Phase shifting interferometric method, interferometer apparatus and method of manufacturing an optical element

This invention describes a way to precisely measure objects using light. It works by shining light on an object, combining it with a reference beam, and taking at least four pictures of the resulting interference patterns, each with a slightly different light alignment. The clever part is that it doesn't rely on pre-set light alignments; instead, it figures out the exact alignment changes from the pictures themselves, often by comparing them to a computer simulation to get a highly accurate measurement.