Micro-Raman Analysis of Carbon Inclusions in Heavy-Metal Fluoride Glasses

While vitreous carbon crucibles can be used to produce high-quality heavy-metal fluoride glasses using low concentrations of SF₆ gas (15%), pure SF₆ gas produces low-quality and high-scattering glasses. This has been attributed to contamination by vitreous carbon particles by a fallback mechanism due to reaction of SF₆ gas with the crucible walls above the melt. The detrimental effect of carbon particles is further highlighted by their high scattering efficiency factor which indicates that only 37 particles of 1-μm diameter can be tolerated in an optical fiber for attaining 0.01 dB/km loss.