The At-Wavelength Metrology Facility at BESSY-II Helmholtz-Zentrum

The At-Wavelength Metrology Facility at BESSY II is dedicated to short-term characterization of novel UV, EUV and XUV optical elements, such as di raction gratings, mirrors, multilayers and nano-optical devices like re ection zone plates. It consists of an Optics Beamline PM-1 and a Reectometer in a clean-room hutch as a xed end station. The bending magnet Beamline is a Plane Grating Monochromator beamline (c-PGM) equipped with an SX700 monochromator. The beamline is specially tailored for e cient high-order suppression and stray light reduction. The versatile 11-axes UHV-Re ectometer can house life-sized optical elements, which are fully adjustable and of which the re ection properties can be measured in the full incidence angular range as well as in the full azimuthal angular range to determine polarization properties.


Introduction
The At-Wavelength Metrology Facility (Schäfers et al., 2016) consists of an Optics Beamline PM-1 (Sokolov et al., 2014) and a Re ectometer (Eggenstein et al., 2014(Eggenstein et al., , 2013) ) as a xed end station in a cleanroom surrounding.It is dedicated to at-wavelength characterization and calibration of the in-house produced di raction gratings and nano-optical devices as well as of mirrors and multilayer systems.It is coupled to a versatile 4-circle UHV-Re ectometer as a permanent end station which is located in a moderate clean-room hutch and which allows to carry out Re ectometry experiments on a very high precision level.The Plane Grating Monochromator beamline attached to a bending magnet is operated in collimated light (c-PGM) (Follath, 2001).The SX700 monochromator is equipped by new blazed gratings of our own production.The beamline is matched to re ectometry requirements: Over the large operating range from 10 to 2000 eV this bending magnet beamline has very high spectral purity achieved by (1) a four-mirror arrangement of di erent coatings which can be inserted into the beam path at di erent angles and (2) by absorber lters for high order suppression.Stray light and scattered radiation is removed e ciently by in-situ exchangeable apertures and slits.The incident beam has a low divergence and a moderate energy resolution.The main feature of the 11-axes Re ectometer is the possibility to incorporate large samples (up to 4 kg and 360 mm in length) into the UHV-chamber.The samples are adjustable within six degrees of freedom by a novel compact UHV-tripod system.The re ectivity can be measured in the full incidence angular range of 90°for both s-and p-polarization geometry by azimuthal rotation of the sample around the beam direction.A variety of in-situ exchangeable detectors with di erent angular resolution and dynamic range are available.

Instrument Applications
• At Wavelength metrology (quality control) of UV, EUV and XUV-optics: Multilayers, mirrors, gratings, zoneplates, crystals, thin lms • Re ectivity, e ciency, transmission, di raction • Scattering (specular -non specular) • Non-destructive investigation and characterisation of optical surfaces • In depth analysis of internal material structure including buried layers and interfaces • Optical constants derived from accurate re ectivity measurements

Source
The source is the bending magnet D1.1 with the following parameters: The optical layout of the beamline is described in in Figure 1.M1 is a toroidal mirror which collimates the light vertically and focusses it approximately 1:1 horizontally.The plane mirror M2 is used to vary the deviation angle at the plane grating PG (SX700 monochromator with 600 and 1200 l/mm, respectively (Schäfers et al., 2016).Vertically, the di racted light is focused onto the exit slit by the cylindrical mirror M3.The subsequent astigmatic refocusing of horizontal and vertical focus onto the sample position in the re ectometer is performed by the toroidal mirror M4.Two systems for high order suppression provide a wide exibility for light shaping upstream of the re ectometer: 1.The high order suppression system (HiOS) is a four mirror system with di erent coatings which can be inserted into the beam under selectable incidence angles to freely determine the highenergy cut-o .2. The Filter and Slit Unit (FSU) houses a set of 12 absorber lters and slits and pinholes of di erent sizes upstream and downstream the lters for beam shaping and stray light reduction.

Figure 1 :Figure 2 :
Figure 1: Optical layout of beamline PM-1 with Re ectometer end station

Figure 3 :
Figure 3: The clean-room hutch at the experimental oor of BESSY-II with the M4-mirror chamber, the Filter and Slit Unit (FSU) and the Re ectometer inside (Light comes from the right side).

Table 1 :
BESSY II source characteristics of the dipole section DIP 1.1 4 Optics Beamline PM-1: Optical Design