The Extreme Ultraviolet Imager (EUI) instrument for the Solar Orbiter mission will image the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm) spectral ranges. The development of the EUI instrument has been successfully completed with the optical alignment of its three channels’ telescope, the thermal and mechanical environmental verification, the electrical and software validations, and an end-toend on-ground calibration of the two-units’ flight instrument at the operating wavelengths. The instrument has been delivered and installed on the Solar Orbiter spacecraft, which is now undergoing all preparatory activities before launch.
Space-based missions exploring the spectral ranges of extreme- and vacuum-ultraviolet radiation (EUV, VUV) require on-ground, at-wavelength calibration of their detectors and imaging systems. With the use of monochromatized synchrotron radiation, traceable calibrations regarding the spectral responsivity of the instruments can be provided. A dedicated vacuum chamber is used to house space instruments up to 100 kg weight for calibration measurements. Currently, the development of calibration procedures for the EUI instrument of the Solar Orbiter is still underway.
SPICE is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths, 70.4 – 79.0 nm and 97.3 -
104.9 nm. It is a facility instrument on the Solar Orbiter mission. SPICE will address the key science goals of Solar
Orbiter by providing the quantitative knowledge of the physical state and composition of the plasmas in the solar
atmosphere, in particular investigating the source regions of outflows and ejection processes which link the solar surface
and corona to the heliosphere. By observing the intensities of selected spectral lines and line profiles, SPICE will derive
temperature, density, flow and composition information for the plasmas in the temperature range from 10,000 K to
10MK. The instrument optics consists of a single-mirror telescope (off-axis paraboloid operating at near-normal
incidence), feeding an imaging spectrometer. The spectrometer is also using just one optical element, a Toroidal Variable
Line Space grating, which images the entrance slit from the telescope focal plane onto a pair of detector arrays, with a
magnification of approximately x5. Each detector consists of a photocathode coated microchannel plate image
intensifier, coupled to active-pixel-sensor (APS). Particular features of the instrument needed due to proximity to the Sun
include: use of dichroic coating on the mirror to transmit and reject the majority of the solar spectrum, particle-deflector
to protect the optics from the solar wind, and use of data compression due to telemetry limitations.
In this paper, the optical and electrical performance of a newly developed silicon photodiode based on pure boron CVD
technology (PureB-diodes) is introduced. Due to their extremely shallow p-n junction, with the depletion zone starting
only a few nanometers below the surface, and nm-thin pure-boron-layer coverage of the anode surface, PureB-diodes
have so far demonstrated the highest reported spectral responsivity in all sub-visible ultraviolet (UV) ranges: DUV (deep
ultraviolet), VUV (vacuum ultraviolet) and EUV (extreme ultraviolet), covering a spectrum from 220 nm down to few
nanometersMoreover, the measured responsivity at 13.5 nm wavelengths (EUV) approaches the theoretical
maximum (~0.27A/W). PureB-diodes also maintain excellent electrical characteristics, with saturation-current
values typical for high-quality silicon diodes, and a high breakdown voltage. Experimental results have demonstrated the
extremely high radiation hardness of PureB-diodes when exposed to high EUV radiant exposures in the order of a few
hundred kJ/cm<sup>2</sup>. No change in the responsivity is observed within the experimental uncertainty. In the more
challenging DUV and especially VUV ranges, PureB-diodes demonstrate a slight initial drop of responsivity (1 to 2%),
after which they stabilizes their performance.
For the eROSITA X-ray telescope, which is planned to be launched in 2012, detectors were developed and
fabricated at the MPI Semiconductor Laboratory. The fully depleted, back-illuminated pnCCDs have an ultrathin
pn-junction to improve the low-energy X-ray response function and quantum efficiency. The device thickness of
450 μm is fully sensitive to X-ray photons yielding high quantum efficiency of more than 90% at photon energies of
10 keV. An on-chip filter is deposited on top of the entrance window to suppress visible and UV light which would
interfere with the X-ray observations. The pnCCD type developed for the eROSITA telescope was characterized
in terms of quantum efficiency and spectral response function. The described measurements were performed in
2009 at the synchrotron radiation sources BESSY II and MLS as cooperation between the MPI Semiconductor
Laboratory and the Physikalisch-Technische Bundesanstalt (PTB). Quantum efficiency measurements over a
wide range of photon energies from 3 eV to 11 keV as well as spectral response measurements are presented. For
X-ray energies from 3 keV to 10 keV the quantum efficiency of the CCD including on-chip filter is shown to be
above 90% with an attenuation of visible light of more than five orders of magnitude. A detector response model
is described and compared to the measurements.
