In this paper we describe a filter which utilizes magneto-optical effects for velocity fields measurements. The working principle of the instrument is described and its transmission profiles are given. Velocitygrams are shown of the five minutes oscillations (FMO) and the results compared with the expected (theoretical) signal from the instrument. We found a V~s of 400 m s -1 for the FMO.
Transmission curves and theoretical calculi of the magneto-optical filter, designed and built by the authors, are shown together with some observed transmission spectra. At present the filter has a total halfwidth of ~ 80 m/~; and the maximum transmission is 25 ~. From the analysis of the theoretical curves and from the observed spectra, we deduced the possibility of making up a filter with a very narrow passband (less than 30 rr~) and a very high transmission (up to nearly 100% apart from losses arising from the glass cell, lenses and polarizers).The article concludes with a selection and discussion of photographs obtaine, d with the filter.* Present address: Osservatorio Astrofisico di Arcetri, Firenze, where the whole of this research has been carried out. Solar Physics 44 (1975) 509-518. AH Rights Reserved Copyright 9 1975 by D. Reidel Publiahing Company, Dordrecht-Holland
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