The Development of technology is causing the smaller devices. So, optical components are decreasing in volume. For example, the DOE(Diffractive Optical Elements) Si lens is thin than a lens, it was usually used for biomedical devices, hologram, optical sensor, mobile phone, etc. But the fabrication of the DOE Si lens have very limited to machining. The ultra-precision machining of DOE by using the DTM(Diamond Turning Machine) could have cause surface defects such as whitening phenomenon and rainbow effect on the surface. This problems cause optical defect such as a scattering of light. We carried out a ultra-precision machining of the DOE(Diffractive Optical Elements) Si lens by using the DTM with laser assisted module. We can be optimize the machining conditions in several machine processes, such as edge angle of diamond tool, power of laser, cutting depth, feed rate. As a result, we are successfully machined the DOE Si lens with a surface roughness of several nano-meter
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