Investigation of single point diamond turning of optical-quality germanium substrates

Germanium is an important semiconductor metalloid element used in various fields, including optical fibers, catalysis, infrared optics, solar cells, and light-emitting diodes. Its excellent performance in the infrared wavelength range makes germanium a valuable material in optical systems. Single-crystal germanium has a high refractive index, which allows for the miniaturization of optical systems and the development of thermal camera systems. This study investigates the effect of cutting parameters on surface roughness in the machining of germanium lenses. Germanium lenses are widely used in infrared imaging systems, and the surface quality of these lenses is a critical factor that directly affects the performance of the devices. The aim of this work is to process 40 mm diameter germanium lens surfaces under 12 different experimental conditions, using various cutting parameters, and to determine the average surface roughness (Sa). Additionally, the effect of the crystal orientation of the germanium material during machining is also observed. The experiments were carried out using a diamond-tipped lathe, with specific parameters, and surface roughness was measured using a red laser interferometer and white light interferometer. The Sa values and the corresponding topographic models were obtained. The experimental design was based on factorial design principles, and the effects of cutting parameters on surface roughness were examined in detail. The best Sa value was found to be 1.065 nm, which is well below the acceptable upper limit of 4.640 nm. Finally, the effect of cutting parameters on Sa was determined, and a regression prediction model was developed using the obtained data. This model allows for the prediction of surface roughness (Sa) under specific cutting parameters.