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Imaging polarimetry is an essential diagnostic tool in astronomy and solar physics. Standard instruments, other than being generally expensive, complex and/or with moving parts (all of which are problematic features for space applications), provide measurements of the components of the polarized light sampled at different points of time and/or space (depending on the scheme adopted), thus introducing artefacts difficult to eliminate, especially when the subjects are moving or the illumination is variable.
Development of compact on-chip polarization sensitive detectors is therefore of great interest and, recently, polarimetric image sensors based on a pattern of wire-grid polarizers directly deposited on chip have been introduced in the market. In order to obtain compact imaging detectors able to simultaneously detect the polarization state of the light at each pixel, to minimize and control the systematic errors of the polarimetric measures, we investigated a different approach based on the use of organic conjugated systems possessing both high extinction coefficients and emi ssion efficiencies in selected bands, combined with intrinsic anisotropy originating from the 1D molecular structure, which makes them intrinsically sensitive to the polarization of the incoming light.
As a proof of concept, we developed films able to convert the polarization components of the incoming light into different colors, and coupled them to standard color image sensor. Preliminary tests with commercial color cameras are described.
Spectroscopic observations in the far and extreme ultraviolet (FUV/EUV, 40-200nm) is of great interest in various scientific fields, such as in Solar Physics, in physics of interstellar medium and in planetary exospheres studies. Microchannel plates-based detectors have been for a long time the detectors of choice for astronomical applications in this range of wavelength, due to their photon counting capability (since the expected photon flux are low) and the possibility of solar blindness (photon flux in the visible range are order of magnitudes higher and filtering may be an issue).
However, the spectral features observed in the targets are characterized by a high range of intensities, which can cover several orders of magnitude. Response of MCP detectors at high flux is limited ultimately by the MCP itself, but generally the readout system introduces further restrictions, thus the technique of lowering the efficiency in the area interested by the most intense lines is often adopted.
In the framework of technological R&D for future astronomical FUV/EUV spectrograph, we are developing a photon counting, solar blind, UV detector with readout system based on a 2D anode array integrated in a custom designed Read Out Integrated Circuit (MIRA - Microchannel plate Readout ASIC), with the aim of achieving high performances characteristics, in particular unprecedented performance in terms of dynamic range combined with spatial resolution close to 30 μm. This detector will allow to measure, simultaneously and without the necessity of filters, spectral lines with different intensities of orders of magnitude, exploiting the maximum Signal to Noise Ratio provided by the statistical limit.
A first prototype has been realized, based on a demonstrator of the MIRA ASIC, 32×32 pixels, 35×35 μm2 size, for a total chip area of 2×2 mm2, to be integrated with a standard demountable MCP intensifier.
The entire alignment and verification phase has been performed by the Metis team in collaboration with Thales Alenia Space Torino and took place in ALTEC (Turin) at the Optical Payload System Facility using the Space Optics Calibration Chamber infrastructure, a vacuum chamber especially built and tested for the alignment and calibration of the Metis coronagraph, and suitable for tests of future payloads.
The goal of the alignment, integration, verification and calibration processes is to measure the parameters of the telescope, and the characteristics of the two Metis channels: visible and ultraviolet. They work in parallel thanks to the peculiar optical layout. The focusing and alignment performance of the two channels must be well understood, and the results need to be easily compared to the requirements. For this, a dedicated illumination method, with both channels fed by the same source, has been developed; and a procedure to perform a simultaneous through focus analysis has been adopted.
In this paper the final optical performance achieved by Metis is reported and commented.
The stray light calibration was performed in a clean environment in front of the OPSys solar disk divergence simulator (at ALTEC, in Torino, Italy), which is able to emulate different heliocentric distances. Ground calibrations were a unique opportunity to map the Metis stray light level thanks to a pure solar disk simulator without the solar corona. The stray light calibration was limited to the visible light case, being the most stringent. This work is focused on the description of the laboratory facility that was used to perform the stray light calibration and on the calibration results.
Metis features two channels to image the solar corona in two different spectral bands: in the HI Lyman ∝ at 121.6 nm, and in the polarized visible light band (580 – 640 nm). Metis is a solar coronagraph adopting an “inverted occulted” configuration. The inverted external occulter (IEO) is a circular aperture followed by a spherical mirror which back rejects the disk light. The reflected disk light exits the instrument through the IEO aperture itself, while the passing coronal light is collected by the Metis telescope. Common to both channels, the Gregorian on-axis telescope is centrally occulted and both the primary and the secondary mirror have annular shape.
Classic alignment methods adopted for on-axis telescope cannot be used, since the on-axis field is not available. A novel and ad hoc alignment set-up has been developed for the telescope alignment.
An auxiliary visible optical ground support equipment source has been conceived for the telescope alignment. It is made up by four collimated beams inclined and dimensioned to illuminate different sections of the annular primary mirror without being vignetted by other optical or mechanical elements of the instrument.
To overcome these limitations, we started in 2012 to design a facility aimed at generating a broad (170 x 60 mm2), uniform and low-divergent (1.5 arcsec HEW) X-ray beam within a small lab (∼ 9 x 18 m2), to characterize the ATHENA MM. BEaTriX (the Beam Expander Testing X-ray facility) makes use of an X-ray microfocus source, a paraboloidal mirror, a crystal monochromation system, and an asymmetrically-cut diffracting crystal for the beam expansion. These optical components, in addition to a modular low-vacuum level (10-3 mbar), enable to match the ATHENA SPO acceptance requirements.
The realization of this facility at INAF-OAB in Merate (Italy) is now on going. Once completed, BEaTriX can be used to test the Silicon Pore Optics modules of the ATHENA X-ray observatory, as well as other optics, like the ones of the Arcus mission. In this paper we report the advancement status of the facility.
To exemplify the AETC capabilities we present a number of simulations for specific science cases, useful for studying the capabilities of next generation AO imaging cameras for Extremely Large Telescopes.
Characterization of a photon-counting intensified active pixel sensor (PC-IAPS): preliminary results
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