We present the preliminary optical design of METIS, the Mid-infrared E-ELT Imager and Spectrograph, and study the end-to-end performance regarding wavefront errors and non-common path aberrations. We discuss the results of the Monte Carlo simulations that contain the manufacturing and alignment errors of the opto-mechanical system. We elaborate on the wavefront error budget of the instrument detailing all contributors. We investigate the mid and high spatial frequency errors of the optical surfaces, which we model using simulated surface height errors maps of one dimensional Power Spectral Density (PSD) functions.
Extreme UltraViolet instrumentation often requires the use of multilayer coated optics. Such coatings have a limited working bandwidth, and therefore are optimized to perform in correspondence of specific EUV spectral lines. Nevertheless, contemporary observations of the same target in other spectral region would strongly improve scientific knowledge. In this work we present a study on multilayers optimized to achieve high efficiency also in other spectral bands. These coatings would allow the realization of very compact instruments, such as UVCI on board of the Solar Orbiter.
Probing of Hermean Exosphere By Ultraviolet Spectroscopy (PHEBUS) is a dual channels spectrometer working in the Extreme UltraViolet (EUV) and Far UltraViolet (FUV) range. It will be on board of ESA BepiColombo cornerstone mission and it will be devoted to investigate the composition, the dynamic, the formation and the feeding mechanisms of Mercury’s exosphere system. A consistent interpretation of the observational data collected by PHEBUS requires a deeply knowledge of its radiometric behavior. The Mueller’s matrix formalism can be adopted to derive an accurate radiometric model able to takes into account also the polarization state of the source observed by PHEBUS. Moreover, this theoretical model can be further verified and refined during an experimental ground calibration campaign. In this work we present the radiometric model derived for PHEBUS spectrometer together with some results obtained during the Flight Model (FM) ground calibration which is still ongoing. In particular, the obtained results employing this approach show that this is a complete and versatile method to perform the radiometric calibration of a generic space instrument.
Single layer thin films have been exposed to low energy alpha particles (4keV). Implanted doses are equivalent to those accumulated in 1, 2, 4 and 6 years of ESA Solar Orbiter mission operation. Two ions fluences have been considered. In order to change the total dose accumulated, for each ion flux the time of exposure was varied. Reflectance in the visible spectral range has been measured prior and after implantation. Results show no significant change in performances in gold and palladium, while a small decrease in performances is observed in iridium. The implantation rate does not seem to affect the experiment.
The interest in graphene–like materials involves many research areas, including the development of biosensors devices. We have recently studied the use of graphene/metal bilayer for surface plasmon resonance (SPR) equipment devoted to detection of chemical processes and biomolecules recognition. The dual role of graphene is to protect the metal layer underneath and to enhance the bioaffinity by adsorbing biomolecules with carbon–based ring structures. Depending on the application, it may be necessary laser and chemical treatments of graphene to improve the performances of the whole device. The processing effects will be investigated by near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The use of synchrotron light is mandatory for NEXAFS analysis since a continuous EUV source of selected polarization is required. The ideas, the analysis and the results are the subjects of this work.
The concept of a tunable surface-plasmon resonance system able to switch between imaging and Kretschmann angular resolved systems by exploiting a tunable optical module is presented. This scheme allows to perform complementary measurements (SPR angular resolve and SPR imaging) on the same setup with no moving parts. Furthermore, this switching capability can be used to calibrate the imaging with the angular resolved measurements, to enhance the quality of the image and SPR curve and to change/optimize the penetration depth of the evanescent wave probe at the interface metal/target.
The European Space Agency mission Solar Orbiter (SOLO) is dedicated to the study of the solar atmosphere and heliosphere. As a part of the payload, the instrument METIS (Multi Element Telescope for Imaging and Spectroscopy) will provide images of the corona, both in the visible range and at the hydrogen Lyman-α emission line (121.6 nm). The realization of optical coatings, based on Al and MgF2, able to reflect/transmit such spectral components is, therefore, necessary. Since optical characteristics of materials in the vacuum ultraviolet range are not well studied and vary greatly with the realization process, we implemented a study of their properties in different deposition conditions. This is aimed to the realization of a custom designed filter able to transmit the 121.6 nm wavelength while reflecting visible light, and thus separating visible from ultraviolet light paths in the METIS instrument.
The optimization of a silicon solar cell involves also the design of a proper antireflective coating (AR). We have considered different bilayer structures. The use of bilayers is oriented to have an antireflective effect on a broader range of wavelengths compared to single film AR. The materials considered include silicon oxide, magnesium fluoride, silicon nitride and titanium oxide. The thickness of each film in each structure has been optimized by theoretical calculations in order to minimize the weighted reflectivity, <i>R</i><sub>w</sub>. This is calculated taking into account the optical reflectivity, the internal quantum efficiency of the silicon solar cell and the solar flux on all the range of wavelengths of interest. Some of these optimized structures have been realized by e-beam vapor deposition as first tests. The improved optical performance of the samples have been verified at the UV-vis-NIR spectrophotometer.
The practical use of graphene and graphene oxide beyond the research laboratories is strictly related to the fine tuning of
new methodologies for processing and mass–production purposes. The photoreduction processing is an innovative route
allowing exquisite control of the optoelectronic properties of graphene–like materials irradiated by coherent and
incoherent light. We have investigated the effects induced by a mercury lamp on graphene/palladium bilayer; the change
on the optical properties of the sample has been detected by using a surface plasmon resonance setup. The analysis, the
perspectives and the preliminary results are shown thereafter.
