Michelson interferometer

This thing is a Michelson interferometer,

http://en.wikipedia.org/wiki/Michelson_interferometer

It can be used to measure relative motion with nanometer precision and accuracy. This is done by counting interference fringes generated by the constructive and destructive interference of coherent light. A transition from constructive to destructive interference corresponds to a movement of half the wavelength of the light used.

It consists of a laser holder, laser, a beam splitter, two mirrors, a diffusing lens an optional photodetector and the framework for fixing the position of all the parts.

Good luck implementing it as a position feedback system on your 3D printer ;-)

It's mostly based off of a kinematic mirror mount http://www.thingiverse.com/thing:30727

Video demonstrations:
http://youtu.be/IsIFKxLLVd0
http://youtu.be/0OLO-GWjg9E

There are two images include that show the interferometer mounted vertically. These were an attempt at making a load-displacement testing tool. Unfortunately the vibration in the linear actuator was too great, making displacement measurements erroneous.

Next step is to mount a piezo buzzer behind one of the mirrors to determine its stroke.