M. G. Pelizzo

Stability of extreme ultraviolet multilayer coatings to low energy proton bombardment

In this work we present results of an new experiment related to low energy protons bombardments on nano-structured optical coatings. Multilayer structures protected by different capping layers have been fabricated and exposed to low energy protons (1 keV). The experimental parameters have been selected considering the potential application of the coatings to solar mission instrumentation. Future solar missions will investigate the Sun from very close distances and optical components are constantly exposed to low energy ion particles irradiation. The experiment was repeated fixing the proton flux while varying the total dose accumulated. Results show that physical processes occurred at the uppermost interfaces can strongly damage the structure.

Stability of EUV multilayer coatings to low energy alpha particles bombardment

Future solar missions will investigate the Sun from very close distances and optical components are constantly exposed to low energy ions irradiation. In this work we present the results of a new experiment related to low energy alpha particles bombardments on Mo/Si multilayer optical coatings. Different multilayer samples, with and without a protecting capping layer, have been exposed to low energy alpha particles (4keV), fixing the ions fluency and varying the time of exposure in order to change the total dose accumulated. The experimental parameters have been selected considering the potential application of the coatings to future solar missions. Results show that the physical processes occurred at the uppermost interfaces can strongly damage the structure.

Reflectance measurements and optical constants in the extreme ultraviolet-vacuum ultraviolet regions for SiC with a different C/Si ratio

Reflectance versus incidence angle measurements have been performed from 5 to 152 nm on samples of SiC with a different C/Si ratio deposited with rf magnetron sputtering. The optical constants of the material at different wavelengths have been determined by using a curve-fitting technique of reflectance values versus incidence angle. Complementary measurements of the incident beam polarization, film thickness, surface roughness, and stoichiometry were performed to complete the analysis of the samples.

Effects of helium ion bombardment on metallic gold and iridium thin films

Single layer mirrors have been prepared by evaporating gold and iridium on silicon substrates. The samples have been exposed to 4 keV He + ion flux at different total fluences, simulating the effect of solar wind ions on optical coatings. We show that the ion implantation significantly affects the optical characteristics of the metallic films. The phenomena are explained and modeled also considering the related material modifications observed with chemical and morphological analysis.

SPR Sensor Platform Based on a Novel Metal Bilayer Applied on D–Shaped Plastic Optical Fibers for Refractive Index Measurements in the Range 1.38–1.42

A surface plasmon resonance sensor based on a D-shaped plastic optical fiber and a palladium/gold (Pd/Au) bilayer was designed, implemented, and characterized. The platform was properly thought to work in the 1.38-1.42 refractive index range, where it exhibits excellent performances. This refractive index range is very important when a thin polymer layer is used on the planar metal surface for bio-chemical sensing applications.

Exploring EUV near absorption edge optical constants for enhanced and sensitive grazing incidence reflectivity

A characterization procedures to test multilayers in the EUV and soft X-Ray wavelengths are theoretically studied in this paper. The fact that most candidate elements have absorption edge energies in the EUV and soft X-Ray has demanded extensive studies on the optical constants and their possible impact on multilayer design and reflectivity. Thus, EUV and soft X-Ray multilayers are preliminary designed and tested for various parameters. Effects and impacts of interface roughness, interlayer thickness, optical constants fluctuations, different phases of interlayer compounds on the reflectivity of multilayers are investigated in this piece of work. Two theoretical models are used each contributing different properties of the multilayers. Near absorption edge and off-absorption edge wavelengths are compared and contrasted to investigate what optical constants near the resonance edges can render in the EUV and soft X-Ray regime. Almost in all simulations the near absorption edge reflectivity have shown superior sensitivity to fluctuations of various design parameters. In addition, possible engineering tips of near absorption edge optical constants are indicated.

Optical subsystems calibration and derived radiometric instrument response of the PHEBUS spectrometer on board of the BepiColombo Mission

Probing of Hermean By Ultraviolet Spectroscopy (PHEBUS) is a double spectrometer that will fly onboard of the BepiColombo mission. It will investigate the composition and dynamic of Mercurys exosphere to better understand the coupled surface - exosphere - magnetosphere system of the planet. The radiometric calibration tests are ongoing and an approach based on the Mueller Matrix formalism has been adopted to determine the pure efficiency of the instrument. To our knowledge, this is the first time that a such complete method is applied to the calibration of space instrumentation.

Plasmonic response of different metals for specific applications

Each metal presents different characteristics when used in a surface plasmon resonance (SPR) experiment. These include the shape of the SPR figure, the wavelength of better operation, the tendency to oxidize, the sensitivity to environmental changes, the range of refractive indices detectable and the capability of binding to specific targets or analytes. When choosing the metal for our SPR experiment all of these characteristics have to be taken into account. We investigate the behavior of metals, which are less or have never been used in this kind of application, comparing their characteristics to gold. We deeply investigate both theoretically and experimentally the behavior of palladium. This metal leads to an inverted curve with a maximum of reflected intensity instead of a minimum. In fact, in this case we speak of Inverted Surface Plasmon Resonance (ISPR). Aluminum and copper have also been considered because of their potentiality in specific applications.

Extreme and near ultraviolet experimental facility for calibration of space instrumentation

The calibration of space instrumentations requires devoted tools to characterize optical subsystems and whole instruments. Then, new facilities in the Extreme and Near UltraViolet spectral regions have been developed and already used for the preliminary ground calibration activities of PHEBUS, the spectrometer that will flight onboard of BepiColombo mission.

Optical components in harsh space environment

Space exploration is linked to the development of increasingly innovative instrumentation, able to withstand the operation environment, rich in ion particles and characterized by high temperatures. Future space missions such as JUICE and SOLAR ORBITER will operate in a very harsh and extreme environment-. Electrons and ions are considered among the causes of potential damage of the optical instrumentation and components. Development of hard coatings capable to preserve their optical properties is pivotal. Different coating materials have been exposed to ion irradiation in particle accelerators. Change in optical performances has been observed in the extreme ultraviolet and visible spectral region and structural properties have been analyzed by different techniques. The knowledge of the damage mechanisms and thresholds allows the selection of more promising candidate materials to realize the optical components for the new frontiers space missions.