The precision by which an electron spin polarization measurement can be
made using a noble-gas polarimeter depends directly on the accuracy of
a light-polarization measurement. Since the electron–noble gas
collisions occur in a vacuum chamber and the optical polarimeter is
generally outside the chamber, this work examines the effect the
vacuum window has on the perceived optical polarization. A model light
source, lens system, and optical polarimeter are used that approximate
the situation found in a typical atomic physics experiment. It was
demonstrated that a pressure difference of 1 atm on a lens will alter
the perceived polarization by as much as 0.05% with typical
borosilicate (BK) lenses. This effect was demonstrated to scale with
the thickness of the lens used and changes signs when the direction of
the stress is reversed.