For more than 25 years, the Physikalisch-Technische Bundesanstalt has been strongly engaged in the field of metrology using synchrotron radiation. In Berlin, this research programme started together with the user operation of the electron storage ring BESSY I in the early 1980s. At the beginning, the work was focused on fundamental radiometry, i.e. using the storage ring as a primary radiation source standard and operating beamlines for source and detector calibration in the vacuum ultraviolet spectral range. Meanwhile, at the electron storage rings BESSY II and Metrology Light Source in Berlin-Adlershof, the activities have been extended to a broad range of fundamental and applied photon metrology in the range from the far infrared to hard X-rays, including methods like cryogenic radiometry, reflectometry and X-ray fluorescence spectroscopy. In the present review, we give a short historical introduction to this work, describe our laboratories and the basic radiometric principles, and present examples of recent applications, largely performed within the framework of scientific cooperations with external partners from industry and research. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A quarter-century of metrology using synchrotron radiation by PTB in Berlin

We investigate the influence of the Mo-layer thickness on the EUV reflectance of Mo/Si mirrors with a set of unpolished and interface-polished Mo/Si/C multilayer mirrors. The Mo-layer thickness is varied in the range from 1.7 nm to 3.05 nm. We use a novel combination of specular and diffuse intensity measurements to determine the interface roughness throughout the multilayer stack and do not rely on scanning probe measurements at the surface only. The combination of EUV and X-ray reflectivity measurements and near-normal incidence EUV diffuse scattering allows to reconstruct the Mo layer thicknesses and to determine the interface roughness power spectral density. The data analysis is conducted by applying a matrix method for the specular reflection and the distorted-wave Born approximation for diffuse scattering. We introduce the Markov-chain Monte Carlo method into the field in order to determine the respective confidence intervals for all reconstructed parameters. We unambiguously detect a threshold thickness for Mo in both sample sets where the specular reflectance goes through a local minimum correlated with a distinct increase in diffuse scatter. We attribute that to the known appearance of an amorphous-to-crystallization transition at a certain thickness threshold which is altered in our sample system by the polishing.

Interface morphology of Mo/Si multilayer systems with varying Mo layer thickness studied by EUV diffuse scattering.

The term metrology refers to the art and science of measurement. In the last three hundred years approaches and tools have been developed that allow for precise and reliable measurements with known measurement uncertainty in a multitude of disciplines in physics and technology. Trust in measurement results, comparability and interoperability are crucial for technology in everyday life. With the advent of THz science and technology new sophisticated measurement techniques have been developed that allow for insights that cannot be obtained otherwise. By now commercial systems making use of THz radiation are appearing on the market and the question of the reliability of measurements becomes increasingly important.

THz metrology

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.

Quantum efficiency measurements of eROSITA pnCCDs

The Physikalisch‐Technische Bundesanstalt (PTB), the German national metrology institute, has set up the low‐energy electron storage ring Metrology Light Source (MLS) in close cooperation with the Helmholtz‐Zentrum Berlin (HZB, formerly BESSY). This new storage ring has been in regular user operation since April 2008 and is dedicated to synchrotron‐radiation‐based metrology and technological developments in the far‐IR/THz, IR, UV, VUV and EUV spectral range. The MLS has a double‐bend‐achromate lattice structure, injection is from a 105 MeV racetrack microtron. The electron energy can be ramped to any value from 105 MeV up to 630 MeV and the electron beam current covers the range from one stored electron (1 pA) up to 200 mA. The MLS is the first electron storage ring optimized for the generation of coherent synchrotron radiation, based on an electron bunch shortening mode. In this mode, MLS delivers coherent radiation in the far‐IR/THz spectral range with enhanced intensity as compared to the normal mode of operation. Several beamlines are in operation or in construction, including one undulator beamline, bending magnet beamlines for the calibration of radiation sources and detectors and for reflectometry, an EUV metrology beamline and three IR/THz beamlines.

http://rupac2006.inp.nsk.su/ready/mono06.pdf

Status of the Metrology Light Source

The Physikalisch-Technische Bundesanstalt (PTB) is currently constructing a low-energy electron storage ring in the close vicinity of BESSY II where PTB operates a laboratory for synchrotron-radiation-based metrology, mainly in the X-ray spectral region. The new storage ring, which is called ‘Metrology Light Source’ (MLS), will mainly be dedicated to radiometry and technological development in the UV, VUV and EUV spectral range and will thus fill the gap in the spectral range that has opened up since the shut-down of BESSY I. Moreover, the MLS will deliver intense radiation in the IR and FIR/THz spectral range. The MLS can be operated with parameters optimized for special calibration tasks, which, at a multi-user facility such as BESSY II, is rarely possible. The electron energy can be tuned in the range from 200 MeV up to 600 MeV and the electron beam current can be adjusted from 1 pA (single electron) up to 200 mA. All relevant storage ring parameters can be measured with high accuracy, thus making the MLS a source of calculable synchrotron radiation, i.e. a primary source standard. The MLS is designed in close co-operation with the BESSY GmbH, construction has started in the autumn of 2004 and user operation is scheduled to begin in 2008.

The Metrology Light Source – The new dedicated electron storage ring of PTB ☆

The Physikalisch‐Technische Bundesanstalt (PTB) is currently constructing a low‐energy electron storage ring in the close vicinity of BESSY II where PTB operates a laboratory for synchrotron‐radiation‐based metrology, mainly in the X‐ray spectral region. The new storage ring, which will be called ‘Metrology Light Source’ (MLS), will mainly be dedicated to metrology and technological development in the UV, EUV and VUV spectral range and will thus fill the gap in the spectral range that has opened up since the shut‐down of BESSY I. Moreover, the MLS will deliver intense radiation in the IR and FIR/THz spectral range. The MLS can be operated with parameters optimized for special calibration tasks, which, at a multi‐user facility such as BESSY II is rarely possible. The electron energy can be tuned in the range from 200 MeV up to 600 MeV and the electron beam current can be adjusted from 1pA (single electron) up to 200 mA. All relevant storage ring parameters can be measured with high accuracy, thus making th...

The Metrology Light Source — the New Dedicated Electron Storage Ring of PTB

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The Metrology Light Source – The new dedicated electron storage ring of PTB ☆

The Metrology Light Source — the New Dedicated Electron Storage Ring of PTB