Nonlinearity of a double-path interferometer qualified with a non-constant moving speed.

A new double-path heterodyne interferometer with spatially separated input beams was developed to minimize the influence of periodic errors. The fully fiber-coupled optics exhibit balanced beam paths which reduce the influence of variations of the ambient conditions. The use of corner cube reflectors enables the interferometer to tolerate larger angular motions of the measuring mirror, compared with common plane mirror interferometers.