Interferometer for multi-degree-of-freedom measurement using ball lens and liquid crystal

In this research, by using the principle of transmissive liquid crystals in interferometry, simultaneous measurement of multi-degree-of-freedom (DOF) motion is realized in a single measurement system. Therefore, by using it in combination with a polarizer to arbitrarily switch the light path of the interferometer between transmission and block during measurement, it is possible to perform multiple motion measurements simultaneously. In this research, multiple ball lenses (BL) are used as target mirrors, and since BLs have the property of retroreflecting incident light, light enters the photodetector if the laser beam enters the BLs, regardless of the movement of the target. By switching between light transmission and block, multi-degree-of-freedom measurement becomes possible. In this paper, one-DOF measurement of horizontal translational motion perpendicular to the optical axis direction was performed.