Refractive-Index Interpolation for Fused Silica*

The advantages of a four-term Sellmeier-equation fit to refractive indexes of recently produced fused silica are described. The four-term fit gives more accurate smoothing and interpolation of data than the three-term fit used previously and also indicates data of questionable accuracy. After the suspect data had been eliminated, fits with an average deviation of 4.3 · 10−6 were obtained with both three- and four-term equations over the range 0.21–2.32 μ.