Analysis of surface quality and processing optimization of magnetorheological polishing of KDP crystal

A new non-aqueous and abrasive-free magnetorheological (MRF) polishing method is adopted for processing KDP crystal due to its low hardness, high brittleness, temperature sensitivity, and water solubility. Water content in magnetorheological fluids has an important effect on polishing surface quality. In addition to affecting the removal efficiency and fogging, the recrystallization of KDP can produce great influence on surface quality. This paper analyzes the formation of recrystallization process, chemical composition, influence factors and finds a method to restrain recrystallization. Results indicate the surface roughness of KDP crystal by MRF is 0.624 nm (Ra), 0.809 nm (RMS). We get neat, non-nick and ultra smooth surface after MRF polishing. Besides the improvement of surface roughness, the tool marks imported by single-point diamond turning (SPDT) are eliminated clearly. This has significant meaning on KDP crystal processing. Large size KDP crystal is widely used in high power laser system. The cutting tool marks will affect the laser induced damage threshold (LIDT) clearly. This means after MRF polishing the KDP crystal has better performance in high power laser system without recrystallization, obvious scratch, and tool marks. © 2015, The Optical Society of India.