Lens protectors from Mate Precision Tooling have clear apertures

Fiber Shield windows are designed to shield optical components in laser beam delivery systems from debris, fumes, and other pollutants. The fused-silica windows have clear apertures for maximum absorption and reflection, and a coating to protect against dross, oils, and particulates. They are available in diameters from 0.47 to 2.17 in.
Mate Precision Tooling
Anoka, MN
www.matelaser.com