Radiometry Laboratory Of Physikalisch-Technische Bundesanstalt Research Articles

The two normal-incidence monochromator beam lines of PTB at BESSY II

In the present contribution the two normal-incidence monochromator beam lines of the Physikalisch-Technische Bundesanstalt (PTB) for the calibration of radiation sources and detectors and the characterisation of optical components are briefly described. After shut down of BESSY I these bending magnet beam lines have been transferred to the radiometry laboratory of PTB at BESSY II. Emphasis is laid on the technical aspects linked with the change from BESSY I to BESSY II such as, e.g., the out-of-plane acceptance of the synchrotron radiation to reduce the heat load on the normal-incidence optics caused by the higher characteristic energy of BESSY II bending magnet radiation compared to BESSY I.

X-ray detector calibration in the PTB radiometry laboratory at the electron storage ring BESSY II

The Physikalisch-Technische Bundesanstalt (PTB) currently operates a laboratory for radiometry from the VUV to the hard X-ray spectral range at the 1.7 GeV electron storage ring BESSY II. Detector calibration, performed by the PTB at BESSY I up to photon energies of about 1.5 keV, can now be extended up to 10.5 keV based on an electrical substitution radiometer as a primary detector standard and on the use of monochromatized bending magnet and undulator radiation of high spectral purity. This energetic range will be further extended up to 50 keV by using radiation from a 7 T wavelength shifter. Moreover, BESSY II is a primary source standard offering calculable bending magnet radiation. The PTB uses these primary standards for the absolute calibration of detectors with relative uncertainties below 1%. Up until now, photodiodes, energy-dispersive semiconductor detectors and also superconducting tunnel junctions have been characterized for photon energies up to 10.5 keV.

High-accuracy detector calibration in the 3-1500 eV spectral range at the PTB radiometry laboratory.

State-of-the-art detector calibration in the UV/VUV and soft X-ray spectral ranges at the Physikalisch-Technische Bundesanstalt (PTB) is based on the primary detector standard SYRES, a cryogenic electrical substitution radiometer capable of measuring radiant power of a few micro W. At the PTB radiometry laboratory at the synchrotron radiation facility BESSY, two dedicated beamlines are operated, providing monochromatic radiation of high spectral purity, high radiant power and tunable photon energy in the 3-1500 eV range. The spectral responsivity of detectors, e.g. photodiodes, can be measured with a relative uncertainty of about 1% by direct comparison with SYRES, as will be demonstrated for PtSi/Si and GaAsP/Au Schottky and silicon n-on-p photodiodes. The calibration of photon-counting detectors traceable to SYRES can by accomplished by exploiting the unique capability to scale the spectral photon flux over several orders of magnitude by changing the stored electron current. Calibrations of CCDs and photomultipliers are presented as examples.

Detector calibration at the PTB radiometry laboratory at BESSY

In the vacuum ultraviolet (VUV) and soft X-ray spectral ranges the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the synchrotron radiation facility BESSY offers two different methods for the calibration of radiation detectors: The electron storage ring BESSY, in combination with suitable monochromators, reproducibly produces monochromatic radiation of tunable photon energy, high spectral purity (< 1% false light contribution), high spectral resolving power and high radiant power, which can be scaled down over twelve orders of magnitude. With this source of monochromatic radiation a cryogenic electrically substituted radiometer (ESR) is operated as a primary detector standard in the photon energy range from 3 to 1500 eV. The ESR is optimized for synchrotron radiation, capable of measuring radiant power in the order of some μW with an uncertainty below 0.2%. Sufficiently stable radiation detectors can be calibrated against the ESR with uncertainties well below 1%. Recent progress in this field will be demonstrated for the calibration of photodiodes. The electron storage ring BESSY is also used as a primary source standard, in the photon energy range from the infrared to the soft X-ray range. The spectral and spatial distribution of the broadband radiation emitted in the range from 1 to 15 keV is calculable from the known storage ring parameters with uncertainties from 0.04% to 0.35%. respectively. This allows the detection efficiency of energy-dispersive detectors such as solid-state detectors, charge coupled devices and others to be determined, provided the detector response function to monochromatic radiation is measured as well.