Schott Ag

Lars Ortmann

Lutz Parthier

Andreas Menzel

Matthias Mueller

Gordon Von Der Goenna

Joerg Kandler

Single crystals with low scattering, small refractive index differences and few small angle grain boundaries have a bi-directional scattering distribution function value (BSDF) of less than 1.5*10or 5*10.

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The method provides CaFsingle crystals with low scattering, small refractive index differences and few small angle grain boundaries, which can be tempered at elevated temperatures. In the method a CaFstarting material is heat-treated for at least five hours at temperatures between 1000&#xb0; C. and 1250&#xb0; C. and then sublimed at a sublimation temperature of at least 1100&#xb0; C. in a vacuum of at most 5*10mbar to form a vapor. The vapor is condensed at a condensation temperature of at least 500&#xb0; C., which is at least 20&#xb0; C. below the sublimitation temperature, to form a condensate. Then a melt formed from the condensate is cooled in a controlled manner to obtain the single crystal, which is subsequently tempered. The method is preferably performed with a CaFstarting material including waste material and cuttings from previously used melts.

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Jena, Germany

Lars Ortmann