Optical finishing of nonlinear crystals by single point diamond turning

Abstract

We have demonstrated that diamond turning can produce λ/10 surface with a residual roughness of <50 Å in soft, organic nonlinear crystals such as L-arginine phosphate (LAP) and urea. Recent damage testing of diamond turned LAP plates showed that the damage threshold was as high as 50 J/cm2 for 10-ns pulses at 1.06-μm wave length. We have also developed diamond turning methods for hard, high temperature materials such as lithium niobate and barium metaborate. Polished lithium niobate exhibits laser-induced surface damage at extremely low fluences—<5 J/cm2 for 10-ns pulses at 1.06 μm. We have identified diamond machining conditions in which lithium niobate exhibits ductilemode cutting, with residual surface roughness of <20 Å in 2- × 2-cm2 pieces. This roughness is more than an order of magnitude lower than previously reported results with this crystal. However, some tool wear and built-up edge formation on the tool cutting edge has been observed. We have studied the effect of cutting orientation, rake angle, and cutting fluid on tool wear and surface quality.