J. Eur. Opt. Society-Rapid Publ. 21, 12( 2025) 133
Figure 13. Ultra-fine ground Alvarez freeform using optimized parameters as a reference for subsequent PJ polishing:( A) photography of a sample and( B) shape representation measured by WLI.
( A)
( B)
Figure 14. Topographical comparison( figure error topographies) for one Alvarez sample after( A) D30 fine grinding and the same sample( B) after D16 ultra-fine grinding measured by telecentric WLI.
precise for the subsequent process. In order to achieve high production efficiency, it is important to avoid the formation of grinding marks that are beyond the scope of possible smoothing. Conversely, it is imperative to refrain from“ over-accuracy,” which entails the avoidance of grinding marks that would be undetectable after PJP. The initial estimations of the grinding marks to be avoided can be made using a filter function that describes the PJP [ 29 ]. Figure 17 shows an examples of topography measurements of ground surfaces that are not yet sufficiently prepared for PJP. The horizontal grinding marks in Figure 17( A) are clearly recognizable, but vertical marks are not concise. However, the PSD function along the x-direction in Figure 17( C) indicates a prominent peak at a spatial frequency of 2.510 �3 lm �1. The areal mapping after applying the filter function confirms that presence( see Fig. 17( B)). For completeness, the PSD function in y-direction, given in Figure 17( D), shows the prominent peak at about 510 �3 lm �1 which significantly decreases when applying PJP. The disappearance of the numerous peaks at spatial frequencies above 110 �2 lm �1 is most obvious in Figure 17( D). These result from the engagement of grinding grains and can almost completely be smoothened by the PJP process.
Further investigation of the influence of improved grinding parameters on PJP results was conducted by experiment with a number of samples. The variation of grinding parameters is outlined in Table 1.