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Highlights • SnTe as capping layer coatings in the vacuum and extreme ultraviolet spectral regions. • Design and fabrication of VUV quarter wave plates (QWP) based on SnTe/Al bilayer. • Extreme ultraviolet (EUV) improved facility for ellipsometric measurements. • Studying the polarimetric properties of SnTe/Al sample at the wavelength of (121.6 nm). • Angle-dependence phase retarder properties of SnTe/Al also reported in this study. Abstract Vacuum ultraviolet and extreme ultraviolet polarized light plays a significant role in many applications from materials science and solar physics investigations to optical components development. In this paper, we study the optical performances and the quarter wave retarder properties of aluminum coating capped with SnTe/Al thin film. The measurements have been performed by using a reflectometer properly improved for ellipsometric characterizations. The specimen has been fully characterized at hydrogen Lyman–alpha line (121.6 nm) by deriving the reflectance and the ellipsometric parameters, i.e. the ratio r and the phase difference δ. We found that the SnTe/Al bilayer behaves as phase retarder, although the performances differ from the ideal case. In fact, the polarimetric analysis combined with the optical test at different wavelengths allowed to identify carbon contamination on the top layer and a mild oxidation of the aluminum coating that affect the optical throughput. [ABSTRACT FROM AUTHOR]

Geometric morphometric studies of dolphins have traditionally concentrated on the skull, while the mandible and its modularity have been little explored. We investigated the mandible variability and modularity in three strictly related Mediterranean dolphins:Stenella coeruleoalba,Delphinus delphisandTursiops truncatus. The aims were to describe the interspecific differences in the size and shape of the mandible as a whole, and of its structural modules, and to detect the influence of adaptive pressures on trait variation. Data were collected on 96 specimens from the Mediterranean Sea. Eight and 10 two-dimensional landmarks were recorded respectively in the lateral and medial sides of the mandible. After General Procrustes Analysis (GPA) transformation, measurement error, sexual dimorphism and ontogenetic allometry were first investigated to allow further pooling of samples. Univariate analysis of variance (ANOVA) of centroid size was used to evaluate size differences among the species; multivariate ordination, classification and clustering methods were used to investigate interspecific variation of shape variables. Different subsets of landmarks representing distinct mandibular subunits were tested for modular integration through the RV coefficient; two-block partial least squares statistics was used to explore the patterns of covariation between modules. Size and shape differences in the whole mandible of the three species evidenced a clear morphological divergence ofTursiops truncatusand a close similarity ofStenella coeruleoalbaandDelphinus delphis. The analysis of modularity identified the corpus and the ramus, with its internal foramen, as distinct modules. The corpus and ramus patterns of variation could discriminate betweenT. truncatusvs. the other two species. The mandibular foramen was the only trait able to discriminate each species, and the corresponding shape differences were related to selective pressures toward the differentiation of communication patterns. [ABSTRACT FROM AUTHOR]

The experimental characterization of a stigmatic spectroscopic system for the diagnostics of laser-produced plasmas in the 50–450 Å spectral region is presented. The instrument provides stigmatic spectra for on-axis sources and fully preserves spectral resolution also for off-axis sources. Expected theoretical performances have been compared with experimental results. Spectral and spatial resolution capabilities have been proved to match the nominal ones theoretically predicted. A laser-produced plasma experiment has been also carried out to demonstrate the instrument capabilities. The use of a stigmatic spectrometer and an image detector gives spectrally and spatially resolved images of the plasma source. The good instrumental sensitivity and high dynamic range allow to acquire complete spectra in almost single-shot experiments. [ABSTRACT FROM AUTHOR]

Abstract: A stigmatic spectrometer for the 2.5–40nm extreme-ultraviolet (EUV) region has been realized. The design consists of a grazing-incidence spherical varied-line-spaced grating with flat-field properties and of a spherical mirror mounted in the Kirkpatrick–Baez configuration that compensates for the astigmatism. The spectrum is acquired on a fluorescent screen and intensified CCD detector that can be moved along the spectral focal curve to select the spectral region to be acquired. This stigmatic design has also spectral and spatial resolution capability for extended sources. The spectral and spatial resolution of the system has been characterized by using the emission from a hollow-cathode lamp or a laser-produced plasma. At present, the instrument is installed at the vacuum–ultraviolet free-electron-laser (VUV FEL) at DESY for the spectral monitoring of the FEL beam in the 20–40nm region. [Copyright &y& Elsevier]

