This is fused quartz.
This is College Physics Answers with Shaun Dychko. Light reflected from this window is polarized. And so that means this incident angle is probably a Brewster's angle. We'll assume that this is the minimum angle at which this reflected light is polarized. So that's 55.6 degrees. And the question is what is the index of refraction of this material from which it is reflecting. So, we have tangent of Brewster's angle is the index of refraction of this second material divided by the index of refraction of the initial material which is air. And so we're gonna solve for <i>n two</i> by multiplying both sides by <i>n one</i>. And so we have the index refraction of the glass is <i>n one</i> times tangent of Brewster's angle. So, that’s 1.0 index refraction of air multiplied by tangent of 55.6 degrees which gives us an index of refraction of the glass of 1.46 and this is likely fused quartz.