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Viewports - Fused Silica - Introduction

ISI’s Fused Silica Viewports are designed and rated for high and ultra-high vacuum applications. They are constructed using vacuum grade materials including high purity silicon dioxide, 304 stainless steel and vacuum tube-grade braze alloys. Fused silica is a polycrystalline, isotropic material with no crystal orientation. Its physical, thermal, dielectric and optical properties are uniform in all directions of measurement. Conventional fused quartz is suitable for basic non-demanding optical applications. Impurities in fused quartz cause a blue-violet fluorescence when exposed to ultraviolet radiation at 253.7µ. This fluorescence is not evident in synthetic fused silica, which is manufactured by flame hydrolysis of silicon tetrachloride.

ISI offers three ultraviolet grades of fused silica. A base ultraviolet and two deep ultraviolet grades, DUV-200 and EUV-185. The base UV grade material is suitable for all but the most demanding optical applications and certified to >= 80%/cm @185nm external transmittance. DUV-200 fused silica is equivalent to Suprasil-1® and similar to the base grade with the exception of inclusion specifications. EUV-185 is an Excimer grade window material which offers excellent performance for Excimer-UV laser applications.This material is certified to meet >= 85%/cm @185nm external transmittance.

Infrared fused silica windows with low "OH" content can be quoted for applications requiring IR transmission to about 3600nm. This material has less than 1ppm OH content which eliminates the typical absorption band found in other materials. Fused Silica Viewports are preferred over Glass Viewports because of their transparency to ultraviolet radiation. Other advantages include a higher abrasion resistance and a low coefficient of thermal expansion, making them very resistant to thermal shock. Poor surface finish can contribute as much as 10% to overall transmission losses. All viewports are supplied with flat faces which have been finished to standards suitable for most applications. ISI’s standard finish for fused silica viewports is 40-20 scratch-dig. Other finishes are available on request at additional cost. For Deep-UV grade materials, the optics industry typically recommends a 20-10 scratch-dig optical finish for service below .25 microns.

Insulator Seal (ISI) brand catalog and custom engineered ceramic to metal seal products are manufactured to ISO 9001:2008 standard utilizing our qualified hermetic brazing and joining processes. 

General Specifications
Transmission Range:(1)(4)
Fused Quartz 0.300 to 2.50µm
Base Ultraviolet (UV) 0.200 to 2.00µm
Deep Ultraviolet (DUV-200) 0.200 to 2.00µm
Eximer Ultraviolet (EUV-185) 0.185 to 2.30µm
Infrared, Low OH (On Request) 0.180 to 3.60µm
Material Inclusion class number Total Inclusion Cross-Section Maximum Inclusion Cross-Section Index Homogeneity Grade ppm
UV 2 0.10-0.25mm2 0.50mm F <=5
DUV 0 0.00-0.03mm2 0.10mm A <=1
EUV-185 0 0.00-0.03mm2 0.10mm C <=2
Infrared 0 0.00-0.03mm2 0.20mm A <=5
Temperature Rating:(2)
Weldable & Del-Seal CF 200°C(3)
ISO NW Kwik-Flange 150°C


Fused Silica Transmission Curve


(1) Transmission curves are approximations, intended for reference only. They are based on a 10mm sample thickness as tested by Quartz manufacturers.
(2) Thermal gradient should not exceed 25°C/minute
(3) lead-silver braze alloy melts at 305°C.
(4) extended UV and IR range viewports are detailed in section 7.4