For the determination of absolute photon fluxes from high-intense, pulsed VUV and soft X-ray sources like free-electron lasers, a gas-monitor detector system based on the photoionization of rare gases was developed. A prototype system was successfully used for the characterization of VUV free-electron laser radiation at the TESLA test facility (phase 1) in Hamburg. Pulse-resolved measurements at peak powers of more than 100 MW at a wavelength of 87 nm were demonstrated. In order to provide a photon-beam diagnostic of VUV-FEL radiation during phase 2 of the TTF project, a set of four new detectors has been constructed, based on the prototype. The new detector system can be used not only for intensity measurement and monitoring, but also for measuring the beam position. The detector set was calibrated in the Radiometry Laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II. The calibration was performed using spectrally-dispersed synchrotron radiation at low intensities and a semiconductor photodiode as a transfer standard.
Characterization of optical materials and components is one of the major tasks for the Radiometry Laboratory of the Physikalisch-Technische Bundesanstalt, Germany's national metrology institute, at the synchrotron radiation source BESSY II. Using spectrally dispersed synchrotron radiation, reflectometry measurements have been performed on highly pure CaF2 crystals in the VUV spectral region between 90 nm and 130 nm wavelength in the vicinity of the absorption edge. Here, the optical constants are influenced by an excitonic resonance directly correlated to the recently found anisotropy of the crystal at 157-nm wavelength. To investigate temperature-dependent effects, the reflectometer sample holder has been equipped with a heater/cooler stage, which currently enables measurements at stable temperatures in the range between -50° C and 80° C.
Solar ultraviolet imaging instruments in space pose most demanding requirements on their detectors in terms of dynamic range, low noise, high speed, and high resolution. Yet UV detectors used on missions presently in space have major drawbacks limiting their performance and stability. In view of future solar space missions we have started the development of new imaging array devices based on wide band gap materials (WBGM), for which the expected benefits of the new sensors - primarily visible blindness and radiation hardness - will be highly valuable. Within this initiative, called “Blind to Optical Light Detectors (BOLD)”, we have investigated devices made of AlGa-nitrides and diamond. We present results of the responsivity measurements extending from the visible down to extreme UV wavelengths. We discuss the possible benefits of these new devices and point out ways to build new imaging arrays for future space missions.
Degradation of EUV optics during irradiation is a crucial topic as regards lifetime and performance in EUV lithography. To simulate irradiation conditions for future lithography tools, PTB (the German national metrology institute) operates two dedicated beamlines at the electron storage ring BESSY II. Both, undispersed undulator radiation from an EUV optimized undulator as well as focused and filtered bending magnet radiation can be used. Both beamlines provide EUV radiation with power densities of several mW / mm<SUP>2</SUP>. A dedicated irradiation chamber with sample load lock and differential pumping allows components such as substrates, multilayer mirrors or filters to be exposed to EUV radiation under different vacuum conditions. At the same laboratory, high-accuracy EUV reflectometry can be performed for proximate assessment of the resulting performance.
The development of EUV lithography, has made high-accuracy at-wavelength metrology necessary. Radiometry using synchrotron radiation has been performed by the German national metrology institute, the Physikalisch-Technische Bundesanstalt (PTB), for almost 20 years. Recently, PTB has set up four new beamlines for EUV metrology at the electron storage ring BESSY II. At a bending magnet, a monochromator for soft X-ray radiometry is routinely used for reflectometry and detector characterisation. A reflectometer designed for mirrors up to 550 mm in diameter and 50 kg in mass will be operational in January 2002. Detector characterisation is based on a primary detector standard, a cryogenic electrical substitution radiometer. Measuring tools for EUV source characterisation are calibrated on this basis. Detector testing at irradiation levels comparable to the anticipated conditions in EUV tools is feasible at a plane grating monochromator, installed at an undulator optimised for EUV radiation. A test beamline for EUV optics alignment and system metrology has been installed, using undispersed undulator radiation. Bending magnet radiation is available at a station for irradiation testing. A focusing mirror collects a radiant power of about 10 mW within the multilayer bandwidth and a 1 mm² focal spot.