We present a new class of interferometer system that is capable of simultaneous measurement of absolute position and rotation in all six degrees of freedom (DOF) with nanometer precision. This novel capability is due to the employment of a system of interference fringes that is not periodic. One of the key strengths offered by this new approach is that the absolute position of the system can be determined with a single measurement, rather than by counting fringes during displacement from a known location. The availability of a simultaneous measurement of all six DOF eliminates many problems associated with conventional interferometry.
Burt, D. P., Dobson, P. S., Docherty, K. E., Jones, C. W., Leach, R. K., Thoms, S., … & Zhang, Y. (2012). Aperiodic interferometer for six degrees of freedom position measurement. Optics letters, 37(7), 1247-1249.