THERMAL LENSING IN HEAVY-METAL FLUORIDE GLASSES

The effect of glass composition on the theoretical thermal lensing of a ZrF4-BaF2-LaF3-AlF3 NaF (ZBLAN) heavy metal fluoride glasses (HMF) has been examined. A number of composition substitutions, i.e., HfF4 for ZrF4, PbF2 for BaF2, and LiF and NaCl for NaF, have been made, and the effects of these substitutions on critical properties have been determined. These substitutions have significant effects on the refractive index, coefficient of thermal expansion (CTE), and the thermo-optic coefficient (dn/dT). The changes in properties can be used to develop glass compositions that will show no thermal lensing when heated by laser fluences. The elimination of thermal lensing by composition changes is evaluated in terms of changes in heat capacity, glass stability and processing parameters that might be detrimental to large scale window production.