Abstract: Optical constants of SiC thin films deposited with RF magnetron sputtering have been derived in the VUV. The films have been deposited with different parameters resulting in various C/Si ratios. Reflectance measurements have been made with a dedicated facility in the range 300–1300Ǻ. Index of refraction and absorption coefficient have been derived by fitting the reflectance data with the calculated ones. [Copyright &y& Elsevier]

Stigmatic spectroscopic observations of laser produced plasma have been performed in the 50-200 Å spectral interval. The purpose was to demonstrate the good instrumental performances of an intensified bidimensional detector installed on a stigmatic soft x-ray spectrometer. The latter is the combination of a grating spectrograph in Rowland circle mount and a toroidal mirror, both working at grazing incidence. The detector is composed of a scintillator on the spectrograph focal circle, an image intensifier, and a charge coupled device. The resulting spatial and spectral resolution are of 60 µm and 1000, respectively. The observations show a marked improvement in term of dynamic range, sensitivity, ease of operation, and real-time data presentation in comparison to both traditional photographic film and photodiode array detection technique. [ABSTRACT FROM AUTHOR]

• Nb/Zr free-standing filter shows a peak transmittance of 60% at 7.02 nm. • Over 20 nm, the ratio of the out-of-band to the band transmittance goes lower than 2%. • Zr and Zr/Nb thin films deposited on Si 3 N 4 techniques showed compressive stress. • Nb and Nb/Zr thin films deposited on Si 3 N 4 showed tensile stress on the surface. • Nb/Zr filter shows better mechanical stability than Zr filter. Optical and structural properties of Niobium and Zirconium bilayer structures (Nb/Zr and Zr/Nb) were investigated in order to develop free-standing transmittance filters in the Extreme Ultraviolet region (EUV) between 5 and 20 nm. Samples of Nb/Zr and Zr/Nb were deposited on Silicon Nitride (Si 3 N 4) membranes by magnetron sputtering technique, using metallic targets of Nb and Zr. A single layer of Zr and Nb on Si 3 N 4 membrane has also been deposited and studied for a better understanding of the performance of these structures and their optical and mechanical properties. Optical microscope images of Zr and Zr/Nb structures on the membranes reveal compressive stress while Nb and Nb/Zr structures present tensile stress behavior. Nb and Nb/Zr self-standing filters were obtained by etching the silicon nitride membrane, with free-standing areas up to 3 × 3 mm2 with 100 nm of thickness. The transmittance performance of the samples has been measured by using EUV synchrotron radiation. The results show the highest peak transmittance of 60% at 7.02 nm and very good performance in the targeted range. [ABSTRACT FROM AUTHOR]

The knowledge and the manipulation of light polarization state in the vacuum ultraviolet and extreme ultraviolet (EUV) spectral regions play a crucial role from materials science analysis to optical component improvements. In this paper, we present an EUV spectroscopic ellipsometer facility for polarimetry in the 90-160 nm spectral range. A single layer aluminum mirror to be used as a quarter wave retarder has been fully characterized by deriving the optical and structural properties from the amplitude component and phase difference δ measurements. The system can be suitable to investigate the properties of thin films and optical coatings and optics in the EUV region. [ABSTRACT FROM AUTHOR]

The Selective Production of Exotic Species project is under construction at Laboratori Nazionali di Legnaro-INFN. The aim of the collaboration is to produce highly pure Radioactive Ion Beams (RIBs) from fission fragments of a uranium carbide (UCx) target activated by a cyclotron proton beam. In order to select a specific atomic species, the main tool to be applied is the resonant laser ionization technique. We have just completed the installation of a dedicated all solid state laser system whose elements are tunable to transitions of all the elements/isotopes of interest for the project. The new laser system is based on three Titanium:sapphire laser sources, independently pumped by three Nd:YLF pump lasers, and it can be coupled to two high harmonic generation (second harmonic generation, third harmonic generation, and fourth harmonic generation) setups. The power, wavelength, and position of the laser beams are continuously monitored and stabilized by using automated active systems to improve the beam production stability of RIBs. This paper presents the main features of the laser system and examples of application of a laser ion source, including a first demonstration of photoionization of stable silver, one of the most requested elements for RIB application. [ABSTRACT FROM AUTHOR]

