If you're in need of measuring nanometer scale displacements on the cheap, this tutorial is what you've been looking for.
Over the years I've had to measure some unusual processes in systems, and one of the most common 'tough' problems has been the measurement of displacement. For mm-scale motion I've used mice (mechanical and optical) to record movement, but I once found myself needing to record nanometric scale displacements and so I was led to interferometry.
Source: Instructables via Hackaday
Learn more at: http://paxinstruments.com/desktop-michelson-morely-interferometer/