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The accuracy of detector calibration in the UV, vacuum-ultraviolet, and soft-x-ray spectral ranges could be significantly improved by the use of the synchrotron radiation electrical substitution radiometer (SYRES) as the primary detector standard. The SYRES radiometer is optimized for use with spectrally dispersed synchrotron radiation as supplied by two monochromator beam lines in the radiometry laboratory of the Physikalisch-Technische Bundesanstalt at the Berlin electron-storage ring (BESSY). Wavelength ranges from 0.8 to 25 nm and from 35 to 400 nm are covered. The typically available radiant power of [approximately]1-10 [micro]W can be measured with the SYRES radiometer with a standard relative uncertainty of less than 0.2%. The spectral responsivity of qualified photodiodes for use as secondary detector standards is determined by direct comparison with the primary detector standard at an arbitrary wavelength. At present, the scale of spectral responsivity is realized with a standard relative uncertainty of well below 1% in the spectral ranges 0.8-3.5 nm, 5-25 nm, and 120-400 nm. We provide a comprehensive description of the SYRES radiometer and of the two facilities for detector calibration in the UV and vacuum-ultraviolet spectral ranges and in the soft-x-ray spectral range, respectively, and we discuss the achievable uncertainties in the calibration of detectors. Key words: Radiometry, cryogenics, electrical substitution, detector standards, PTB, synchrotron radiation.

A multipass optical system external to the optical head of a cryostat has been designed for use with a Bruker IFS 120 HR interferometer. A White cell using mirrors with a focal length of 10 cm is the central feature of the system. Nearly all optical elements, including those in the cryostat, have been optimized with thin-film technology for maximum signal throughput in the 6000 to 7000 cm to the -1 range. The extension of the path length of the sample, in a cell limited to 3.8 cm in length, is illustrated with spectra of solid para-H2 at 12 K. The cell was limited to four passes in this application because of refraction of the infrared radiation at the sample surface. Twelve to 20 passes are possible for a sample with an index of refraction close to 1 and with smaller aperture settings.