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
The phase delay induced by multilayer (ML) mirrors is an important feature in many fields such as attosecond pulses
compression, photolithography or in pump and probe experiments performed with Free Electron Laser (FEL) pulses. The
experimental characterization of the ML phase delay can be obtained by the standing wave distribution measurement (by
using Total Electron Yield (TEY) signal) combined to reflectance measurement. In this work, a ML structure with
aperiodic capping-layers was designed and deposited for FEL applications and their reflectance and phase delay was
characterized. The method adopted allows to retrieve the ML phase delay by using the TEY signals taken at different
working configurations and it doesn’t require the comparison with a bulk reference sample. The results obtained are
presented and discussed.
The ESA mission Solar Orbiter (SOLO) is dedicated to the study of Solar Atmosphere and Heliosphere. As a part of the
payload, the instrument METIS (Multi Element Telescope for Imaging and Spectroscopy) will provide images of the
corona, both in the visible range and at the hydrogen Lyman-α emission line (121.6 nm). The realization of optical
coatings, based on Al and MgF2, able to reflect/transmit such spectral component is therefore necessary. Since optical
characteristics of materials in the VUV range are not well studied and greatly varying with realization process, we
implemented a study of their properties in different deposition conditions. This is aimed to the realization of a custom
designed filter, able to transmit the 121.6 nm while reflecting the visible light, and thus separate visible from UV light
paths in the METIS instrument.
Future solar missions will investigate the Sun from very close distances and optical components are
constantly exposed to low energy ions irradiation. Single layer thin films as well as extreme ultraviolet
multilayer coatings have been exposed to low energy alpha particles (4keV). In order to change the total dose
accumulated, for each ion fluency the time of exposure was varied. The experiment was carried out
considering typical doses accumulated during the ESA Solar Orbiter mission. Results show that ion
implantation affects the performances of both single and multilayer coatings.
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.
Multilayers coatings for space and solar applications are usually exposed to harsh environments. Thermal stress, ion
bombardments and natural aging process can affect their performances over time. We have investigated the α–particles
stability of UV and EUV optical coatings suitable for high–performance solar instrumentation. Experimental procedures,
analysis and preliminary results are discussed hereafter.
The performances of an Inverted Surface Plasmon Resonance (ISPR) biosensor based on novel materials have been
studied theoretically and experimentally. The principle of ISPR is based on a maximum of reflectivity at the coupling
angle instead of the common used minimum of reflectivity; this solution has not been extensively explored yet. The
sensor response has been firstly simulated by the use of a dedicated Matlab routine. Different structures involving
different materials have been considered and compared, in order to find the optimized solution. The metals have been
deposited on a flat substrate made of optical glass. Different noble metals of optimized thickness have been then
deposited on top of it. The substrates have been finally coupled with a prism to test the ISPR response. The metallic
layers have been deposited at our lab by Electron Beam Evaporation. The process have been optimized for each material considered. The response of the sensors has been tested at our laboratory on a dedicated optical-bench set-up based on the Kretschmann configuration with angular modulation. The theoretical and experimental data are reported.
Calibration of optical systems is a fundamental step in the development of a space instrumentation. We have built a new
cleanroom environment, divided in different areas characterized by a different level of contamination control. A vacuum
chamber (a tube of 80 cm diameter, and 2 m length), able to accommodate optical components as well as whole
instruments, is interfaced with a ISO6 area, allowing the handling of the instrumentation in a clean environment. The
vacuum system is dimensioned to reach 10<sup>-7</sup> mbar pressure in the chamber. Inside, a two axis platform allows the rotation
of the instrument with respect to the incident collimating beam, in order to test the response of the instrument to light
coming from different points of the field of view. A monochromator coupled with different sources provides radiation in
the 40-350 nm spectral range, while a parabolic mirror is used as a collimator. As source, different spectral lamps can be
used to generate emission lines, while a Xe lamp can be used to have continuum spectrum. An high brilliant hollow
cathode lamp has been fabricated by the group to generate extreme ultraviolet radiation. Different calibrated detectors
and other completing optical components are available.
In this work we present a theoretical and experimental work due to develop a performing configuration for gas-sensing
through the employ of Surface Plasmon Resonance effect.
Different sensing layers have been studied and tested on our optical bench assembly. Metallic (Au) and bimetallic
(Ag/Au) layers have been properly designed through simulations and then have been realized through electron-beam
evaporation. TiO<sub>2</sub> and TiO<sub>2</sub> - Au doped layers have been deposited on the top of some of the metallic samples. These
layers were prepared by the sol gel route. This kind of material is expected to be suitable as a gas sensor for its
nanosized structure and its stability.
The optical bench configuration for the experimental exploitation of SPR is presented. It is based on a collimated beam, a
rotational stage with a triangular prism and a single photodiode.
Finally the sensing properties of the different sensing layers prepared was tested to some organic vapours. Preliminary
results are presented.
A polarimetric measurement technique based on the analysis of the reflection data given by a single mirror rotated around the incidence beam axis is presented. In the extreme ultraviolet spectral region, a multilayer coated mirror must be used. The multilayer mirror must be fully characterized before the experiment. Theory demonstrates how this method allows complete determination of Stoke's parameters in case of a totally polarized beam. A simulation code has been
developed in order to model the experiment in case of synchrotron radiation propagating in a bending magnet beamline and impinging a multilayer mirror. The simulation is useful to verify each time the effectiveness of the method in the different experimental conditions considered. Finally an experimental application is presented.