Towards 1 W, High Accuracy, Absolute Radiometer

Emerging applications require a calibration at 1 W with greater accuracy than is currently available. Conventional free beam absolute electrical substitution radiometers (ESRs) operate at cryogenic conditions have historically provided the highest accuracy but operate at optical power levels < 2 mW. To improve the accuracy of calibrations at 1 W, we compare possible approaches to realize a primary standard for 1 W optical power measurements. We describe and evaluate two diverse concepts based on bolometer detectors: The first design is an adapted cryogenic approach while the second system is operating at room temperature (RT). With the proposed uncertainty budgets, we estimate an expanded uncertainty for the RT layout to be < 0.06 % (k = 2) while the cryogenic design approaches 0.02 % (k = 2).