Exploring Feynman's Theory on Reflection of Light from Glass Surfaces

[Srihari05]

I recently started reading Feynmans book QED. There are a couple of questions I have regarding his theory on the percentage of light that is reflected of two surfaces of glass.

My question is as follows,

A piece of glass in fact has four surfaces. The front of the glass the back side of the front of the glass the back of the glass and the back side of the back of the glass. In the situation described by Feynman the light penetrates the front of the glass or reflects of the front of the glass. 4% of the light hitting the front of the glass is is reflected and the remaining 96% is passed through and continues on to the back of the glass either reflecting or passing through. Again with the 96% passing through and 4% reflecting. Now on their return path the 4% that is reflecting of the back surface is passing through the backside of the front glass. So In fact the amount of light that is passing through the front glass is actually 96% of the 4% that is originally reflected of the back surface. I just wanted to clarify whether this understanding is correct, or if this detail is accounted for or neglected?

 

[Cryo]

This is a common problem/question in optical etalons (https://en.wikipedia.org/wiki/Fabry–Pérot_interferometer). In my experience taking all these reflections into account becomes very tedious very fast, so it is easier to solve the wave-equation in three domains and stich up the solutions at the boundaries.