Here - PMOD/WRC

Calibration of Space Instrumentation in the Vacuum Ultraviolet
M. Richter, A. Gottwald, W. Paustian, F. Scholze, R. Thornagel, G. Ulm
Physikalisch-Technische Bundesanstalt, Berlin, Germany
Abstract. At the Physikalisch-Technische Bundesanstalt
(PTB), various radiometric techniques for the calibration
of space instrumentation with synchrotron radiation in the
spectral range from ultraviolet radiation to X-rays have
been developed and applied. In this context, the present
contribution gives an overview of PTB’s measurement
capabilities at the electron storage ring BESSY II. Recent
examples for the calibration of space instrumentation in
the vacuum ultraviolet are discussed.
Introduction
The Physikalisch-Technische Bundesanstalt (PTB) uses
synchrotron radiation at the electron storage ring BESSY
II for the calibration of radiation sources, detectors, and
spectrometers as well as for the characterization of optical
components in the spectral range from ultraviolet (UV)
radiation to X-rays (Klein et al. 2002). Most of the
measurements are based on two different primary
standards, BESSY II itself as primary source standard and
cryogenic radiometers as primary detector standards. They
allow radiometric calibrations to be performed with
relative uncertainties below 1 %. Many activities are
related to the calibration of space instrumentation for
extraterrestrial, solar, and astronomical missions, e.g. of
the space agencies NASA and ESA (Richter et al. 2005).
Calibration Techniques
BESSY II is used as a primary source standard of
calculable synchrotron radiation within the framework of
source-based radiometry. This method is applied, e.g., for
the calibration of transfer source standards, such as
deuterium lamps or hollow cathode (HC) plasma sources,
by comparison of the radiation with the help of a movable
spectrometer. PTB had established HC sources as transfer
standards in the vacuum-UV (VUV) spectral range from
13 nm to 125 nm for the calibration of space
Figure 1. The MOSES instrument within the vacuum tank at the
Rutherford Appleton Laboratory (RAL) during calibration by
RAL and PTB with the CDS calibration source.
instrumentation. Outstanding examples have been the
calibration of the SUMER and CDS telescopes of the Solar
and Heliospheric Observatory (SOHO). Recently, the CDS
calibration source has been used within a scientific
cooperation at the Rutherford Appleton Laboratory (RAL)
to characterize the EUV Imaging Spectrometer (EIS) for
the Solar B mission and NASA’s Multi-Order Solar EUV
Spectrograph (MOSES, Fig. 1).
Within the framework of detector-based radiometry, PTB
operates the cryogenic radiometers SYRES I and SYRES
II to measure the radiant power of spectrally dispersed
synchrotron radiation in absolute terms. It allows to
calibrate transfer detector standards such as semiconductor
photodiodes with low uncertainty. The corresponding
beamlines in the PTB laboratory at BESSY II cover the
wavelength range from 400 nm down to 0.12 nm. At the
same beamlines also reflectometry is performed, i.e. the
Figure 2. Spectral responsivity in the UV/VUV of different
solar-blind diamond photodetectors.
characterization of optical components by relative
measurements of reflected, transmitted, or diffracted
radiation with respect to the photon intensity incident on a
sample. In this context, PTB characterizes detection
systems and optics for various space instruments. As an
example, Fig. 2 shows spectral responsivity curves of
solar-blind diamond detectors which have been developed
within the framework of a scientific cooperation with the
Max Planck Institute for Solar System Resarch and the
Solar Orbiter Detector Development Program BOLD
(Blind to Optical Light Diamond). A first application of
these detectors is scheduled for the Lyman-alpha
Radiometer LYRA and the SWAP (Sun Watcher using APS
detectors and image Processing) instrument of ESA’s
PROBA II mission.
References
Klein, R., Krumrey, M., Richter, M., Scholze, F., Thornagel, R.,
Ulm, G., Synchrotron Radiation News, 15, No. 1, 23-29, 2002.
Richter, M., Gottwald, A., Scholze, F., Thornagel, R., Ulm, G.,
Advances in Space Research, 2005, in press.
Proceedings NEWRAD, 17-19 October 2005, Davos, Switzerland 89