UNIVERSAL BIREFRINGENT FILTER WITH A NEW DOUBLE PASSBAND MODE

This article describes the universal birefringent filter (UBF) which w ill be mounted at Taiwan. The UBF permits observations of solar images , vector magnetic fields and/or line-of-sight velocity fields in any F raunhofer line in the wavelength region from 4000 Angstrom to 7000 Ang strom with half width from 0.05 Angstrom to 0.14 Angstrom. We have tes ted it at ten Fraunhofer lines under a spectral telescope in Huairou S tation of Beijing Astronomical Observatory and obtained the passband p rofiles. The principles of magnetic field and velocity field measureme nt with the UBF are also described.