Simple Michelson interferometer with a test and reference arm at 90 degrees. I'm passing the test arm through a sample of glass and returning the light via a flat mirror. I adjust the return mirror to fluff the fringe (remove tip and tilt). The sample is slightly tilted to avoid back reflections. I'm phase shifting the reference mirror, using a 3 bucket approach. I think if I get the phase and unwrap it, the resultant OPD over the image should lead me directly to the homogeneity of the sample. Has anyone done this before?