So this summer I will be working for a company called Lumetrics which is an engineering company that develops ways to measure very thing object without ever touching said object. They do this by using light and reflection of light. This technology is currently limited to transparent and translucent material but it's still really cool. By shinning a light into an object, some of the light bounces back at the first edge, some passes through. The light that continues through hits the back edge and more is reflected back. This difference in distance travel creates a phase shift which can be used along with the index of refraction of the material to calculate the thickness. I don't really understand works but I'm sure I'll learn all about it when I start work.