Spectroscopic experiments requiring the knowledge of the specific state of light polarization for synchrotron radiation, high-order laser harmonics and free-electron lasers are increasing in the recent years. Correspondingly, there has been an increasing demand for systems to measure polarization in the extreme ultraviolet (XUV) and soft X-ray (SX) regions. Polarization can be measured at a specific wavelength through the use of polarizers based on multilayer coatings, that are almost routinely available. The measurement on a broad band requires to operate at grazing incidence with metallic coatings. It is here presented the design and performances of a reflection polarimeter to be used in the 50-100 eV region with transition metal-coated optics. With respect to standard polarimeters, based on gold-coated optics, the presented coatings gives higher flux and higher contrast between phase and reflectivity responses for s- and p-polarized light. The optical and mechanical design of the polarimeter and the estimated throughput are discussed.
In this paper, we will present the measurements of diffraction efficiency of commercially available replica reflection gratings which are applied to the realization of monochromators for soft X-rays in the classical and off-plane geometry. The efficiency curves for different blaze wavelengths has been measured at the Circular Polarization beamline of the ELETTRA Synchrotron (Italy) and simulated with GSolver, which is a full vector implementation of a class of algorithms known as Rigorous Coupled Wave Analysis (RCWA). Aim of the measurements is the comparison between the two diffraction geometries when used for the realization of instruments with ultrafast response. The advantages and drawbacks of both configurations when applied to the spectral selection of ultrafast pulses below 10 nm are discussed.
The design and realization of a plane-grating monochromator mainly intended for high-energy resolution in the extreme-ultraviolet and soft-X-ray spectral regions is presented. The principal application is the spectral selection of high-order laser harmonics generated in gas combined with the possibility to achieve sub-20-meV bandwidth, approaching synchrotron-like beamlines resolution performances. This geometry has three optical elements: a uniform-line-spaced plane grating illuminated by the converging light coming from a focusing cylindrical mirror and an additional plane mirror that is needed to change the grating subtended angle to keep the system in focus on a fixed slit. The parameters of the focusing mirror are determined to introduce a coma that compensates for the coma given by the grating. A monochromator for the 12-50 eV region has been realized to show the feasibility and the performances of the configuration.
We discuss the design of double plane grating compressors to be used for chirped pulse amplification on free-electron laser (FEL) ultrashort pulses at energies higher than 100 eV. In particular, the design of a grating compressor for wavelength emission centered at 10 nm is demonstrated. The XUV efficiency measurements in the 8-12 nm range of the gratings to be used in a double plane grating compressor realized for an upcoming experiment planned at FERMI is presented and discussed. The overall instrument efficiency is furthermore analyzed.
We present the optical layout of soft X-rays compressors using reflective grating specifically designed to give both
positive or negative group-delay dispersion (GDD). They are tailored for chirped-pulse-amplification experiments with
FEL sources. The optical design originates from an existing compressor with plane gratings already realized and tested at
FERMI, that has been demonstrated capable to introduce tunable negative GDD. Here, we discuss two novel designs for
compressors using deformable gratings capable to give both negative and positive GDD. Two novel designs are
discussed: 1) a design with two deformable gratings and an intermediate focus between the twos, that is demonstrated
capable to introduce positive GDD; 2) a design with one deformable grating giving an intermediate focus, followed by a
concave mirror and a plane grating, that is capable to give both positive and negative GDD depending on the distance
between the second mirror and the second grating. Both the designs are tunable in wavelength and GDD, by acting on
the deformable gratings, that are rotated to tune the wavelength and the GDD and deformed to introduce the radius
required to keep the spectral focus. The deformable gratings have a laminar profile and are ruled on a thin silicon plane
substrate. A piezoelectric actuator is glued on the back of the substrate and is actuated to give a radius of curvature that is
varying from infinite (plane) to few meters. The ruling procedure, the piezoelectric actuator and the efficiency
measurements in the soft X-rays will be presented. Some test cases are discussed for wavelengths shorter than 12 nm.