Ductile regime machining of single-crystal CaF2 for aspherical lenses

Single-crystal calcium fluoride (CaF2) is an important optical material used for dark-field imaging systems and short-wavelength photolithography systems. The fabrication of aspherical lenses using CaF2 effectively eliminates the problems of color aberration and spherical aberration. The present paper describes a ductile regime machining system developed for fabricating aspherical surfaces on CaF2 by single point diamond turning. In this system, the aspherical surface is enveloped by a straight-nosed diamond tool under three-axis simultaneous numerical control. The formation mechanism of the machining form error is analyzed and a rapid tool setting system is developed to aid the improvement of machining accuracy. The experimental results show that the system is effective for high-efficiency manufacturing of ultra-precision CaF2 optics.