Germanium, an optical material, has high transmittance and refractive index and low light scattering in the infrared region, and research is being conducted to utilize it in various industrial fields. Various forms of optical lenses can be subjected to ultra-precision machining with high quality surface roughness, and they form accuracy through single point diamond turning (SPDT). In particular, the diamond tool with a negative rake angle and the u-LAM process that applies a 1,064 nm laser to the material have been studied to fabricate brittle materials into optical lenses. In this study, the effects of process parameters, such as laser power (W), spindle speed (RPM), feed rate (mm/min), and depth of cut (μm), on the surface roughness of a sub-nanometer scale and the occurrence of defects during the machining process were analyzed for Germanium materials. The process of removing these defects was also analyzed.

Infrared (IR) optic lens can be fabricated by a single point diamond turning (SPDT) machine without subsequent polishing process. However, this machining process often leaves microcracks that deteriorate the surface quality. In this work, we propose an experimental design to remove micro-cracks on IR lens. The proposed design gathered data between cutting process condition and Rt surface roughness. This is of great importance because the scale of microcracks is a few micrometer. Rt surface roughness is suitable for analyzing maximum peak height signals of the profile. The experimental results indicate that feed per revolution variable is one of the most dominant variable, affecting the generation micro-cracks on IR lens surfaces.