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Comparison of the PTB Radiometric Scales for UV Source Calibration<br />
R. Friedrich, J. Hollandt, W. Paustian, M. Richter, P. Sperfeld, R. Thornagel<br />
Physikalisch-Technische Bundesanstalt, Braunschweig and Berlin, Germany<br />
Abstract. The radiometric scales of the<br />
Physikalisch-Technische Bundesanstalt for the calibration<br />
of radiation sources in the ultraviolet have been compared.<br />
The work refers to the measurement of spectral radiant<br />
intensity, spectral irradiance, and spectral radiance of<br />
deuterium and tungsten lamps in the wavelength range<br />
from 120 nm to 400 nm. The scales are based on<br />
calculable temperature radiation of black body radiators as<br />
primary source standards as well as calculable synchrotron<br />
radiation of the electron storage rings BESSY I and<br />
BESSY II. As a result, the agreement is within a few<br />
percent, i.e. well within the combined measurement<br />
uncertainties.<br />
Introduction<br />
The Physikalisch-Technische Bundesanstalt (PTB) has<br />
realized different radiometric scales for source calibration<br />
by spectrally dispersed measurements. Within the<br />
framework of applied radiometry, spectral irradiance<br />
calibrations are performed in the ultraviolet (UV), visible<br />
(VIS), and infrared (IR) based on calculable<br />
high-temperature black body radiation (Sperfeld et al.<br />
1998). Black body radiators are used as primary source<br />
standards also within the framework of high-temperature<br />
physics to measure, e.g., spectral radiance of UV, VIS, and<br />
IR sources (Friedrich et al. 2000). Photon metrology at<br />
shorter wavelengths, i.e. in the spectral range of UV,<br />
vacuum-UV (VUV) radiation, and X-rays, is performed<br />
using calculable synchrotron radiation in the PTB<br />
laboratory at the electron storage ring BESSY II. Within<br />
the framework of UV and VUV radiometry, deuterium<br />
(D2) lamps are calibrated in the wavelength range from<br />
120 nm to 400 nm with respect to spectral radiant intensity<br />
and spectral radiance using BESSY II as a primary source<br />
standard (Richter et al. 2003). In the UV, the different<br />
scales overlap allowing a radiometric comparison. The<br />
present work also includes measurements performed at the<br />
former storage ring BESSY I which was shut down in<br />
1999.<br />
Results<br />
Fig. 1 summarizes the results. The red lines represent<br />
the ratio of spectral radiant intensity of D2 lamps as<br />
measured at BESSY I with respect to BESSY II. The<br />
results were obtained by the calibration of two different<br />
lamps in the wavelength range from 120 nm to 165 nm and<br />
from 165 nm to 400 nm, respectively, with different<br />
spectral resolution. Within the regime of continuous<br />
emission of a D2 lamp above 180 nm, the agreement is<br />
perfect, i.e. better than 1 %. The increasing variations of<br />
the measured ratio towards shorter wavelengths are due to<br />
the D2 lamp emission consisting more and more of a<br />
discrete distribution of numerous spectral lines. This<br />
makes the measurements more sensitive to the<br />
reproducibility of the wavelength scale of the spectrometer<br />
used and increases the measurement uncertainties. The<br />
relative standard uncertainties (k=1) for the BESSY II<br />
calibrations with respect to spectral radiant intensity are<br />
indicated by the dashed lines in Fig. 1.<br />
The green data points in Fig. 1 represent the ratio of<br />
spectral irradiance of a standard D2 lamp as measured<br />
within the framework of applied radiometry, traceable to<br />
black body radiation, with respect to measurements<br />
performed at BESSY II. For this comparison, the BESSY<br />
II spectral radiant intensity data were divided by the square<br />
of the distance for the black body irradiance measurements<br />
and, by that, transformed also into spectral irradiance<br />
values. The excellent agreement indicates the latter<br />
transformation to be valid for the standard D2 lamp used<br />
Figure 1. Comparison of radiometric scales and primary source<br />
standards of PTB in the UV and VUV: BESSY I vs. BESSY II via<br />
spectral radiant intensity of deuterium lamps (red),<br />
high-temperature black body radiator vs. BESSY II via spectral<br />
irradiance of a deuterium lamp (green), high-temperature black<br />
body radiator vs. BESSY II via spectral radiance of a tungsten<br />
ribbon lamp (blue). The dashed lines represent the standard<br />
uncertainty range (k=1) of the BESSY II calibrations.<br />
which may be regarded as a point source for the<br />
measurement geometries applied.<br />
The blue data points in Fig. 1, finally, represent the ratio of<br />
spectral radiance of a standard tungsten ribbon lamp as<br />
measured within the framework of high-temperature<br />
physics, traceable to black body radiation, with respect to<br />
corresponding measurements performed at BESSY II. The<br />
agreement is better than 2 % which is in the order of<br />
magnitude of non-uniformities in the emission along the<br />
tungsten band.<br />
References<br />
Sperfeld P., Metzdorf J., Galal Yousef S., Stock K.D., Möller W.,<br />
Metrologia, 35, 267, 1998.<br />
Friedrich, R., Fischer, J., Metrologia, 37, 539, 2000.<br />
Richter, M., Hollandt, J., Kroth, U., Paustian, W., Rabus, H.,<br />
Proceedings NEWRAD, 17-19 October 2005, Davos, Switzerland 333