09.01.2015
Fig. 1: Facility for source calibration at the MLS. It can be oriented to face either the MLS or the source to be calibrated (as shown in the picture). The source to be calibrated (the deuterium lamp) is visible at the bottom left of the picture.
Fig. 2: Spectral radiance of a deuterium lamp, measured at the source calibration facility at BESSY II (red) and at the MLS (green). Bottom: Ratio of the two data sets. The dotted line illustrates the combined relative measurement uncertainty. The red dots are values averaged across groups of emission lines.
A newly installed radiation comparator allows the calibration of radiation sources to be traced to the calculable synchrotron radiation of the Metrology Light Source (MLS) in the spectral range from 7 nm to 400 nm.
A wavelength-dispersive transfer system is used as a radiation comparator, since neither the radiation of the primary source standard MLS, nor that of the sources to be calibrated is monochromatic. This comparator can be displaced on air cushions in such a way that it can face either the calculable radiation of the MLS or the radiation of a radiation source to be calibrated. In each of these positions, the radiation source is always located at the same distance (approx. 10 m) (see Fig. 1).
The transfer system mainly consists of an ellipsoidal pre-mirror (which minimizes the source point of the radiation source at a 1:10 ratio and images it at the level of the entrance slit of a monochromator), the monochromator itself and diverse detectors. Six exchangeable vacuum dispersion gratings (3 vertical ones (NI geometry) and 3 grazing ones (GI geometry)) are available to cover the large spectral range from 7 nm to 400 nm. Different optical configurations for spectral partial ranges (i.e. different materials for the coating of mirrors and gratings) as well as different optical filters ensure the maximum possible spectral purity for monochromatization.
The first step of our work consisted in validating, by means of internal comparisons, the commercially relevant spectral range from 115 nm to 400 nm in which the main transfer sources used are deuterium lamps. For this purpose, different deuterium lamps – whose calibration was carried out by means of the facility available at BESSY II and was traceable to this electron storage ring – were characterized at the new facility at the MLS. In addition, a tungsten strip lamp, whose calibration was traced to a blackbody, was characterized at the new facility. Both measurements showed excellent agreement within the combined measurement uncertainties (see Fig. 2).
Publication:
R. Thornagel, R. Klein, S. Kroth, W. Paustian, M. Richter, “Validation of a new facility at the Metrology Light Source for the calibration of radiation sources in the wavelength range from116 nm to 400 nm”, Metrologia 51, 528–538 (2014)Contact:
R. Thornagel, 7.14, e-mail: Reiner.Thornagel(at)ptb.de
R. Klein, 7.14, e-mail: Roman.Klein(at)ptb.de