Very narrowband transmission filters, as parts of an instrument for the study of lightning phenomena, are described. Their performance must be maintained at an incidence angle of +-5.5 deg and this condition poses some limitations on the minimum bandwidth of the order of a few nanometers. The fabrication of such coatings on large area substrates is quite challenging because of the required thickness accuracy. Moreover, their performance should be not influenced by the environmental conditions in space.
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