n this section we present the vacuum windows (viewports) from Allectra.
For applications where the user only wants to see what is happening in the vacuum chamber, Kodial (boro-silicate) glass is the best choice as it has a low cost and is available on a wide range of flange types and sizes.
Fused silica is synthetically made quartz. It is a very pure material with minimal inclusions or bubbles. Viewports made from this material extend the transmission to the Ultra Violet (UV) and near Infra Red (IR) range.
The full range of materials is shown on the right.
The quality of polishing is normally given by two numbers called scratch/dig. The first one refers to the maximum width of a scratch in μm, the second gives the diameter of digs or bubble defects in 10 μm. So, a typical polish of 40/20 refers to a maximum scratch width of 0.04 mm and a maximum dig diameter of 0.2 mm. Two digs must be separated by minimum 20 mm from each other
The range of materials is shown below:
Sapphire: Standard, UV Grade & DUV Grade.
Fused silica: UV Grade, DUV, EXCIMER Grade, near IR Grade and non- magnetic.
Calcium fluoride / Magnesium fluoride.