Method for making large-volume CaF2 single cystals with reduced scattering and improved laser stability, the crystals made by the method and uses thereof

US7393409B2 · kind B2 · utility

Assignee

• Schott AG · DE

Inventors

• Lars Ortmann · Jena, DE
• Joerg Kandler · Cospeda, DE
• Andreas Menzel · Jena, DE
• Matthias Mueller · Harsefeld, DE
• Lutz Parthier · Kleinmachnow, DE
• Gordon Von Der Goenna · Jena, DE

Key dates

• Filing date: Feb 22, 2005
• Grant date: Jul 1, 2008
• Expiry date: Aug 25, 2025

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01P2006/80
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

The method provides CaF2 single 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 CaF2 starting material is heat-treated for at least five hours at temperatures between 1000° C. and 1250° C. and then sublimed at a sublimation temperature of at least 1100° C. in a vacuum of at most 5*10−4 mbar to form a vapor. The vapor is condensed at a condensation temperature of at least 500° C., which is at least 20° 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 CaF2 starting material including waste material and cuttings from previously used melts.