Viewports for vacuum applications: correlation between viewport thickness and stress induced birefringence

The paper gives an introduction into vacuum viewports and its stress introduced birefringence effects. The effect of the stress induced birefringence is measured for viewports of different thicknesses under vacuum conditions. Line scans across the viewports are done to investigate heterogeneity effects also. The variation of thickness is realized with elastomer sealed viewports. In order to compare those results measurements are done also with thermally sealed viewports as well as adhesively sealed viewports.