Standard Glass Viewports for HV/UHV from Allectra

Observing the real-time process conditions in high-vacuum and ultra-vacuum (HV/UHV) chambers is essential for many research and development (R&D) and manufacturing applications. Hermetically-sealed feedthroughs enable the integration of high-precision thermocouples and process control equipment into the vacuum system to perform in-situ adjustments or acquire data without inhibiting the highly depressurized atmosphere. Direct observation of the process environment with the naked eye, however, requires a transparent viewport with a high-performance flange.


Allectra specializes in the development and supply of various HV/UHV components, including specialized and standard viewports suitable for demanding pressure regimes. In this blog post, we outline some of the standard viewports available in our portfolio of HV/UHV products.

Allectra Standard Viewports: An Overview

All our standard viewports come equipped with high-performance Kodial glass, which is also known as borosilicate due to its primary constituents: silica and boron trioxide (B2O3). This glass material is renowned for extremely low coefficients of thermal expansion (CTE) and outstanding thermodynamic stability, making it ideal for heat treatment applications under vacuum conditions. As borosilicate glass is highly resistant to thermally-induced physical variations, its precise optical properties are retained across its full operating temperature.

The peak operating temperature of Allectra’s standard viewports and the window diameter varies significantly. Diameters range from narrow apertures (16mm) up to extremely wide fields of view (152mm). This geometric range has no effect on optical transmissivity however, with each of our standard viewports covering much of the ultraviolet-visible and near-infrared (UV-Vis-NIR) spectrum (300—2500nm).

Our glass viewport with the largest viewing diameter is the 120-CPGO-ISO160, with a viewing diameter of 152mm. Its body material is grade 304 stainless steel with a Viton O-ring vacuum seal. This component offers the broadest field of view for direct observation of process conditions, but its sealing component limits it to HV applications with a leak rate of 1×10-8mbar liters per second (l/s). Conversely, our CF glass viewports can have from a maximum viewing diameter of 135 mm for instance on the 120-VPG-C200 down to the smallest glass viewport, the 120-VPG-C16, with a viewing diameter of just 16mm. These are used with annealed copper (Cu) gaskets, offering a vacuum leak rate to 5×10-10 mbar l/s and raising the maximum use temperature from  150°C (302°F) to 400°C (752°F).

All our standard viewports are engineered from the highest quality materials to meet distinct customer specifications in HV and UHV processing applications. We also offer an extensive range of specialized viewports engineered for more challenging processing conditions. If you would like to learn more about these, read our previous blog post: Why Use a Sapphire Viewport?

Otherwise, if you have any questions about our range of standard viewports, please do not hesitate to contact us directly.