Phase-shifting Interferometer
A phase measuring interferometer detects the difference in phase between the test and reference legs of a split laser source, enabling measurement of surface deviations on the nanometer scale.
Phase data can be acquired by physically changing the path length of one of the interferometer arms between each measurement. The data can also be acquired simultaneously, using various optical techniques to spatially separate the phase-shifted data, which enables measurement despite environmental vibration or air turbulence.