Multidimensional stitching method with wavelength tuned interferometry and unconstrained support tooling for large-thin parallel plate.

Limited by measurement methods, measuring the surfaces and thickness of large thin parallel plates has been challenging. In this paper, we propose a multi-dimensional stitching method using thickness alignment (MSuTA), which use the sub-aperture stitching method based on the phenomenon of parallel plate self-interference with wavelength-tuned interferometer (WTI) for measuring the surfaces and thickness of large thin parallel plates. We establish the stitching correction model based on Legendre polynomial to separate the aberrations caused by the elastic deformation of the thin plate in the unconstrained support tooling by analyzing the influence of the stress state of the thin plate with unconstrained three-point support. The stitching experiment has carried out on 6.3 mm thick, 6-inch parallel plates that the stitching residual is better than 0.35 nm RMS. Compared with 12-inch vertical interferometer, the surfaces and thickness deviation are better than 0.8 nm RMS, and the 36 standard Legendre polynomial coefficient deviation are better than 2.5 nm. Moreover, MSuTA can improves the lateral resolution of the measurement by nearly four times, allowing for a display of more comprehensive surface information. The stitching method proposed in this paper will be widely applied in the manufacture and measurement of large thin parallel plates, and provide reference for the elastic deformation analysis of the thin optical elements in the unconstrained support tooling.