In Mediterranean climates, adoption and use of the ET-based scheduling method is limited to regions characterized by considerable contributions to evapotranspiration from fog interception, dew, and light rainfall. While the crop evapotranspiration is often accurately estimated, the water balance is frequently in error because a considerable portion of the energy expended is used to vaporize water from the plant surfaces rather from inside the leaves (i.e., transpiration). Growers in regions with considerable fog, dew, and light rainfall are hesitant to use ET-based scheduling because the cumulative crop evapotranspiration between irrigations is often considerably higher than the soil water depletion. A correction for these surface contributions is clearly needed to improve the water balance calculations and to enhance adoption of the ET-based scheduling method. In this paper, we present a simple, practical method to estimate the contribution of fog interception, dew, and light rainfall to daily crop evapotranspiration, and we show how to use the method to improve water balance calculations. [ABSTRACT FROM AUTHOR]

New multilayers of boron carbide/cerium dioxide (B4C/CeO2) combination on silicon (Si) substrate are manufactured to represent reflective-optics candidates for future lithography at 6.x nm wavelength. This is one of only a few attempts to make multilayers of this kind. Combination of several innovative experiments enables detailed study of optical properties, structural properties, and interface profiles of the multilayers in order to open up a room for further optimization of the manufacturing process. The interface profile is visualized by high-angle annular dark-field imaging which provides highly sensitive contrast to atomic number. Synchrotron based at-wavelength extreme ultraviolet (EUV) reflectance measurements near the boron (B) absorption edge allow derivation of optical parameters with high sensitivity to local atom interactions. X-ray reflectivity measurements at Cu-Kalpha (8 keV) determine the period of multilayers with high in-depth resolution. By combining these measurements and choosing robust nonlinear curve fitting algorithms, accuracy of the results has been significantly improved. It also enables a comprehensive characterization of multilayers. Interface diffusion is determined to be a major cause for the low reflectivity performance. Optical constants of B4C and CeO2 layers are derived in EUV wavelengths. Besides, optical properties and asymmetric thicknesses of inter-diffusion layers (interlayers) in EUV wavelengths near the boron edge are determined. Finally, ideal reflectivity of the B4C/CeO2 combination is calculated by using optical constants derived from the proposed measurements in order to evaluate the potentiality of the design. [ABSTRACT FROM AUTHOR]

The SPES laser ion source has been tested at ISOLDE Offline 2, CERN. A two-step single resonance photo-ionization scheme has been used to ionize gallium atoms in the SPES tantalum hot-cavity ion source. The ion beam time structure, laser enhancement of ion yield, and ionization efficiency are investigated in relation to the ion source temperature and ion load. From the time structures, it is inferred that a significant fraction of the extracted ions are generated in the transfer line rather than just in the hot cavity. The effect of the electrostatic axial field on the movement of ions inside the ion source is discussed. Generally, there is an inverse relationship between total ion load and the laser enhancement factor. This dependency is enhanced at lower operating temperature of the ion source. This is explained by the influence of thermionic electron emission and ion density on the transverse laser-ion confinement, and therefore the survival of ions as they drift towards the extraction region of the ion source. At 2200 °C, the nominal temperature for on-line operation of the ion source, the ratio of laser-ionized to surface-ionized gallium was stable around 55 during the measurement campaign, and independent of the total extracted ion current up to the measured value of 1.1 μ A. A resonance laser ionization efficiency value of 27.2% for gallium has been measured. [ABSTRACT FROM AUTHOR]

This paper describes the innovative optical design of the Metis coronagraph for the Solar Orbiter ESA-NASA mission. Metis is a multi-wavelength, externally occulted telescope for the imaging of the solar corona in both the visible and ultraviolet wavelength ranges. Metis adopts a novel occultation scheme for the solar disk, that we named "inverse external occulter", for reducing the extremely high thermal load on the instrument at the spacecraft perihelion. The core of the Metis optical design is an aplanatic Gregorian telescope common to both the visible and ultraviolet channels. A suitable dichroic beam-splitter, optimized for transmitting a narrow-band in the ultraviolet (121.6 nm, HI Lyman-α) and reflecting a broadband in the visible (580–640 nm) spectral range, is used to separate the two optical paths. Along the visible light optical path, a liquid crystal electro-optical modulator, used for the first time in space, allows making polarimetric measurements. [ABSTRACT FROM AUTHOR]

