Methods For Evaluating The Surface Of Single Crystal Germanium In Ultra-precision Machining

With the development of ultra-precision processing technology, the products supported by ultra-precision technology has stepped into people’s lives. And with advances in machining technology, the testing technology continues to develop. The aim that introducing power spectral density method and fractal dimension method in this paper is to judge which crystal Germanium surface has a better quality when they have the same surface roughness. Both methods can be applied to analyzed the processing surface and then to evaluate its processing quality.Firstly, we test how cutting parameters influence the quality of lens’ surface and the consistency between traditional machining and SPDT with an experiment. Then I introduce the definition of the power spectral density and correct the spectral density by several correction methods. With turning crystal Germanium lens and collecting discrete points by surface profile detector, I analysis the data by using the power spectral density method.The results show that the power spectral density method can accurately evaluate the surface quality of crystal Germanium and further differentiate the quality when two lens have the same surface roughness.Subsequently I introduced the fractal dimension method as the second analytical method.By the fractal dimension method, the quality of each crystal Germanium lens can be expressed by a figure.Compared to the power spectral density method,it is more accurate to distinguish their quality among two crystal Germanium lens.