Theoretical limits of low optic loss in multicomponent halide glass materials

Abstract

Multicomponent halide glasses, as a class of materials, are thought to possess the potential for significantly lower attenuation of radiation within their optic window regimes than the lowest yet attained for silica (viz. 0.16 dB/km). This paper discusses a method whereby the minimum attenuation αmin and its associated vacuum wavelength λmin can be estimated for any vitreous multicomponent halide and presents specific numerical predictions for glasses based on such network formers as BeF2, CdF2, AlF3, ZrF4, HfF4, ThF4, CdCl2, BiCl3, ThCl4 and CdI2. If such multicomponent glasses can be prepared which are homogeneous on the scale of λmin, then the ultimate low attenuation (in the absence of impurities or defects) is of order 0.002 dB/km. This limit can be approached in divalent-cationic fluoride materials as well as in several heavier-halide glasses. The associated vacuum wavelength varies from ≈ 3 μm for the fluoride cases to as much as ≈ 9 μm for iodide glass examples. Most multicomponent halide glasses seem capable in ideal circumstances of attenuation limits ≲ 0.01 dB/km, the exceptions being primarily those containing constituents with very light cations such as Li or Be and in some circumstances Mg or Al.