The magnetic field shapes the structure of the solar corona, but we still know little about the interrelationships between the coronal magnetic field configurations and the resulting quasi-stationary structures observed in coronagraphic images (such as streamers, plumes, and coronal holes). One way to obtain information on the large-scale structure of the coronal magnetic field is to extrapolate it from photospheric data and compare the results with coronagraphic images. Our aim is to verify whether this comparison can be a fast method to systematically determine the reliability of the many methods that are available for modeling the coronal magnetic field. Coronal fields are usually extrapolated from photospheric measurements that are typically obtained in a region close to the central meridian on the solar disk and are then compared with coronagraphic images at the limbs, acquired at least seven days before or after to account for solar rotation. This implicitly assumes that no significant changes occurred in the corona during that period. In this work, we combine images from three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) that observe the Sun from different viewing angles to build Carrington maps that cover the entire corona to reduce the effect of temporal evolution to about five days. We then compare the position of the observed streamers in these Carrington maps with that of the neutral lines obtained from four different magnetic field extrapolations to evaluate the performances of the latter in the solar corona. Our results show that the location of coronal streamers can provide important indications to distinguish between different magnetic field extrapolations. [ABSTRACT FROM AUTHOR]

Abstract: Multilayers coatings are widely used in different fields ranging from new generation sources applications to astrophysical observations. Novel materials couples have been recently considered to improve the efficiency performances in different spectral regions. The deposition of capping layer structures onto standard periodic Mo/Si multilayers is used to add specific properties, such as high resistance to aging and different damage processes, or to regulate the reflectance in other spectral regions. This solution is adopted in the development of multilayer to be used in FERMI@ELETTRA FEL beam transport systems for third harmonics selection. [Copyright &y& Elsevier]

Abstract: Damage analysis of Mo/Si multilayer coatings exposed to fs infrared laser irradiation has been performed. The Mo/Si a-periodic multilayer samples were specifically designed with wide reflectivity bandwidth and suitable phase chirp in order to reflect attosecond pulses. After irradiation, the mirror surface was analyzed by using an optical microscope and a profilometer. The stoichiometry of the compounds formed at the sample surface after the irradiation was investigated using X-Ray photoemission spectroscopy. The performances of the irradiated samples with the reflected pulse characteristics have been derived via reflectivity and phase measurements. [Copyright &y& Elsevier]

Thin films of silicon carbide (SiC) have been prepared by means of pulsed laser deposition (PLD) on sapphire (AlO) and Si(100) substrates with a Nd-YAG laser 1064 nm. We achieved the growth of cubic silicon carbide (3C-SiC) films at the temperatures of 650°C from a SiC target in vacuum. The as-deposited films are morphologically and structurally characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The use of off-axis PLD method placing the sample at 90° with respect to the target leads to a good quality smooth film. [ABSTRACT FROM AUTHOR]

The article presents research which examined the beta-SiC prepared through Pulsed Laser Deposition (PLD) at 1064 nanometers (nm). The researchers aimed to assess the potential applications of the compound in high-temperature, high-power and high-frequency devices. They also used Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) to identify the morphological and crystalline properties of the compound that were deposited in thin films.

Abstract: Silicon carbide (SiC) is an important material for several applications ranging from electronics to Extreme UltraViolet (EUV) space optics. Crystalline cubic SiC (3C–SiC) has a wide band gap (near 2.4eV) and it is a promising material to be used in high frequency and high energetic electronic devices. We have deposited, by means of pulsed laser deposition (PLD), different SiC films on sapphire and silicon substrates both at mild (650°C) and at room temperature. The resulted films have different structures such as: highly oriented polycrystalline, polycrystalline and amorphous which have been studied by means of X-ray absorption spectroscopy (XAS) near the Si L2,3 edge and the C K edge using PES (photoemission spectroscopy) for the analysis of the valence bands structure and film composition. The samples obtained by PLD have shown different spectra among the grown films, some of them showing typical 3C–SiC absorption structure, but also the presence of some Si–Si and graphitic bonds. [Copyright &y& Elsevier]

