High accuracy piston and wobble sensor based on heterodyne interferometry

Heterodyne laser interferometry has proved to be a valuable technique for high accuracy optical displacement metrology. In many applications in science and engineering, it is required a highly accurate measurement of multiple degrees of freedom of a critical device with regard to a mechanical system reference. An example is the primary calibration of standard accelerometers by interferometry. In this context, it is proposed a multi-channel system based on a heterodyne interferometer for simultaneous measurement of piston and wobble of the accelerometer top surface. The implemented system is based on a Michelson interferometer, with four parallel beams of equal intensity that enable simultaneous measurement of different points of the surface. The parallel approach reduces the complexity due the simultaneous use of common units (laser source, modulators and some optics), maintaining the high resolution associated with interferometric sources. In this paper we present a new metrology concept based on heterodyne interferometry that can allow the simultaneous measurement of a surface piston and wobble movement, detailing the physical model of the sensor, the prototype implementation and the performance characterized by the test result. The future steps towards an implementation in a primary standard accelerometer calibration setup are also described.