How to Observe Real-Time Processes in High Vacuum and UHV

It is vital to observe the real-time process conditions in high-vacuum and ultra-vacuum (HV/UHV) chambers when undertaking both manufacturing and research and development (R&D) applications. The integration of high-precision thermocouples and process control equipment into the vacuum system is facilitated by hermetically sealed feedthroughs to perform in-situ alterations or obtain data without restricting the highly depressurized atmosphere.

However, a transparent viewport with a high-performance flange is required for direct observation of the process environment with the naked eye.


The development and supply of various HV/ UHV components are areas of Allectra’s expertise, which additionally includes specialized and standard viewports suitable for complex and challenging pressure regimes. This article explores a selection of the standard viewports available in Allectra’s range of HV/UHV products.

An Overview of Standard Viewpoints

Each of our standard viewpoints is fully equipped with high-performance Kodial glass. This glass is also known as borosilicate, given that its primary constituents comprise boron trioxide (B2O3) and silica.

This glass material possesses outstanding thermodynamic stability and is known for its particularly low coefficients of thermal expansion (CTE). These qualities render it suitable for heat treatment applications under vacuum conditions. The precise optical properties of borosilicate glass are retained across its full operating temperature, thanks to the fact that it is very resistant to thermally induced physical variations.

Across each of Allectra’s standard viewpoints, the peak operating temperature and window diameter has significant variation. The range of diameters is from narrow apertures (16 mm) up to significantly wide fields of view (152 mm). However, this geometric range does not affect optical transmissivity, with each standard viewport that Allectra produces covering a great deal of the ultraviolet-visible and near-infrared (UV-Vis-NIR) spectrum (300—2500 nm).

The glass viewport that has the largest viewing diameter currently available is the 120-CPGO-ISO160, which has a viewing diameter of 152 mm. The body material of the glass viewport is grade 304 stainless steel, which has a Viton O-ring vacuum seal. This component provides the broadest field of view for use in direct observation of process conditions. However, its sealing component means that it is restricted to HV applications, with a leak rate of 1×10-8 mbar liters per second (l/s).

In contrast to this, Allectra’s CF glass viewports range from a maximum viewing diameter of 135 mm, for example, on the 120-VPG-C200, to the smallest glass viewport, the 120-VPG-C16, which has a viewing diameter of a tiny 16 mm. Annealed copper (Cu) gaskets are used here in conjunction, offering a vacuum leak rate to 5×10-10 mbar l/s and increasing the maximum use temperature from  150 °C (302 °F) to 400 °C (752 °F).

Each of Allectra’s standard viewports is crafted from materials of the highest quality materials to ensure they match the unique and necessary customer specifications in HV and UHV processing applications. Allectra additionally offers an extensive range of specialized viewports, which are engineered for increasingly challenging processing conditions.

This information has been sourced, reviewed and adapted from materials provided by Allectra Limited.

For more information on this source, please visit Allectra Limited.


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