A grating interferometer for improving optical subdivision in Z-axis measurement

The grating interferometer, with its advantages of high resolution, low cost, and robustness in various environmental conditions, plays an irreplaceable role in the field of ultra-precision measurement. However, the existing Z-axis measurement methods have relatively low resolution, which limits their precision to atomic levels. In order to further improve the accuracy of the heterodyne grating interferometer, this paper proposes an improved optical path for increasing the optical subdivision number in the Z direction. By utilizing a combination of beam splitters and polarizing beam splitters, the Z direction achieves quadruple optical subdivision, enabling sub-nanometer level measurements. Experimental verification demonstrates that this approach can achieve a Z-direction resolution better than 0.2nm, with a 50nm travel repeatable accuracy of 0.5nm, a 50nm step size linear accuracy of 0.04%, and a system stability of 4nm within 5 minutes. The periodic nonlinear error is better than 1nm. In addition, The proposed improved optical path in the Z direction can be further extended to a three-degree-of-freedom measurement system, making it more compact and suitable for achieving sub-nanometer level measurements. This method has the advantages of simple installation, high precision, and stability. It holds significant practical value in industrial production, and can be applied in precision mechanical manufacturing, scanning beam interferometric lithography, and other ultraprecision positioning applications.