In the optical systems field, key components such as spectroscopic elements often require the use of optical materials with high-refractive indices to achieve miniaturization and lightweight characteristics. However, high-refractive index optical materials have low machinability due to their brittle characteristic. In this study, we investigated the changes in surface characteristics during precision pattern machining of high-refractive index materials; specifically, a low fracture toughness, for use in grating spectroscopic elements. The experiment involved diamond turning for the primary machining, and for the secondary pattern machining, the tool rake angle, tool feed rate, and depth of cut were set as variable conditions. Surface roughness measurements and surface quality analyses were carried out using a white-light interferometer and tool microscopy. The results provide insights into the influence of conditions on the surface properties during the machining of high-refractive index materials for grating spectroscopic components. Under the machining conditions with a tool rake angle of -65o, tool feed rate of 5,000 mm/min, and a depth of cut 10 nm, the surface roughness of Ra 8.0 nm was achieved. Based on these findings, we plan to conduct further research on the mechanical fabrication of the blaze angle for grating spectroscopic components.

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.