiation onto the pyroelectric detector. The pyroelectric detector has a window with an 8 µm to 14 µm filter for selecting the thermal radiation, and the detector and preamplifier are packaged into a hermetically sealed container. The incident radiation is modulated using a reflecting chopper wheel, and the modulated signals are measured using a commercial lock-in detector.
This design results in a radiation thermometer which can resolve sub mK temperature changes of ambient objects. The long-term non-contact temperature measurement stability of the device relies upon stable, encapsulated thermistors. This new device can also measure down to -50 deg C with few mK noise.