The irradiation effects of multiple ultrafast shots of laser beams with estimated fluences of some tens of
mJ/cm<sup>2</sup> on a EUV Mo/Si multilayer have been studied. Irradiation damage has been induced by multiple shots of two
different lasers (100 fs 400 nm the first, 1.5 ns 46.9 nm the second). The study has been motivated by the need of
multilayer Mo/Si optics for the delay lines of the FEL source FERMI@Elettra, where these mirrors will be used to
reflect 100 fs pulses at 13 nm with a fluence of some mJ/cm<sup>2</sup>. The analysis has been performed by means of different
techniques as EUV and soft X-ray reflectivity, XPS, and Standing wave enhanced XPS. Simulations have been carried
on by means of an indigenously developed software OPAL (Optical Properties of Anisotropic Layers) for the
calculation of the absorbed energy by the stratified medium. AFM and SEM surface images have been also acquired. In
the irradiation at 400 nm, we observed a significant change in the multilayer performance at fluences of 100 mJ/cm<sup>2</sup> and
above with a significant reduction of reflectivity. Spectroscopic analysis allowed to correlate the decrease of reflectivity
with the degradation of the multilayer stacking, ascribed to Mo-Si intermixing at the Mo/Si interfaces of the first few
layers, close to the surface of the mirror. Preliminary tests have been also performed on the sample irradiated at 46.9
FERMI@Elettra is a Free Electron Laser (FEL) user facility currently under construction at Sincrotrone Trieste,
Italy. It will provide a spatial coherent transform-limited beam in the sub-ps regime, covering the wavelength
range from 100 nm to 3 nm with the goal of 1 nm (by using third harmonics). The transform-limited beam is
supposed to have a natural energy bandwidth of the order of 50-100 meV. Nevertheless, one of the three future
beamlines, the one dedicated to Low Density Matter (LDM) studies, needs a monochromator to clean the signal.
It must cover the whole wavelength range with eventual omission of the lower energy part. We will report the
design of a fixed included angle monochromator employing three gratings. The optical system will be described,
and particular attention will be given to the constraints like the pulse broadening, the focus displacement and, of
course, the flux. Engineering constraints and manufacturers tolerances also taken into account will be presented,
The FERMI@Elettra free electron laser (FEL) user facility is currently under construction at the Sincrotrone Trieste
laboratory in Trieste (Italy). It is a based on a seeded scheme that will provide an almost perfect transform limited beam
and fully spatial coherent. It will cover the wavelength range from 100 to about 3 nm and in a short future down to 1 nm
(by using higher harmonics). It is expected to be fully operative in the late summer of 2010. In this presentation we will
report the layout of the photon beam diagnostics section with the preliminary tests, the radiation transport system to the
experimental area, and the experimental hall facilities. A particular emphasis will be given to the optical solution and
constrains due to the need of preserving the wave front and to avoid damage on the different optical elements, including
slits, mirrors, gratings and all the diagnostic facilities. One of the main problems will be the necessity of using very large
grazing incidence angle (up to 45°) on multilayers and single coating mirrors. These elements are mandatory to perform
the transient grating experiments and to realize the delay lines, where time delay up to 1 nsec are required. This issue
poses a serious problem in terms of energy density delivered and adsorbed by the optics and great care must be taken
into the choice of the proper multilayer materials. Some studies on the reflectivity of multilayers and Carbon coated
mirrors will be reported as well as the diagnostic tools to monitor the quality of the optics in operative conditions.
The interest of the scientific community in the use of synchrotron radiation has become higher and higher with the improvement of instrumentation and with publication of better and better results. For this reason, the concept of standard beamline could not be used anymore, and a lot of solutions must be considered to satisfy the requests of the different users. A very important part of these "solutions" involves mirrors, gratings and crystals adopted to carry out the light from the source to the experimental chamber. In the last years, for instance, we have seen an increased interest for the mechanically deformable mirrors, as well as normal incidence mirrors (for IR or UV photons). From the point of view of the optical metrology, this implies the use of different methods and different instruments to guarantee the quality of the optics and consequently of the delivered photons. In this work, we compare the performance of two "state of the art" instruments, aimed at the non-contact measuring of optical surface profiles. The first one is an in house modified version of the Long Trace Profiler (LTP) developed for grazing incidence optics by P.Z. Takacs and Al. The second is a Fizeau like interferometer (a WYKO RTI 4100), primarily used for 2D mapping of surfaces. The aim of this paper is to outline when, according to our experience, an instrument is preferable with respect to the other, what are the limits of both and what kind of improvement could be made. Some examples will be reported. Spatial frequency, calibration and systematic errors will be compared and outlined.
