Detector-stabilized FEL lamps as transfer standards in an international comparison of spectral irradiance

The spectral irradiance of lamp standards can be stabilized within a limited spectral range using a suitable selective detector to control the irradiance of the lamps. The capability of one commercial lamp facility incorporating a computer-controlled power supply was tested in an international comparison. A set of three lamps and the detector-stabilized power supply were circulated between the Physikalisch-Technische Bundesanstalt (PTB, Germany), the Helsinki University of Technology (HUT, Finland) and the Swedish National Testing and Research Institute (SP, Sweden) for the comparison, EUROMET project No. 475.