The PTB high-accuracy spectral responsivity scale in the ultraviolet

The Physikalisch-Technische Bundesanstalt (PTB) has established spectral responsivity standards for photodetectors in the wavelength range between 200 nm and 400 nm based on cryogenic electrical-substitution radiometers. In order to obtain standards over a continuous wavelength range with low uncertainty, combined use is made of both the dispersed synchrotron radiation of the storage ring BESSY I and quasi-monochromatic laser radiation. Taking advantage of the specific properties of the monochromatized synchrotron radiation and the laser radiation, relative standard uncertainties between 10(-3) and 5 x 10(-3) are achieved in the calibration of trap detectors in the spectral range 400 nm to 200 nm.