GOLD, in a collaboration with various Italian groups, has been developing far UV linear polarizers based on coatings. The Italian collaborating scientists are Prof. Marco Malvezzi, Prof. Stefano Nannarone, and Dr. Angelo Giglia from Istituto Officina dei Materiali – CNR, and Dr. Silvano Fineschi, Dr. Gerardo Capobianco, and Mr. Giuseppe Massone from INAF – Osservatorio Astrofisico di Torino.
High performance polarizers can be obtained with optimized coatings. Interference coatings can tune polarizers at the desired spectral line(s). Example application: polarimetry to measure the magnetic field of the solar atmosphere.
Reflectance polarizers
Efficient linear polarizers operating by reflection have been developed tuned at the desired wavelength.
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Coating polarizer tuned at 121.6 nm and at 65° (from normal incidence) operating by reflection
Transmitance polarizers
Innovative linear polarizers operating by transmission have been also developed, with the advantage that the light beam is not deviated.
Transmission polarizers were seen to provide also filtering properties to reject long-wavelength radiation, as it can be seen in the picture.
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Coating polarizer tuned at 121.6 nm operating by transmission at the indicated angles of incidence (from the normal)
Beamsplitter polarizer tuned at 121.6 nm that preferentially reflects s polarization and transmits p polarization at 75° (from normal incidence)
Beamsplitter polarizers
The two sorts of coating polarizers have been combined in a single element. This gives rise to a beamsplitter polarizer. This element is designed to be more efficient to reflect one polarization component and at the same to be more efficient to transmit the perpendicular one.
In space instruments, the limitation of mass and room makes beamsplitter polarizers very desirable, because they separate the two polarization components with a single polarizer, which also results in a higher efficiency in collection of polarization data. For space polarimetry, we require a large reflectance and transmittance difference over the two perpendicular polarization components.
Beamsplitter polarizers have been developed for hydrogen Lyman α line (121.6 nm), which is key for solar physics.
Beamsplitter polarizers can be also tuned at more than one spectral line. Research is under way to develop beamsplitter polarizers simultaneously tuned at CIV line 155 nm and at Mg II line 280 mn.
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