Analysis of 3D microtopography in machined KDP crystal surfaces based on fractal and wavelet methods

Potassium dihydrogen phosphate (KDP) crystal surfaces machined by precise milling and single point diamond turning (SPDT) methods are analyzed in this paper. The frequency information of 3D-machined KDP crystal surfaces are decomposed and analyzed by wavelet transform method, and 3D fractal properties of different KDP crystal surfaces are calculated and analyzed by fractal method. Through the integration of fractal and wavelet analysis, it can be found that the high-frequency information of machined surfaces is incorrelate with the machining process and it can reflect the anisotropic features of material structure. The anisotropy of the machined KDP surfaces is determined by the machining process. From analysis, the strong anisotropic surfaces are easier to form microscale waveness so as to impact the optical performance of KDP crystal components severely. The result of analysis reveals that the different machining method may produce unique feature in the machined surfaces and choosing reasonable machining method may improve the microtopographic structure of machined KDP crystal surface.