Repeatability of absolute terahertz power measurement using a sensitive calorimeter

In this paper, we report the repeatability of calorimetric measurement of absolute terahertz (THz) power at room temperature. Highly sensitive measurement at a sub-microwatt level was performed by using a calorimeter based on an isothermal temperature-control technique. The experiment was demonstrated at 1 THz using a photomixer as a THz source. Type A uncertainty in repeatability was evaluated to be 2.4% for five repetitions at an incident power of 0.81 μW. A very small drift of 30 pW/s was evaluated as well.