Comparison of Synchrotron Radiation-Based Ultraviolet Source Calibrations at PTB and NIST

Because of the ever increasing interest into ultraviolet radiation and its properties, National Measurement Laboratories like the PTB and NIST are providing ultraviolet source and detector transfer standards and related services. In addition not only the absolute calibration of transfer standards is important, but also the accurate conversion of different spectro-radiometric quantities into each other. The work reported here is an example of a successful bilateral comparison between NIST and PTB in which deuterium lamps are used as transfer standards, but different calibrations are performed at the two laboratories. The PTB at BESSY II performs calibrations in vacuum that result into spectral radiant intensities, whereas at NIST using SURF III spectral irradiances are measured in air.