Abstract: Extreme ultraviolet multilayer coatings consist of periodic or aperiodic stack of two or more material layers in the nanometric scale. They are fundamental in a very wide range of applications: in atto-physics they allow manipulation of high order harmonics by compressing ultrafast pulses in the atto-second regime; in the free electron laser beamlines they can be used to select the proper harmonics while rejecting unwanted ones; in space experiments they are employed in astrophysical instrumentation dedicated to space weather studies for the observation of solar disk and coronal plasmas; in microelectronics industry they are used as coatings of mirrors and projection masks in extreme ultraviolet lithographic apparatus for integrated circuit production. The more and more sophisticated level of such experiments and apparatus required the realization of multilayers with very strict requirements; in particular high control of reflecting curve shape and phase, and stability with respect to deposition process can be achieved only by deposition of aperiodic structure. Optimization of such structures usually requires a quite complex mathematical approach; an innovative software tool to perform such designs is presented. [ABSTRACT FROM AUTHOR]

Abstract: Probing of Hermean exosphere by ultraviolet spectroscopy (PHEBUS) is a double spectrometer for the Extreme Ultraviolet range (55–155nm) and the Far Ultraviolet range (145–315nm) devoted to the characterization of Mercury''s exosphere composition and dynamics, and surface–exosphere connections. This French-led instrument is implemented in a cooperative scheme involving Japan (detectors), Russia (scanner) and Italy (ground calibration). PHEBUS will address the following main scientific objectives relative to Mercury''s exosphere: determination of the composition and the vertical structure of the exosphere; characterization of the exospheric dynamics: day to night circulation, transport between active and inactive regions; study of surface release processes; identification and characterization of the sources of exospheric constituents; detection and characterization of ionized species and their relation with the neutral atmosphere; space and time monitoring of exosphere/magnetosphere exchange and transport processes; study and quantification of escape, global scale source/sink balance and geochemical cycles synergistically with other experiments of BepiColombo (Mercury Sodium Atmospheric Spectral Imager (MSASI), Mercury Plasma Particle Experiment (MPPE) on Mercury Magnetospheric Orbiter (MMO); Mercury imaging X-ray spectrometer (MIXS), Search for exosphere refilling and emitted neutral abundance (SERENA) on Mercury Planetary Orbiter (MPO)). Two gratings and two detectors are used according to a specific, compact design. The spectrum detection is based on the photon counting method and is realized using micro-channel plate (MCP) detectors with Resistive Anode Encoder (RAE). Typical photocathodes are CsI or KBr for the extreme ultra-violet (EUV) range, CsTe for the far ultra-violet (FUV) range. Extra visible lines are monitored using a photo-multiplier (PM) that is also used in photon counting mode. In order to prevent sensitivity losses which are critical in UV ranges, a minimum of reflections is achieved inside the instrument using only an off-axis parabola and a set of holographic gratings. A one degree-of-freedom scanning system allows to probe, at the highest possible signal-to-noise ratio, selected regions and altitude ranges of interest. Different modes of observation will be used sequentially (vertical scans, along-orbit scans, grazing observations at twilight, etc.). During the mission, the instrument will be regularly calibrated on well chosen stars, in such a way to quantitatively estimate the overall degradation of the sensitivity of the instrument. [Copyright &y& Elsevier]

Abstract: We describe an experimental system designed for single-shot photoelectron spectroscopy on free atoms and molecules at the Free Electron Laser in Hamburg (FLASH at DESY). The combination of the extreme ultra-violet (EUV) Free Electron Laser and a temporally synchronized optical fs laser (Ti:Sapphire) enables a variety of two-color pump-probe experiments. The spectral, temporal and spatial characteristics of both the EUV FEL and the optical laser pulses, the experimental procedure to control their overlap as well as the performance of an electron spectrometer used to obtain single-shot photoelectron spectra are discussed. As an illustration of the capabilities of this set-up, some results on two-photon two-color ionization of rare gases are presented. [Copyright &y& Elsevier]

Abstract: B4C optical coating represents, together with Ir, Pt, SiC, one of best choice for high reflectance in the extreme ultraviolet region. This material is also used combined with others materials in multilayer such as Si/B4C or as interlayer in Mo/Si multilayer to avoid interdiffusion. In this study we have performed optical, compositional and structural analyses for thin film of B4C deposited by means of magnetron sputtering and on preliminary samples deposited by e-beam evaporation. Here we report reflectivity measurements and the derived optical constants of B4C in the 400–1500Å region. [Copyright &y& Elsevier]