The optical metrology laboratory of Elettra is equipped with some state of the art instruments for the characterization of high precision optical components for the UV and x-ray energy range. Among them, the most important is the Long Trace Profiler, which is capable of very accurate measurement of the shape of long aspheric mirrors. It is a direct slope measurement device, able to measure slope errors below the mrad level, once properly operated and calibrated. Our device is an LTP II model dating back to 1992. Nevertheless, it has been deeply in house modified during these years. Recently we have assembled a second optic head (OH) that could be used in spite of (or together with) the original one. This second OH works without folding mirrors and uses a set of short focal distance Fourier Transform lenses. The absence of folding mirrors reduces the source of systematic errors and the use of short focal distance lenses increases the angular acceptance of the instrument. This fact is particularly useful when short radius of curvature mirrors as well as high groove density variation gratings have to be measured. Some other modifications have been made to help the stitching procedure or to change the measurement set-up. These will be described in details.
A diffraction plane grating with single-layer coating able to reach photon energy up to 3 keV (possibly 4 keV) will be adopted at the TwinMic beamline at ELETTRA. The TwinMic beamline will exploit the unique capabilities of the novel twin X-ray microscope, which combines scanning and full-field imaging microscopes in a single multipurpose end-station. The needed moderate energy resolving power will be provided by a variable included angle plane grating monochromator working in a collimated light mode (also known as collimated SX700). This configuration allows freely selection of the incidence and diffraction angles at the grating, therefore permitting, for instance, to optimize its efficiency. This monochromator uses two mechanically ruled gratings to cover a very wide working energy range. The first grating goes from 150 eV to 1000 eV while the second goes from 600 eV to 4 keV. The two gratings were ruled using the CARL ZEISS Grating Ruling Engine GTM6, which is operated under interferometric control. The high-energy plane grating, with a line density of 600 lines/mm, has a triangular profile with a blaze angle of 0.4° and an apex angle of 178°. The grating profile is ruled on a silicon substrate and is covered with a 30 nm thick gold film. The small blaze angle permits one to work in blaze condition at very grazing incidence angles and therefore allows reaching high photon energies not accessible by means of conventional gratings.
The Long Trace Profiler (LTP) has proved to be one of the major metrological aids for the characterization of synchrotron radiation optics. Currently the optical components installed at the beamlines face higher and higher demands, requiring a precise calibration and control of the measuring conditions. One important parameter to be considered while scanning is the temperature drifts afflicting the measuring sessions. We will review our experiences about the influence of this parameter on the LTP ability in measuring very accurate optical surfaces. It is possible to discriminate at least four major sources of perturbations due to temperature changes: air turbulence, deformation in the optical train inside the LTP optics head, deformation of the optical surface under test (SUT) and deformation of the holders of the SUT itself. Some addresses on the curing of these perturbations can be obtained.
Two bendable elliptical cylinder mirrors arranged in a Kirkpatrick-Baez (KB) geometry are installed at the Nanospectroscopy beamline at ELETTRA for refocusing soft x-rays provided by an APPLE II type undulator. This achromatic focusing device delivers the beam to a micrometer-scale, high photon density spot, which is the source for a Spectroscopic Photoemission and Low Energy Electron Microscope (SPELEEM). A similar second pair of KB mirrors will refocus the monochromated light in a second experimental station for a different imaging microscope. These four mirrors, developed by S.E.S.O., are manufactured from Glidcop™ in a U shaped design with 380mm length. They are electroless nickel plated for polishing and are bent into an elliptical shape applying two unequal end moments. They have been tested in the optical metrology laboratory of ELETTRA using an in-house modified version of the Long Trace Profiler (LTP): the surface slope variation as a function of the bender actuators has been measured to characterize the behavior of the bender mechanism and the accuracy of the elliptical profiles that can be achieved. Both metrological optical data and x-rays performances show the achievement of a microradian accuracy for the different profiles in which each mirror can be bent and the possibility to vary the focal distance by about 30-40% around the nominal value.
The optics metrology laboratory of Sincrotrone Trieste is operating some non-contact interferometers since 1992, in order to characterise slope errors, figure deviations and surface roughness for synchrotron radiation optics (SR) up to 1.4 metres in length, prior to their installation at the beamlines. During these years, prompted by the increasing needs of experimentalists, the requirements for FEL and SR optical components have become more and more severe. We will review here the history of our measurements during the last nine years, comparing the match between the given specifications and measured optical quality of the delivered items. We will also illustrate which has been the evolution of the main optical concepts, that has ultimately boosted the suppliers to develop machining and testing methods to a novel level of accuracy.