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

MaterialTransmission Band
Silicon0.30 - 37 Wavelength (microns)
In the IR Range
Sapphire 0.3 - 5.0 Wavelength (microns)
> 80% transmission
Fused Quartz / Silica0.2 - 3.5 Wavelength (microns)
Zerodur 0.3 - 2.5 Wavelength (microns)
Reference Materials
Diamondn/a
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) :  Transmission Band;

Check Different Properties

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