Light scattering in heavy-metal fluoride glasses in the infrared spectral region.

The light scattering characteristics in heavy-metal fluoride glasses were measured directly for the first time in the infrared spectral region of interest for ultra-low loss optical fiber applications using a tunable color-center laser as an excitation source. The total scattering coefficients obtained between wavelengths of 2.4 and 3.2microns exhibit a typical Raleigh lambda-4 dependence and lie near the theoretically predicted intrinsic minimum values for these materials. In addition, light scattering measurements in the visible spectral region performed independently at two research laboratories on the same glass specimen have not only confirmed this Rayleigh behavior, but more importantly have established that high optical quality fluoride glasses possess total scattering loss 1/2 to 2/3 that of the best synthetic silicas. The low scattering levels obtained in both infrared and visible spectral regions were uniformly retained throughout the entire volume of the bulk fluoride glasses and were completely unaffected by the size of the focused laser beam, suggesting that the MIE scattering centers were totally absent from the glass samples.