Determination of length difference between two gauge blocks using a Michelson interferometer

The length difference between two gauge block were measured by using Michelson interferometer with stabilized He-Ne laser at 633 nm. The phase-shifting method was employed in order to create four interferograms. All interferograms were acquired by CCD camera and sent to computer. Length difference of any two gauge blocks was determined from phase difference at the central position of gauge blocks. The measurement uncertainty of 20 nm was achieved.