F. Senf

A NOVEL UNDULATOR-BASED PGM BEAMLINE FOR CIRCULARLY POLARISED SYNCHROTRON RADIATION AT BESSY II

Abstract We present the design of a beamline for circularly polarised radiation from an elliptical double undulator to be built at BESSY II. The UE56 undulator of Sasaki type will emit simultaneously two angularly separated circularly polarised beams of opposite helicities. The undulator will, through emissions in first, third and fifth harmonics, provide circularly polarised radiation in the energy range 89–1328 eV. The beamline essentially consists of a plane grating monochromator (PGM) working with collimated light and employing only one set of optical elements for steering and monochromatising the two beams. A high energy resolution from 6000 to 13 000 can be achieved at a flux between about 10 10 and 10 12 photon/s, respectively. The helicity of circular polarisation can be switched dynamically in the beamline at a high rate (>100 Hz) by use of a suitable chopper. The degree of circular polarisation of the source ranging from 78 to 100% is well preserved by the beamline. In the worst case — at the lowest energy — the degree of polarisation is reduced by 5%. In the higher energy range above 357 eV the input degree of circular polarisation can even be increased by the beamline.

A plane-grating monochromator beamline for the PTB undulators at BESSY II.

At the BESSY II storage ring, the Physikalisch-Technische Bundesanstalt (PTB) will operate insertion devices dedicated to radiometric use. One branch of the appendant beamline system will be equipped with a grazing-incidence monochromator, described here. The monochromator concept is based on a plane grating operated in parallel light; therefore exact focusing is maintained for all photon energies irrespective of the angular setting at the grating. The monochromator has been optimized for small higher-order transmittance and high power throughput, as required by radiometric applications in the wide photon energy range from 20 eV to 1900 eV.

First results of the soft X-ray microfocus beamline U41-PGM

Abstract We present the first experimental data obtained from the new microfocus beamline U41-PGM recently put into operation. The optical layout of the beamline has been designed to conserve the high spectral brillance of the undulator source. The beamline consists of a collimated plane grating monochromator (PGM) and a subsequent refocusing stage. A toroidal mirror is used for refocusing onto the sample surface. With the 600 1/mm grating an absolute photon flux between 10 12 and 10 13 photons per second has been recorded over the whole energy range. Although the monochromator is not designed to deliver highest energy resolution, a resolving power of up to 6000 at the nitrogen K-edge has been obtained recently. The fixfocus constant c ff is variable in a wide range. According to the experimental requirements it can be set to select either high photon flux or energy resolution.

The at-wavelength metrology facility for UV- and XUV-reflection and diffraction optics at BESSY-II

A new optics beamline and a versatile 11-axes UHV-reflectometer for at-wavelength characterization of real life-sized UV- and XUV-reflection gratings and other (nano-) optical elements has been set up and is in operation at BESSY-II. Azimuthal rotation of samples allows for reflectometry and polarimetry measurements in s- and p-polarization.

An XUV optics beamline at BESSY II

The design for a new XUV-Optics Beamline is presented. The collimated plane grating monochromator (PGM-) beamline at a bending magnet is setup at the BESSY-II synchrotron radiation facility within the framework of the blazed-grating production facility. Coupled to a versatile four-circle (ten axes) UHV- reflectometer as a permanent end station the whole setup is dedicated to at-wavelength characterization and calibration of the in-house produced precision gratings and novel nano-optical devices as well as mirrors, multilayered systems etc. It is also open to external projects employing reflectometry, spectroscopy or scattering techniques. According to its purpose, this beamline has specific features, such as: very high spectral purity, provided by two independent high order suppression systems, an advanced aperture system for suppression of stray light and scattered radiation, a broad energy range between 10 eV and 2000 eV, small beam divergence and spot size on the sample. Thus this Optics Beamline will become a powerful metrology tool for reflectivity measurements in s- or p-polarisation geometry with linearly or elliptically polarized light on real optics up to 360 mm length and 4 kg weight.

THE BESSY CONSTANT LENGTH ROWLAND CIRCLE MONOCHROMATOR

Abstract The BESSY constant length Rowland circle monochromator (CL-RCM) was designed for high resolution spectroscopy in the soft x-ray region. The principle is based on a spherical grating/plane mirror assembly, which is moved between the fixed entrance and exit slits for photon energy scan. By this means, the Rowland conditions are fulfilled over an energy range of 270–590 eV, yielding excellent resolution. Fast beamline optimization and, most important, the efficient use of beamtime in routine user operation is considerably enhanced by the newly implemented on-the-fly measuring mode, as demonstrated by the first results obtained on the beamline.

A new UHV angle encoder for high-resolution synchrotron radiation monochromators.

The high precision of 0.1 arcsec required for the positioning of optical elements in new two-axes monochromators at the undulator beamlines at BESSY II has led to the development of UHV-compatible high-precision angle encoders. Mounted directly on the rotation axes, they provide substantial advantages over measuring systems connected outside the vacuum vessel. Making use of a fast closed-loop control system, an accuracy of 0.1 arcsec at a resolution of less than 0.01 arcsec has been experimentally verified.

Installation of a technological center for highly efficient optical gratings at Helmholtz-Zentrum Berlin (HZB)

In 2009 Carl Zeiss stopped the manufacture of precision gratings. All users of their gratings were very concerned about this decision, since they all need precision gratings for their experiments. One of the institutes of the HZB, the Institute for Nanometer Optics and Technology (INT), has extensive experience in micro fabrication (technology group). In spring 2010, HZB decided to take over the old C. Zeiss grating fabrication and build up its own technology center for grating fabrication. In March 2010, the INT applied to the Senate of Berlin for funding for our project from the European Regional Development Fund (ERDF). In October 2010, HZB received an approval of its application from the Senate of Berlin (contract No 20072013 2/43). Using this governmental support, HZB will install all necessary equipment and processes to fulfill these demands until end of 2013.

At-wavelength metrology facility for soft X-ray reflection optics.

A new Optics Beamline coupled to a versatile UHV reflectometer is successfully operating at BESSY-II. It is used to carry out at-wavelength characterization and calibration of in-house produced gratings and novel nano-optical devices as well as mirrors and multilayer systems in the UV and XUV spectral region. This paper presents most recent commissioning data of the beamline and shows their correlation with initial beamline design calculations. Special attention is paid to beamline key parameters which determine the quality of the measurements such as high-order suppression and stray light behavior. The facility is open to user operation.

STARS - a two-stage high-gain harmonic generation FEL demonstrator

BESSY is proposing a demonstration facility, called STARS, for a two-stage high-gain harmonic generation free electron laser (HGHG FEL). STARS is planned for lasing in the wavelength range 40 to 70 nm, requiring a beam energy of 325 MeV and peak current of 500 A. The facility consists of a normal conducting gun, three superconducting TESLA-type acceleration modules modified for CW operation, a single stage bunch compressor and finally a two-stage HGHG cascaded FEL. This paper describes the faciliy layout and the rationale behind the operation parameters.