Here is a virtual frequency scanning interferometer implementation for measuring the index homogeneity and surface figure of an optical substrate. This code implements the technique described by Leslie Deck with the Zygo corporation.

This is a way to build an interferometer using a frequency scanning source, where phase shifting is not necessary.

This is not an example of excellent programming, but of the implementation of a tricky physics and mathematical system. I wrote this long ago, and write much better software every day.