Thermo-optic coefficient of barium gallogermanate glass.

Barium gallogermanate (BGG) glasses are currently being explored as a viable low cost material for numerous U.S. defense and commercial visible-infrared window applications. These glasses are transparent from 0.4 mum to beyond 5.0 mum and can be easily made in large optics and complex shapes with high index homogeneity. For high-energy laser (HEL) applications, knowledge of the thermo-optic coefficient (dn/dT) of the window material is important in determining the optical path distortion. The dn/dT measurements were made on BGG glass at 633 and 3390 nm and compared with the values for multispectral ZnS. The dn/dT for BGG glass was approximately 1/5 the value for multispectral ZnS, giving BGG glass a clear advantage for HEL applications.