Polishing technique for KDP crystal based on two-phase air–water fluid

Abstract

This paper proposes a polishing technique for potassium dihydrogen phosphate (KDP) crystal. The proposed method uses the two-phase air–water fluid (TAWF) as a catalyst to achieve controllable deliquescence of the KDP crystal without any abrasive and chemical contaminant. Surface planarization is implemented by using the mechanical action deriving from a polishing pad. To obtain controllable deliquescence, the factors influencing deliquescence are analyzed. A TAWF polishing system is then developed. During the polishing process, the surface characteristics of the KDP crystal are investigated using a metallographic microscope and a 3D surface profiler. The effects of the polishing parameters on surface planarization are analyzed, and the preliminary optimization of the polishing process is performed. Additionally, the removal mechanism in polishing is also discussed. The results show that the deliquescence of the KDP crystal is significantly correlated with moisture content, temperature, and surface micro-topography. Controllable deliquescence can be implemented if these are considered. Furthermore, by employing the proposed technique, the initial surface texture of the KDP crystal is completely removed in 20 min and RMS surface roughness is reduced to 5 nm.