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