Tried this simple Michelson interferometer for measuring the error of a 100mm translation stage yesterday. The interferometer and stage are mounted to the same optical table, but there’s still a fair amount of vibration of the measurement corner-cube which causes instability in the signal when the stage is not moving. Some sample data here: interf_data. One [...]

This is how the interferograms from the Bath interferometer look like. Using either fringe-tracing or Fourier transform-based analysis it is possible to calculate the shape of the mirror. The most popular analysis programs seem to be FringeXP and OpenFringe.

Most interferometer types used for optical surface testing require an expensive reference element from which the reference beam is bounced off. The interferometer then compares the wavefront from the reference element to the wavefront from the surface being tested. The Bath interferometer is a clever design which uses the test-mirror for both the reference beam [...]