The interferometer includes the dual frequency laser, the four beam splitters, the reference lens, the diaphragm, the two polarization beam splitters, the three pyramid prisms and analyzers, the measuring mirror, the reflector and the four photo-detectors. The structures of two Michelsons interferometers are in the optical paths. The wavelengths 1 and 2 from the synthesis wave s. The measurement in sub nano precision is realized by using the s to subdivide the 2. The measurement in nano precision in millimeter range is realized by counting the number of the interference fringe formed by 2. The nano displacement of the measuring mirror is measured by the first and the second photo-detectors. The analyzers and the photo-detectors measure the millimeter displacements of the measuring mirror and the reference mirror. |