The Pico-Watt ACR (pW-ACR) project, led by NIST, aims to create a highly sensitive absolute cryogenic radiometer capable of calibrating optical power as low as 1 pico-watt with less than 1% uncertainty. This new device is over 1,000 times more sensitive than current models while keeping the same response time. The improvements come from three key design changes: a more sensitive thermometer, a weaker thermal link between the receiver and heat sink, and a smaller, lighter receiver cavity.
The pW-ACR uses a novel transition edge sensor (TES) thermometer, which is much more sensitive than the current germanium resistance thermometer used in existing models. A weaker thermal link made from thin Kapton tubing reduces noise, and the miniaturized cavity lowers heat capacity, helping maintain a fast response time. These changes allow the pW-ACR to measure extremely low optical power levels with high accuracy, extending calibration capabilities to new limits. The project is still in development, with testing and refinement ongoing.
Source: https://www.nist.gov/programs-projects/pico-watt-acr
Keywords: Quantum thermometer, cryogenic radiometer, optical power calibration
