Designer's Guide Results
The following is a list of materials, selected and ranked per your specification.

MaterialIndex of Refraction
Cubic Zirconia2.24
Sapphire1.768
Ordinary ray, No, c-axis
1.760
Extraordinary ray, Ne, c-axis
Silicon1.54
Zerodur1.54
Corning ULE Glass1.48
Corning Pyrex1.474
Fused Quartz / Silica1.459
Reference Materials
Diamond2.375
Stainless Steeln/a
Tool Steeln/a

All properties values are at room temperature unless otherwise noted. Engineering data are representative, and are not intended as absolute nor warrantable. Data shown is blended from multiple sources and therefore illustrates the marketplace. The relative rankings are approximate and are based on representative values if the particular material has a range of values for a given property.

Wikipedia Definition(s) :  Index of Refraction;

Check Different Properties

Please Note:  This Designers guide is compiled of materials currently machined by Insaco and a few others included for reference.