Single point diamond turning of KDP inorganic nonlinear optical crystals for laser fusion

Abstract

Potassium dihydrogen phosphate (KH2PO4) called KDP is a key material for performing the next generation laser fusion program using MJ-class glass lasers. Big KDP crystals can be used for second and third harmonic generation in laser fusion due to the features of wider phase matching angle acceptance and higher laser induced damage threshold, though the crystal has weakpoints such as soft, brittle and deliquescent from the machining point of view. Various experiments have been done for getting the optimum machining conditions in single point diamond turning of higher productivity under dry condition. The finished surface roughness is affected by the crystal orientation, rake angle, nose radius, feed and cutting speed. The optical surface of 1.09nm rms, 9.97nm Ry in surface roughness, measured with TOPO-3D, 40X has been obtained by using a diamond tool having a rake angle of - 25 degree and nose radius of 1mm at the cutting speed of 500m/min, feed 2μm/rev and depth of cut 1μm.