Surface morphology in plasma jet polishing: theoretical description and application

Atmospheric pressure plasma jets are effective for generating optical freeform surfaces and correcting figure errors. They can also reduce high spatial frequency surface roughness, potentially replacing mechanical-abrasive polishing. Plasma jet polishing (PJP) involves thermally driven material redistribution. Current research aims to predict surface topography and roughness by analyzing initial surface topography and the local effect of the plasma jet tool. The tool interaction function was mathematically described by evaluating a microstructure pattern before and after PJP, revealing a 2D Gaussian convolution function. This function can be applied to areal topography measurements of lapped and mechanically ground surfaces to predict the polishing performance with respect to reduction of tool marks originating from pre-machining processes. Additionally, the convolution function can be used to predict the dimensions of an initial surface structure in order to produce a defined smooth microstructure using PJP. Evaluating the smoothing capability of PJP helps identify suitable pre-machining conditions in optics manufacturing, such as grinding or laser micromachining, enabling a more efficient process chain for freeform optics fabrication.