Surface quality of large KDP crystal fabricated by single-point diamond turning

Abstract

Ptassium dihydrogen phosphate (KDP) crystals are used as key components in high power density solid-state laser for Inertial Confinement Fusion. Surface quality is an important factor for KDP crystals implemented in high power lasers. At present Single Point Diamond Turning(SPDT) is the only way to get the required transmitted wavefront and damage threshold KDP. The paper introduces something about the defects of KDP crystals fabricating and analyses some reasons. Based on the analysis of the reasons, the process parameters can be adjusted to meet the critical requirements of high energy density application. A piece of 320X320 mm² KDP is acquired. The roughness of the 320X320 mm² crystal surface was already to reach an rms about 5 nm. Data were measured by an interferometric microscope. The wavefront p-v is lower than 0.5λ(λ=632nm).