Abstract: SWAP (Sun Watcher using Active Pixel system detector and image processing) is a solar imager in the extreme ultraviolet (EUV) that has been selected to fly in 2007 on the PROBA 2 technological platform, an ESA program. SWAP will use an off-axis Ritchey Chrétien telescope equipped with an EUV enhanced active pixel sensor detector (coated APS). This type of detector has advantages that promise to be very profitable for solar EUV imaging. SWAP will provide solar coronal images at a 1-min cadence in a bandpass centered on 17.5nm. Observations with this specific wavelength allow detecting phenomena, such as solar flares or EIT-waves, associated with the early phase of coronal mass ejections. Image processing software will be developed that automatically detects these phenomena and sends out space weather warnings. Together with its sister instrument LYRA, also onboard PROBA 2, SWAP will serve as a high performance solar monitoring tool to be used in operational space weather forecasting. The SWAP data will complement the solar observations provided by instruments like SOHO-EIT, and STEREO-SECCHI. [Copyright &y& Elsevier]

A study of Mo/a-Si:H multilayer for EUV mirrors produced by rf-magnetron sputtering in pure Ar, Xe and Ar/H2 gas mixtures is presented. The high reflectance mirrors are designed for solar space experiments at 17, 19 and 30.4 nm and for the lithography applications at 13 nm. The multilayers are grown in different ion bombardment conditions determined by different bias levels of the substrate. Plasma diagnostics are performed to correctly evaluate flux and energy of plasma ions bombardment. The a-Si:H layers have been obtained by introducing H2 gas in the sputtering chamber at different partial pressures during silicon deposition. The deposition rates as well as the composition of Mo and Si layers have been investigated by Ion Beam Analysis (RBS and ERDA). The coating microstructure has been characterised primarily by X-ray micro-diffraction (micro-XRD). X-Ray Reflection analysis (XRR) has been carried out to investigate the layer density and the multilayer structure. RBS analyses show that noble gas (Ar, Xe) incorporation is limited to the Si layers and depends on the sample bias. Noble gas concentration is correlated to the different ion bombardment growth conditions that influence also the (110) orientation of Mo nano-crystals. ERD analyses of Si layers show hydrogen incorporation up to 30 at.% as a function of the H2 partial pressure. Hydrogen incorporation leads to a decrease of the a-Si layer density. Hydrogen content in Mo layers is less than 0.5 at.% even at the highest H2 partial pressure. The optical properties of these mirrors have been characterised by EUV reflection measurements. [Copyright &y& Elsevier]

We describe a recently designed and constructed system based on a 1 m normal incidence vacuum monochromator with corrected (toroidal) optics that produces a wavelength tuneable and collimated vacuum-ultraviolet (VUV) (λ=30–100 nm) beam. The VUV continuum source is a laser-generated gold plasma. The primary function of the system is the measurement of time resolved “images” or spatial distributions of photoabsorption/photoionization in expanding laser plasma plumes. This is achieved by passing the beam through the sample of interest (in our case a second synchronised plasma) and recording the “footprint” of the attenuated beam on a charge coupled device. Using this VUV photoabsorption imaging or “shadowgraphy” technique we track and extract column density distributions in expanding plasma plumes. We can also measure the plume front velocity. We have characterized the system, particularly in relation to spectral and spatial resolution and the experimental results meet very well the expectations from ray tracing done at the design phase. We present first photoabsorption images and column density distributions of laser produced Ca plumes from the system. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Pump and probe experiments are one of the most attractive and powerful tools offered by a free electron laser facility. In these experiments it is fundamental to pump the system with a particular wavelength (usually the fundamental one) and to probe it with a second wavelength (e.g. higher emitted harmonics). Radiation emitted at the fundamental wavelength is 100 or more times the number of photons emitted in higher harmonics; selection of higher harmonics can be therefore critical. Multilayer (ML) mirrors that are able to provide high reflectivity peak at the desired harmonic wavelength while rejecting the fundamental have been designed and their application is foreseen to the FERMI@Elettra FEL beam transport system. The photon beam will be split into two and one of these will pass through a set of ML mirrors optimized for third harmonics selection; this scheme is also useable to realize a delay line in which the few nanosecond time delay will be controlled by changing the mirrors distance. A set of target wavelengths has been considered and multilayer structure materials have been selected. The MLs have been designed using a method based on the control of standing wave distribution at the fundamental and third harmonics wavelength, using a capping layer as a key element to achieve the willing rejection. Fabrication and test of such structures are foreseen. [Copyright &y& Elsevier]