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 SF ₆ gas (15%), pure SF ₆ 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 SF ₆ 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.