Nanometer-resolution 4-Probe Laser Interferometric Displacement Sensor Performance Evaluation: Principles and Operations

A 4-probe laser interferometric displacement sensor (4pLIDS) has advantages over a single-probe LIDS in a micro-thruster calibration system. By synchronously measuring the displacements at four points and differentiating the measured data, the common-mode noise can be greatly suppressed, thereby improving the measurement accuracy. Based on the design requirements of the nanometer-resolution 4pLIDS, we discussed the connections among various performance aspects of LIDS, designed evaluation schemes, and conducted tests. We devised the schemes to evaluate the 4-probe performances related to synchronicity using a single nanopositioning stage as the displacement reference, and considering the agreement and output temporal uniformity from each probe. We further analyzed the influences of the non-ideal performances of the displacement reference on the evaluation results to ensure that the results truly reveal the LIDS's performances. The evaluation results show that the resolution of the 4pLIDS reaches 0.7 nm, the standard deviation (SD) of the 4pLIDS repeatability is no more than 0.15 nm and the inconsistency error among the 4 probes is within ±0.4 nm. The actual differential measurement results using the 4pLIDS conform to the predictions from the evaluated performances and demonstrate the effectiveness of the evaluation.