Terahertz power calibration using absolute reference calorimeter

Here, we demonstrate an accurate terahertz (THz) power calibration toward tens of nanowatt levels at room temperature. A power reference standard based on a calorimeter with extremely low noise is realized by introducing vacuum insulation panels utilized for thermal insulation. The standard provides a measurement capability of 26.7 nW with the expanded uncertainty of 4.2% ( k  = 2) at 1 THz. The direct‐comparison calibration of a commercially available power meter is performed by considering its detectable power levels using the standard. A thermopile‐type power meter is used as the device under test, and its calibration factors are determined at 1 and 1.5 THz over a power‐level range of 0.66–1.56 µW. We evaluate the measurement uncertainties of the calibration and find a relative expanded uncertainty of 4.8–9.0% ( k  = 2). © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.