Accu-Glass' Fused silica vacuum viewports are rated for both high and ultrahigh (UHV) vacuum applications. Vacuum Viewports are offered in two (2) fused silica grades... our UV (ultraviolet) material is suitable for most optical applications and certified to meet or exceed 80% external transmittance at 185nm. The DUV (deep ultraviolet) grade is equivalent to Suprasil‑1® and with the exception of inclusion specification, is virtually identical to the UV material. Fused silica viewports outperform glass viewports in their transparency to ultraviolet radiation and a high resistance to discoloration. Since poor surface finish can contribute as much as 10% to overall transmission losses, our UV and DUV viewports are supplied with flat faces that have been polished to a 40-20 and 20-10 scratch-DIG specification respectively. DUV viewports are recommended for service below 200nm.